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{{Short description|Frozen water: the solid state of water}}
{{Short description|Frozen water: the solid state of water}}
{{good article}}
{{About|water ice|the broader concept of "ices" as used in the planetary sciences|Volatile (astrogeology)|other uses}}
{{About|water ice|the broader concept of "ices" as used in the planetary sciences|Volatile (astrogeology)|other uses}}
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{{pp-vandalism|small=yes}}
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| refractive_index = 1.309
| refractive_index = 1.309
| chemical formula = {{chem2|H2O}}
| youngs_modulus = 3400 to 37,500 [[Kilogram-force|kg-force]]/cm<sup>3</sup><ref name=Voitkovskii>{{Citation
| youngs_modulus = 3400 to 37,500 [[Kilogram-force|kg-force]]/cm<sup>3</sup><ref name=Voitkovskii>{{Citation
|last = Voitkovskii
|last = Voitkovskii
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'''Ice''' is [[water]] that is [[freezing|frozen]] into a [[solid]] state, typically forming at or below temperatures of 0 °[[Celsius|C]], 32 °[[Fahrenheit|F]], or 273.15 [[Kelvin|K]].<ref>{{Cite web|url=https://flexbooks.ck12.org/cbook/ck-12-chemistry-flexbook-2.0/section/15.2/primary/lesson/structure-of-ice-chem/|title=CK-12 Chemistry for High School 15.2 Structure of Ice|website=ck12.org|language=en|access-date=2023-08-17}}</ref> As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a [[mineral]].<ref>{{Cite book |last=Demirbas |first=Ayhan |url=https://books.google.com/books?id=WFefWAq1Sh0C&pg=PA90 |title=Methane Gas Hydrate |date=2010 |publisher=Springer Science & Business Media |isbn=978-1-84882-872-8 |page=90}}</ref><ref>{{cite web |title=The Mineral Ice |url=https://www.minerals.net/mineral/ice.aspx |access-date=2019-01-09 |website=minerals.net}}</ref> Depending on the presence of [[Impurity|impurities]] such as particles of soil or bubbles of air<!--was: air inclusions-->, it can appear transparent or a more or less [[Opacity (optics)|opaque]] bluish-white color.
'''Ice''' is [[water]] that is [[freezing|frozen]] into a [[solid]] state, typically forming at or below temperatures of 0 °[[Celsius|C]], 32 °[[Fahrenheit|F]], or 273.15 [[Kelvin|K]]. It occurs naturally on [[Earth]], on other planets<!-- including those as close to the Sun as [[Mercury (planet)|Mercury]] -->, in [[Oort cloud]] objects, and as [[interstellar ice]]. As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a [[mineral]]. Depending on the presence of [[Impurity|impurities]] such as particles of [[soil]] or bubbles of [[air]], it can appear transparent or a more or less [[Opacity (optics)|opaque]] bluish-white color.


Virtually all of the ice on Earth is of a [[Hexagonal crystal system|hexagonal]] [[Crystal structure|crystalline structure]] denoted as ''ice I<sub>h</sub>'' (spoken as "ice one h"). Depending on temperature and pressure, at least nineteen [[phases of ice|phases]] ([[Sphere packing|packing geometries]]) can exist. The most common [[phase transition]] to ice I<sub>h</sub> occurs when liquid water is cooled below {{val|0|ul=°C}} ({{val|273.15|ul=K}}, {{val|32|ul=°F}}) at [[standard atmospheric pressure]]. When water is cooled rapidly ([[quenching]]), up to three types of amorphous ice can form. Interstellar ice is overwhelmingly low-density amorphous ice (LDA), which likely makes LDA ice the most abundant type in the universe. When cooled slowly, correlated proton tunneling occurs below {{val|-253.15|ul=°C}} ({{val|20|ul=K}}, {{val|-423.67|ul=°F}}) giving rise to [[macroscopic quantum phenomena]].
Ice exhibits at least nineteen [[phases of ice|phases]] ([[Sphere packing|packing geometries]]), depending on temperature and pressure. When water is cooled rapidly ([[quenching]]), up to three types of amorphous ice can form depending on its history of pressure and temperature. When cooled slowly, correlated proton tunneling occurs below {{val|-253.15|ul=°C}} ({{val|20|ul=K}}, {{val|-423.67|ul=°F}}) giving rise to [[macroscopic quantum phenomena]]. In the [[Solar System]], ice occurs naturally from as close to the Sun as [[Mercury (planet)|Mercury]] to as far away as the [[Oort cloud]] objects. Beyond the Solar System, it occurs as [[interstellar ice]], which is overwhelmingly amorphous. Yet, virtually all of the ice on Earth is of a [[Hexagonal crystal system|hexagonal]] [[Crystal structure|crystalline structure]] denoted as ''ice I<sub>h</sub>'' (spoken as "ice one h").
<!--GAN IN PROGRESS ..... please allow the GA nominator to edit here: If you need to comment, please do so on talk or GAN page, not here. Many thanks from the reviewer-->


The most common [[phase transition]] to ice I<sub>h</sub> occurs when liquid water is cooled below {{val|0|ul=°C}} ({{val|273.15|ul=K}}, {{val|32|ul=°F}}) at [[standard atmospheric pressure]]. Ice formed in this way is abundant on the Earth's surface, particularly [[Polar ice cap|in the polar regions]] and above the [[snow line]], where it can aggregate from snow to form [[glaciers]] and [[ice sheet]]s. As [[snowflakes]] and [[hail]], ice is a common form of [[precipitation]], and it may also be [[Deposition (phase transition)|deposited]] directly by [[water vapor]] as [[frost]]. The transition from ice to water is melting and from ice directly to water vapor is [[Sublimation (phase transition)|sublimation]]. These processes plays a key role in Earth's [[water cycle]] and [[climate]]. In the recent decades, ice volume on Earth has been decreasing due to [[climate change]]. The largest declines have occurred in the [[Arctic]] and in the mountains located outside of the polar regions.
Ice is abundant on the Earth's surface, particularly [[Polar ice cap|in the polar regions]] and above the [[snow line]], where it can aggregate from snow to form [[glaciers]] and [[ice sheet]]s. As [[snowflakes]] and [[hail]], ice is a common form of [[precipitation]], and it may also be [[Deposition (phase transition)|deposited]] directly by [[water vapor]] as [[frost]]. The transition from ice to water is melting and from ice directly to water vapor is [[Sublimation (phase transition)|sublimation]]. These processes plays a key role in Earth's [[water cycle]] and [[climate]]. In the recent decades, ice volume on Earth has been decreasing due to [[climate change]]. The largest declines have occurred in the [[Arctic]] and in the mountains located outside of the polar regions. The loss of grounded ice (as opposed to floating [[sea ice]]) is the primary contributor to [[sea level rise]].


Humans have been using ice for various purposes for thousands of years. Some historic structures designed to hold ice to provide cooling are over 2,000 years old. Before the invention of [[refrigeration]] technology, the only way to safely store food without modifying it through [[preservative]]s was to use ice. Sufficiently solid surface ice makes [[waterway]]s accessible to land transport during winter, and dedicated [[ice road]]s may be maintained. Ice also plays a major role in [[winter sport]]s.
Humans have been using ice for various purposes for thousands of years. Some historic structures designed to hold ice to provide cooling are over 2,000 years old. Before the invention of [[refrigeration]] technology, the only way to safely store food without modifying it through [[preservative]]s was to use ice. Sufficiently solid surface ice makes [[waterway]]s accessible to land transport during winter, and dedicated [[ice road]]s may be maintained. Ice also plays a major role in [[winter sport]]s.


==Physical properties==
==Physical properties==
{{Further|Water (properties)#Density of water and ice}}
[[File:Ice Ih Crystal Lattice.png|thumb|The three-dimensional crystal structure of H{{sub|2}}O ice I<sub>h</sub> (c) is composed of bases of H{{sub|2}}O ice molecules (b) located on lattice points within the two-dimensional hexagonal space lattice (a).<ref name="Physics of Ice">Physics of Ice, V. F. Petrenko, R. W. Whitworth, Oxford University Press, 1999, {{ISBN|9780198518945}}</ref><ref>{{cite journal|doi = 10.1063/1.1749327|title = A Theory of Water and Ionic Solution, with Particular Reference to Hydrogen and Hydroxyl Ions|year = 1933|author1=Bernal, J. D. |author2=Fowler, R. H. |journal = The Journal of Chemical Physics|volume = 1|issue = 8|page = 515|bibcode = 1933JChPh...1..515B }}</ref>]]
[[File:Ice Ih Crystal Lattice.png|thumb|The three-dimensional crystal structure of H{{sub|2}}O ice I<sub>h</sub> (c) is composed of bases of H{{sub|2}}O ice molecules (b) located on lattice points within the two-dimensional hexagonal space lattice (a).<ref name="Physics of Ice">Physics of Ice, V. F. Petrenko, R. W. Whitworth, Oxford University Press, 1999, {{ISBN|9780198518945}}</ref><ref>{{cite journal|doi = 10.1063/1.1749327|title = A Theory of Water and Ionic Solution, with Particular Reference to Hydrogen and Hydroxyl Ions|year = 1933|author1=Bernal, J. D. |author2=Fowler, R. H. |journal = The Journal of Chemical Physics|volume = 1|issue = 8|page = 515|bibcode = 1933JChPh...1..515B }}</ref>]]


Ice possesses a regular [[crystalline]] structure based on the [[molecule]] of water, which consists of a single [[oxygen]] atom [[covalently]] bonded to two [[hydrogen atom]]s, or H–O–H. However, many of the physical properties of water and ice are controlled by the formation of [[hydrogen bond]]s between adjacent oxygen and hydrogen atoms; while it is a weak bond, it is nonetheless critical in controlling the structure of both water and ice.<ref name=bjerrum>{{cite journal|last=Bjerrum|first=N|title=Structure and Properties of Ice|journal=Science|date=11 April 1952|volume=115|issue=2989|pages=385–390|doi=10.1126/science.115.2989.385|pmid=17741864|bibcode = 1952Sci...115..385B }}</ref>
Ice possesses a regular [[crystalline]] structure based on the [[molecule]] of water, which consists of a single [[oxygen]] atom [[covalently]] bonded to two [[hydrogen atom]]s, or H–O–H. However, many of the physical properties of water and ice are controlled by the formation of [[hydrogen bond]]s between adjacent oxygen and hydrogen atoms; while it is a weak bond, it is nonetheless critical in controlling the structure of both water and ice.<ref name=bjerrum>{{cite journal|last=Bjerrum|first=N|title=Structure and Properties of Ice|journal=Science|date=11 April 1952|volume=115|issue=2989|pages=385–390|doi=10.1126/science.115.2989.385|pmid=17741864|bibcode = 1952Sci...115..385B }}</ref>


An unusual property of water is that its solid form—ice frozen at [[atmospheric pressure]]—is approximately 8.3% less dense than its liquid form; this is equivalent to a volumetric expansion of 9%. The [[density]] of ice is 0.9167<ref name=CRC>{{cite book |chapter=Properties of Ice and Supercooled Water |first=Allan H. |last=Harvey |editor1= Haynes, William M. |editor2 = Lide, David R. |editor3=Bruno, Thomas J. |title = CRC Handbook of Chemistry and Physics |edition = 97th |location = Boca Raton, FL |publisher = CRC Press |year = 2017 |isbn = 978-1-4987-5429-3}}</ref>–0.9168<ref name=Voitkovskii/>&nbsp;g/cm<sup>3</sup> at 0&nbsp;°C and standard atmospheric pressure (101,325 Pa), whereas water has a density of 0.9998<ref name=CRC/>–0.999863<ref name=Voitkovskii/> g/cm<sup>3</sup> at the same temperature and pressure. Liquid water is densest, essentially 1.00&nbsp;g/cm<sup>3</sup>, at 4&nbsp;°C and begins to lose its density as the water molecules begin to form the [[Hexagonal (crystal system)|hexagonal]] [[crystal]]s of [[ice crystals|ice]] as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. Density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm<sup>3</sup> at −180&nbsp;°C (93 K).<ref>{{RubberBible86th}}</ref>
An unusual property of water is that its solid form—ice frozen at [[atmospheric pressure]]—is approximately 8.3% less dense than its liquid form; this is equivalent to a volumetric expansion of 9%. The [[density]] of ice is 0.9167<ref name=CRC>{{cite book |chapter=Properties of Ice and Supercooled Water |first=Allan H. |last=Harvey |editor1= Haynes, William M. |editor2 = Lide, David R. |editor3=Bruno, Thomas J. |title = CRC Handbook of Chemistry and Physics |edition = 97th |location = Boca Raton, FL |publisher = CRC Press |year = 2017 |isbn = 978-1-4987-5429-3}}</ref>–0.9168<ref name=Voitkovskii/>&nbsp;g/cm<sup>3</sup> at 0&nbsp;°C and standard atmospheric pressure (101,325&nbsp;Pa), whereas water has a density of 0.9998<ref name=CRC/>–0.999863<ref name=Voitkovskii/>&nbsp;g/cm<sup>3</sup> at the same temperature and pressure. Liquid water is densest, essentially 1.00&nbsp;g/cm<sup>3</sup>, at 4&nbsp;°C and begins to lose its density as the water molecules begin to form the [[Hexagonal (crystal system)|hexagonal]] [[crystal]]s of [[ice crystals|ice]] as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. The density of ice increases slightly with decreasing temperature and has a value of 0.9340&nbsp;g/cm<sup>3</sup> at −180&nbsp;°C (93&nbsp;K).<ref>{{RubberBible86th}}</ref>


When water freezes, it increases in volume (about 9% for fresh water).<ref name="LibreTexts">{{Cite web |last1=Richardson |first1=Eliza |title=Ice, Water, and Vapor |url=https://geo.libretexts.org/Bookshelves/Oceanography/Essentials_of_Oceanography_(Richardson)/03%3A_From_Rock_to_Salt/3.02%3A_Ice_Water_and_Vapor |website=LibreTexts Geosciences |date=20 June 2021 |language=en |access-date=26 April 2024 }}</ref> The effect of expansion during freezing can be dramatic, and ice expansion is a basic cause of [[freeze-thaw]] weathering of rock in nature and damage to building foundations and roadways from [[frost heaving]]. It is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes.<ref name="Akyurt2002">{{cite journal |last1=Akyurt |first1=M. |last2=Zaki |first2=G. |last3=Habeebullah |first3=B. |title=Freezing phenomena in ice–water systems |journal=Energy Conversion and Management |date=15 May 2002 |volume=43 |issue=14 |pages=1773–1789 |doi=10.1016/S0196-8904(01)00129-7 |bibcode=2002ECM....43.1773A }}</ref>
When water freezes, it increases in volume (about 9% for fresh water).<ref name="LibreTexts">{{Cite web |last1=Richardson |first1=Eliza |title=Ice, Water, and Vapor |url=https://geo.libretexts.org/Bookshelves/Oceanography/Essentials_of_Oceanography_(Richardson)/03%3A_From_Rock_to_Salt/3.02%3A_Ice_Water_and_Vapor |website=LibreTexts Geosciences |date=20 June 2021 |language=en |access-date=26 April 2024 }}</ref> The effect of expansion during freezing can be dramatic, and ice expansion is a basic cause of [[freeze-thaw]] weathering of rock in nature and damage to building foundations and roadways from [[frost heaving]]. It is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes.<ref name="Akyurt2002">{{cite journal |last1=Akyurt |first1=M. |last2=Zaki |first2=G. |last3=Habeebullah |first3=B. |title=Freezing phenomena in ice–water systems |journal=Energy Conversion and Management |date=15 May 2002 |volume=43 |issue=14 |pages=1773–1789 |doi=10.1016/S0196-8904(01)00129-7 |bibcode=2002ECM....43.1773A }}</ref>
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[[File:Iceberg in the Arctic with its underside exposed.jpg|thumb|left|This iceberg can stay afloat in spite of its size because it is less dense than water]]
[[File:Iceberg in the Arctic with its underside exposed.jpg|thumb|left|This iceberg can stay afloat in spite of its size because it is less dense than water]]


Because ice is less dense than liquid water, it floats, and this prevents bottom-up freezing of the bodies of water. Instead, a sheltered environment for animal and plant life is formed beneath the floating ice, which protects the underside from short-term weather extremes such as [[wind chill]]. Sufficiently thin floating ice allows light to pass through, supporting the [[photosynthesis]] of bacterial and algal colonies.<ref>{{cite web|url=http://www.haydenplanetarium.org/tyson/read/1998/05/01/water-water|title=Water, Water|author=Tyson, Neil deGrasse|publisher=haydenplanetarium.org|url-status=live|archive-url=https://web.archive.org/web/20110726095920/http://www.haydenplanetarium.org/tyson/read/1998/05/01/water-water|archive-date=26 July 2011}}</ref> When sea water freezes, the ice is riddled with brine-filled channels which sustain [[Sympagic ecology|sympagic organisms]] such as bacteria, algae, [[copepod]]s and [[annelid]]s. In turn, they provide food for animals such as [[krill]] and specialised fish like the [[bald notothen]], fed upon in turn by larger animals such as [[emperor penguins]] and [[minke whales]].<ref>[http://www.acecrc.sipex.aq/access/page/?page=d664da82-b244-102a-8ea7-0019b9ea7c60 Sea Ice Ecology] {{webarchive|url=https://web.archive.org/web/20120321204557/http://www.acecrc.sipex.aq/access/page/?page=d664da82-b244-102a-8ea7-0019b9ea7c60 |date=21 March 2012 }}. Acecrc.sipex.aq. Retrieved 30 October 2011.</ref>
Because ice is less dense than liquid water, it floats, and this prevents bottom-up freezing of the bodies of water. Instead, a sheltered environment for animal and plant life is formed beneath the floating ice, which protects the underside from short-term weather extremes such as [[wind chill]]. Sufficiently thin floating ice allows light to pass through, supporting the [[photosynthesis]] of bacterial and algal colonies.<ref>{{cite web|url=http://www.haydenplanetarium.org/tyson/read/1998/05/01/water-water|title=Water, Water|author=Tyson, Neil deGrasse|publisher=haydenplanetarium.org|url-status=live|archive-url=https://web.archive.org/web/20110726095920/http://www.haydenplanetarium.org/tyson/read/1998/05/01/water-water|archive-date=26 July 2011}}</ref> When sea water freezes, the ice is riddled with brine-filled channels which sustain [[Sympagic ecology|sympagic organisms]] such as bacteria, algae, [[copepod]]s and [[annelid]]s. In turn, they provide food for animals such as [[krill]] and specialized fish like the [[bald notothen]], fed upon in turn by larger animals such as [[emperor penguins]] and [[minke whales]].<ref>[http://www.acecrc.sipex.aq/access/page/?page=d664da82-b244-102a-8ea7-0019b9ea7c60 Sea Ice Ecology] {{webarchive|url=https://web.archive.org/web/20120321204557/http://www.acecrc.sipex.aq/access/page/?page=d664da82-b244-102a-8ea7-0019b9ea7c60 |date=21 March 2012 }}. Acecrc.sipex.aq. Retrieved 30 October 2011.</ref>


[[File:Feather ice 1, Alta plateau, Norway.jpg|thumb|So-called feather ice on the plateau near [[Alta, Norway]]. The crystals form at temperatures below −30&nbsp;°C (−22&nbsp;°F) and contain a lot of trapped air, making them light enough to be supported by the thin branch]]
[[File:Feather ice 1, Alta plateau, Norway.jpg|thumb|So-called feather ice on the plateau near [[Alta (town)|Alta]], [[Norway]]. The crystals form at temperatures below −30&nbsp;°C (−22&nbsp;°F) and contain a lot of trapped air, making them light enough to be supported by the thin branch]]
[[File:Frozen Wappinger Creek.JPG|thumb|Frozen waterfall in southeast [[New York (state)|New York]]]]
[[File:Frozen Wappinger Creek.JPG|thumb|Frozen waterfall in southeast [[New York (state)|New York]]]]


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[[Image:Melting curve of water.svg|thumb|Pressure dependence of ice melting]]
[[Image:Melting curve of water.svg|thumb|Pressure dependence of ice melting]]


Most liquids under increased pressure freeze at ''higher'' temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: for some pressures higher than {{convert|1|atm|MPa|abbr=on}}, water freezes at a temperature ''below'' {{cvt|0|C|F}}. Ice, water, and [[water vapour]] can coexist at the [[triple point]], which is exactly {{cvt|273.16|K|C}} at a pressure of 611.657&nbsp;[[Pascal (unit)|Pa]].<ref>{{cite journal |last1=Wagner |first1=Wolfgang |last2=Saul |first2=A. |last3=Pruss |first3=A. |title=International Equations for the Pressure Along the Melting and Along the Sublimation Curve of Ordinary Water Substance |journal=Journal of Physical and Chemical Reference Data |date=May 1994 |volume=23 |issue=3 |pages=515–527 |doi=10.1063/1.555947 |bibcode=1994JPCRD..23..515W }}</ref><ref>{{cite journal|doi=10.1256/qj.04.94 | volume=131 | issue=608 | title=Review of the vapour pressures of ice and supercooled water for atmospheric applications | year=2005 | journal=Quarterly Journal of the Royal Meteorological Society | pages=1539–1565 | last1 = Murphy | first1 = D. M.| bibcode=2005QJRMS.131.1539M | s2cid=122365938 | url=https://zenodo.org/record/1236243 | doi-access=free }}</ref> The [[kelvin]] was defined as {{sfrac|1|273.16}} of the difference between this triple point and [[absolute zero]],<ref>{{cite web|url=http://www1.bipm.org/en/si/base_units/|title=SI base units|publisher=Bureau International des Poids et Mesures|access-date=31 August 2012|url-status=live|archive-url=https://web.archive.org/web/20120716202131/http://www.bipm.org/en/si/base_units/|archive-date=16 July 2012}}</ref> though this definition [[2019 redefinition of SI base units|changed]] in May 2019.<ref>{{cite web |url=https://www.bipm.org/utils/common/pdf/SI-statement.pdf |title=Information for users about the proposed revision of the SI |publisher=Bureau International des Poids et Mesures |access-date=6 January 2019 |archive-date=21 January 2018 |archive-url=https://web.archive.org/web/20180121160000/https://www.bipm.org/utils/common/pdf/SI-statement.pdf |url-status=dead }}</ref> Unlike most other solids, ice is difficult to [[Superheating|superheat]]. In an experiment, ice at −3&nbsp;°C was superheated to about 17&nbsp;°C for about 250 [[picosecond]]s.<ref>{{cite journal|journal=Nature|volume=439|pages=183–186|year=2006| doi=10.1038/nature04415|pmid=16407948|title=Ultrafast superheating and melting of bulk ice|bibcode=2006Natur.439..183I|last1=Iglev|first1=H.|last2=Schmeisser|first2=M.|last3=Simeonidis|first3=K.|last4=Thaller|first4=A.|last5=Laubereau|first5=A.|issue=7073|s2cid=4404036}}</ref>
Most liquids under increased pressure freeze at ''higher'' temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: for some pressures higher than {{convert|1|atm|MPa|abbr=on}}, water freezes at a temperature ''below'' {{cvt|0|C|F}}. Ice, water, and [[water vapour]] can coexist at the [[triple point]], which is exactly {{cvt|273.16|K|C}} at a pressure of 611.657&nbsp;[[Pascal (unit)|Pa]].<ref>{{cite journal |last1=Wagner |first1=Wolfgang |last2=Saul |first2=A. |last3=Pruss |first3=A. |title=International Equations for the Pressure Along the Melting and Along the Sublimation Curve of Ordinary Water Substance |journal=Journal of Physical and Chemical Reference Data |date=May 1994 |volume=23 |issue=3 |pages=515–527 |doi=10.1063/1.555947 |bibcode=1994JPCRD..23..515W }}</ref><ref>{{cite journal|doi=10.1256/qj.04.94 | volume=131 | issue=608 | title=Review of the vapour pressures of ice and supercooled water for atmospheric applications | year=2005 | journal=Quarterly Journal of the Royal Meteorological Society | pages=1539–1565 | last1 = Murphy | first1 = D. M.| bibcode=2005QJRMS.131.1539M | s2cid=122365938 | url=https://zenodo.org/record/1236243 | doi-access=free }}</ref> The [[kelvin]] was defined as {{sfrac|1|273.16}} of the difference between this triple point and [[absolute zero]],<ref>{{cite web|url=http://www1.bipm.org/en/si/base_units/|title=SI base units|publisher=Bureau International des Poids et Mesures|access-date=31 August 2012|url-status=live|archive-url=https://web.archive.org/web/20120716202131/http://www.bipm.org/en/si/base_units/|archive-date=16 July 2012}}</ref> though this definition [[2019 revision of the SI|changed]] in May 2019.<ref>{{cite web |url=https://www.bipm.org/utils/common/pdf/SI-statement.pdf |title=Information for users about the proposed revision of the SI |publisher=Bureau International des Poids et Mesures |access-date=6 January 2019 |archive-date=21 January 2018 |archive-url=https://web.archive.org/web/20180121160000/https://www.bipm.org/utils/common/pdf/SI-statement.pdf |url-status=dead }}</ref> Unlike most other solids, ice is difficult to [[Superheating|superheat]]. In an experiment, ice at −3&nbsp;°C was superheated to about 17&nbsp;°C for about 250 [[picosecond]]s.<ref>{{cite journal|journal=Nature|volume=439|pages=183–186|year=2006| doi=10.1038/nature04415|pmid=16407948|title=Ultrafast superheating and melting of bulk ice|bibcode=2006Natur.439..183I|last1=Iglev|first1=H.|last2=Schmeisser|first2=M.|last3=Simeonidis|first3=K.|last4=Thaller|first4=A.|last5=Laubereau|first5=A.|issue=7073|s2cid=4404036}}</ref>


Subjected to higher pressures and varying temperatures, ice can form in nineteen separate known crystalline phases at various densities, along with hypothetical proposed phases of ice that have not been observed.<ref name="Metcalfe-2021">{{cite news|last1=Metcalfe|first1=Tom|date=9 March 2021|title=Exotic crystals of 'ice 19' discovered|language=en|work=Live Science|url=https://www.livescience.com/exotic-ice-19-discovered.html}}</ref> With care, at least fifteen of these phases (one of the known exceptions being ice X) can be recovered at ambient pressure and low temperature in [[metastable]] form.<ref>{{cite journal|last=La Placa|first=S. J.|author2=Hamilton, W. C.|author3=Kamb, B.|author4=Prakash, A.|year=1972|title=On a nearly proton ordered structure for ice IX|journal=Journal of Chemical Physics|volume=58|issue=2|pages=567–580|doi=10.1063/1.1679238|bibcode = 1973JChPh..58..567L }}</ref><ref>{{cite journal|last=Klotz|first=S.|author2=Besson, J. M.|author3=Hamel, G.|author4=Nelmes, R. J.|author5=Loveday, J. S.|author6=Marshall, W. G.|year=1999|title=Metastable ice VII at low temperature and ambient pressure|journal=Nature|volume=398|issue=6729|pages=681–684|doi=10.1038/19480|bibcode = 1999Natur.398..681K |s2cid=4382067}}</ref> The types are differentiated by their crystalline structure, proton ordering,<ref>{{cite web|url=https://www.uwgb.edu/dutchs/Petrology/Ice%20Structure.HTM|title=Ice Structure|last=Dutch|first=Stephen|publisher=University of Wisconsin Green Bay|access-date=12 July 2017|url-status=dead|archive-url=https://web.archive.org/web/20161016143124/http://www.uwgb.edu/dutchs/petrology/Ice%20Structure.HTM|archive-date=16 October 2016}}</ref> and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are Ice IV and Ice XII. Ice XII was discovered in 1996. In 2006, Ice XIII and Ice XIV were discovered.<ref>{{cite journal |last1=Salzmann |first1=Christoph G. |last2=Radaelli |first2=Paolo G. |last3=Hallbrucker |first3=Andreas |last4=Mayer |first4=Erwin |last5=Finney |first5=John L. |title=The Preparation and Structures of Hydrogen Ordered Phases of Ice |journal=Science |date=24 March 2006 |volume=311 |issue=5768 |pages=1758–1761 |doi=10.1126/science.1123896 |pmid=16556840 |bibcode=2006Sci...311.1758S |s2cid=44522271 }}</ref> Ices XI, XIII, and XIV are hydrogen-ordered forms of ices I{{sub|h}}, V, and XII respectively. In 2009, ice XV was found at extremely high pressures and −143&nbsp;°C.<ref>{{cite magazine|url=http://www.sciencenews.org/view/generic/id/47258/title/A_very_special_snowball|title=A Very Special Snowball|author=Sanders, Laura|magazine=Science News|date=11 September 2009|access-date=11 September 2009|url-status=live|archive-url=https://web.archive.org/web/20090914174027/http://www.sciencenews.org/view/generic/id/47258/title/A_very_special_snowball|archive-date=14 September 2009}}</ref> At even higher pressures, ice is predicted to become a [[metal]]; this has been variously estimated to occur at 1.55 TPa<ref>{{cite journal |last1=Militzer |first1=Burkhard |last2=Wilson |first2=Hugh F. |title=New Phases of Water Ice Predicted at Megabar Pressures |journal=Physical Review Letters |date=2 November 2010 |volume=105 |issue=19 |page=195701 |doi=10.1103/PhysRevLett.105.195701 |pmid=21231184 |arxiv=1009.4722 |bibcode=2010PhRvL.105s5701M |s2cid=15761164 }}</ref> or 5.62 TPa.<ref>{{cite journal|author=MacMahon, J. M.|title=Ground-State Structures of Ice at High-Pressures|doi=10.1103/PhysRevB.84.220104|arxiv=1106.1941|bibcode=2011PhRvB..84v0104M|year=1970|journal=Physical Review B|volume=84|issue=22|pages=220104|s2cid=117870442}}</ref>
Subjected to higher pressures and varying temperatures, ice can form in nineteen separate known crystalline phases at various densities, along with hypothetical proposed phases of ice that have not been observed.<ref name="Metcalfe-2021">{{cite news|last1=Metcalfe|first1=Tom|date=9 March 2021|title=Exotic crystals of 'ice 19' discovered|language=en|work=Live Science|url=https://www.livescience.com/exotic-ice-19-discovered.html}}</ref> With care, at least fifteen of these phases (one of the known exceptions being ice X) can be recovered at ambient pressure and low temperature in [[metastable]] form.<ref>{{cite journal|last=La Placa|first=S. J.|author2=Hamilton, W. C.|author3=Kamb, B.|author4=Prakash, A.|year=1972|title=On a nearly proton ordered structure for ice IX|journal=Journal of Chemical Physics|volume=58|issue=2|pages=567–580|doi=10.1063/1.1679238|bibcode = 1973JChPh..58..567L }}</ref><ref>{{cite journal|last=Klotz|first=S.|author2=Besson, J. M.|author3=Hamel, G.|author4=Nelmes, R. J.|author5=Loveday, J. S.|author6=Marshall, W. G.|year=1999|title=Metastable ice VII at low temperature and ambient pressure|journal=Nature|volume=398|issue=6729|pages=681–684|doi=10.1038/19480|bibcode = 1999Natur.398..681K |s2cid=4382067}}</ref> The types are differentiated by their crystalline structure, proton ordering,<ref>{{cite web|url=https://www.uwgb.edu/dutchs/Petrology/Ice%20Structure.HTM|title=Ice Structure|last=Dutch|first=Stephen|publisher=University of Wisconsin Green Bay|access-date=12 July 2017|url-status=dead|archive-url=https://web.archive.org/web/20161016143124/http://www.uwgb.edu/dutchs/petrology/Ice%20Structure.HTM|archive-date=16 October 2016}}</ref> and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are Ice IV and Ice XII. Ice XII was discovered in 1996. In 2006, Ice XIII and Ice XIV were discovered.<ref>{{cite journal |last1=Salzmann |first1=Christoph G. |last2=Radaelli |first2=Paolo G. |last3=Hallbrucker |first3=Andreas |last4=Mayer |first4=Erwin |last5=Finney |first5=John L. |title=The Preparation and Structures of Hydrogen Ordered Phases of Ice |journal=Science |date=24 March 2006 |volume=311 |issue=5768 |pages=1758–1761 |doi=10.1126/science.1123896 |pmid=16556840 |bibcode=2006Sci...311.1758S |s2cid=44522271 }}</ref> Ices XI, XIII, and XIV are hydrogen-ordered forms of ices I{{sub|h}}, V, and XII respectively. In 2009, ice XV was found at extremely high pressures and −143&nbsp;°C.<ref>{{cite magazine|url=http://www.sciencenews.org/view/generic/id/47258/title/A_very_special_snowball|title=A Very Special Snowball|author=Sanders, Laura|magazine=Science News|date=11 September 2009|access-date=11 September 2009|url-status=live|archive-url=https://web.archive.org/web/20090914174027/http://www.sciencenews.org/view/generic/id/47258/title/A_very_special_snowball|archive-date=14 September 2009}}</ref> At even higher pressures, ice is predicted to become a [[metal]]; this has been variously estimated to occur at 1.55&nbsp;TPa<ref>{{cite journal |last1=Militzer |first1=Burkhard |last2=Wilson |first2=Hugh F. |title=New Phases of Water Ice Predicted at Megabar Pressures |journal=Physical Review Letters |date=2 November 2010 |volume=105 |issue=19 |page=195701 |doi=10.1103/PhysRevLett.105.195701 |pmid=21231184 |arxiv=1009.4722 |bibcode=2010PhRvL.105s5701M |s2cid=15761164 }}</ref> or 5.62&nbsp;TPa.<ref>{{cite journal|author=MacMahon, J. M.|title=Ground-State Structures of Ice at High-Pressures|doi=10.1103/PhysRevB.84.220104|arxiv=1106.1941|bibcode=2011PhRvB..84v0104M|year=1970|journal=Physical Review B|volume=84|issue=22|pages=220104|s2cid=117870442}}</ref>


As well as crystalline forms, solid water can exist in amorphous states as [[amorphous solid water]] (ASW) of varying densities. In outer space, hexagonal crystalline ice is present in the [[ice volcano]]es,<ref>{{cite news|url=https://www.nytimes.com/2004/12/09/science/09ice.html|title=Astronomers Contemplate Icy Volcanoes in Far Places|author=Chang, Kenneth|work=The New York Times|date=9 December 2004|access-date=30 July 2012|url-status=live|archive-url=https://web.archive.org/web/20150509123243/http://www.nytimes.com/2004/12/09/science/09ice.html|archive-date=9 May 2015}}</ref> but is extremely rare otherwise. Even icy moons like [[Ganymede (moon)|Ganymede]] are expected to mainly consist of other crystalline forms of ice.<ref>{{cite journal |url=http://www.jhuapl.edu/techdigest/TD/td2602/Prockter.pdf |title=Ice in the Solar System |author=Prockter, Louise M. |journal=Johns Hopkins APL Technical Digest |volume=26 |issue=2 |year=2005 |page=175 |url-status=dead |archive-url=https://web.archive.org/web/20150319063545/http://www.jhuapl.edu/techdigest/TD/td2602/Prockter.pdf |archive-date=19 March 2015 |access-date=21 December 2013 }}</ref><ref name=showman1997>{{Cite journal | doi = 10.1006/icar.1997.5778| title = Coupled Orbital and Thermal Evolution of Ganymede| journal = Icarus| volume = 129| issue = 2| pages = 367–383| year = 1997| last1 = Showman | first1 = A. | bibcode = 1997Icar..129..367S| url = http://www.lpl.arizona.edu/~showman/publications/showman-etal-1997.pdf}}</ref> Water in the [[interstellar medium]] is dominated by amorphous ice, making it likely the most common form of water in the universe.<ref name="stanley">{{cite journal|last1=Debennetti|first1=Pablo G. |last2=Stanley |first2=H. Eugene |year=2003 |title=Supercooled and Glassy Water |journal=Physics Today |volume=56 |issue=6 |pages=40–46 |bibcode=2003PhT....56f..40D|doi=10.1063/1.1595053 |url=http://polymer.bu.edu/hes/articles/ds03.pdf |access-date=19 September 2012 }}</ref> Low-density ASW (LDA), also known as hyperquenched glassy water, may be responsible for [[noctilucent clouds]] on Earth and is usually formed by [[vapor deposition|deposition]] of water vapor in cold or vacuum conditions.<ref>{{cite journal |last1=Lübken |first1=F.-J. |last2=Lautenbach |first2=J. |last3=Höffner |first3=J. |last4=Rapp |first4=M. |last5=Zecha |first5=M. |title=First continuous temperature measurements within polar mesosphere summer echoes |journal=Journal of Atmospheric and Solar-Terrestrial Physics |date=March 2009 |volume=71 |issue=3–4 |pages=453–463 |doi=10.1016/j.jastp.2008.06.001|bibcode=2009JASTP..71..453L }}</ref> High-density ASW (HDA) is formed by compression of ordinary ice I{{sub|h}} or LDA at GPa pressures. Very-high-density ASW (VHDA) is HDA slightly warmed to 160&nbsp;K under 1–2&nbsp;GPa pressures.<ref>{{cite journal|doi=10.1039/b108676f|title=A second distinct structural "state" of high-density amorphous ice at 77 K and 1 bar|year=2001|author1-link=Thomas Loerting|last1=Loerting|first1=Thomas|last2=Salzmann|first2=Christoph|last3=Kohl|first3=Ingrid|last4=Mayer|first4=Erwin|last5=Hallbrucker|first5=Andreas|s2cid=59485355|journal=Physical Chemistry Chemical Physics |volume=3 |pages=5355–5357 |issue=24 |bibcode=2001PCCP....3.5355L }}</ref>
As well as crystalline forms, solid water can exist in amorphous states as [[amorphous solid water]] (ASW) of varying densities. In outer space, hexagonal crystalline ice is present in the [[ice volcano]]es,<ref>{{cite news|url=https://www.nytimes.com/2004/12/09/science/09ice.html|title=Astronomers Contemplate Icy Volcanoes in Far Places|author=Chang, Kenneth|work=The New York Times|date=9 December 2004|access-date=30 July 2012|url-status=live|archive-url=https://web.archive.org/web/20150509123243/http://www.nytimes.com/2004/12/09/science/09ice.html|archive-date=9 May 2015}}</ref> but is extremely rare otherwise. Even icy moons like [[Ganymede (moon)|Ganymede]] are expected to mainly consist of other crystalline forms of ice.<ref>{{cite journal |url=http://www.jhuapl.edu/techdigest/TD/td2602/Prockter.pdf |title=Ice in the Solar System |author=Prockter, Louise M. |journal=Johns Hopkins APL Technical Digest |volume=26 |issue=2 |year=2005 |page=175 |url-status=dead |archive-url=https://web.archive.org/web/20150319063545/http://www.jhuapl.edu/techdigest/TD/td2602/Prockter.pdf |archive-date=19 March 2015 |access-date=21 December 2013 }}</ref><ref name=showman1997>{{Cite journal | doi = 10.1006/icar.1997.5778| title = Coupled Orbital and Thermal Evolution of Ganymede| journal = Icarus| volume = 129| issue = 2| pages = 367–383| year = 1997| last1 = Showman | first1 = A. | bibcode = 1997Icar..129..367S| url = http://www.lpl.arizona.edu/~showman/publications/showman-etal-1997.pdf}}</ref> Water in the [[interstellar medium]] is dominated by amorphous ice, making it likely the most common form of water in the universe.<ref name="stanley">{{cite journal|last1=Debennetti|first1=Pablo G. |last2=Stanley |first2=H. Eugene |year=2003 |title=Supercooled and Glassy Water |journal=Physics Today |volume=56 |issue=6 |pages=40–46 |bibcode=2003PhT....56f..40D|doi=10.1063/1.1595053 |url=http://polymer.bu.edu/hes/articles/ds03.pdf |access-date=19 September 2012 }}</ref> Low-density ASW (LDA), also known as hyperquenched glassy water, may be responsible for [[noctilucent clouds]] on Earth and is usually formed by [[vapor deposition|deposition]] of water vapor in cold or vacuum conditions.<ref>{{cite journal |last1=Lübken |first1=F.-J. |last2=Lautenbach |first2=J. |last3=Höffner |first3=J. |last4=Rapp |first4=M. |last5=Zecha |first5=M. |title=First continuous temperature measurements within polar mesosphere summer echoes |journal=Journal of Atmospheric and Solar-Terrestrial Physics |date=March 2009 |volume=71 |issue=3–4 |pages=453–463 |doi=10.1016/j.jastp.2008.06.001|bibcode=2009JASTP..71..453L }}</ref> High-density ASW (HDA) is formed by compression of ordinary ice I{{sub|h}} or LDA at GPa pressures. Very-high-density ASW (VHDA) is HDA slightly warmed to 160&nbsp;K under 1–2&nbsp;GPa pressures.<ref>{{cite journal|doi=10.1039/b108676f|title=A second distinct structural "state" of high-density amorphous ice at 77 K and 1 bar|year=2001|author1-link=Thomas Loerting|last1=Loerting|first1=Thomas|last2=Salzmann|first2=Christoph|last3=Kohl|first3=Ingrid|last4=Mayer|first4=Erwin|last5=Hallbrucker|first5=Andreas|s2cid=59485355|journal=Physical Chemistry Chemical Physics |volume=3 |pages=5355–5357 |issue=24 |bibcode=2001PCCP....3.5355L }}</ref>

Ice from a theorized superionic water may possess two crystalline structures. At pressures in excess of {{convert|500000|bar|psi}} such ''superionic ice'' would take on a [[body-centered cubic]] structure. However, at pressures in excess of {{convert|1000000|bar|psi}} the structure may shift to a more stable [[face-centered cubic]] lattice. It is speculated that superionic ice could compose the interior of ice giants such as Uranus and Neptune.<ref name=Phys.org-2013-04-25>{{cite news |website=Phys.org |url=http://phys.org/news/2013-04-phase-dominate-interiors-uranus-neptune.html |title=New phase of water could dominate the interiors of Uranus and Neptune |first=Lisa |last=Zyga |date=25 April 2013}}</ref>
Ice from a theorized superionic water may possess two crystalline structures. At pressures in excess of {{convert|500000|bar|psi}} such ''superionic ice'' would take on a [[body-centered cubic]] structure. However, at pressures in excess of {{convert|1000000|bar|psi}} the structure may shift to a more stable [[face-centered cubic]] lattice. It is speculated that superionic ice could compose the interior of ice giants such as Uranus and Neptune.<ref name=Phys.org-2013-04-25>{{cite news |website=Phys.org |url=http://phys.org/news/2013-04-phase-dominate-interiors-uranus-neptune.html |title=New phase of water could dominate the interiors of Uranus and Neptune |first=Lisa |last=Zyga |date=25 April 2013}}</ref>


===Friction properties===
===Friction properties===
[[File:2011 Figure Skating WC Takahiko Kozuka.jpg|thumb|[[Takahiko Kozuka]] figure skating - an act which is only possible due to ice's low frictional properties]]
[[File:2011 Figure Skating WC Takahiko Kozuka.jpg|thumb|[[Takahiko Kozuka]] figure skating - an act which is only possible due to ice's low frictional properties]]
Ice is "[[slipperiness|slippery]]" because it has a low coefficient of friction. This subject was first scientifically investigated in the 19th century. The preferred explanation at the time was "[[Pressure melting point|pressure melting]]" -i.e. the blade of an ice skate, upon exerting pressure on the ice, would melt a thin layer, providing sufficient lubrication for the blade to glide across the ice.<ref name="Rosenberg-2005" /> Yet, 1939 research by Frank P. Bowden and T. P. Hughes found that skaters would experience a lot more friction than they actually do if it were the only explanation. Further, the optimum temperature for figure skating is {{convert|5.5|C|F K|0}} and {{convert|−9|C|F K|0}} for hockey; yet, according to pressure melting theory, skating below {{convert|−4|C|F K|0}} would be outright impossible.<ref name="Chang2006" /> Instead, Bowden and Hughes argued that heating and melting of the ice layer is caused by friction. However, this theory does not sufficiently explain why ice is slippery when standing still even at below-zero temperatures.<ref name="Rosenberg-2005">{{cite journal |last1=Rosenberg |first1=Robert |title=Why Is Ice Slippery? |journal=Physics Today |date=2005 |volume=58 |issue=12 |pages=50–54 |doi=10.1063/1.2169444 |bibcode=2005PhT....58l..50R |doi-access=free }}</ref>
Ice is "[[slipperiness|slippery]]" because it has a low coefficient of friction. This subject was first scientifically investigated in the 19th century. The preferred explanation at the time was "[[Pressure melting point|pressure melting]]" -i.e. the blade of an ice skate, upon exerting pressure on the ice, would melt a thin layer, providing sufficient lubrication for the blade to glide across the ice.<ref name="Rosenberg-2005" /> Yet, 1939 research by Frank P. Bowden and T. P. Hughes found that skaters would experience a lot more friction than they actually do if it were the only explanation. Further, the optimum temperature for figure skating is {{convert|-5.5|C|F K|0}} and {{convert|−9|C|F K|0}} for hockey; yet, according to pressure melting theory, skating below {{convert|−4|C|F K|0}} would be outright impossible.<ref name="Chang2006" /> Instead, Bowden and Hughes argued that heating and melting of the ice layer is caused by friction. However, this theory does not sufficiently explain why ice is slippery when standing still even at below-zero temperatures.<ref name="Rosenberg-2005">{{cite journal |last1=Rosenberg |first1=Robert |title=Why Is Ice Slippery? |journal=Physics Today |date=2005 |volume=58 |issue=12 |pages=50–54 |doi=10.1063/1.2169444 |bibcode=2005PhT....58l..50R |doi-access=free }}</ref>


Subsequent research suggested that ice molecules at the interface cannot properly bond with the molecules of the mass of ice beneath (and thus are free to move like molecules of liquid water). These molecules remain in a semi-liquid state, providing lubrication regardless of pressure against the ice exerted by any object. However, the significance of this hypothesis is disputed by experiments showing a high [[coefficient of friction]] for ice using [[atomic force microscopy]].<ref name=Chang2006>{{cite news |first=Kenneth |last=Chang |title=Explaining Ice: The Answers Are Slippery |work=[[The New York Times]] |date=21 February 2006 |access-date=8 April 2009 |url=https://www.nytimes.com/2006/02/21/science/21ice.html?pagewanted=all |url-status=live |archive-url=https://web.archive.org/web/20081211055112/http://www.nytimes.com/2006/02/21/science/21ice.html?pagewanted=all |archive-date=11 December 2008 }}</ref> Thus, the mechanism controlling the frictional properties of ice is still an active area of scientific study.<ref>{{cite journal |last1=Canale |first1=L. |title=Nanorheology of Interfacial Water during Ice Gliding |journal=[[Physical Review X]] |date=4 September 2019 |volume=9 |issue=4 |page=041025 |doi=10.1103/PhysRevX.9.041025 |arxiv=1907.01316 |bibcode=2019PhRvX...9d1025C |doi-access=free }}</ref> A comprehensive theory of ice friction must take into account all of the aforementioned mechanisms to estimate friction coefficient of ice against various materials as a function of temperature and sliding speed. 2014 research suggests that frictional heating is the most important process under most typical conditions.<ref name=Makkonen2014>{{cite journal|last1=Makkonen|first1=Lasse|last2=Tikanmäki|first2=Maria|title=Modeling the friction of ice|journal=Cold Regions Science and Technology|date=June 2014|volume=102|pages=84–93|doi=10.1016/j.coldregions.2014.03.002|bibcode=2014CRST..102...84M }}</ref>
Subsequent research suggested that ice molecules at the interface cannot properly bond with the molecules of the mass of ice beneath (and thus are free to move like molecules of liquid water). These molecules remain in a semi-liquid state, providing lubrication regardless of pressure against the ice exerted by any object. However, the significance of this hypothesis is disputed by experiments showing a high [[coefficient of friction]] for ice using [[atomic force microscopy]].<ref name=Chang2006>{{cite news |first=Kenneth |last=Chang |title=Explaining Ice: The Answers Are Slippery |work=[[The New York Times]] |date=21 February 2006 |access-date=8 April 2009 |url=https://www.nytimes.com/2006/02/21/science/21ice.html?pagewanted=all |url-status=live |archive-url=https://web.archive.org/web/20081211055112/http://www.nytimes.com/2006/02/21/science/21ice.html?pagewanted=all |archive-date=11 December 2008 }}</ref> Thus, the mechanism controlling the frictional properties of ice is still an active area of scientific study.<ref>{{cite journal |last1=Canale |first1=L. |title=Nanorheology of Interfacial Water during Ice Gliding |journal=[[Physical Review X]] |date=4 September 2019 |volume=9 |issue=4 |page=041025 |doi=10.1103/PhysRevX.9.041025 |arxiv=1907.01316 |bibcode=2019PhRvX...9d1025C |doi-access=free }}</ref> A comprehensive theory of ice friction must take into account all of the aforementioned mechanisms to estimate friction coefficient of ice against various materials as a function of temperature and sliding speed. 2014 research suggests that frictional heating is the most important process under most typical conditions.<ref name=Makkonen2014>{{cite journal|last1=Makkonen|first1=Lasse|last2=Tikanmäki|first2=Maria|title=Modeling the friction of ice|journal=Cold Regions Science and Technology|date=June 2014|volume=102|pages=84–93|doi=10.1016/j.coldregions.2014.03.002|bibcode=2014CRST..102...84M }}</ref>
Line 91: Line 95:
The term that collectively describes all of the parts of the Earth's surface where water is in frozen form is the ''[[cryosphere]].'' Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and [[snowpack]]s are an important storage mechanism for fresh water; over time, they may sublimate or melt. [[Snowmelt]] is an important source of seasonal fresh water.<ref name="HKH2019Cryo" /><ref name="HKH2019Water" /> The [[World Meteorological Organization]] defines several kinds of ice depending on origin, size, shape, influence and so on.<ref name=wmo>[http://www.aari.nw.ru/gdsidb/XML/volume1.php?lang1=0&lang2=1&arrange=0&self=0 "WMO SEA-ICE NOMENCLATURE"] {{webarchive |url=https://web.archive.org/web/20130605124444/http://www.aari.nw.ru/gdsidb/XML/volume1.php?lang1=0&lang2=1&arrange=0&self=0 |date=5 June 2013 }} ([http://www.aari.nw.ru/gdsidb/XML/wmo_259.php Multi-language] {{webarchive |url=https://web.archive.org/web/20120414141500/http://www.aari.nw.ru/gdsidb/XML/wmo_259.php |date=14 April 2012 }}) ''World Meteorological Organization'' / ''[[Arctic and Antarctic Research Institute]]''. Retrieved 8 April 2012.</ref> [[Clathrate hydrate]]s are forms of ice that contain gas molecules trapped within its crystal lattice.<ref>{{Cite journal|doi=10.1021/ie00019a001|title=Clathrate hydrates|year=1993 |last1=Englezos |first1=Peter|journal=Industrial & Engineering Chemistry Research |volume=32|issue=7|pages=1251–1274}}</ref><ref>{{citation |publisher=U.S. Geological Survey |url=https://woodshole.er.usgs.gov/project-pages/hydrates/what.html |date=31 August 2009 |access-date=28 December 2014 |title=Gas Hydrate: What is it? |url-status=dead |archive-url=https://web.archive.org/web/20120614141539/http://woodshole.er.usgs.gov/project-pages/hydrates/what.html |archive-date=June 14, 2012}}</ref>
The term that collectively describes all of the parts of the Earth's surface where water is in frozen form is the ''[[cryosphere]].'' Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and [[snowpack]]s are an important storage mechanism for fresh water; over time, they may sublimate or melt. [[Snowmelt]] is an important source of seasonal fresh water.<ref name="HKH2019Cryo" /><ref name="HKH2019Water" /> The [[World Meteorological Organization]] defines several kinds of ice depending on origin, size, shape, influence and so on.<ref name=wmo>[http://www.aari.nw.ru/gdsidb/XML/volume1.php?lang1=0&lang2=1&arrange=0&self=0 "WMO SEA-ICE NOMENCLATURE"] {{webarchive |url=https://web.archive.org/web/20130605124444/http://www.aari.nw.ru/gdsidb/XML/volume1.php?lang1=0&lang2=1&arrange=0&self=0 |date=5 June 2013 }} ([http://www.aari.nw.ru/gdsidb/XML/wmo_259.php Multi-language] {{webarchive |url=https://web.archive.org/web/20120414141500/http://www.aari.nw.ru/gdsidb/XML/wmo_259.php |date=14 April 2012 }}) ''World Meteorological Organization'' / ''[[Arctic and Antarctic Research Institute]]''. Retrieved 8 April 2012.</ref> [[Clathrate hydrate]]s are forms of ice that contain gas molecules trapped within its crystal lattice.<ref>{{Cite journal|doi=10.1021/ie00019a001|title=Clathrate hydrates|year=1993 |last1=Englezos |first1=Peter|journal=Industrial & Engineering Chemistry Research |volume=32|issue=7|pages=1251–1274}}</ref><ref>{{citation |publisher=U.S. Geological Survey |url=https://woodshole.er.usgs.gov/project-pages/hydrates/what.html |date=31 August 2009 |access-date=28 December 2014 |title=Gas Hydrate: What is it? |url-status=dead |archive-url=https://web.archive.org/web/20120614141539/http://woodshole.er.usgs.gov/project-pages/hydrates/what.html |archive-date=June 14, 2012}}</ref>


===On the oceans===
=== In the oceans ===
{{main|Sea ice}}
{{main|Sea ice}}
Ice that is found at sea may be in the form of [[drift ice]] floating in the water, [[fast ice]] fixed to a shoreline or [[anchor ice]] if attached to the seafloor.<ref>{{cite report |date=2014 |title=WMO Sea-ice Nomenclature |url=https://library.wmo.int/records/item/41953-wmo-sea-ice-nomenclature |publisher=Secretariat of the World Meteorological Organization }}</ref> Ice which [[Ice calving|calves]] (breaks off) from an [[ice shelf]] or a coastal glacier may become an iceberg.<ref>{{cite journal | last1 = Benn | first1 = D. | last2 = Warren | first2 = C. | last3 = Mottram | first3 = R. | year = 2007 | title = Calving processes and the dynamics of calving glaciers | url = http://stuff.mit.edu/~heimbach/papers_glaciology/earthscirev_benn_etal_2007_calving.pdf | journal = Earth-Science Reviews | volume = 82 | issue = 3–4| pages = 143–179 | doi=10.1016/j.earscirev.2007.02.002| bibcode = 2007ESRv...82..143B }}</ref> The aftermath of calving events produces a loose mixture of snow and ice known as [[Ice mélange]].<ref>{{Cite journal|last=Robel|first=Alexander A.|date=2017-03-01|title=Thinning sea ice weakens buttressing force of iceberg mélange and promotes calving|journal=Nature Communications|language=en|volume=8|pages=14596|doi=10.1038/ncomms14596|pmid=28248285|pmc=5339875|bibcode=2017NatCo...814596R |issn=2041-1723}}</ref>
[[File:Ridge MOSAiC.jpg|thumb|left|A first-year sea ice ridge, photographed by the [[MOSAiC Expedition|MOSAiC expedition]] on July 4, 2020]]

Ice that is found at sea may be in the form of [[drift ice]] floating in the water, [[fast ice]] fixed to a shoreline or [[anchor ice]] if attached to the sea bottom.<ref>{{cite report |date=2014 |title=WMO Sea-ice Nomenclature |url=https://library.wmo.int/records/item/41953-wmo-sea-ice-nomenclature |publisher=Secretariat of the World Meteorological Organization }}</ref> Ice which [[Ice calving|calves]] (breaks off) from an [[ice shelf]] or glacier may become an iceberg.<ref>{{cite journal | last1 = Benn | first1 = D. | last2 = Warren | first2 = C. | last3 = Mottram | first3 = R. | year = 2007 | title = Calving processes and the dynamics of calving glaciers | url = http://stuff.mit.edu/~heimbach/papers_glaciology/earthscirev_benn_etal_2007_calving.pdf | journal = Earth-Science Reviews | volume = 82 | issue = 3–4| pages = 143–179 | doi=10.1016/j.earscirev.2007.02.002| bibcode = 2007ESRv...82..143B }}</ref>
Sea ice forms in several stages. At first, small, millimeter-scale crystals accumulate on the water surface in what is known as [[frazil ice]]. As they become somewhat larger and more consistent in shape and cover, the water surface begins to look "oily" from above, so this stage is called [[grease ice]].<ref>{{Cite book |last1=Smedsrud |first1=Lars H. |last2=Skogseth |first2=Ragnheid |title=Field Measurements of Arctic Grease Ice Properties and Processes |publisher=Cold Regions Science and Technology 44 |year=2006 |pages=171–183 }}</ref> Then, ice continues to clump together, and solidify into flat cohesive pieces known as [[ice floe]]s. Ice floes are the basic building blocks of sea ice cover, and their horizontal size (defined as half of their [[diameter]]) varies dramatically, with the smallest measured in centimeters and the largest in hundreds of kilometers.<ref>{{cite journal |last1=Roach |first1=Lettie A. |last2=Horvat |first2=Christopher |last3=Dean |first3=Samuel M. |last4=Bitz |first4=Cecilia M. |title=An Emergent Sea Ice Floe Size Distribution in a Global Coupled Ocean-Sea Ice Model |journal=JGR Oceans |date=6 May 2018 |volume=123 |issue=6 |pages=4322–4337 |doi=10.1029/2017JC013692 |bibcode=2018JGRC..123.4322R }}</ref> An area which is over 70% ice on its surface is said to be covered by pack ice.<ref>{{cite book|author1=Qin Zhang|author2=Roger Skjetne|title=Sea Ice Image Processing with MATLAB|url=https://books.google.com/books?id=DuJLDwAAQBAJ&pg=PP43|date=13 February 2018|publisher=CRC|isbn=978-1-351-06918-2|page=43}}</ref>


Sea ice can be forced together by currents and winds to form [[Pressure ridge (ice)|pressure ridges]] up to {{convert|12|m}} tall.<ref>{{Cite journal |last1=Leppäranta |first1=Matti |last2=Hakala |first2=Risto |date=25 April 1991 |title=The structure and strength of first-year ice ridges in the Baltic Sea |journal=Cold Regions Science and Technology |volume=20 |issue=3 |pages=295–311 |doi=10.1016/0165-232X(92)90036-T }}</ref> On the other hand, active wave activity can reduce sea ice to small, regularly shaped pieces, known as [[pancake ice]].<ref>{{Cite journal|last=Squire|first=Vernon A.|date=2020|title=Ocean Wave Interactions with Sea Ice: A Reappraisal |journal=Annual Review of Fluid Mechanics |volume=52 |issue=1 |pages=37–60 |bibcode=2020AnRFM..52...37S |doi=10.1146/annurev-fluid-010719-060301|s2cid=198458049 |issn=0066-4189 |doi-access=free}}</ref> Navigation through areas of thick sea ice either occurs in openings called "[[polynya]]s" or "[[Lead (sea ice)|leads]]" or requires the use of a special ship called an "[[icebreaker]]".<ref name="Sahari2021">{{cite journal |last1=Sahari |first1=Aaro |last2=Matala |first2=Saara |date=9 December 2021 |title=Of a titan, winds and power: Transnational development of the icebreaker, 1890-1954 |journal=International Journal of Maritime History |volume=33 |issue=4 |pages=722–747 |doi=10.1177/08438714211062493 }}</ref>
Fully formed sea ice can be forced together by currents and winds to form [[Pressure ridge (ice)|pressure ridges]] up to {{convert|12|m}} tall.<ref>{{Cite journal |last1=Leppäranta |first1=Matti |last2=Hakala |first2=Risto |date=25 April 1991 |title=The structure and strength of first-year ice ridges in the Baltic Sea |journal=Cold Regions Science and Technology |volume=20 |issue=3 |pages=295–311 |doi=10.1016/0165-232X(92)90036-T }}</ref> On the other hand, active wave activity can reduce sea ice to small, regularly shaped pieces, known as [[pancake ice]].<ref>{{Cite journal|last=Squire|first=Vernon A.|date=2020|title=Ocean Wave Interactions with Sea Ice: A Reappraisal |journal=Annual Review of Fluid Mechanics |volume=52 |issue=1 |pages=37–60 |bibcode=2020AnRFM..52...37S |doi=10.1146/annurev-fluid-010719-060301|s2cid=198458049 |issn=0066-4189 |doi-access=free}}</ref> Sometimes, wind and wave activity "polishes" sea ice to perfectly spherical pieces known as [[ice eggs]].<ref>{{Cite news |date=2019-11-07 |title='Ice eggs' cover Finland beach in rare weather event |language=en-GB |work=BBC News |url=https://www.bbc.com/news/world-europe-50338447 |access-date=2022-04-22}}</ref><ref>{{Cite web |last=geographyrealm |date=2019-11-14 |title=How Ice Balls Form |url=https://www.geographyrealm.com/how-ice-balls-form/ |access-date=2022-04-23 |website=Geography Realm |language=en-US}}</ref>

<gallery mode="packed" heights="150px">
File:GreaseIce2.jpg|Grease ice in the [[Bering Sea]]
File:Greenland East Coast 7.jpg|Loose drift ice on the east coast of Greenland
File:Jää on kulmunud pallideks (Looduse veidrused). 05.jpg|Ice eggs (diameter 5–10 cm) on Stroomi Beach, Tallinn, Estonia
File:IceNomenclature-2LightPack.jpg|Ice floes in Antarctica, 1919
File:Ridge MOSAiC.jpg|A first-year sea ice ridge in the Central Arctic, photographed by the [[MOSAiC Expedition|MOSAiC expedition]] on July 4, 2020
File:A_Mélange_of_Ice_-_NASA_Earth_Observatory.jpg|Ice mélange on Greenland's western coast, 2012
File:Anchor ice under sea ice.JPG|Anchor ice on the seafloor at [[McMurdo Sound]], Antarctica.
</gallery>


=== On land ===
=== On land ===
[[File:AA bedrock surface.4960.tif|thumb|[[NASA]] image of the Antarctic ice sheet]]
[[File:AA bedrock surface.4960.tif|thumb|[[NASA]] image of the Antarctic ice sheet]]
The largest ice formations on Earth are the two [[ice sheet]]s which almost completely cover the world's largest island, [[Greenland]], and the continent of [[Antarctica]]. These ice sheets have an average thickness of over {{convert|1|km|mi|1|abbr=on}} and have existed for millions of years.<ref name="BBC2017">{{cite web |title=How Greenland would look without its ice sheet |date=14 December 2017 |url=https://www.bbc.com/news/science-environment-42260580 |publisher=[[BBC News]] |access-date=7 December 2023 |archive-date=7 December 2023 |archive-url=https://web.archive.org/web/20231207201039/https://www.bbc.com/news/science-environment-42260580 |url-status=live }}</ref><ref name="Fretwell2013" />
The largest ice formations on Earth are the two [[ice sheet]]s which almost completely cover the world's largest island, [[Greenland]], and the continent of [[Antarctica]]. These ice sheets have an average thickness of over {{convert|1|km|mi|1|abbr=on}} and have existed for millions of years.<ref name="BBC2017">{{cite web |title=How Greenland would look without its ice sheet |date=14 December 2017 |url=https://www.bbc.com/news/science-environment-42260580 |publisher=[[BBC News]] |access-date=7 December 2023 |archive-date=7 December 2023 |archive-url=https://web.archive.org/web/20231207201039/https://www.bbc.com/news/science-environment-42260580 |url-status=live }}</ref><ref name="Fretwell2013" />


Other major ice formations on land include [[ice cap]]s, [[ice field]]s, [[ice stream]]s and [[glacier]]s. In particular, the [[Hindu Kush]] region is known as the Earth's "Third Pole" due to the large number of glaciers it contains. They cover an area of around {{cvt|80,000|sqkm|sqmi}}, and have a combined volume of between 3,000-4,700&nbsp;km<sup>3</sup>.<ref name="HKH2019Cryo">{{Cite book |last1=Bolch |first1=Tobias |last2=Shea |first2=Joseph M. |last3=Liu |first3=Shiyin |last4=Azam |first4=Farooq M. |last5=Gao |first5=Yang |last6=Gruber |first6=Stephan |last7=Immerzeel |first7=Walter W. |last8=Kulkarni |first8=Anil |last9=Li |first9=Huilin |last10=Tahir |first10=Adnan A. |last11=Zhang |first11=Guoqing |last12=Zhang |first12=Yinsheng |title=The Hindu Kush Himalaya Assessment |date=5 January 2019 |chapter=Status and Change of the Cryosphere in the Extended Hindu Kush Himalaya Region |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-92288-1_7 |pages=209–255 |doi=10.1007/978-3-319-92288-1_7 |isbn=978-3-319-92287-4 |s2cid=134814572 }}</ref> These glaciers are nicknamed "Asian water tower", because their meltwater run-off feeds into rivers which provide water for an estimated two billion people.<ref name="HKH2019Water">{{Cite book |last1=Scott |first1=Christopher A. |last2=Zhang |first2=Fan |last3=Mukherji |first3=Aditi |last4=Immerzeel |first4=Walter |last5=Mustafa |first5=Daanish |last6=Bharati |first6=Luna |title=The Hindu Kush Himalaya Assessment |date=5 January 2019 |chapter=Water in the Hindu Kush Himalaya |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-92288-1_8 |pages=257–299 |doi=10.1007/978-3-319-92288-1_8 |isbn=978-3-319-92287-4 |s2cid=133800578 }}</ref>
Other major ice formations on land include [[ice cap]]s, [[ice field]]s, [[ice stream]]s and [[glacier]]s. In particular, the [[Hindu Kush]] region is known as the Earth's "Third Pole" due to the large number of glaciers it contains. They cover an area of around {{cvt|80,000|sqkm|sqmi}}, and have a combined volume of between 3,000-4,700&nbsp;km<sup>3</sup>.<ref name="HKH2019Cryo">{{Cite book |last1=Bolch |first1=Tobias |last2=Shea |first2=Joseph M. |last3=Liu |first3=Shiyin |last4=Azam |first4=Farooq M. |last5=Gao |first5=Yang |last6=Gruber |first6=Stephan |last7=Immerzeel |first7=Walter W. |last8=Kulkarni |first8=Anil |last9=Li |first9=Huilin |last10=Tahir |first10=Adnan A. |last11=Zhang |first11=Guoqing |last12=Zhang |first12=Yinsheng |title=The Hindu Kush Himalaya Assessment |date=5 January 2019 |chapter=Status and Change of the Cryosphere in the Extended Hindu Kush Himalaya Region |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-92288-1_7 |pages=209–255 |doi=10.1007/978-3-319-92288-1_7 |isbn=978-3-319-92287-4 |s2cid=134814572 }}</ref> These glaciers are nicknamed "Asian water towers", because their meltwater run-off feeds into rivers which provide water for an estimated two billion people.<ref name="HKH2019Water">{{Cite book |last1=Scott |first1=Christopher A. |last2=Zhang |first2=Fan |last3=Mukherji |first3=Aditi |last4=Immerzeel |first4=Walter |last5=Mustafa |first5=Daanish |last6=Bharati |first6=Luna |title=The Hindu Kush Himalaya Assessment |date=5 January 2019 |chapter=Water in the Hindu Kush Himalaya |chapter-url=https://link.springer.com/chapter/10.1007/978-3-319-92288-1_8 |pages=257–299 |doi=10.1007/978-3-319-92288-1_8 |isbn=978-3-319-92287-4 |s2cid=133800578 }}</ref>


[[Permafrost]] refers to [[soil]] or underwater [[sediment]] which continuously remains below {{cvt|0|C|F}} for two years or more.<ref>{{cite web |url=https://climate.mit.edu/explainers/permafrost |title=Permafrost |last1=McGee |first1=David |last2=Gribkoff |first2=Elizabeth |date=4 August 2022 |website=MIT Climate Portal |access-date=27 September 2023 }}</ref> The ice within permafrost is divided into four categories: pore ice, vein ice (also known as ice wedges), buried surface ice and intrasedimental ice (from the freezing of underground waters).<ref>{{Cite journal |last1=Lacelle |first1=Denis |last2=Fisher |first2=David A. |last3=Verret |first3=Marjolaine |last4=Pollard |first4=Wayne |date=17 February 2022 |title=Improved prediction of the vertical distribution of ground ice in Arctic-Antarctic permafrost sediments |journal=Communications Earth & Environment |volume=3 |issue=31 |page=31 |doi=10.1038/s43247-022-00367-z |bibcode=2022ComEE...3...31L |s2cid=246872753 }}</ref> One example of ice formation in permafrost areas is [[aufeis]] - layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick.<ref>{{Cite journal |last1=Huryn |first1=Alexander D. |last2=Gooseff |first2=Michael N. |last3=Hendrickson |first3=Patrick J. |last4=Briggs |first4=Martin A. |last5=Tape |first5=Ken D. |last6=Terry |first6=Neil C. |date=2020-10-13 |title=Aufeis fields as novel groundwater-dependent ecosystems in the arctic cryosphere |journal=Limnology and Oceanography |volume=66 |issue=3 |pages=607–624 |doi=10.1002/lno.11626 |s2cid=225139804 |issn=0024-3590|doi-access=free }}</ref> [[Snow line]] and [[snow field]]s are two related concepts, in that snow fields accumulate on top of and ablate away to the equilibrium point (the snow line) in an ice deposit.<ref>{{Cite book |last1=Johnson |first1=Chris |url=https://slcc.pressbooks.pub/introgeology/chapter/14-glaciers/ |title=An Introduction to Geology |last2=Affolter |first2=Matthew D. |last3=Inkenbrandt |first3=Paul |last4=Mosher |first4=Cam |date=July 1, 2017 |chapter=14 Glaciers}}</ref>
=== On surfaces ===

[[File:Ice on stairway, 1968 (32085554416).jpg|thumb|left|upright|Icicles on a [[stairway]] in [[Seattle]]. Photo taken on 29 January 1968]]

As water drips and re-freezes, it can form hanging [[icicle]]s, or [[stalagmite]]-like structures on the ground.<ref>{{cite journal|last=Makkonen |first=Lase |title=Models for the growth of rime, glaze, icicles and wet snow deposits on structures |journal=Philosophical Transactions of the Royal Society of London A |date=15 November 2000 |volume=358 |issue=1776 |pages=2913–2939 |doi=10.1098/rsta.2000.0690 }}</ref> On sloped roofs, buildup of ice can produce an [[Ice dam (roof)|ice dam]], which stops melt water from draining properly and potentially leads to damaging leaks.<ref>{{cite web |title=Dealing with and preventing ice dams |url=https://extension.umn.edu/protecting-home-rain-and-ice/dealing-and-preventing-ice-dams |publisher=[[University of Minnesota]] Extension |access-date=10 April 2024 }}</ref>

[[Aufeis]] is layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick.<ref>{{Cite journal |last1=Huryn |first1=Alexander D. |last2=Gooseff |first2=Michael N. |last3=Hendrickson |first3=Patrick J. |last4=Briggs |first4=Martin A. |last5=Tape |first5=Ken D. |last6=Terry |first6=Neil C. |date=2020-10-13 |title=Aufeis fields as novel groundwater-dependent ecosystems in the arctic cryosphere |journal=Limnology and Oceanography |volume=66 |issue=3 |pages=607–624 |doi=10.1002/lno.11626 |s2cid=225139804 |issn=0024-3590|doi-access=free }}</ref> [[Snow line]] and [[snow field]]s are two related concepts.


===On rivers and streams===
===On rivers and streams===
[[File:Frozen rivulet in Pennsylvania.JPG|thumb|A small frozen [[rivulet]]]]
[[File:Frozen rivulet in Pennsylvania.JPG|thumb|A small frozen [[rivulet]]]]
Ice which forms on moving water tends to be less uniform and stable than ice which forms on calm water. [[Ice jam]]s (sometimes called "ice dams"), when broken chunks of ice pile up, are the greatest ice hazard on rivers. Ice jams can cause flooding, damage structures in or near the river, and damage vessels on the river. Ice jams can cause some [[hydropower]] industrial facilities to completely shut down. An ice dam is a blockage from the movement of a glacier which may produce a [[proglacial lake]]. Heavy ice flows in rivers can also damage vessels and require the use of an icebreaker to keep navigation possible.<ref>{{cite web|url=http://www.nws.noaa.gov/floodsafety/ice_jam.shtml |title=Ice Jams |publisher=Nws.noaa.gov |date=2013-03-13 |access-date=11 January 2014 }}</ref><ref>{{Cite news|url=https://www.popularmechanics.com/science/environment/a473/2272511/ |title=Ice Dams: Taming An Icy River|last=Staff writer|date=7 February 2006 |work=Popular Mechanics|access-date=27 March 2018 |language=en-US}}</ref>
Ice which forms on moving water tends to be less uniform and stable than ice which forms on calm water. [[Ice jam]]s (sometimes called "ice dams"), when broken chunks of ice pile up, are the greatest ice hazard on rivers. Ice jams can cause flooding, damage structures in or near the river, and damage vessels on the river. Ice jams can cause some [[hydropower]] industrial facilities to completely shut down. An ice dam is a blockage from the movement of a glacier which may produce a [[proglacial lake]]. Heavy ice flows in rivers can also damage vessels and require the use of an [[icebreaker]] vessel to keep navigation possible.<ref>{{cite web|url=http://www.nws.noaa.gov/floodsafety/ice_jam.shtml |title=Ice Jams |publisher=Nws.noaa.gov |date=2013-03-13 |access-date=11 January 2014 }}</ref><ref>{{Cite news|url=https://www.popularmechanics.com/science/environment/a473/2272511/ |title=Ice Dams: Taming An Icy River|last=Staff writer|date=7 February 2006 |work=Popular Mechanics|access-date=27 March 2018 |language=en-US}}</ref>


[[Ice disc]]s are circular formations of ice floating on river water. They form within [[Eddy (fluid dynamics)|eddy current]]s, and their position results in asymmetric melting, which makes them continuously rotate at a low speed.<ref>{{Cite web |url=http://modernnotion.com/crop-circles-ice-ice-circles-form/ |title=Crop Circles in the Ice: How Do Ice Circles Form? |date=22 December 2015 |website=Modern Notion |language=en-US |access-date=16 January 2019}}</ref><ref>{{cite journal |last1=Dorbolo |first1=S |last2=Adami |first2=N. |last3=Dubois |first3=C. |last4=Caps |first4=H. |last5=Vandewalle |first5=N. |last6=Barbois-Texier |first6=B. |title=Rotation of melting ice disks due to melt fluid flow |journal=Phys. Rev. E |year=2016 |volume=93 |issue=3 |pages=1–5 |doi=10.1103/PhysRevE.93.033112 |pmid=27078452 |bibcode=2016PhRvE..93c3112D |hdl=2268/195696 |s2cid=118380381 |url=https://orbi.uliege.be/handle/2268/195696|arxiv=1510.06505 }}</ref>
[[Ice disc]]s are circular formations of ice floating on river water. They form within [[Eddy (fluid dynamics)|eddy current]]s, and their position results in asymmetric melting, which makes them continuously rotate at a low speed.<ref>{{Cite web |url=http://modernnotion.com/crop-circles-ice-ice-circles-form/ |title=Crop Circles in the Ice: How Do Ice Circles Form? |date=22 December 2015 |website=Modern Notion |language=en-US |access-date=16 January 2019 |archive-date=8 August 2017 |archive-url=https://web.archive.org/web/20170808193720/http://modernnotion.com/crop-circles-ice-ice-circles-form/ |url-status=dead }}</ref><ref>{{cite journal |last1=Dorbolo |first1=S |last2=Adami |first2=N. |last3=Dubois |first3=C. |last4=Caps |first4=H. |last5=Vandewalle |first5=N. |last6=Barbois-Texier |first6=B. |title=Rotation of melting ice disks due to melt fluid flow |journal=Phys. Rev. E |year=2016 |volume=93 |issue=3 |pages=1–5 |doi=10.1103/PhysRevE.93.033112 |pmid=27078452 |bibcode=2016PhRvE..93c3112D |hdl=2268/195696 |s2cid=118380381 |url=https://orbi.uliege.be/handle/2268/195696|arxiv=1510.06505 }}</ref>


===On lakes{{anchor|Ice_on_lakes}}===
===On lakes{{anchor|Ice_on_lakes}}===
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Ice forms on calm water from the shores, a thin layer spreading across the surface, and then downward. Ice on lakes is generally four types: primary, secondary, superimposed and agglomerate.<ref>Petrenko, Victor F. and Whitworth, Robert W. (1999) ''Physics of ice''. Oxford: Oxford University Press, pp. 27–29, {{ISBN|0191581348}}</ref><ref>Eranti, E. and Lee, George C. (1986) ''Cold region structural engineering''. New York: McGraw-Hill, p. 51, {{ISBN|0070370346}}.</ref> Primary ice forms first. Secondary ice forms below the primary ice in a direction parallel to the direction of the heat flow. Superimposed ice forms on top of the ice surface from rain or water which seeps up through cracks in the ice which often settles when loaded with snow. An [[ice shove]] occurs when ice movement, caused by ice expansion and/or wind action, occurs to the extent that ice pushes onto the shores of lakes, often displacing sediment that makes up the shoreline.<ref>{{cite journal |last1=Dionne |first1=J |title=Ice action in the lacustrine environment. A review with particular reference to subarctic Quebec, Canada |journal=Earth-Science Reviews |date=November 1979 |volume=15 |issue=3 |pages=185–212 |doi=10.1016/0012-8252(79)90082-5 |bibcode=1979ESRv...15..185D }}</ref>
Ice forms on calm water from the shores, a thin layer spreading across the surface, and then downward. Ice on lakes is generally four types: primary, secondary, superimposed and agglomerate.<ref>Petrenko, Victor F. and Whitworth, Robert W. (1999) ''Physics of ice''. Oxford: Oxford University Press, pp. 27–29, {{ISBN|0191581348}}</ref><ref>Eranti, E. and Lee, George C. (1986) ''Cold region structural engineering''. New York: McGraw-Hill, p. 51, {{ISBN|0070370346}}.</ref> Primary ice forms first. Secondary ice forms below the primary ice in a direction parallel to the direction of the heat flow. Superimposed ice forms on top of the ice surface from rain or water which seeps up through cracks in the ice which often settles when loaded with snow. An [[ice shove]] occurs when ice movement, caused by ice expansion and/or wind action, occurs to the extent that ice pushes onto the shores of lakes, often displacing sediment that makes up the shoreline.<ref>{{cite journal |last1=Dionne |first1=J |title=Ice action in the lacustrine environment. A review with particular reference to subarctic Quebec, Canada |journal=Earth-Science Reviews |date=November 1979 |volume=15 |issue=3 |pages=185–212 |doi=10.1016/0012-8252(79)90082-5 |bibcode=1979ESRv...15..185D }}</ref>


[[Shelf ice]] is formed when floating pieces of ice are driven by the wind piling up on the windward shore. This kind of ice may contain large air pockets under a thin surface layer, which makes it particularly hazardous to walk across it.<ref>{{Cite news |last=Schwarz |first=Phil |date=19 February 2018 |title=Dangerous shelf ice forms along Lake Michigan |url=https://abc7chicago.com/3109973/ |work=abc7chicago.com |accessdate=2020-02-05 }}</ref> Another dangerous form of [[rotten ice]] to traverse on foot is candle ice, which develops in columns perpendicular to the surface of a lake. Because it lacks a firm horizontal structure, a person who fell through has nothing to hold onto to pull themselves out.<ref>{{Cite encyclopedia|title=Candle ice|encyclopedia=Glossary of Meteorology|publisher=[[American Meteorological Society]]|url=https://glossary.ametsoc.org/wiki/Candle_ice|access-date=2021-03-17|date=2012-02-20}}</ref>
[[Shelf ice]] is formed when floating pieces of ice are driven by the wind piling up on the windward shore. This kind of ice may contain large air pockets under a thin surface layer, which makes it particularly hazardous to walk across it.<ref>{{Cite news |last=Schwarz |first=Phil |date=19 February 2018 |title=Dangerous shelf ice forms along Lake Michigan |url=https://abc7chicago.com/3109973/ |work=abc7chicago.com |accessdate=2020-02-05 }}</ref> Another dangerous form of [[rotten ice]] to traverse on foot is candle ice, which develops in columns perpendicular to the surface of a lake. Because it lacks a firm horizontal structure, a person who has fallen through has nothing to hold onto to pull themselves out.<ref>{{Cite encyclopedia|title=Candle ice|encyclopedia=Glossary of Meteorology|publisher=[[American Meteorological Society]]|url=https://glossary.ametsoc.org/wiki/Candle_ice|access-date=2021-03-17|date=2012-02-20}}</ref>

=== As precipitation ===
{{Main|Precipitation}}
====Snow and freezing rain ====
{{Main|Snow|Snowflake}}
[[File:SnowflakesWilsonBentley.jpg|thumb|[[Snowflake]]s by [[Wilson Bentley]], 1902]]
Snow crystals form when tiny [[supercool]]ed cloud droplets (about 10&nbsp;[[μm]] in diameter) [[freezing|freeze]]. These droplets are able to remain liquid at temperatures lower than {{convert|-18|C|K F}}, because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus". Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than {{convert|-35|C|K F}}.<ref name=Mason>{{cite book|author = Mason, Basil John| publisher= Clarendon Press| isbn= 978-0-19-851603-3|year = 1971|title = Physics of Clouds|url = https://archive.org/details/physicsofclouds0000maso|url-access = registration}}</ref> In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. Our understanding of what particles make efficient ice nuclei is poor&nbsp;– what we do know is they are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective,<ref name=Christner2008>{{cite journal |last1=Christner |first1=Brent C. |last2=Morris |first2=Cindy E. |last3=Foreman |first3=Christine M. |last4=Cai |first4=Rongman |last5=Sands |first5=David C. |title=Ubiquity of Biological Ice Nucleators in Snowfall |journal=Science |date=29 February 2008 |volume=319 |issue=5867 |pages=1214 |doi=10.1126/science.1149757 |pmid=18309078 |bibcode=2008Sci...319.1214C |citeseerx=10.1.1.714.4002 |s2cid=39398426 }}</ref> although to what extent is unclear. Artificial nuclei are used in [[cloud seeding]].<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=cloud+seeding&submit=Search|title=Cloud seeding|author=Glossary of Meteorology|year=2009|access-date=28 June 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20120315161127/http://amsglossary.allenpress.com/glossary/search?p=1&query=cloud+seeding&submit=Search|archive-date=15 March 2012}}</ref> The droplet then grows by condensation of water vapor onto the ice surfaces.<ref>{{cite journal |last1=Pelley |first1=Janet |title=Does cloud seeding really work? |journal=Chemical and Engineering News|date=30 May 2016|volume=94 |issue=22 |pages=18–21 |url=http://cen.acs.org/articles/94/i22/Does-cloud-seeding-really-work.html |access-date=26 May 2024 |archive-date=10 November 2016 |archive-url=https://web.archive.org/web/20161110235130/http://cen.acs.org/articles/94/i22/Does-cloud-seeding-really-work.html |url-status=live}}</ref>


===In the air===
====Glaze and rime====
[[File:Icy Japanese Maple branch, Boxborough, Massachusetts, 2008.jpg|thumb|left|upright=1.05|Ice on [[deciduous tree]] after freezing rain]]
[[Ice storm]] is a type of winter storm characterized by [[freezing rain]], which produces a [[glaze ice|glaze]] of ice on surfaces, including roads and [[power line]]s. In the United States, a quarter of winter weather events produce glaze ice, and utilities need to be prepared to minimize damages.<ref>{{cite journal |last1=Sanders |first1=Kristopher J. |last2=Barjenbruch |first2=Brian L. |title=Analysis of Ice-to-Liquid Ratios during Freezing Rain and the Development of an Ice Accumulation Model |journal=Weather Forecasting |date=1 August 2016 |volume=31 |issue=4 |pages=1041–1060 |doi=10.1175/WAF-D-15-0118.1 |bibcode=2016WtFor..31.1041S }}</ref>
[[Ice storm]] is a type of winter storm characterized by [[freezing rain]], which produces a [[glaze ice|glaze]] of ice on surfaces, including roads and [[power line]]s. In the United States, a quarter of winter weather events produce glaze ice, and utilities need to be prepared to minimize damages.<ref>{{cite journal |last1=Sanders |first1=Kristopher J. |last2=Barjenbruch |first2=Brian L. |title=Analysis of Ice-to-Liquid Ratios during Freezing Rain and the Development of an Ice Accumulation Model |journal=Weather Forecasting |date=1 August 2016 |volume=31 |issue=4 |pages=1041–1060 |doi=10.1175/WAF-D-15-0118.1 |bibcode=2016WtFor..31.1041S }}</ref>


==== Hard forms ====
Glaze may also appear on surfaces as they come in contact with water droplets (i.e. from [[fog]]) at low temperatures, in what is known as [[atmospheric icing]]. Sometimes, drops of water crystallize on cold objects as [[Rime ice|rime]] instead of glaze. Soft rime has a density between a quarter and two thirds that of pure ice.,<ref>{{cite journal |last1=Podolskiy |first1=Evgeny Andreevich |last2=Nygaard |first2=Bjørn Egil Kringlebotn |last3=Nishimura |first3=Kouichi |last4=Makkonen |first4=Lasse |last5=Lozowski |first5=Edward Peter |title=Study of unusual atmospheric icing at Mount Zao, Japan, using the Weather Research and Forecasting model |journal=Journal of Geophysical Research: Atmospheres |date=27 June 2012 |volume=112 |issue=D2 |doi=10.1029/2011JD017042 |bibcode=2012JGRD..11712106P }}</ref> due to a high proportion of trapped air, which also makes soft rime appear white. Hard rime is denser, more transparent, and more likely to appear on ships and aircraft.<ref>{{Cite web |title=hard rime (Glossary of Meteorology) |url=https://glossary.ametsoc.org/wiki/Hard_rime |date=30 March 2024 |publisher=American Meteorological Society |language=en-US |access-date=11 April 2024 }}</ref><ref>{{Cite web |title=soft rime (Glossary of Meteorology) |url=https://glossary.ametsoc.org/wiki/Soft_rime |date=30 March 2024 |publisher=American Meteorological Society |language=en-US |access-date=11 April 2024 }}</ref>
{{Further|Ice crystal}}

===Pellets===
{{Main|Ice pellets}}
[[File:Sleet on the ground.jpg|thumb|right|An accumulation of ice pellets]]
[[Ice pellets]] are a form of precipitation consisting of small, [[translucent]] balls of ice. This form of precipitation is also referred to as "sleet" by the United States [[National Weather Service]].<ref>{{cite web|url=http://www.weather.gov/glossary/index.php?word=sleet|title=Sleet (glossary entry)|publisher=National Oceanic and Atmospheric Administration's National Weather Service|access-date=20 March 2007|url-status=live|archive-url=https://web.archive.org/web/20070218030309/http://www.weather.gov/glossary/index.php?word=sleet|archive-date=18 February 2007}}</ref> (In [[British English]] "sleet" refers to [[Rain and snow mixed|a mixture of rain and snow]].) Ice pellets are usually smaller than hailstones.<ref>{{cite web|url=http://www.weather.gov/glossary/index.php?word=hail|title=Hail (glossary entry)|publisher=National Oceanic and Atmospheric Administration's National Weather Service|access-date=20 March 2007|url-status=live|archive-url=https://web.archive.org/web/20071127004804/http://www.weather.gov/glossary/index.php?word=hail|archive-date=27 November 2007}}</ref> They often bounce when they hit the ground, and generally do not freeze into a solid mass unless mixed with [[freezing rain]]. The [[METAR]] code for ice pellets is ''PL''.<ref name="METAR"/>

Ice pellets form when a layer of above-freezing air is located between {{convert|1500|and|3000|m|ft}} above the ground, with sub-freezing air both above and below it. This causes the partial or complete melting of any snowflakes falling through the warm layer. As they fall back into the sub-freezing layer closer to the surface, they re-freeze into ice pellets. However, if the sub-freezing layer beneath the warm layer is too small, the precipitation will not have time to re-freeze, and freezing rain will be the result at the surface. A temperature profile showing a warm layer above the ground is most likely to be found in advance of a [[warm front]] during the cold season,<ref>{{cite web|publisher=Weatherquestions.com|url=http://www.weatherquestions.com/What_causes_ice_pellets.htm|title=What causes ice pellets (sleet)?|access-date=8 December 2007|url-status=live|archive-url=https://web.archive.org/web/20071130071143/http://www.weatherquestions.com/What_causes_ice_pellets.htm|archive-date=30 November 2007}}</ref> but can occasionally be found behind a passing [[cold front]].

====Hail====
{{Main|Hail}}
[[File:Granizo.jpg|right|thumb|A large hailstone, about {{convert|6|cm|in|abbr=on}} in diameter]]
[[File:Granizo.jpg|right|thumb|A large hailstone, about {{convert|6|cm|in|abbr=on}} in diameter]]
Like other precipitation, hail forms in storm [[cloud]]s when [[supercooled]] water droplets freeze on contact with [[condensation nuclei]], such as [[dust]] or [[dirt]]. The storm's [[updraft]] blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of {{convert|5|mm|in}} or more.<ref name="gloss">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=hail1|title=Hail|year=2009|access-date=15 July 2009|author=Glossary of Meteorology|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20100725142407/http://amsglossary.allenpress.com/glossary/search?id=hail1|archive-date=25 July 2010}}</ref> Within [[METAR]] code, GR is used to indicate larger hail, of a diameter of at least {{convert|6.4|mm|in}} and GS for smaller.<ref name="METAR">{{cite web|url=http://www.alaska.faa.gov/fai/afss/metar+taf/sametara.htm|title=SA-METAR|author=Alaska Air Flight Service Station|publisher=[[Federal Aviation Administration]] via the Internet Wayback Machine|access-date=29 August 2009|date=10 April 2007|url-status=dead|archive-url=https://web.archive.org/web/20080501074014/http://www.alaska.faa.gov/fai/afss/metar%20taf/sametara.htm|archive-date=1 May 2008}}</ref> Stones of {{Convert|0.75|in|mm|order=flip}}, {{Convert|1.0|in|mm|order=flip}} and {{Convert|1.75|in|mm|order=flip}} are the most frequently reported hail sizes in North America.<ref>{{cite web|url=http://www.spc.noaa.gov/publications/jewell/hailslsc.pdf|title=P9.5 Evaluation of an Alberta Hail Growth Model Using Severe Hail Proximity Soundings in the United States|author1=Jewell, Ryan|author2=Brimelow, Julian|date=17 August 2004|access-date=15 July 2009|url-status=live|archive-url=https://web.archive.org/web/20090507044027/http://www.spc.noaa.gov/publications/jewell/hailslsc.pdf|archive-date=7 May 2009}}</ref> Hailstones can grow to {{convert|15|cm|in|0}} and weigh more than {{convert|0.5|kg|lb|1}}.<ref>{{cite web|url=http://www.photolib.noaa.gov/htmls/nssl0001.htm|title=Aggregate hailstone|author=National Severe Storms Laboratory|publisher=National Oceanic and Atmospheric Administration|date=23 April 2007|access-date=15 July 2009|url-status=live|archive-url=https://web.archive.org/web/20090810182627/http://www.photolib.noaa.gov/htmls/nssl0001.htm|archive-date=10 August 2009}}</ref> In large hailstones, [[latent heat]] released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones.<ref>{{cite journal|title=Modeling Maximum Hail Size in Alberta Thunderstorms|journal=Weather and Forecasting|author1=Brimelow, Julian C. |author2=Reuter, Gerhard W. |author3=Poolman, Eugene R. |pages=1048–1062|volume=17|issue=5|doi=10.1175/1520-0434(2002)017<1048:MMHSIA>2.0.CO;2|bibcode = 2002WtFor..17.1048B|year=2002|doi-access=free}}</ref> The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud.<ref>{{cite web|url=http://www.ucar.edu/communications/factsheets/Hail.html|title=Hail Fact Sheet|date=10 April 2000|author=Marshall, Jacque|access-date=15 July 2009|publisher=University Corporation for Atmospheric Research|url-status=dead|archive-url=https://web.archive.org/web/20091015141754/http://www.ucar.edu/communications/factsheets/Hail.html|archive-date=15 October 2009}}</ref>
[[Hail]] forms in storm [[cloud]]s when [[supercooled]] water droplets freeze on contact with [[condensation nuclei]], such as [[dust]] or [[dirt]]. The storm's [[updraft]] blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of {{convert|5|mm|in}} or more.<ref name="gloss">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?id=hail1|title=Hail|year=2009|access-date=15 July 2009|author=Glossary of Meteorology|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20100725142407/http://amsglossary.allenpress.com/glossary/search?id=hail1|archive-date=25 July 2010}}</ref> Within [[METAR]] code, GR is used to indicate larger hail, of a diameter of at least {{convert|6.4|mm|in}} and GS for smaller.<ref name="METAR">{{cite web|url=http://www.alaska.faa.gov/fai/afss/metar+taf/sametara.htm|title=SA-METAR|author=Alaska Air Flight Service Station|publisher=[[Federal Aviation Administration]] via the Internet Wayback Machine|access-date=29 August 2009|date=10 April 2007|url-status=dead|archive-url=https://web.archive.org/web/20080501074014/http://www.alaska.faa.gov/fai/afss/metar%20taf/sametara.htm|archive-date=1 May 2008}}</ref> Stones of {{Convert|0.75|in|mm|order=flip}}, {{Convert|1.0|in|mm|order=flip}} and {{Convert|1.75|in|mm|order=flip}} are the most frequently reported hail sizes in North America.<ref>{{cite web|url=http://www.spc.noaa.gov/publications/jewell/hailslsc.pdf|title=P9.5 Evaluation of an Alberta Hail Growth Model Using Severe Hail Proximity Soundings in the United States|author1=Jewell, Ryan|author2=Brimelow, Julian|date=17 August 2004|access-date=15 July 2009|url-status=live|archive-url=https://web.archive.org/web/20090507044027/http://www.spc.noaa.gov/publications/jewell/hailslsc.pdf|archive-date=7 May 2009}}</ref> Hailstones can grow to {{convert|15|cm|in|0}} and weigh more than {{convert|0.5|kg|lb|1}}.<ref>{{cite web|url=http://www.photolib.noaa.gov/htmls/nssl0001.htm|title=Aggregate hailstone|author=National Severe Storms Laboratory|publisher=National Oceanic and Atmospheric Administration|date=23 April 2007|access-date=15 July 2009|url-status=live|archive-url=https://web.archive.org/web/20090810182627/http://www.photolib.noaa.gov/htmls/nssl0001.htm|archive-date=10 August 2009}}</ref> In large hailstones, [[latent heat]] released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones.<ref>{{cite journal|title=Modeling Maximum Hail Size in Alberta Thunderstorms|journal=Weather and Forecasting|author1=Brimelow, Julian C. |author2=Reuter, Gerhard W. |author3=Poolman, Eugene R. |pages=1048–1062|volume=17|issue=5|doi=10.1175/1520-0434(2002)017<1048:MMHSIA>2.0.CO;2|bibcode = 2002WtFor..17.1048B|year=2002|doi-access=free}}</ref> The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud.<ref>{{cite web|url=http://www.ucar.edu/communications/factsheets/Hail.html|title=Hail Fact Sheet|date=10 April 2000|author=Marshall, Jacque|access-date=15 July 2009|publisher=University Corporation for Atmospheric Research|url-status=dead|archive-url=https://web.archive.org/web/20091015141754/http://www.ucar.edu/communications/factsheets/Hail.html|archive-date=15 October 2009}}</ref>
[[File:2013-02-23_03_59_28_Graupel_(snow_pellets)_in_Elko,_Nevada.JPG|thumb|left|
Soft hail, or graupel, in [[Nevada]]]]
Hail forms in strong [[thunderstorm]] clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing {{convert|0|C|F|0}}.<ref name="gloss"/> Hail-producing clouds are often identifiable by their green coloration.<ref>{{cite web|url=http://www.abc.net.au/news/australia/qld/toowoomba/200410/s1222665.htm|archive-url=https://web.archive.org/web/20100306021712/http://www.abc.net.au/news/australia/qld/toowoomba/200410/s1222665.htm|archive-date=6 March 2010|title=Hail storms rock southern Qld|publisher=Australian Broadcasting Corporation|date=19 October 2004|access-date=15 July 2009}}</ref><ref>{{cite web|url=http://australiasevereweather.com/storm_news/arc1997.htm|title=Severe Thunderstorm Images of the Month Archives|year=1997|author1=Bath, Michael|author2=Degaura, Jimmy|access-date=15 July 2009|url-status=live|archive-url=http://archive.wikiwix.com/cache/20110713110215/http://australiasevereweather.com/storm_news/arc1997.htm|archive-date=13 July 2011}}</ref> The growth rate is maximized at about {{convert|-13|C|F|0}}, and becomes vanishingly small much below {{convert|-30|C|F|0}} as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of {{convert|11000|ft|m}}.<ref>{{cite web|url=http://www.meted.ucar.edu/resource/soo/MesoAnalyst.htm|archive-url=https://web.archive.org/web/20030320222147/http://www.meted.ucar.edu/resource/soo/MesoAnalyst.htm|archive-date=20 March 2003|title=Meso-Analyst Severe Weather Guide|author=Wolf, Pete|date=16 January 2003|access-date=16 July 2009|publisher=University Corporation for Atmospheric Research}}</ref> [[Entrainment (meteorology)|Entrainment]] of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporative cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the [[atmosphere]] over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.<ref>{{cite book|url=https://books.google.com/books?id=UbtG3vFfNtoC&pg=PA41|title=Climate, change and risk|author1=Downing, Thomas E. |author2=Olsthoorn, Alexander A. |author3=Tol, Richard S. J. |pages=41–43|publisher=Routledge|year=1999|isbn=978-0-415-17031-4}}</ref>
[[File:Sleet on the ground.jpg|thumb|An accumulation of ice pellets]]
Ice pellets ([[METAR]] code ''PL''<ref name="METAR"/>) are a form of precipitation consisting of small, [[translucent]] balls of ice, which are usually smaller than hailstones.<ref>{{cite web|url=http://www.weather.gov/glossary/index.php?word=hail|title=Hail (glossary entry)|publisher=National Oceanic and Atmospheric Administration's National Weather Service|access-date=20 March 2007|url-status=live|archive-url=https://web.archive.org/web/20071127004804/http://www.weather.gov/glossary/index.php?word=hail|archive-date=27 November 2007}}</ref> This form of precipitation is also referred to as "sleet" by the United States [[National Weather Service]].<ref>{{cite web|url=http://www.weather.gov/glossary/index.php?word=sleet|title=Sleet (glossary entry)|publisher=National Oceanic and Atmospheric Administration's National Weather Service|access-date=20 March 2007|url-status=live|archive-url=https://web.archive.org/web/20070218030309/http://www.weather.gov/glossary/index.php?word=sleet|archive-date=18 February 2007}}</ref> (In [[British English]] "sleet" refers to [[Rain and snow mixed|a mixture of rain and snow]].) Ice pellets typically form alongside freezing rain, when a wet [[warm front]] ends up between colder and drier atmospheric layers. There, raindrops would both freeze and shrink in size due to evaporative cooling.<ref>{{cite web|publisher=Weatherquestions.com|url=http://www.weatherquestions.com/What_causes_ice_pellets.htm|title=What causes ice pellets (sleet)?|access-date=8 December 2007|url-status=live|archive-url=https://web.archive.org/web/20071130071143/http://www.weatherquestions.com/What_causes_ice_pellets.htm|archive-date=30 November 2007}}</ref> So-called snow pellets, or [[graupel]], form when multiple water droplets freeze onto snowflakes until a soft ball-like shape is formed.<ref>{{cite web | url = https://sgil.ba.ars.usda.gov/snowsite/rimegraupel/rg.html | title = Rime and Graupel | website = [[U.S. Department of Agriculture]] Electron Microscopy Unit, Beltsville Agricultural Research Center | access-date = 2020-03-23 | archive-url = https://web.archive.org/web/20170711205706/https://sgil.ba.ars.usda.gov/snowsite/rimegraupel/rg.html | archive-date = 2017-07-11}}</ref> So-called "[[diamond dust]]", (METAR code ''IC''<ref name="METAR" />) also known as ice needles or ice crystals, forms at temperatures approaching {{convert|-40|C|F}} due to air with slightly higher moisture from aloft mixing with colder, surface-based air.<ref name="glossdia">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|title=Diamond Dust|author=Glossary of Meteorology|date=June 2000|publisher=American Meteorological Society|archive-url=https://web.archive.org/web/20090403084329/http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|archive-date=3 April 2009|url-status=dead|access-date=21 January 2010}}</ref>


=== On surfaces ===
Hail forms in strong [[thunderstorm]] clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing {{convert|0|C|F|0}}.<ref name="gloss"/> Hail-producing clouds are often identifiable by their green coloration.<ref>{{cite web|url=http://www.abc.net.au/news/australia/qld/toowoomba/200410/s1222665.htm|archive-url=https://web.archive.org/web/20100306021712/http://www.abc.net.au/news/australia/qld/toowoomba/200410/s1222665.htm|archive-date=6 March 2010|title=Hail storms rock southern Qld|publisher=Australian Broadcasting Corporation|date=19 October 2004|access-date=15 July 2009}}</ref><ref>{{cite web|url=http://australiasevereweather.com/storm_news/arc1997.htm|title=Severe Thunderstorm Images of the Month Archives|year=1997|author1=Bath, Michael|author2=Degaura, Jimmy|access-date=15 July 2009|url-status=live|archive-url=http://archive.wikiwix.com/cache/20110713110215/http://australiasevereweather.com/storm_news/arc1997.htm|archive-date=13 July 2011}}</ref> The growth rate is maximized at about {{convert|-13|C|F|0}}, and becomes vanishingly small much below {{convert|-30|C|F|0}} as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of {{convert|11000|ft|m}}.<ref>{{cite web|url=http://www.meted.ucar.edu/resource/soo/MesoAnalyst.htm|archive-url=https://web.archive.org/web/20030320222147/http://www.meted.ucar.edu/resource/soo/MesoAnalyst.htm|archive-date=20 March 2003|title=Meso-Analyst Severe Weather Guide|author=Wolf, Pete|date=16 January 2003|access-date=16 July 2009|publisher=University Corporation for Atmospheric Research}}</ref> [[Entrainment (meteorology)|Entrainment]] of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporational cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the [[atmosphere]] over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.<ref>{{cite book|url=https://books.google.com/books?id=UbtG3vFfNtoC&pg=PA41|title=Climate, change and risk|author1=Downing, Thomas E. |author2=Olsthoorn, Alexander A. |author3=Tol, Richard S. J. |pages=41–43|publisher=Routledge|year=1999|isbn=978-0-415-17031-4}}</ref>
As water drips and re-freezes, it can form hanging [[icicle]]s, or [[stalagmite]]-like structures on the ground.<ref>{{cite journal|last=Makkonen |first=Lase |title=Models for the growth of rime, glaze, icicles and wet snow deposits on structures |journal=Philosophical Transactions of the Royal Society of London A |date=15 November 2000 |volume=358 |issue=1776 |pages=2913–2939 |doi=10.1098/rsta.2000.0690 }}</ref> On sloped roofs, buildup of ice can produce an [[Ice dam (roof)|ice dam]], which stops melt water from draining properly and potentially leads to damaging leaks.<ref>{{cite web |title=Dealing with and preventing ice dams |url=https://extension.umn.edu/protecting-home-rain-and-ice/dealing-and-preventing-ice-dams |publisher=[[University of Minnesota]] Extension |access-date=10 April 2024 }}</ref> More generally, [[water vapor]] depositing onto surfaces due to high [[relative humidity]] and then freezing results in various forms of [[atmospheric icing]], or [[frost]]. Inside buildings, this can be seen as ice on the surface of un-insulated windows.<ref>{{cite web |url=http://www.weatherquestions.com/What_causes_frost.htm |title=What causes frost? |access-date=2007-12-05 |url-status=live |archive-url=https://web.archive.org/web/20071210230539/http://www.weatherquestions.com/What_causes_frost.htm |archive-date=2007-12-10 }}</ref> Hoar frost is common in the environment, particularly in the low-lying areas such as [[valley]]s.<ref>{{cite web|url=http://www.weatheronline.co.uk/reports/wxfacts/Frost-hollow.htm|title=Weather Facts: Frost hollow – Weather UK – weatheronline.co.uk|work=weatheronline.co.uk|url-status=live|archive-url=https://web.archive.org/web/20130212022607/http://www.weatheronline.co.uk/reports/wxfacts/Frost-hollow.htm|archive-date=2013-02-12}}</ref> In Antarctica, the temperatures can be so low that [[electrostatic attraction]] is increased to the point hoarfrost on snow sticks together when blown by wind into [[tumbleweed]]-like balls known as [[yukimarimo]].<ref>{{Cite journal|last1=Kameda|first1=T.|last2=Yoshimi|first2=H.|last3=Azuma|first3=N.|last4=Motoyama|first4=H.|date=1999|title=Observation of "yukimarimo" on the snow surface of the inland plateau, Antarctic ice sheet|journal=Journal of Glaciology|language=en|volume=45|issue=150|pages=394–396|doi=10.1017/S0022143000001891|bibcode=1999JGlac..45..394K|issn=0022-1430|doi-access=free}}</ref>

====Snow====
{{Main|Snow|Snowflake}}
[[File:SnowflakesWilsonBentley.jpg|thumb|[[Snowflake]]s by [[Wilson Bentley]], 1902]]
Snow crystals form when tiny [[supercool]]ed cloud droplets (about 10 [[μm]] in diameter) [[freezing|freeze]]. These droplets are able to remain liquid at temperatures lower than {{convert|-18|C|K F}}, because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus". Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than {{convert|-35|C|K F}}.<ref name=Mason>{{cite book|author = Mason, Basil John| publisher= Clarendon Press| isbn= 978-0-19-851603-3|year = 1971|title = Physics of Clouds|url = https://archive.org/details/physicsofclouds0000maso|url-access = registration}}</ref> In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. Our understanding of what particles make efficient ice nuclei is poor&nbsp;– what we do know is they are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective,<ref name=Christner2008>{{cite journal |last1=Christner |first1=Brent C. |last2=Morris |first2=Cindy E. |last3=Foreman |first3=Christine M. |last4=Cai |first4=Rongman |last5=Sands |first5=David C. |title=Ubiquity of Biological Ice Nucleators in Snowfall |journal=Science |date=29 February 2008 |volume=319 |issue=5867 |pages=1214 |doi=10.1126/science.1149757 |pmid=18309078 |bibcode=2008Sci...319.1214C |citeseerx=10.1.1.714.4002 |s2cid=39398426 }}</ref> although to what extent is unclear. Artificial nuclei are used in [[cloud seeding]].<ref>{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=cloud+seeding&submit=Search|title=Cloud seeding|author=Glossary of Meteorology|year=2009|access-date=28 June 2009|publisher=American Meteorological Society|url-status=dead|archive-url=https://web.archive.org/web/20120315161127/http://amsglossary.allenpress.com/glossary/search?p=1&query=cloud+seeding&submit=Search|archive-date=15 March 2012}}</ref> The droplet then grows by condensation of water vapor onto the ice surfaces.


Sometimes, drops of water crystallize on cold objects as [[Rime ice|rime]] instead of glaze. Soft rime has a density between a quarter and two thirds that of pure ice,<ref>{{cite journal |last1=Podolskiy |first1=Evgeny Andreevich |last2=Nygaard |first2=Bjørn Egil Kringlebotn |last3=Nishimura |first3=Kouichi |last4=Makkonen |first4=Lasse |last5=Lozowski |first5=Edward Peter |title=Study of unusual atmospheric icing at Mount Zao, Japan, using the Weather Research and Forecasting model |journal=Journal of Geophysical Research: Atmospheres |date=27 June 2012 |volume=112 |issue=D2 |doi=10.1029/2011JD017042 |bibcode=2012JGRD..11712106P }}</ref> due to a high proportion of trapped air, which also makes soft rime appear white. Hard rime is denser, more transparent, and more likely to appear on ships and aircraft.<ref>{{Cite web |title=hard rime (Glossary of Meteorology) |url=https://glossary.ametsoc.org/wiki/Hard_rime |date=30 March 2024 |publisher=American Meteorological Society |language=en-US |access-date=11 April 2024 }}</ref><ref>{{Cite web |title=soft rime (Glossary of Meteorology) |url=https://glossary.ametsoc.org/wiki/Soft_rime |date=30 March 2024 |publisher=American Meteorological Society |language=en-US |access-date=11 April 2024 }}</ref> Cold wind specifically causes what is known as ''advection frost'' when it collides with objects. When it occurs on plants, it often causes damage to them.<ref>{{Cite journal |last1=Beerling |first1=D. J. |last2=Terry |first2=A. C. |last3=Mitchell |first3=P. L. |last4=Callaghan |first4=T. V. |last5=Gwynn-Jones |first5=D. |last6=Lee |first6=J. A. |date=April 2001 |title=Time to chill: effects of simulated global change on leaf ice nucleation temperatures of subarctic vegetation |url=http://doi.wiley.com/10.2307/2657062 |journal=American Journal of Botany |language=en |volume=88 |issue=4 |pages=628–633 |doi=10.2307/2657062|jstor=2657062 |pmid=11302848 }}</ref> Various methods exist to protect agricultural crops from frost - from simply covering them to using wind machines.<ref name="Pan2023" /><ref>{{cite web |date=June 2010 |title=Wind machines for minimizing cold injury to horticultural crops |url=https://www.ontario.ca/page/wind-machines-minimizing-cold-injury-horticultural-crops |publisher=Ontario state government |access-date=30 May 2024 }}</ref> In recent decades, [[irrigation sprinkler]]s have been calibrated to spray just enough water to preemptively create a layer of ice that would form slowly and so avoid a sudden temperature shock to the plant, and not be so thick as to cause damage with its weight.<ref name="Pan2023">{{cite journal |last1=Pan |first1=Qingmin |last2=Lu |first2=Yongzong |last3=Hu |first3=Huijie |last4=Hu |first4=Yongguang |title=Review and research prospects on sprinkler irrigation frost protection for horticultural crops |journal=Scientia Horticulture |date=15 December 2023 |volume=326 |doi=10.1016/j.scienta.2023.112775 }}</ref>
====Diamond dust====


<gallery mode="packed" heights="150px">
{{Main|Diamond dust}}
File:Saint-Amant_16_Gelée_blanche_2008.jpg|Grass partially covered in hoarfrost, 2008
So-called "diamond dust", also known as ice needles or ice crystals, forms at temperatures approaching {{convert|-40|C|F}} due to air with slightly higher moisture from aloft mixing with colder, surface-based air.<ref name="glossdia">{{cite web|url=http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|title=Diamond Dust|author=Glossary of Meteorology|date=June 2000|publisher=American Meteorological Society|archive-url=https://web.archive.org/web/20090403084329/http://amsglossary.allenpress.com/glossary/search?p=1&query=diamond+dust&submit=Search|archive-date=3 April 2009|url-status=dead|access-date=21 January 2010}}</ref> The METAR identifier for diamond dust within international hourly weather reports is ''IC''.<ref name="METAR" />
File:Dülmen, Hausdülmen, Distel -- 2021 -- 5079.jpg|Frost on a thistle in [[Dülmen|Hausdülmen]], [[North Rhine-Westphalia]], Germany
File:Frostweb.jpg|A [[spiderweb]] covered in frost
File:Icy Japanese Maple branch, Boxborough, Massachusetts, 2008.jpg|Ice on [[deciduous tree]] after freezing rain
File:Ice on stairway, 1968 (32085554416).jpg|Icicles on a [[stairway]] in [[Seattle]], 1968
File:WindowFrostNewmarketOntario1986.jpg|Fern frost on a window
File:HoarFrost.jpg|Hoar frost atop snow
File:Yukimarimo south pole dawn 2009.jpg|Yukimarimo at [[South Pole Station]], Antarctica, in 2008
</gallery>


==Ablation==
==Ablation==
Line 162: Line 175:
[[File:Aufbrechendes Eis auf dem Silvaplaner See bei Tauwetter April 2014 (1).jpg|thumb|The melting of floating ice]]
[[File:Aufbrechendes Eis auf dem Silvaplaner See bei Tauwetter April 2014 (1).jpg|thumb|The melting of floating ice]]


Ablation of ice refers to both its [[melting]] and its [[dissolution (chemistry)|dissolution]].
Ablation of ice refers to both its [[melting]] and its [[dissolution (chemistry)|dissolution]].<ref>{{Cite book |last=Paterson |first=W. S. B. |url=https://books.google.com/books?id=X75dmp9QFbgC |title=Physics of Glaciers |date=1994 |publisher=Butterworth-Heinemann |isbn=978-0-7506-4742-7 |pages=27 |language=en}}</ref>


The melting of ice entails the breaking of [[hydrogen bonds]] between the water molecules. The ordering of the molecules in the solid breaks down to a less ordered state and the solid melts to become a liquid. This is achieved by increasing the internal energy of the ice beyond the [[melting point]]. When ice melts it absorbs as much energy as would be required to heat an equivalent amount of water by 80&nbsp;°C. While melting, the temperature of the ice surface remains constant at 0&nbsp;°C. The rate of the melting process depends on the efficiency of the energy exchange process. An ice surface in [[fresh water]] melts solely by [[free convection]] with a rate that depends linearly on the water temperature, ''T''<sub>∞</sub>, when ''T''<sub>∞</sub> is less than 3.98&nbsp;°C, and superlinearly when ''T''<sub>∞</sub> is equal to or greater than 3.98&nbsp;°C, with the rate being proportional to (T<sub>∞</sub>&nbsp;−&nbsp;3.98&nbsp;°C)<sup>''α''</sup>, with ''α''&nbsp;=&nbsp;{{sfrac|5|3}} for ''T''<sub>∞</sub> much greater than 8&nbsp;°C, and α&nbsp;=&nbsp;{{sfrac|4|3}} for in between temperatures ''T''<sub>∞</sub>.<ref>{{cite journal|last1=Keitzl|first1=Thomas|last2=Mellado|first2=Juan Pedro|last3=Notz|first3=Dirk|title=Impact of Thermally Driven Turbulence on the Bottom Melting of Ice|journal=J. Phys. Oceanogr.|volume=46 |issue=4|pages=1171–1187|doi=10.1175/JPO-D-15-0126.1|year=2016|bibcode=2016JPO....46.1171K|doi-access=free|hdl=2117/189387|hdl-access=free}}</ref>
The melting of ice entails the breaking of [[hydrogen bonds]] between the water molecules. The ordering of the molecules in the solid breaks down to a less ordered state and the solid melts to become a liquid. This is achieved by increasing the internal energy of the ice beyond the [[melting point]]. When ice melts it absorbs as much energy as would be required to heat an equivalent amount of water by 80&nbsp;°C. While melting, the temperature of the ice surface remains constant at 0&nbsp;°C. The rate of the melting process depends on the efficiency of the energy exchange process. An ice surface in [[fresh water]] melts solely by [[free convection]] with a rate that depends linearly on the water temperature, ''T''<sub>∞</sub>, when ''T''<sub>∞</sub> is less than 3.98&nbsp;°C, and superlinearly when ''T''<sub>∞</sub> is equal to or greater than 3.98&nbsp;°C, with the rate being proportional to (T<sub>∞</sub>&nbsp;−&nbsp;3.98&nbsp;°C)<sup>''α''</sup>, with ''α''&nbsp;=&nbsp;{{sfrac|5|3}} for ''T''<sub>∞</sub> much greater than 8&nbsp;°C, and α&nbsp;=&nbsp;{{sfrac|4|3}} for in between temperatures ''T''<sub>∞</sub>.<ref>{{cite journal|last1=Keitzl|first1=Thomas|last2=Mellado|first2=Juan Pedro|last3=Notz|first3=Dirk|title=Impact of Thermally Driven Turbulence on the Bottom Melting of Ice|journal=J. Phys. Oceanogr.|volume=46 |issue=4|pages=1171–1187|doi=10.1175/JPO-D-15-0126.1|year=2016|bibcode=2016JPO....46.1171K|doi-access=free|hdl=2117/189387|hdl-access=free}}</ref>


In salty ambient conditions, dissolution rather than melting often causes the ablation of ice. For example, the temperature of the [[Arctic Ocean]] is generally below the melting point of ablating sea ice. The phase transition from solid to liquid is achieved by mixing [[salt]] and water molecules, similar to the dissolution of [[sugar]] in water, even though the water temperature is far below the melting point of the sugar. However, the dissolution rate is limited by salt concentration and is therefore slower than melting.<ref>{{cite journal|last1=Woods|first1=Andrew W.|title=Melting and dissolving|journal=J. Fluid Mech.|volume=239|pages=429–448|doi=10.1017/S0022112092004476|year=1992|bibcode=1992JFM...239..429W|s2cid=122680287 }}</ref>
In salty ambient conditions, dissolution rather than melting often causes the ablation of ice. For example, the temperature of the [[Arctic Ocean]] is generally below the melting point of ablating sea ice. The phase transition from solid to liquid is achieved by mixing [[salt]] and water molecules, similar to the dissolution of [[sugar]] in water, even though the water temperature is far below the melting point of the sugar. However, the dissolution rate is limited by salt concentration and is therefore slower than melting.<ref>{{cite journal|last1=Woods|first1=Andrew W.|title=Melting and dissolving|journal=J. Fluid Mech.|volume=239|pages=429–448|doi=10.1017/S0022112092004476|year=1992|doi-broken-date=1 November 2024 |bibcode=1992JFM...239..429W|s2cid=122680287 }}</ref>


==Role in human activities==
==Role in human activities==
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[[File:Yakhchal_radiative_cooling.svg|thumb|left|A schematic showing how the ancient yakhchals used ice to provide radiative cooling]]
[[File:Yakhchal_radiative_cooling.svg|thumb|left|A schematic showing how the ancient yakhchals used ice to provide radiative cooling]]


Ice has long been valued as a means of cooling. In 400 BC Iran, [[Achaemenid Empire|Persian]] engineers had already mastered the technique of storing ice in the middle of summer in the desert. The ice was brought in from ice pools or during the winters from nearby mountains in bulk amounts, and stored in specially designed, naturally cooled ''refrigerators'', called [[yakhchal]] (meaning ''ice storage''). This was a large underground space (up to 5000 m<sup>3</sup>) that had thick walls (at least two meters at the base) made of a special mortar called ''[[sarooj]]'', composed of sand, clay, egg whites, lime, goat hair, and ash in specific proportions, and which was known to be resistant to heat transfer. This mixture was thought to be completely water impenetrable. The space often had access to a [[qanat]], and often contained a system of [[windcatcher]]s which could easily bring temperatures inside the space down to frigid levels on summer days. The ice was used to chill treats for royalty.<ref>{{cite journal |last1=Hosseini |first1=Bahareh |last2=Namazian |first2=Ali |title=An Overview of Iranian Ice Repositories, an Example of Traditional Indigenous Architecture |journal=METU Journal of the Faculty of Architecture |year=2012 |volume=29 |issue=2 |pages=223–234 |doi=10.4305/METU.JFA.2012.2.10 }}</ref><ref>{{cite news |url=https://eartharchitecture.org/?p=570 |title=Yakhchal: Ancient Refrigerators |date=9 September 2009 |work=Earth Architecture}}</ref>
Ice has long been valued as a means of cooling. In 400 BC Iran, [[Achaemenid Empire|Persian]] engineers had already developed techniques for ice storage in the desert through the summer months. During the winter, ice was transported from harvesting pools and nearby mountains in large quantities to be stored in specially designed, naturally cooled ''refrigerators'', called [[yakhchal]] (meaning ''ice storage''). Yakhchals were large underground spaces (up to 5000&nbsp;m<sup>3</sup>) that had thick walls (at least two meters at the base) made of a specific type of mortar called ''[[sarooj]]'' made from sand, clay, egg whites, lime, goat hair, and ash. The mortar was resistant to heat transfer, helping to keep the ice cool enough not to melt; it was also impenetrable by water. Yakhchals often included a [[qanat]] and a system of [[windcatcher]]s that could lower internal temperatures to frigid levels, even during the heat of the summer. One use for the ice was to create chilled treats for royalty.<ref>{{cite journal |last1=Hosseini |first1=Bahareh |last2=Namazian |first2=Ali |title=An Overview of Iranian Ice Repositories, an Example of Traditional Indigenous Architecture |journal=METU Journal of the Faculty of Architecture |year=2012 |volume=29 |issue=2 |pages=223–234 |doi=10.4305/METU.JFA.2012.2.10 }}</ref><ref>{{cite news |url=https://eartharchitecture.org/?p=570 |title=Yakhchal: Ancient Refrigerators |date=9 September 2009 |work=Earth Architecture}}</ref>


====Harvesting====
====Harvesting====
{{Main|Ice cutting}}
{{Main|Ice cutting|Ice trade}}
[[File:Slaves Unloading Ice in Cuba 1832.jpg|thumb|Slaves in [[Captaincy General of Cuba|Spanish Cuba]] unloading ice from [[Maine]] in 1832]]
[[File:Llanddulas and Rhyd-y-Foel - Gwrych Castle - 20220416142439.jpg|thumb|Gwrych Castle, North Wales, with 18 towers, one of which is called the 'Ice Tower' designed specifically to store ice, the construction of the tower was completed in 1822.]]
[[File:Ice Harvesting on Lake St Clair Michigan circa 1905--photograph courtesy Detroit Publishing Company.jpg|thumb|Harvesting ice on [[Lake St. Clair]] in [[Michigan]], c. 1905]]
There were thriving industries in 16th–17th century England whereby low-lying areas along the [[Thames Estuary]] were flooded during the winter, and ice harvested in carts and stored inter-seasonally in insulated wooden houses as a provision to an icehouse often located in large country houses, and widely used to keep fish fresh when caught in distant waters. This was allegedly copied by an Englishman who had seen the same activity in China. Ice was imported into England from Norway on a considerable scale as early as 1823.<ref name=cne>{{Cite Collier's|wstitle=Ice}}</ref>
There were thriving industries in 16th–17th century England whereby low-lying areas along the [[Thames Estuary]] were flooded during the winter, and ice harvested in carts and stored inter-seasonally in insulated wooden houses as a provision to an icehouse often located in large country houses, and widely used to keep fish fresh when caught in distant waters. This was allegedly copied by an Englishman who had seen the same activity in China. Ice was imported into England from Norway on a considerable scale as early as 1823.<ref name=cne>{{Cite Collier's|wstitle=Ice}}</ref>


In the United States, the first cargo of ice was sent from New York City to [[Charleston, South Carolina]], in 1799,<ref name=cne/> and by the first half of the 19th century, ice harvesting had become a big business. [[Frederic Tudor]], who became known as the "Ice King", worked on developing better insulation products for long distance shipments of ice, especially to the tropics; this became known as the [[ice trade]].<ref>{{Cite web |last=Hutton |first=Mercedes |title=The icy side to Hong Kong history |publisher=[[BBC]] |date=23 January 2020 |url=https://www.bbc.com/travel/story/20200122-the-icy-side-to-hong-kong-history |accessdate=23 January 2020 }}</ref>
In the United States, the first cargo of ice was sent from New York City to [[Charleston, South Carolina]], in 1799,<ref name=cne/> and by the first half of the 19th century, ice harvesting had become a big business. [[Frederic Tudor]], who became known as the "Ice King", worked on developing better insulation products for long distance shipments of ice, especially to the tropics; this became known as the ice trade.<ref>{{Cite web |last=Hutton |first=Mercedes |title=The icy side to Hong Kong history |publisher=[[BBC]] |date=23 January 2020 |url=https://www.bbc.com/travel/story/20200122-the-icy-side-to-hong-kong-history |accessdate=23 January 2020 }}</ref>

[[File:Ice Harvesting on Lake St Clair Michigan circa 1905--photograph courtesy Detroit Publishing Company.jpg|thumb|left|upright=1.1|Harvesting ice on [[Lake St. Clair]] in [[Michigan]], c. 1905]]


Between 1812 and 1822, under [[Lloyd Hesketh Bamford-Hesketh|Lloyd Hesketh Bamford Hesketh]]'s instruction, [[Gwrych Castle]] was built with 18 large towers, one of those towers is called the 'Ice Tower'. Its sole purpose was to store Ice.<ref>{{cite web |url=https://www.countrylife.co.uk/architecture/gwrych-castle-217018 | title=Gwrych Castle: The astonishing fantasy castle saved by the dreams and bravery of a 12-year-old boy | date=11 November 2020 }}</ref>
Between 1812 and 1822, under [[Lloyd Hesketh Bamford-Hesketh|Lloyd Hesketh Bamford Hesketh]]'s instruction, [[Gwrych Castle]] was built with 18 large towers, one of those towers is called the 'Ice Tower'. Its sole purpose was to store Ice.<ref>{{cite web |url=https://www.countrylife.co.uk/architecture/gwrych-castle-217018 | title=Gwrych Castle: The astonishing fantasy castle saved by the dreams and bravery of a 12-year-old boy | date=11 November 2020 }}</ref>


[[Trieste]] sent ice to [[Egypt]], [[Corfu]], and [[Zante]]; Switzerland, to France; and Germany sometimes was supplied from [[Bavaria]]n lakes.<ref name=cne/> The [[Hungarian Parliament]] building used ice harvested in the winter from [[Lake Balaton]] for air conditioning.
[[Trieste]] sent ice to [[Egypt]], [[Corfu]], and [[Zante]]; Switzerland, to France; and Germany sometimes was supplied from [[Bavaria]]n lakes.<ref name=cne/> From 1930s and up until 1994, the [[Hungarian Parliament]] building used ice harvested in the winter from [[Lake Balaton]] for air conditioning.<ref>{{Cite web |last=Kay |first=Nathan |title=The secrets and symbols of Hungary's Parliament building |publisher=[[CNN]] |date=3 January 2019 |url=https://edition.cnn.com/travel/article/secrets-of-the-hungarian-parliament-building/index.html |archive-url=https://web.archive.org/web/20190317194908/https://edition.cnn.com/travel/article/secrets-of-the-hungarian-parliament-building/index.html |archive-date=17 March 2019 }}</ref>


[[Ice house (building)|Ice house]]s were used to store ice formed in the winter, to make ice available all year long, and an early type of [[refrigerator]] known as an [[icebox]] was cooled using a block of ice placed inside it. In many cities, it was not unusual to have a regular ice [[Delivery (commerce)|delivery]] service during the summer. The advent of artificial refrigeration technology has since made delivery of ice obsolete.<ref name="Prewitt2023" />
[[Ice house (building)|Ice house]]s were used to store ice formed in the winter, to make ice available all year long, and an early type of [[refrigerator]] known as an [[icebox]] was cooled using a block of ice placed inside it. Many cities had a regular ice [[Delivery (commerce)|delivery]] service during the summer. The advent of artificial refrigeration technology made the delivery of ice obsolete.<ref name="Prewitt2023" />


Ice is still harvested for [[List of ice and snow sculpture events|ice and snow sculpture events]]. For example, a [[swing saw]] is used to get ice for the [[Harbin International Ice and Snow Sculpture Festival]] each year from the frozen surface of the [[Songhua River]].<ref name="coldestcity">{{cite web|url=https://www.smh.com.au/travel/ice-is-money-in-chinas-coldest-city-20081113-62yj.html|title=Ice is money in China's coldest city|date=13 November 2008|agency=AFP|work=The Sydney Morning Herald|access-date=26 December 2009|url-status=dead|archive-url=https://web.archive.org/web/20091002152548/http://www.smh.com.au/travel/ice-is-money-in-chinas-coldest-city-20081113-62yj.html|archive-date=2 October 2009}}</ref>
Ice is still harvested for [[List of ice and snow sculpture events|ice and snow sculpture events]]. For example, a [[swing saw]] is used to get ice for the [[Harbin International Ice and Snow Sculpture Festival]] each year from the frozen surface of the [[Songhua River]].<ref name="coldestcity">{{cite web|url=https://www.smh.com.au/travel/ice-is-money-in-chinas-coldest-city-20081113-62yj.html|title=Ice is money in China's coldest city|date=13 November 2008|agency=AFP|work=The Sydney Morning Herald|access-date=26 December 2009|url-status=dead|archive-url=https://web.archive.org/web/20091002152548/http://www.smh.com.au/travel/ice-is-money-in-chinas-coldest-city-20081113-62yj.html|archive-date=2 October 2009}}</ref>


====Artificial production====
====Artificial production====
{{main|Icemaker}}
[[File:PSM V39 D031 Interior of an ice factory.jpg|thumb|Layout of a late 19th-century ice factory]]
[[File:PSM V39 D031 Interior of an ice factory.jpg|thumb|Layout of a late 19th-century ice factory]]
The earliest known written process to artificially make ice is by the 13th-century writings of Arab historian [[Ibn Abu Usaybia]] in his book ''Kitab Uyun al-anba fi tabaqat-al-atibba'' concerning medicine in which Ibn Abu Usaybi’a attributes the process to an even older author, Ibn Bakhtawayhi, of whom nothing is known.<ref>{{cite book |last1=Weir |first1=Caroline |last2=Weir |first2= Robin |title=Ice Creams, Sorbets & Gelati:The Definitive Guide |date=2010 |page=217}}</ref>
The earliest known written process to artificially make ice is by the 13th-century writings of Arab historian [[Ibn Abu Usaybia]] in his book ''Kitab Uyun al-anba fi tabaqat-al-atibba'' concerning medicine in which Ibn Abu Usaybia attributes the process to an even older author, Ibn Bakhtawayhi, of whom nothing is known.<ref>{{cite book |last1=Weir |first1=Caroline |last2=Weir |first2= Robin |title=Ice Creams, Sorbets & Gelati:The Definitive Guide |date=2010 |page=217}}</ref>


Ice is now produced on an industrial scale, for uses including food storage and processing, chemical manufacturing, concrete mixing and curing, and consumer or packaged ice.<ref name="ashrae">[[ASHRAE]]. "Ice Manufacture". ''2006 [[ASHRAE Handbook]]: Refrigeration.'' Inch-Pound Edition. {{nat|p. 34-1.}} {{ISBN|1-931862-86-9}}.</ref> Most commercial [[icemaker]]s produce three basic types of fragmentary ice: flake, tubular and plate, using a variety of techniques.<ref name="ashrae"/> Large batch ice makers can produce up to 75 tons of ice per day.<ref>Rydzewski, A.J. "Mechanical Refrigeration: Ice Making." ''[[Marks' Standard Handbook for Mechanical Engineers]].'' 11th ed. McGraw Hill: New York. pp. 19–24. {{ISBN|978-0-07-142867-5}}.</ref> In 2002, there were 426 commercial ice-making companies in the United States, with a combined value of shipments of $595,487,000.<ref>U.S. Census Bureau. [https://www.census.gov/prod/ec02/ec0231i312113.pdf "Ice manufacturing: 2002."] {{webarchive|url=https://web.archive.org/web/20170722052238/https://www.census.gov/prod/ec02/ec0231i312113.pdf |date=22 July 2017 }} ''2002 Economic Census''.</ref> Home refrigerators can also make ice with a built in [[icemaker]], which will typically make [[ice cube]]s or crushed ice. Stand-alone icemaker units that make ice cubes are often called ice machines.
Ice is now produced on an industrial scale, for uses including food storage and processing, chemical manufacturing, concrete mixing and curing, and consumer or packaged ice.<ref name="ashrae">[[ASHRAE]]. "Ice Manufacture". ''2006 [[ASHRAE Handbook]]: Refrigeration.'' Inch-Pound Edition. {{nat|p. 34-1.}} {{ISBN|1-931862-86-9}}.</ref> Most commercial [[icemaker]]s produce three basic types of fragmentary ice: flake, tubular and plate, using a variety of techniques.<ref name="ashrae"/> Large batch ice makers can produce up to 75 tons of ice per day.<ref>Rydzewski, A.J. "Mechanical Refrigeration: Ice Making." ''[[Marks' Standard Handbook for Mechanical Engineers]].'' 11th ed. McGraw Hill: New York. pp. 19–24. {{ISBN|978-0-07-142867-5}}.</ref> In 2002, there were 426 commercial ice-making companies in the United States, with a combined value of shipments of $595,487,000.<ref>U.S. Census Bureau. [https://www.census.gov/prod/ec02/ec0231i312113.pdf "Ice manufacturing: 2002."] {{webarchive|url=https://web.archive.org/web/20170722052238/https://www.census.gov/prod/ec02/ec0231i312113.pdf |date=22 July 2017 }} ''2002 Economic Census''.</ref> Home refrigerators can also make ice with a built in [[icemaker]], which will typically make [[ice cube]]s or crushed ice. The first such device was presented in 1965 by [[Frigidaire]].<ref>{{Cite web |last1=Wroclawski |first1=Daniel |title=How Does an Ice Maker Work? |url=https://reviewed.usatoday.com/refrigerators/features/how-does-an-ice-maker-work |publisher=[[USA Today]] |date=21 July 2015 |language=en |access-date=26 May 2024 }}</ref>


===Land travel===
===Land travel===
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Whenever there is freezing rain or snow which occurs at a temperature near the melting point, it is common for ice to build up on the [[window]]s of vehicles. Often, snow melts, re-freezes, and forms a fragmented layer of ice which effectively "glues" snow to the window. In this case, the frozen mass is commonly removed with [[ice scraper]]s.<ref>{{cite journal |last1=Dhyani |first1=Abhishek |last2=Choi |first2=Wonjae |last3=Golovin |first3=Kevin |last4=Tuteja |first4=Anish |date=4 May 2022 |title=Surface design strategies for mitigating ice and snow accretion |journal=Matter |volume=5 |issue=5 |pages=1423–1454 |doi=10.1016/j.matt.2022.04.012 }}</ref> A thin layer of ice crystals can also form on the inside surface of car windows during sufficiently cold weather. In the 1970s and 1980s, some vehicles such as [[Ford Thunderbird]] could be upgraded with heated windshields as the result. This technology fell out of style as it was too expensive and prone to damage, but rear-window [[defroster]]s are cheaper to maintain and so are more widespread.<ref>{{Cite web |title=A brief history of the heated windshield |last=Braithwaite-Smith |first=Gavin |date=14 December 2022 |url=https://www.hagerty.com/media/automotive-history/a-brief-history-of-the-heated-windshield/ |publisher=Hagerty |language=en |access-date=11 April 2024 }}</ref>
Whenever there is freezing rain or snow which occurs at a temperature near the melting point, it is common for ice to build up on the [[window]]s of vehicles. Often, snow melts, re-freezes, and forms a fragmented layer of ice which effectively "glues" snow to the window. In this case, the frozen mass is commonly removed with [[ice scraper]]s.<ref>{{cite journal |last1=Dhyani |first1=Abhishek |last2=Choi |first2=Wonjae |last3=Golovin |first3=Kevin |last4=Tuteja |first4=Anish |date=4 May 2022 |title=Surface design strategies for mitigating ice and snow accretion |journal=Matter |volume=5 |issue=5 |pages=1423–1454 |doi=10.1016/j.matt.2022.04.012 }}</ref> A thin layer of ice crystals can also form on the inside surface of car windows during sufficiently cold weather. In the 1970s and 1980s, some vehicles such as [[Ford Thunderbird]] could be upgraded with heated windshields as the result. This technology fell out of style as it was too expensive and prone to damage, but rear-window [[defroster]]s are cheaper to maintain and so are more widespread.<ref>{{Cite web |title=A brief history of the heated windshield |last=Braithwaite-Smith |first=Gavin |date=14 December 2022 |url=https://www.hagerty.com/media/automotive-history/a-brief-history-of-the-heated-windshield/ |publisher=Hagerty |language=en |access-date=11 April 2024 }}</ref>


[[File:CaminoDeLaVidaLeningrado.ogv|thumb|left|upright=0.8|1943 [[American propaganda during World War II|US propaganda]] film devoted to the Road of Life]]
[[File:CaminoDeLaVidaLeningrado.ogv|thumb|left|upright=0.8|1943 [[American propaganda during World War II|US propaganda]] film explaining how the ice of Lake Ladoga became the Road of Life during [[WWII]]]]


In sufficiently cold places, the layers of ice on water surfaces can get thick enough for [[ice road]]s to be built. Some regulations specify that the minimum safe thickness is {{cvt|4|in|cm|frac=2}} for a person, {{cvt|7|in|cm|frac=2}} for a [[snowmobile]] and {{cvt|15|in|cm|frac=2}} for an [[automobile]] lighter than 5 tonnes. For [[truck]]s, effective thickness varies with load - i.e. a vehicle with 9-ton total weight requires a thickness of {{cvt|20|in|cm|frac=2}}. Notably, the speed limit for a vehicle moving at a road which meets its minimum safe thickness is 25&nbsp;km/h (15&nbsp;mph), going up to 35&nbsp;km/h (25&nbsp;mph) if the road's thickness is 2 or more times larger than the minimum safe value.<ref>{{cite report |last1=Daly |first1=Steven |last2=Connor |first2=Billy |last3=Garron |first3=Jessica |last4=Stuefer |first4=Svetlana |last5=Belz |first5=Nathan |last6=Bjella |first6=Kevin |date=1 February 2023 |title=Design and Operation of Ice Roads |url=https://aidc.uaf.edu/media/1580/ice-road-manual_final.pdf |publisher=[[University of Alaska Fairbanks]] |access-date=11 April 2024 }}</ref> There is a known instance where a railroad has been built on ice.<ref name="Makkonen, L. 1994"/>
In sufficiently cold places, the layers of ice on water surfaces can get thick enough for [[ice road]]s to be built. Some regulations specify that the minimum safe thickness is {{cvt|4|in|cm|frac=2}} for a person, {{cvt|7|in|cm|frac=2}} for a [[snowmobile]] and {{cvt|15|in|cm|frac=2}} for an [[automobile]] lighter than 5 tonnes. For [[truck]]s, effective thickness varies with load - i.e. a vehicle with 9-ton total weight requires a thickness of {{cvt|20|in|cm|frac=2}}. Notably, the speed limit for a vehicle moving at a road which meets its minimum safe thickness is 25&nbsp;km/h (15&nbsp;mph), going up to 35&nbsp;km/h (25&nbsp;mph) if the road's thickness is 2 or more times larger than the minimum safe value.<ref>{{cite report |last1=Daly |first1=Steven |last2=Connor |first2=Billy |last3=Garron |first3=Jessica |last4=Stuefer |first4=Svetlana |last5=Belz |first5=Nathan |last6=Bjella |first6=Kevin |date=1 February 2023 |title=Design and Operation of Ice Roads |url=https://aidc.uaf.edu/media/1580/ice-road-manual_final.pdf |publisher=[[University of Alaska Fairbanks]] |access-date=11 April 2024 }}</ref> There is a known instance where a railroad has been built on ice.<ref name="Makkonen, L. 1994"/>
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For ships, ice presents two distinct hazards. Firstly, spray and freezing rain can produce an ice build-up on the superstructure of a vessel sufficient to make it unstable, potentially to the point of [[capsizing]].<ref>{{cite journal |last1=Mintu |first1=Shafiul |last2=Molyneux |first2=David |date=15 August 2022 |title=Ice accretion for ships and offshore structures. Part 1 - State of the art review |journal=Ocean Engineering |volume=258 |doi=10.1016/j.oceaneng.2022.111501 |bibcode=2022OcEng.25811501M }}</ref> Earlier, crewmembers were regularly forced to manually hack off ice build-up. After 1980s, spraying de-icing chemicals or melting the ice through hot water/steam hoses became more common.<ref>{{cite journal |last1=Rashid |first1=Taimur |last2=Khawaja |first2=Hassan Abbas |last3=Edvardsen |first3=Kåre |date=17 August 2016 |title=Review of marine icing and anti-/de-icing systems |journal=Ocean Engineering |volume=15 |issue=2 |pages=79–87 |doi=10.1080/20464177.2016.1216734 |bibcode=2016JMEnT..15...79R }}</ref> Secondly, [[iceberg]]s&nbsp;– large masses of ice floating in water (typically created when glaciers reach the sea)&nbsp;– can be dangerous if struck by a ship when underway. Icebergs have been responsible for the sinking of many ships, the most famous being the [[RMS Titanic|''Titanic'']].<ref>{{cite book |last1=Halpern |first1=Samuel |last2=Weeks |first2=Charles |year=2011 |title=Report into the Loss of the SS ''Titanic'': A Centennial Reappraisal | editor-last = Halpern | editor-first = Samuel | publisher = The History Press | location = Stroud, UK | isbn = 978-0-7524-6210-3 }}</ref>
For ships, ice presents two distinct hazards. Firstly, spray and freezing rain can produce an ice build-up on the superstructure of a vessel sufficient to make it unstable, potentially to the point of [[capsizing]].<ref>{{cite journal |last1=Mintu |first1=Shafiul |last2=Molyneux |first2=David |date=15 August 2022 |title=Ice accretion for ships and offshore structures. Part 1 - State of the art review |journal=Ocean Engineering |volume=258 |doi=10.1016/j.oceaneng.2022.111501 |bibcode=2022OcEng.25811501M }}</ref> Earlier, crewmembers were regularly forced to manually hack off ice build-up. After 1980s, spraying de-icing chemicals or melting the ice through hot water/steam hoses became more common.<ref>{{cite journal |last1=Rashid |first1=Taimur |last2=Khawaja |first2=Hassan Abbas |last3=Edvardsen |first3=Kåre |date=17 August 2016 |title=Review of marine icing and anti-/de-icing systems |journal=Ocean Engineering |volume=15 |issue=2 |pages=79–87 |doi=10.1080/20464177.2016.1216734 |bibcode=2016JMEnT..15...79R }}</ref> Secondly, [[iceberg]]s&nbsp;– large masses of ice floating in water (typically created when glaciers reach the sea)&nbsp;– can be dangerous if struck by a ship when underway. Icebergs have been responsible for the sinking of many ships, the most famous being the [[RMS Titanic|''Titanic'']].<ref>{{cite book |last1=Halpern |first1=Samuel |last2=Weeks |first2=Charles |year=2011 |title=Report into the Loss of the SS ''Titanic'': A Centennial Reappraisal | editor-last = Halpern | editor-first = Samuel | publisher = The History Press | location = Stroud, UK | isbn = 978-0-7524-6210-3 }}</ref>


For [[harbor]]s near the [[geographical pole|pole]]s, being ice-free, ideally all year long, is an important advantage. Examples are [[Murmansk]] (Russia), [[Pechengsky District|Petsamo]] (Russia, formerly Finland), and [[Vardø (town)|Vardø]] (Norway). Harbors which are not ice-free are opened up using specialized vessels, called icebreakers. Icebreakers are also used to open routes through the sea ice for other vessels. A widespread production of icebreakers began during the 19th century. Earlier designs simply had reinforced [[Bow (watercraft)|bows]] in a spoon-like or diagonal shape to effectively crush the ice. Later designs attached a forward [[propeller]] underneath the protruding bow, as the typical rear propellers were incapable of effectively steering the ship through the ice <ref name="Sahari2021" />
For [[harbor]]s near the [[geographical pole|pole]]s, being ice-free, ideally all year long, is an important advantage. Examples are [[Murmansk]] (Russia), [[Pechengsky District|Petsamo]] (Russia, formerly Finland), and [[Vardø (town)|Vardø]] (Norway). Harbors which are not ice-free are opened up using specialized vessels, called icebreakers.<ref name="Sahari2021">{{cite journal |last1=Sahari |first1=Aaro |last2=Matala |first2=Saara |date=9 December 2021 |title=Of a titan, winds and power: Transnational development of the icebreaker, 1890-1954 |journal=International Journal of Maritime History |volume=33 |issue=4 |pages=722–747 |doi=10.1177/08438714211062493 }}</ref> Icebreakers are also used to open routes through the sea ice for other vessels, as the only alternative is to find the openings called "[[polynya]]s" or "[[Lead (sea ice)|leads]]". A widespread production of icebreakers began during the 19th century. Earlier designs simply had reinforced [[Bow (watercraft)|bows]] in a spoon-like or diagonal shape to effectively crush the ice. Later designs attached a forward [[propeller]] underneath the protruding bow, as the typical rear propellers were incapable of effectively steering the ship through the ice <ref name="Sahari2021" />


===Air travel===
===Air travel===
{{Further|Icing conditions|Carburetor icing}}
{{Further|Icing conditions|Carburetor icing}}
[[File:Some Ice on the boots (1527659244).jpg|thumb|left|Rime ice on the leading edge of an aircraft wing. When the build-up is too large, the black [[deicing boot]] inflates to shake it off <ref>{{cite magazine |url = https://books.google.com/books?id=XygDAAAAMBAJ&dq=Popular+Science+1931+plane&pg=PA28 |title = Overshoes For Planes End Ice Danger |date = November 1931 |magazine = Popular Science |page = 28 |via = Google Books }}</ref><ref>{{cite book |first = William M. |last = Leary |title = We Freeze to Please: A History of NASA's Icing Research Tunnel and the Quest for Flight Safety |date = 2002 |location = Washington, DC |publisher = National Aeronautics and Space Administration |page = 10 |oclc = 49558649 }}</ref>]]
[[File:Some Ice on the boots (1527659244).jpg|thumb|left|Rime ice on the leading edge of an aircraft wing, partially released by the [[Ice protection system|black pneumatic boot]]]]
For aircraft, ice can cause a number of dangers. As an aircraft climbs, it passes through air layers of different temperature and humidity, some of which may be conducive to ice formation. If ice forms on the wings or control surfaces, this may adversely affect the flying qualities of the aircraft. During the [[Transatlantic flight of Alcock and Brown|first non-stop flight across the Atlantic]], the British aviators Captain [[John Alcock (RAF officer)|John Alcock]] and Lieutenant [[Arthur Whitten Brown]] encountered such icing conditions&nbsp;– Brown left the cockpit and climbed onto the wing several times to remove ice which was covering the engine air intakes of the [[Vickers Vimy]] aircraft they were flying.<ref>{{cite web |date=22 July 2014 |title=Capt. John Alcock and Lt. Arthur Whitten Brown |url=http://www.aviation-history.com/airmen/alcock.htm |publisher=The Aviation History On-Line Museum }}</ref>
For aircraft, ice can cause a number of dangers. As an aircraft climbs, it passes through air layers of different temperature and humidity, some of which may be conducive to ice formation. If ice forms on the wings or control surfaces, this may adversely affect the flying qualities of the aircraft. In 1919, during the [[Transatlantic flight of Alcock and Brown|first non-stop flight across the Atlantic]], the British aviators Captain [[John Alcock (RAF officer)|John Alcock]] and Lieutenant [[Arthur Whitten Brown]] encountered such icing conditions&nbsp;– Brown left the cockpit and climbed onto the wing several times to remove ice which was covering the engine air intakes of the [[Vickers Vimy]] aircraft they were flying.<ref>{{cite web |date=22 July 2014 |title=Capt. John Alcock and Lt. Arthur Whitten Brown |url=http://www.aviation-history.com/airmen/alcock.htm |publisher=The Aviation History On-Line Museum }}</ref>


One vulnerability effected by icing that is associated with reciprocating internal combustion engines is the [[carburetor]]. As air is sucked through the carburetor into the engine, the local air pressure is lowered, which causes [[adiabatic]] cooling. Thus, in humid near-freezing conditions, the carburetor will be colder, and tend to ice up. This will block the supply of air to the engine, and cause it to fail. Between 1969 and 1975, 468 such instances were recorded, causing 75 aircraft losses, 44 fatalities and 202 serious injuries.<ref>{{cite journal |last1=Newman |first1=Richard L. |year=1981 |title=Carburetor Ice Flight Testing: Use of an Anti-Icing Fuel Additive |journal=Journal of Aircraft |volume=18 |issue=1 |pages=5–6 |doi=10.2514/3.57458 }}</ref> Thus, [[Carburetor heat|carburetor air intake heaters]] were developed. Further, reciprocating engines with [[fuel injection]] do not require carburetors in the first place.<ref>{{cite book
One vulnerability effected by icing that is associated with reciprocating internal combustion engines is the [[carburetor]]. As air is sucked through the carburetor into the engine, the local air pressure is lowered, which causes [[adiabatic]] cooling. Thus, in humid near-freezing conditions, the carburetor will be colder, and tend to ice up. This will block the supply of air to the engine, and cause it to fail. Between 1969 and 1975, 468 such instances were recorded, causing 75 aircraft losses, 44 fatalities and 202 serious injuries.<ref>{{cite journal |last1=Newman |first1=Richard L. |year=1981 |title=Carburetor Ice Flight Testing: Use of an Anti-Icing Fuel Additive |journal=Journal of Aircraft |volume=18 |issue=1 |pages=5–6 |doi=10.2514/3.57458 }}</ref> Thus, [[Carburetor heat|carburetor air intake heaters]] were developed. Further, reciprocating engines with [[fuel injection]] do not require carburetors in the first place.<ref>{{cite book
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[[File:SCENEONICE.jpg|thumb|''Skating fun'' by 17th century Dutch painter [[Hendrick Avercamp]]]]
[[File:SCENEONICE.jpg|thumb|''Skating fun'' by 17th century Dutch painter [[Hendrick Avercamp]]]]


Ice also plays a central role in winter recreation and in many sports such as [[ice skating]], [[tour skating]], [[ice hockey]], [[bandy]], [[ice fishing]], [[ice climbing]], [[curling]], [[broomball]] and sled racing on [[bobsled]], [[luge]] and [[Skeleton (sport)|skeleton]]. Many of the different sports played on ice get international attention every four years during the [[Winter Olympic Games]].<ref>{{cite journal |last1=Dichter |first1=Heather L. |last2=Teetzel |first2=Sarah |date=23 March 2021 |title=The Winter Olympics: A Century of Games on Ice and Snow |journal=The International Journal of the History of Sport |volume=37 |issue=13 |pages=1215–1235 |doi=10.1080/09523367.2020.1866474 }}</ref>
Ice plays a central role in winter recreation and in many sports such as [[ice skating]], [[tour skating]], [[ice hockey]], [[bandy]], [[ice fishing]], [[ice climbing]], [[curling]], [[broomball]] and sled racing on [[bobsled]], [[luge]] and [[Skeleton (sport)|skeleton]]. Many of the different sports played on ice get international attention every four years during the [[Winter Olympic Games]].<ref>{{cite journal |last1=Dichter |first1=Heather L. |last2=Teetzel |first2=Sarah |date=23 March 2021 |title=The Winter Olympics: A Century of Games on Ice and Snow |journal=The International Journal of the History of Sport |volume=37 |issue=13 |pages=1215–1235 |doi=10.1080/09523367.2020.1866474 }}</ref>


Small boat-like craft can be mounted on blades and be driven across the ice by [[sails]]. This sport is known as [[ice yachting]], and it had been practiced for centuries.<ref>{{Cite web|url=https://hvmag.com/things-to-do/explore-the-history-of-ice-yachting-in-the-hudson-valley/|title=Explore the History of Ice Yachting in the Hudson Valley|last=Levine|first=David|website=www.hvmag.com|date=19 November 2013 |language=en|access-date=April 14, 2020}}</ref><ref>{{Cite web|url=https://ice.idniyra.org/|title=IDNIYRA {{!}} International DN Ice Yacht Racing Association|date=December 27, 2017|archive-url=https://web.archive.org/web/20171227121944/https://ice.idniyra.org/|access-date=April 15, 2020|archive-date=December 27, 2017}}</ref> Another vehicular sport is [[ice racing]], where drivers must speed on lake ice, while also controlling the skid of their vehicle (similar in some ways to [[dirt track racing]]). The sport has even been modified for [[ice rink]]s.<ref>{{cite web |url=http://www.motortrend.com/features/112_0407_ice_racing/index.html|title=Racing Fast 'n' Cheap: Ice Racing |last=Markus |first=Frank |publisher=[[Motor Trend]] |access-date=2008-09-30 |archive-date=2011-06-04 |archive-url=https://web.archive.org/web/20110604072725/http://www.motortrend.com/features/112_0407_ice_racing/index.html |url-status=dead }}</ref>
Small boat-like craft can be mounted on blades and be driven across the ice by [[sails]]. This sport is known as [[ice yachting]], and it had been practiced for centuries.<ref>{{Cite web|url=https://hvmag.com/things-to-do/explore-the-history-of-ice-yachting-in-the-hudson-valley/|title=Explore the History of Ice Yachting in the Hudson Valley|last=Levine|first=David|website=www.hvmag.com|date=19 November 2013 |language=en|access-date=April 14, 2020}}</ref><ref>{{Cite web|url=https://ice.idniyra.org/|title=IDNIYRA {{!}} International DN Ice Yacht Racing Association|date=December 27, 2017|archive-url=https://web.archive.org/web/20171227121944/https://ice.idniyra.org/|access-date=April 15, 2020|archive-date=December 27, 2017}}</ref> Another vehicular sport is [[ice racing]], where drivers must speed on lake ice, while also controlling the skid of their vehicle (similar in some ways to [[dirt track racing]]). The sport has even been modified for [[ice rink]]s.<ref>{{cite web |url=http://www.motortrend.com/features/112_0407_ice_racing/index.html|title=Racing Fast 'n' Cheap: Ice Racing |last=Markus |first=Frank |publisher=[[Motor Trend]] |access-date=2008-09-30 |archive-date=2011-06-04 |archive-url=https://web.archive.org/web/20110604072725/http://www.motortrend.com/features/112_0407_ice_racing/index.html |url-status=dead }}</ref>


===Other uses===
===Other uses===

==== As thermal ballast ====
==== As thermal ballast ====
* Ice is still used to cool and preserve food in portable [[cooler]]s.<ref name="Prewitt2023">{{Cite web |last1=Prewitt |first1=Laura |date=23 July 2023 |title=A Chilling History |url=https://www.sciencehistory.org/collections/blog/a-chilling-history/ |publisher=[[Science History Institute]] |language=en |access-date=26 April 2024 }}</ref>
* Ice is still used to cool and preserve food in portable [[cooler]]s.<ref name="Prewitt2023">{{Cite web |last1=Prewitt |first1=Laura |date=23 July 2023 |title=A Chilling History |url=https://www.sciencehistory.org/collections/blog/a-chilling-history/ |publisher=[[Science History Institute]] |language=en |access-date=26 April 2024 }}</ref>
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==== As structural material ====
==== As structural material ====
[[File:USNS Southern Cross at the ice pier in 1983.jpg|thumb|Ice pier during 1983 cargo operations. [[McMurdo Station]], Antarctica.]]
[[File:USNS Southern Cross at the ice pier in 1983.jpg|thumb|Ice pier during 1983 cargo operations. [[McMurdo Station]], Antarctica.]]
* Engineers used the substantial strength of pack ice when they constructed Antarctica's first floating [[ice pier]] in 1973.<ref>[http://antarcticsun.usap.gov/pastIssues/2005-2006/2006_01_08.pdf#page=3 "Unique ice pier provides harbor for ships"], {{webarchive|url=http://archive.wikiwix.com/cache/20110223145229/http://antarcticsun.usap.gov/pastIssues/2005-2006/2006_01_08.pdf |date=23 February 2011 }} Antarctic Sun. 8 January 2006; McMurdo Station, Antarctica.</ref> Such ice piers are used during cargo operations to load and offload ships. Fleet operations personnel make the floating pier during the winter. They build upon naturally occurring frozen seawater in [[McMurdo Sound]] until the dock reaches a depth of about {{convert|22|ft|m}}. Ice piers have a lifespan of three to five years.[[File:Castello di neve in lapponia 02 (2108559776).jpg|thumb|An ice-made dining room of the [[Kemi]]'s [[SnowCastle of Kemi|SnowCastle]] [[ice hotel]] in [[Finland]]]]
* Engineers used the substantial strength of pack ice when they constructed Antarctica's first floating [[ice pier]] in 1973.<ref>[http://antarcticsun.usap.gov/pastIssues/2005-2006/2006_01_08.pdf#page=3 "Unique ice pier provides harbor for ships"], {{webarchive|url=http://archive.wikiwix.com/cache/20110223145229/http://antarcticsun.usap.gov/pastIssues/2005-2006/2006_01_08.pdf |date=23 February 2011 }} Antarctic Sun. 8 January 2006; McMurdo Station, Antarctica.</ref> Such ice piers are used during cargo operations to load and offload ships. Fleet operations personnel make the floating pier during the winter. They build upon naturally occurring frozen seawater in [[McMurdo Sound]] until the dock reaches a depth of about {{convert|22|ft|m}}. Ice piers are inherently temporary structures, although some can last as long as 10 years. Once a pier is no longer usable, it is towed to sea with an icebreaker.<ref>{{cite web |date=10 February 2023 |title=Ocean Disposal of Man-Made Ice Piers |url=https://www.epa.gov/ocean-dumping/ocean-disposal-man-made-ice-piers |publisher=[[United States Environmental Protection Agency|U.S. Environmental Protection Agency]] |archive-url=https://web.archive.org/web/20230701024353/https://www.epa.gov/ocean-dumping/ocean-disposal-man-made-ice-piers |archive-date=1 July 2023 }}</ref>
[[File:Castello di neve in lapponia 02 (2108559776).jpg|thumb|An ice-made dining room of the [[Kemi]]'s [[SnowCastle of Kemi|SnowCastle]] [[ice hotel]] in [[Finland]]]]
* Structures and [[ice sculpture]]s are built out of large chunks of ice or by spraying water<ref name="Makkonen, L. 1994">Makkonen, L. (1994) "Ice and Construction". E & FN Spon, London. {{ISBN|0-203-62726-1}}.</ref> The structures are mostly ornamental (as in the case with [[Ice palace|ice castle]]s), and not practical for long-term habitation. [[Ice hotel]]s exist on a seasonal basis in a few cold areas. [[Igloo]]s are another example of a temporary structure, made primarily from snow.
* Structures and [[ice sculpture]]s are built out of large chunks of ice or by spraying water<ref name="Makkonen, L. 1994">Makkonen, L. (1994) "Ice and Construction". E & FN Spon, London. {{ISBN|0-203-62726-1}}.</ref> The structures are mostly ornamental (as in the case with [[Ice palace|ice castle]]s), and not practical for long-term habitation. [[Ice hotel]]s exist on a seasonal basis in a few cold areas.<ref>{{cite news |last=O'Brien |first=Harriet |date=19 January 2007 |title=Ice Hotels: Cold comforts |newspaper=[[The Independent]] |url=https://www.independent.co.uk/travel/europe/ice-hotels-cold-comforts-432813.html |access-date=26 May 2024 }}</ref> [[Igloo]]s are another example of a temporary structure, made primarily from snow.<ref>{{cite news |last=Cruickshank |first=Dan |date=2 April 2008 |title=What house-builders can learn from igloos |work=[[BBC News]] |url=http://news.bbc.co.uk/1/hi/magazine/7326031.stm |access-date=26 May 2024 |url-status=live |archive-url=https://web.archive.org/web/20090311170506/http://news.bbc.co.uk/1/hi/magazine/7326031.stm |archive-date=11 March 2009 }}</ref>
* Engineers can also use ice to destroy. In [[mining]], drilling holes in rock structures and then pouring water during cold weather is an accepted alternative to using [[dynamite]], as the rock cracks when the water expands as ice.<ref name="Akyurt2002" />
* Engineers can also use ice to destroy. In [[mining]], drilling holes in rock structures and then pouring water during cold weather is an accepted alternative to using [[dynamite]], as the rock cracks when the water expands as ice.<ref name="Akyurt2002" />
* During World War II, [[Project Habbakuk]] was an Allied programme which investigated the use of [[pykrete]] (wood fibers mixed with ice) as a possible material for warships, especially aircraft carriers, due to the ease with which a vessel immune to torpedoes, and a large deck, could be constructed by ice. A small-scale prototype was built,<ref>Gold, L.W. (1993). "The Canadian Habbakuk Project: a Project of the National Research Council of Canada". International Glaciological Society. {{ISBN|0946417164}}.</ref> but the need for such a vessel in the war was removed prior to building it in full-scale.
* During World War II, [[Project Habbakuk]] was an Allied programme which investigated the use of [[pykrete]] (wood fibers mixed with ice) as a possible material for warships, especially aircraft carriers, due to the ease with which a vessel immune to torpedoes, and a large deck, could be constructed by ice. A small-scale prototype was built,<ref>Gold, L.W. (1993). "The Canadian Habbakuk Project: a Project of the National Research Council of Canada". International Glaciological Society. {{ISBN|0946417164}}.</ref> but it soon turned out the project would cost far more than a conventional aircraft carrier while being many times slower and also vulnerable to melting.<ref>{{cite journal |url=http://www.goodeveca.net/CFGoodeve/habakkuk.html |title=The Ice Ship Fiasco |author=Sir Charles Goodeve |journal=Evening Standard |location=London |date=19 April 1951 }}</ref>
* Ice has even been used as the material for a variety of musical instruments, for example by percussionist [[Terje Isungset]].<ref>{{cite web | url=https://www.bbc.co.uk/music/reviews/cj63 | title=Terje Isungset Iceman Is Review | publisher=BBC Music | author=Talkington, Fiona | date=3 May 2005 | access-date=24 May 2011 | url-status=live | archive-url=https://web.archive.org/web/20130924045635/http://www.bbc.co.uk/music/reviews/cj63 | archive-date=24 September 2013 }}</ref>
* Ice has even been used as the material for a variety of musical instruments, for example by percussionist [[Terje Isungset]].<ref>{{cite web | url=https://www.bbc.co.uk/music/reviews/cj63 | title=Terje Isungset Iceman Is Review | publisher=BBC Music | author=Talkington, Fiona | date=3 May 2005 | access-date=24 May 2011 | url-status=live | archive-url=https://web.archive.org/web/20130924045635/http://www.bbc.co.uk/music/reviews/cj63 | archive-date=24 September 2013 }}</ref>


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[[File:Slater 2021 global ice loss.png|thumb|On average, climate change has lowered the thickness of land ice with every year, and reduced the extent of sea ice cover.<ref name="Slater2021" />]]
[[File:Slater 2021 global ice loss.png|thumb|On average, climate change has lowered the thickness of land ice with every year, and reduced the extent of sea ice cover.<ref name="Slater2021" />]]


[[Greenhouse gas emissions]] from human activities unbalance the [[Earth's energy budget]] and so cause an accumulation of [[heat]].<ref name="vonSchuckmann2023" /> About 90% of that heat is added to [[ocean heat content]], 1% is retained in the atmosphere and 3-4% goes to melt major parts of the cryosphere.<ref name="vonSchuckmann2023">{{cite journal |last1=von Schuckmann |first1=Karina |last2=Minière |first2=Audrey. |last3=Gues |first3=Flora |last4=Cuesta-Valero |first4=Francisco José |last5=Kirchengast |first5=Gottfried |last6=Adusumilli |first6=Susheel |last7=Straneo |first7=Flammetta |last8=Ablain |first8=Michaël |last9=Allen |first9=Richard P. |last10=Barker |first10=Paul M. |title=Heat stored in the Earth system 1960-2020: where does the energy go? |journal=Earth System Science Data |date=17 April 2023 |doi=10.5194/essd-15-1675-2023 |doi-access=free |volume=15 |issue=4 |pages=1675-1709 [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License]|bibcode=2023ESSD...15.1675V |hdl=20.500.11850/619535 |hdl-access=free }}</ref> Between 1994 and 2017, 28 trillion tonnes of ice were lost around the globe as the result.<ref name="Slater2021" /> [[Arctic sea ice decline]] accounted for the single largest loss (7.6 trillion tonnes), followed by the melting of Antarctica's [[ice shelves]] (6.5 trillion tonnes), the [[Retreat of glaciers since 1850|retreat of mountain glaciers]] (6.1 trillion tonnes), the melting of [[Greenland ice sheet]] (3.8 trillion tonnes) and finally the melting the [[Antarctic ice sheet]] (2.5 trillion tonnes) and the limited losses of the sea ice in the [[Southern Ocean]] (0.9 trillion tonnes).<ref name="Slater2021">{{cite journal |last1=Slater |first1=Thomas |last2=Lawrence |first2=Isobel R. |last3=Otosaka |first3=Inès N. |last4=Shepherd |first4=Andrew |last5=Gourmelen |first5=Noel |last6=Jakob |first6=Livia |last7=Tepes |first7=Paul |last8=Gilbert |first8=Lin |last9=Nienow |first9=Peter |title=Review article: Earth's ice imbalance |journal=The Cryosphere |date=25 Jan 2021 |doi=10.5194/tc-15-233-2021 |doi-access=free |volume=15 |issue=1 |pages=233–246 [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License]|bibcode=2021TCry...15..233S |hdl=20.500.11820/df343a4d-6b66-4eae-ac3f-f5a35bdeef04 |hdl-access=free }}</ref>
[[Greenhouse gas emissions]] from human activities unbalance the [[Earth's energy budget]] and so cause an accumulation of [[heat]].<ref name="vonSchuckmann2023" /> About 90% of that heat is added to [[ocean heat content]], 1% is retained in the atmosphere and 3-4% goes to melt major parts of the cryosphere.<ref name="vonSchuckmann2023">{{cite journal |last1=von Schuckmann |first1=Karina |last2=Minière |first2=Audrey. |last3=Gues |first3=Flora |last4=Cuesta-Valero |first4=Francisco José |last5=Kirchengast |first5=Gottfried |last6=Adusumilli |first6=Susheel |last7=Straneo |first7=Flammetta |last8=Ablain |first8=Michaël |last9=Allen |first9=Richard P. |last10=Barker |first10=Paul M. |title=Heat stored in the Earth system 1960-2020: where does the energy go? |journal=Earth System Science Data |date=17 April 2023 |doi=10.5194/essd-15-1675-2023 |doi-access=free |volume=15 |issue=4 |pages=1675-1709 [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License]|bibcode=2023ESSD...15.1675V |hdl=20.500.11850/619535 |hdl-access=free }}</ref> Between 1994 and 2017, 28 trillion tonnes of ice were lost around the globe as the result.<ref name="Slater2021" /> [[Arctic sea ice decline]] accounted for the single largest loss (7.6 trillion tonnes), followed by the melting of Antarctica's [[ice shelves]] (6.5 trillion tonnes), the [[Retreat of glaciers since 1850|retreat of mountain glaciers]] (6.1 trillion tonnes), the melting of the [[Greenland ice sheet]] (3.8 trillion tonnes) and finally the melting of the [[Antarctic ice sheet]] (2.5 trillion tonnes) and the limited losses of the sea ice in the [[Southern Ocean]] (0.9 trillion tonnes).<ref name="Slater2021">{{cite journal |last1=Slater |first1=Thomas |last2=Lawrence |first2=Isobel R. |last3=Otosaka |first3=Inès N. |last4=Shepherd |first4=Andrew |last5=Gourmelen |first5=Noel |last6=Jakob |first6=Livia |last7=Tepes |first7=Paul |last8=Gilbert |first8=Lin |last9=Nienow |first9=Peter |title=Review article: Earth's ice imbalance |journal=The Cryosphere |date=25 Jan 2021 |doi=10.5194/tc-15-233-2021 |doi-access=free |volume=15 |issue=1 |pages=233–246 [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License]|bibcode=2021TCry...15..233S |hdl=20.500.11820/df343a4d-6b66-4eae-ac3f-f5a35bdeef04 |hdl-access=free }}</ref>

Other than the sea ice (which already displaces water due to [[Archimedes' principle]]), these losses are a major cause of [[sea level rise]] (SLR) and they are expected to intensify in the future. In particular, the melting of the [[West Antarctic ice sheet]] may accelerate substantially as the floating [[ice shelf|ice shelves]] are lost and can no longer buttress the glaciers. This would trigger poorly understood [[marine ice sheet instability]] processes, which could then increase the SLR expected for the end of the century (between {{cvt|30|cm|ft|frac=2}} and {{cvt|1|m|ft|frac=2}}, depending on future warming), by tens of centimeters more.<ref name="IPCC AR6 WG1 Ch.9">{{Cite journal |last1=Fox-Kemper |first1=B. |last2=Hewitt |first2=Helene T. |author2-link=Helene Hewitt |last3=Xiao |first3=C. |last4=Aðalgeirsdóttir |first4=G. |last5=Drijfhout |first5=S. S. |last6=Edwards |first6=T. L. |last7=Golledge |first7=N. R. |last8=Hemer |first8=M. |last9=Kopp |first9=R. E. |last10=Krinner |first10=G. |last11=Mix |first11=A. |date=2021 |editor-last=Masson-Delmotte |editor-first=V. |editor2-last=Zhai |editor2-first=P. |editor3-last=Pirani |editor3-first=A. |editor4-last=Connors |editor4-first=S. L. |editor5-last=Péan |editor5-first=C. |editor6-last=Berger |editor6-first=S. |editor7-last=Caud |editor7-first=N. |editor8-last=Chen |editor8-first=Y. |editor9-last=Goldfarb |editor9-first=L. |title=Chapter 9: Ocean, Cryosphere and Sea Level Change |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf |journal=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press, Cambridge, UK and New York, NY, US }}</ref>{{rp|1302}}

Ice loss in Greenland and Antarctica also produces large quantities of fresh [[meltwater]], which disrupts the [[Atlantic meridional overturning circulation]] (AMOC) and the [[Southern Ocean overturning circulation]], respectively.<ref name="GTPR2023" /> These two halves of the [[thermohaline circulation]] are very important for the global climate. A continuation of high meltwater flows may cause a severe disruption (up to a point of a "collapse") of either circulation, or even both of them. Either event would be considered an example of [[tipping points in the climate system]], because it would be extremely difficult to reverse.<ref name="GTPR2023">{{cite report |last1=Lenton |first1=T. M. |last2=Armstrong McKay |first2=D.I. |last3=Loriani |first3=S. |last4=Abrams |first4=J.F. |last5=Lade |first5=S.J. |last6=Donges |first6=J.F. |last7=Milkoreit |first7=M. |last8=Powell |first8=T. |last9=Smith |first9=S.R. |last10=Zimm |first10=C. |last11=Buxton |first11=J.E. |last12=Daube |first12=Bruce C. |last13=Krummel |first13=Paul B. |last14=Loh |first14=Zoë |last15=Luijkx |first15=Ingrid T. |year=2023 |title=The Global Tipping Points Report 2023 |url=https://global-tipping-points.org/download/4608/ |publisher=University of Exeter }}</ref> AMOC is generally not expected to collapse during the 21st century, while there is only limited knowledge about the Southern Ocean circulation.<ref name="IPCC AR6 WG1 Ch.9" />{{rp|1214}}


Another example of ice-related tipping point is permafrost thaw. While the organic content in the permafrost causes {{CO2}} and methane emissions once it thaws and begins to decompose,<ref name="GTPR2023" /> ice melting liqufies the ground, causing anything built above the former permafrost to collapse. By 2050, the economic damages from such infrastructure loss are expected to cost tens of billions of dollars.<ref name="Hjort2022">{{Cite journal |last1=Hjort |first1=Jan |last2=Streletskiy |first2=Dmitry |last3=Doré |first3=Guy |last4=Wu |first4=Qingbai |last5=Bjella |first5=Kevin |last6=Luoto |first6=Miska |date=11 January 2022 |title=Impacts of permafrost degradation on infrastructure |journal=Nature Reviews Earth & Environment |volume=3 |issue=1 |pages=24–38 |doi=10.1038/s43017-021-00247-8|bibcode=2022NRvEE...3...24H |hdl=10138/344541 |s2cid=245917456 |url=http://urn.fi/urn:nbn:fi-fe2022101962575 |hdl-access=free }}</ref>
Other than the sea ice, these losses are a major cause of [[sea level rise]] (SLR) and they will likely intensify in the future. In particular, the melting of the [[West Antarctic ice sheet]] may accelerate in the future due to [[marine ice sheet instability]] processes. This could then increase the SLR expected for the end of the century (between {{cvt|30|cm|ft|frac=2}} and {{cvt|1|m|ft|frac=2}}, depending on future warming), by tens of centimeters more.<ref name="IPCC AR6 WG1 Ch.9">{{Cite journal |last1=Fox-Kemper |first1=B. |last2=Hewitt |first2=Helene T. |author2-link=Helene Hewitt |last3=Xiao |first3=C. |last4=Aðalgeirsdóttir |first4=G. |last5=Drijfhout |first5=S. S. |last6=Edwards |first6=T. L. |last7=Golledge |first7=N. R. |last8=Hemer |first8=M. |last9=Kopp |first9=R. E. |last10=Krinner |first10=G. |last11=Mix |first11=A. |date=2021 |editor-last=Masson-Delmotte |editor-first=V. |editor2-last=Zhai |editor2-first=P. |editor3-last=Pirani |editor3-first=A. |editor4-last=Connors |editor4-first=S. L. |editor5-last=Péan |editor5-first=C. |editor6-last=Berger |editor6-first=S. |editor7-last=Caud |editor7-first=N. |editor8-last=Chen |editor8-first=Y. |editor9-last=Goldfarb |editor9-first=L. |title=Chapter 9: Ocean, Cryosphere and Sea Level Change |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter09.pdf |journal=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press, Cambridge, UK and New York, NY, US |page=1302}}</ref> Ice loss in Greenland and Antarctica also produces large quantities of fresh [[meltwater]], which disrupts the [[Atlantic meridional overturning circulation]] and the [[Southern Ocean overturning circulation]], respectively.<ref name="GTPR2023" /> These two halves of the [[thermohaline circulation]] are very important for the global climate. A continuation of high meltwater flows may cause a severe disruption (up to a point of a "collapse") of either circulation, or even both of them. Either event would be considered an example of [[tipping points in the climate system]], because it would be extremely difficult to reverse.<ref name="GTPR2023">{{cite report |last1=Lenton |first1=T. M. |last2=Armstrong McKay |first2=D.I. |last3=Loriani |first3=S. |last4=Abrams |first4=J.F. |last5=Lade |first5=S.J. |last6=Donges |first6=J.F. |last7=Milkoreit |first7=M. |last8=Powell |first8=T. |last9=Smith |first9=S.R. |last10=Zimm |first10=C. |last11=Buxton |first11=J.E. |last12=Daube |first12=Bruce C. |last13=Krummel |first13=Paul B. |last14=Loh |first14=Zoë |last15=Luijkx |first15=Ingrid T. |year=2023 |title=The Global Tipping Points Report 2023 |url=https://global-tipping-points.org/download/4608/ |publisher=University of Exeter }}</ref>


===Predictions===
===Predictions===
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{{portal|Water}}
{{portal|Water}}
{{div col}}
{{div col}}
* {{annotated link|Water (properties)#Density of water and ice|Density of ice versus water}}
* {{annotated link|Ice famine}}
* {{annotated link|Ice famine}}
* {{annotated link|Ice jacking}}
* {{annotated link|Ice jacking}}
* {{annotated link|Jumble ice}}
* {{annotated link|Jumble ice}}
* {{annotated link|Pumpable ice technology}}
* {{annotated link|Pumpable ice technology}}
* {{annotated link|Ice crystal}}
{{div col end}}
{{div col end}}


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{{Ice |expanded}}
{{Ice |expanded}}
{{Water}}
{{Natural resources}}
{{Natural resources}}



Latest revision as of 08:51, 2 November 2024

Ice
A picture of ice
An ice block, photographed at the Duluth Canal Park in Minnesota
Physical properties
Density (ρ)0.9167[1]–0.9168[2] g/cm3
Refractive index (n)1.309
Chemical properties
Chemical formulaH2O
Mechanical properties
Young's modulus (E)3400 to 37,500 kg-force/cm3[2]
Tensile strength (σt)5 to 18 kg-force/cm2[2]
Compressive strength (σc)24 to 60 kg-force/cm2[2]
Poisson's ratio (ν)0.36±0.13[2]
Thermal properties
Thermal conductivity (k)0.0053(1 + 0.0015 θ) cal/(cm s K), θ = temperature in °C[2]
Linear thermal expansion coefficient (α)5.5×10−5[2]
Specific heat capacity (c)0.5057 − 0.001863 θ cal/(g K), θ = absolute value of temperature in °C[2]
Electrical properties
Dielectric constant (εr)~95[3]
The properties of ice vary substantially with temperature, purity and other factors.

Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 °C, 32 °F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color.

Virtually all of the ice on Earth is of a hexagonal crystalline structure denoted as ice Ih (spoken as "ice one h"). Depending on temperature and pressure, at least nineteen phases (packing geometries) can exist. The most common phase transition to ice Ih occurs when liquid water is cooled below °C (273.15 K, 32 °F) at standard atmospheric pressure. When water is cooled rapidly (quenching), up to three types of amorphous ice can form. Interstellar ice is overwhelmingly low-density amorphous ice (LDA), which likely makes LDA ice the most abundant type in the universe. When cooled slowly, correlated proton tunneling occurs below −253.15 °C (20 K, −423.67 °F) giving rise to macroscopic quantum phenomena.

Ice is abundant on the Earth's surface, particularly in the polar regions and above the snow line, where it can aggregate from snow to form glaciers and ice sheets. As snowflakes and hail, ice is a common form of precipitation, and it may also be deposited directly by water vapor as frost. The transition from ice to water is melting and from ice directly to water vapor is sublimation. These processes plays a key role in Earth's water cycle and climate. In the recent decades, ice volume on Earth has been decreasing due to climate change. The largest declines have occurred in the Arctic and in the mountains located outside of the polar regions. The loss of grounded ice (as opposed to floating sea ice) is the primary contributor to sea level rise.

Humans have been using ice for various purposes for thousands of years. Some historic structures designed to hold ice to provide cooling are over 2,000 years old. Before the invention of refrigeration technology, the only way to safely store food without modifying it through preservatives was to use ice. Sufficiently solid surface ice makes waterways accessible to land transport during winter, and dedicated ice roads may be maintained. Ice also plays a major role in winter sports.

Physical properties

The three-dimensional crystal structure of H2O ice Ih (c) is composed of bases of H2O ice molecules (b) located on lattice points within the two-dimensional hexagonal space lattice (a).[4][5]

Ice possesses a regular crystalline structure based on the molecule of water, which consists of a single oxygen atom covalently bonded to two hydrogen atoms, or H–O–H. However, many of the physical properties of water and ice are controlled by the formation of hydrogen bonds between adjacent oxygen and hydrogen atoms; while it is a weak bond, it is nonetheless critical in controlling the structure of both water and ice.[6]

An unusual property of water is that its solid form—ice frozen at atmospheric pressure—is approximately 8.3% less dense than its liquid form; this is equivalent to a volumetric expansion of 9%. The density of ice is 0.9167[1]–0.9168[2] g/cm3 at 0 °C and standard atmospheric pressure (101,325 Pa), whereas water has a density of 0.9998[1]–0.999863[2] g/cm3 at the same temperature and pressure. Liquid water is densest, essentially 1.00 g/cm3, at 4 °C and begins to lose its density as the water molecules begin to form the hexagonal crystals of ice as the freezing point is reached. This is due to hydrogen bonding dominating the intermolecular forces, which results in a packing of molecules less compact in the solid. The density of ice increases slightly with decreasing temperature and has a value of 0.9340 g/cm3 at −180 °C (93 K).[7]

When water freezes, it increases in volume (about 9% for fresh water).[8] The effect of expansion during freezing can be dramatic, and ice expansion is a basic cause of freeze-thaw weathering of rock in nature and damage to building foundations and roadways from frost heaving. It is also a common cause of the flooding of houses when water pipes burst due to the pressure of expanding water when it freezes.[9]

This iceberg can stay afloat in spite of its size because it is less dense than water

Because ice is less dense than liquid water, it floats, and this prevents bottom-up freezing of the bodies of water. Instead, a sheltered environment for animal and plant life is formed beneath the floating ice, which protects the underside from short-term weather extremes such as wind chill. Sufficiently thin floating ice allows light to pass through, supporting the photosynthesis of bacterial and algal colonies.[10] When sea water freezes, the ice is riddled with brine-filled channels which sustain sympagic organisms such as bacteria, algae, copepods and annelids. In turn, they provide food for animals such as krill and specialized fish like the bald notothen, fed upon in turn by larger animals such as emperor penguins and minke whales.[11]

So-called feather ice on the plateau near Alta, Norway. The crystals form at temperatures below −30 °C (−22 °F) and contain a lot of trapped air, making them light enough to be supported by the thin branch
Frozen waterfall in southeast New York

When ice melts, it absorbs as much energy as it would take to heat an equivalent mass of water by 80 °C (176 °F).[12] During the melting process, the temperature remains constant at 0 °C (32 °F). While melting, any energy added breaks the hydrogen bonds between ice (water) molecules. Energy becomes available to increase the thermal energy (temperature) only after enough hydrogen bonds are broken that the ice can be considered liquid water. The amount of energy consumed in breaking hydrogen bonds in the transition from ice to water is known as the heat of fusion.[12][8]

As with water, ice absorbs light at the red end of the spectrum preferentially as the result of an overtone of an oxygen–hydrogen (O–H) bond stretch. Compared with water, this absorption is shifted toward slightly lower energies. Thus, ice appears blue, with a slightly greener tint than liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice.[13] Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. For instance, icebergs containing impurities (e.g., sediments, algae, air bubbles) can appear brown, grey or green.[13]

Because ice in natural environments is usually close to its melting temperature, its hardness shows pronounced temperature variations. At its melting point, ice has a Mohs hardness of 2 or less, but the hardness increases to about 4 at a temperature of −44 °C (−47 °F) and to 6 at a temperature of −78.5 °C (−109.3 °F), the vaporization point of solid carbon dioxide (dry ice).[14]

Phases

Log-lin pressure-temperature phase diagram of water. The Roman numerals correspond to some ice phases listed below.
An alternative formulation of the phase diagram for certain ices and other phases of water[15]
Pressure dependence of ice melting

Most liquids under increased pressure freeze at higher temperatures because the pressure helps to hold the molecules together. However, the strong hydrogen bonds in water make it different: for some pressures higher than 1 atm (0.10 MPa), water freezes at a temperature below 0 °C (32 °F). Ice, water, and water vapour can coexist at the triple point, which is exactly 273.16 K (0.01 °C) at a pressure of 611.657 Pa.[16][17] The kelvin was defined as 1/273.16 of the difference between this triple point and absolute zero,[18] though this definition changed in May 2019.[19] Unlike most other solids, ice is difficult to superheat. In an experiment, ice at −3 °C was superheated to about 17 °C for about 250 picoseconds.[20]

Subjected to higher pressures and varying temperatures, ice can form in nineteen separate known crystalline phases at various densities, along with hypothetical proposed phases of ice that have not been observed.[21] With care, at least fifteen of these phases (one of the known exceptions being ice X) can be recovered at ambient pressure and low temperature in metastable form.[22][23] The types are differentiated by their crystalline structure, proton ordering,[24] and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are Ice IV and Ice XII. Ice XII was discovered in 1996. In 2006, Ice XIII and Ice XIV were discovered.[25] Ices XI, XIII, and XIV are hydrogen-ordered forms of ices Ih, V, and XII respectively. In 2009, ice XV was found at extremely high pressures and −143 °C.[26] At even higher pressures, ice is predicted to become a metal; this has been variously estimated to occur at 1.55 TPa[27] or 5.62 TPa.[28]

As well as crystalline forms, solid water can exist in amorphous states as amorphous solid water (ASW) of varying densities. In outer space, hexagonal crystalline ice is present in the ice volcanoes,[29] but is extremely rare otherwise. Even icy moons like Ganymede are expected to mainly consist of other crystalline forms of ice.[30][31] Water in the interstellar medium is dominated by amorphous ice, making it likely the most common form of water in the universe.[32] Low-density ASW (LDA), also known as hyperquenched glassy water, may be responsible for noctilucent clouds on Earth and is usually formed by deposition of water vapor in cold or vacuum conditions.[33] High-density ASW (HDA) is formed by compression of ordinary ice Ih or LDA at GPa pressures. Very-high-density ASW (VHDA) is HDA slightly warmed to 160 K under 1–2 GPa pressures.[34]

Ice from a theorized superionic water may possess two crystalline structures. At pressures in excess of 500,000 bars (7,300,000 psi) such superionic ice would take on a body-centered cubic structure. However, at pressures in excess of 1,000,000 bars (15,000,000 psi) the structure may shift to a more stable face-centered cubic lattice. It is speculated that superionic ice could compose the interior of ice giants such as Uranus and Neptune.[35]

Friction properties

Takahiko Kozuka figure skating - an act which is only possible due to ice's low frictional properties

Ice is "slippery" because it has a low coefficient of friction. This subject was first scientifically investigated in the 19th century. The preferred explanation at the time was "pressure melting" -i.e. the blade of an ice skate, upon exerting pressure on the ice, would melt a thin layer, providing sufficient lubrication for the blade to glide across the ice.[36] Yet, 1939 research by Frank P. Bowden and T. P. Hughes found that skaters would experience a lot more friction than they actually do if it were the only explanation. Further, the optimum temperature for figure skating is −5.5 °C (22 °F; 268 K) and −9 °C (16 °F; 264 K) for hockey; yet, according to pressure melting theory, skating below −4 °C (25 °F; 269 K) would be outright impossible.[37] Instead, Bowden and Hughes argued that heating and melting of the ice layer is caused by friction. However, this theory does not sufficiently explain why ice is slippery when standing still even at below-zero temperatures.[36]

Subsequent research suggested that ice molecules at the interface cannot properly bond with the molecules of the mass of ice beneath (and thus are free to move like molecules of liquid water). These molecules remain in a semi-liquid state, providing lubrication regardless of pressure against the ice exerted by any object. However, the significance of this hypothesis is disputed by experiments showing a high coefficient of friction for ice using atomic force microscopy.[37] Thus, the mechanism controlling the frictional properties of ice is still an active area of scientific study.[38] A comprehensive theory of ice friction must take into account all of the aforementioned mechanisms to estimate friction coefficient of ice against various materials as a function of temperature and sliding speed. 2014 research suggests that frictional heating is the most important process under most typical conditions.[39]

Natural formation

Frozen landscape in the Northwest Territories of Canada. A large ice circle can be clearly seen floating on water

The term that collectively describes all of the parts of the Earth's surface where water is in frozen form is the cryosphere. Ice is an important component of the global climate, particularly in regard to the water cycle. Glaciers and snowpacks are an important storage mechanism for fresh water; over time, they may sublimate or melt. Snowmelt is an important source of seasonal fresh water.[40][41] The World Meteorological Organization defines several kinds of ice depending on origin, size, shape, influence and so on.[42] Clathrate hydrates are forms of ice that contain gas molecules trapped within its crystal lattice.[43][44]

In the oceans

Ice that is found at sea may be in the form of drift ice floating in the water, fast ice fixed to a shoreline or anchor ice if attached to the seafloor.[45] Ice which calves (breaks off) from an ice shelf or a coastal glacier may become an iceberg.[46] The aftermath of calving events produces a loose mixture of snow and ice known as Ice mélange.[47]

Sea ice forms in several stages. At first, small, millimeter-scale crystals accumulate on the water surface in what is known as frazil ice. As they become somewhat larger and more consistent in shape and cover, the water surface begins to look "oily" from above, so this stage is called grease ice.[48] Then, ice continues to clump together, and solidify into flat cohesive pieces known as ice floes. Ice floes are the basic building blocks of sea ice cover, and their horizontal size (defined as half of their diameter) varies dramatically, with the smallest measured in centimeters and the largest in hundreds of kilometers.[49] An area which is over 70% ice on its surface is said to be covered by pack ice.[50]

Fully formed sea ice can be forced together by currents and winds to form pressure ridges up to 12 metres (39 ft) tall.[51] On the other hand, active wave activity can reduce sea ice to small, regularly shaped pieces, known as pancake ice.[52] Sometimes, wind and wave activity "polishes" sea ice to perfectly spherical pieces known as ice eggs.[53][54]

On land

NASA image of the Antarctic ice sheet

The largest ice formations on Earth are the two ice sheets which almost completely cover the world's largest island, Greenland, and the continent of Antarctica. These ice sheets have an average thickness of over 1 km (0.6 mi) and have existed for millions of years.[55][56]

Other major ice formations on land include ice caps, ice fields, ice streams and glaciers. In particular, the Hindu Kush region is known as the Earth's "Third Pole" due to the large number of glaciers it contains. They cover an area of around 80,000 km2 (31,000 sq mi), and have a combined volume of between 3,000-4,700 km3.[40] These glaciers are nicknamed "Asian water towers", because their meltwater run-off feeds into rivers which provide water for an estimated two billion people.[41]

Permafrost refers to soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more.[57] The ice within permafrost is divided into four categories: pore ice, vein ice (also known as ice wedges), buried surface ice and intrasedimental ice (from the freezing of underground waters).[58] One example of ice formation in permafrost areas is aufeis - layered ice that forms in Arctic and subarctic stream valleys. Ice, frozen in the stream bed, blocks normal groundwater discharge, and causes the local water table to rise, resulting in water discharge on top of the frozen layer. This water then freezes, causing the water table to rise further and repeat the cycle. The result is a stratified ice deposit, often several meters thick.[59] Snow line and snow fields are two related concepts, in that snow fields accumulate on top of and ablate away to the equilibrium point (the snow line) in an ice deposit.[60]

On rivers and streams

A small frozen rivulet

Ice which forms on moving water tends to be less uniform and stable than ice which forms on calm water. Ice jams (sometimes called "ice dams"), when broken chunks of ice pile up, are the greatest ice hazard on rivers. Ice jams can cause flooding, damage structures in or near the river, and damage vessels on the river. Ice jams can cause some hydropower industrial facilities to completely shut down. An ice dam is a blockage from the movement of a glacier which may produce a proglacial lake. Heavy ice flows in rivers can also damage vessels and require the use of an icebreaker vessel to keep navigation possible.[61][62]

Ice discs are circular formations of ice floating on river water. They form within eddy currents, and their position results in asymmetric melting, which makes them continuously rotate at a low speed.[63][64]

On lakes

Candle ice in Lake Otelnuk, Quebec, Canada

Ice forms on calm water from the shores, a thin layer spreading across the surface, and then downward. Ice on lakes is generally four types: primary, secondary, superimposed and agglomerate.[65][66] Primary ice forms first. Secondary ice forms below the primary ice in a direction parallel to the direction of the heat flow. Superimposed ice forms on top of the ice surface from rain or water which seeps up through cracks in the ice which often settles when loaded with snow. An ice shove occurs when ice movement, caused by ice expansion and/or wind action, occurs to the extent that ice pushes onto the shores of lakes, often displacing sediment that makes up the shoreline.[67]

Shelf ice is formed when floating pieces of ice are driven by the wind piling up on the windward shore. This kind of ice may contain large air pockets under a thin surface layer, which makes it particularly hazardous to walk across it.[68] Another dangerous form of rotten ice to traverse on foot is candle ice, which develops in columns perpendicular to the surface of a lake. Because it lacks a firm horizontal structure, a person who has fallen through has nothing to hold onto to pull themselves out.[69]

As precipitation

Snow and freezing rain

Snowflakes by Wilson Bentley, 1902

Snow crystals form when tiny supercooled cloud droplets (about 10 μm in diameter) freeze. These droplets are able to remain liquid at temperatures lower than −18 °C (255 K; 0 °F), because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus". Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than −35 °C (238 K; −31 °F).[70] In warmer clouds an aerosol particle or "ice nucleus" must be present in (or in contact with) the droplet to act as a nucleus. Our understanding of what particles make efficient ice nuclei is poor – what we do know is they are very rare compared to that cloud condensation nuclei on which liquid droplets form. Clays, desert dust and biological particles may be effective,[71] although to what extent is unclear. Artificial nuclei are used in cloud seeding.[72] The droplet then grows by condensation of water vapor onto the ice surfaces.[73]

Ice storm is a type of winter storm characterized by freezing rain, which produces a glaze of ice on surfaces, including roads and power lines. In the United States, a quarter of winter weather events produce glaze ice, and utilities need to be prepared to minimize damages.[74]

Hard forms

A large hailstone, about 6 cm (2.4 in) in diameter

Hail forms in storm clouds when supercooled water droplets freeze on contact with condensation nuclei, such as dust or dirt. The storm's updraft blows the hailstones to the upper part of the cloud. The updraft dissipates and the hailstones fall down, back into the updraft, and are lifted up again. Hail has a diameter of 5 millimetres (0.20 in) or more.[75] Within METAR code, GR is used to indicate larger hail, of a diameter of at least 6.4 millimetres (0.25 in) and GS for smaller.[76] Stones of 19 millimetres (0.75 in), 25 millimetres (1.0 in) and 44 millimetres (1.75 in) are the most frequently reported hail sizes in North America.[77] Hailstones can grow to 15 centimetres (6 in) and weigh more than 0.5 kilograms (1.1 lb).[78] In large hailstones, latent heat released by further freezing may melt the outer shell of the hailstone. The hailstone then may undergo 'wet growth', where the liquid outer shell collects other smaller hailstones.[79] The hailstone gains an ice layer and grows increasingly larger with each ascent. Once a hailstone becomes too heavy to be supported by the storm's updraft, it falls from the cloud.[80]

Soft hail, or graupel, in Nevada

Hail forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing 0 °C (32 °F).[75] Hail-producing clouds are often identifiable by their green coloration.[81][82] The growth rate is maximized at about −13 °C (9 °F), and becomes vanishingly small much below −30 °C (−22 °F) as supercooled water droplets become rare. For this reason, hail is most common within continental interiors of the mid-latitudes, as hail formation is considerably more likely when the freezing level is below the altitude of 11,000 feet (3,400 m).[83] Entrainment of dry air into strong thunderstorms over continents can increase the frequency of hail by promoting evaporative cooling which lowers the freezing level of thunderstorm clouds giving hail a larger volume to grow in. Accordingly, hail is actually less common in the tropics despite a much higher frequency of thunderstorms than in the mid-latitudes because the atmosphere over the tropics tends to be warmer over a much greater depth. Hail in the tropics occurs mainly at higher elevations.[84]

An accumulation of ice pellets

Ice pellets (METAR code PL[76]) are a form of precipitation consisting of small, translucent balls of ice, which are usually smaller than hailstones.[85] This form of precipitation is also referred to as "sleet" by the United States National Weather Service.[86] (In British English "sleet" refers to a mixture of rain and snow.) Ice pellets typically form alongside freezing rain, when a wet warm front ends up between colder and drier atmospheric layers. There, raindrops would both freeze and shrink in size due to evaporative cooling.[87] So-called snow pellets, or graupel, form when multiple water droplets freeze onto snowflakes until a soft ball-like shape is formed.[88] So-called "diamond dust", (METAR code IC[76]) also known as ice needles or ice crystals, forms at temperatures approaching −40 °C (−40 °F) due to air with slightly higher moisture from aloft mixing with colder, surface-based air.[89]

On surfaces

As water drips and re-freezes, it can form hanging icicles, or stalagmite-like structures on the ground.[90] On sloped roofs, buildup of ice can produce an ice dam, which stops melt water from draining properly and potentially leads to damaging leaks.[91] More generally, water vapor depositing onto surfaces due to high relative humidity and then freezing results in various forms of atmospheric icing, or frost. Inside buildings, this can be seen as ice on the surface of un-insulated windows.[92] Hoar frost is common in the environment, particularly in the low-lying areas such as valleys.[93] In Antarctica, the temperatures can be so low that electrostatic attraction is increased to the point hoarfrost on snow sticks together when blown by wind into tumbleweed-like balls known as yukimarimo.[94]

Sometimes, drops of water crystallize on cold objects as rime instead of glaze. Soft rime has a density between a quarter and two thirds that of pure ice,[95] due to a high proportion of trapped air, which also makes soft rime appear white. Hard rime is denser, more transparent, and more likely to appear on ships and aircraft.[96][97] Cold wind specifically causes what is known as advection frost when it collides with objects. When it occurs on plants, it often causes damage to them.[98] Various methods exist to protect agricultural crops from frost - from simply covering them to using wind machines.[99][100] In recent decades, irrigation sprinklers have been calibrated to spray just enough water to preemptively create a layer of ice that would form slowly and so avoid a sudden temperature shock to the plant, and not be so thick as to cause damage with its weight.[99]

Ablation

Different stages of ice melt in a pond
The melting of floating ice

Ablation of ice refers to both its melting and its dissolution.[101]

The melting of ice entails the breaking of hydrogen bonds between the water molecules. The ordering of the molecules in the solid breaks down to a less ordered state and the solid melts to become a liquid. This is achieved by increasing the internal energy of the ice beyond the melting point. When ice melts it absorbs as much energy as would be required to heat an equivalent amount of water by 80 °C. While melting, the temperature of the ice surface remains constant at 0 °C. The rate of the melting process depends on the efficiency of the energy exchange process. An ice surface in fresh water melts solely by free convection with a rate that depends linearly on the water temperature, T, when T is less than 3.98 °C, and superlinearly when T is equal to or greater than 3.98 °C, with the rate being proportional to (T − 3.98 °C)α, with α = 5/3 for T much greater than 8 °C, and α = 4/3 for in between temperatures T.[102]

In salty ambient conditions, dissolution rather than melting often causes the ablation of ice. For example, the temperature of the Arctic Ocean is generally below the melting point of ablating sea ice. The phase transition from solid to liquid is achieved by mixing salt and water molecules, similar to the dissolution of sugar in water, even though the water temperature is far below the melting point of the sugar. However, the dissolution rate is limited by salt concentration and is therefore slower than melting.[103]

Role in human activities

Cooling

A schematic showing how the ancient yakhchals used ice to provide radiative cooling

Ice has long been valued as a means of cooling. In 400 BC Iran, Persian engineers had already developed techniques for ice storage in the desert through the summer months. During the winter, ice was transported from harvesting pools and nearby mountains in large quantities to be stored in specially designed, naturally cooled refrigerators, called yakhchal (meaning ice storage). Yakhchals were large underground spaces (up to 5000 m3) that had thick walls (at least two meters at the base) made of a specific type of mortar called sarooj made from sand, clay, egg whites, lime, goat hair, and ash. The mortar was resistant to heat transfer, helping to keep the ice cool enough not to melt; it was also impenetrable by water. Yakhchals often included a qanat and a system of windcatchers that could lower internal temperatures to frigid levels, even during the heat of the summer. One use for the ice was to create chilled treats for royalty.[104][105]

Harvesting

Slaves in Spanish Cuba unloading ice from Maine in 1832

There were thriving industries in 16th–17th century England whereby low-lying areas along the Thames Estuary were flooded during the winter, and ice harvested in carts and stored inter-seasonally in insulated wooden houses as a provision to an icehouse often located in large country houses, and widely used to keep fish fresh when caught in distant waters. This was allegedly copied by an Englishman who had seen the same activity in China. Ice was imported into England from Norway on a considerable scale as early as 1823.[106]

In the United States, the first cargo of ice was sent from New York City to Charleston, South Carolina, in 1799,[106] and by the first half of the 19th century, ice harvesting had become a big business. Frederic Tudor, who became known as the "Ice King", worked on developing better insulation products for long distance shipments of ice, especially to the tropics; this became known as the ice trade.[107]

Harvesting ice on Lake St. Clair in Michigan, c. 1905

Between 1812 and 1822, under Lloyd Hesketh Bamford Hesketh's instruction, Gwrych Castle was built with 18 large towers, one of those towers is called the 'Ice Tower'. Its sole purpose was to store Ice.[108]

Trieste sent ice to Egypt, Corfu, and Zante; Switzerland, to France; and Germany sometimes was supplied from Bavarian lakes.[106] From 1930s and up until 1994, the Hungarian Parliament building used ice harvested in the winter from Lake Balaton for air conditioning.[109]

Ice houses were used to store ice formed in the winter, to make ice available all year long, and an early type of refrigerator known as an icebox was cooled using a block of ice placed inside it. Many cities had a regular ice delivery service during the summer. The advent of artificial refrigeration technology made the delivery of ice obsolete.[110]

Ice is still harvested for ice and snow sculpture events. For example, a swing saw is used to get ice for the Harbin International Ice and Snow Sculpture Festival each year from the frozen surface of the Songhua River.[111]

Artificial production

Layout of a late 19th-century ice factory

The earliest known written process to artificially make ice is by the 13th-century writings of Arab historian Ibn Abu Usaybia in his book Kitab Uyun al-anba fi tabaqat-al-atibba concerning medicine in which Ibn Abu Usaybia attributes the process to an even older author, Ibn Bakhtawayhi, of whom nothing is known.[112]

Ice is now produced on an industrial scale, for uses including food storage and processing, chemical manufacturing, concrete mixing and curing, and consumer or packaged ice.[113] Most commercial icemakers produce three basic types of fragmentary ice: flake, tubular and plate, using a variety of techniques.[113] Large batch ice makers can produce up to 75 tons of ice per day.[114] In 2002, there were 426 commercial ice-making companies in the United States, with a combined value of shipments of $595,487,000.[115] Home refrigerators can also make ice with a built in icemaker, which will typically make ice cubes or crushed ice. The first such device was presented in 1965 by Frigidaire.[116]

Land travel

Ice formation on exterior of vehicle windshield

Ice forming on roads is a common winter hazard, and black ice particularly dangerous because it is very difficult to see. It is both very transparent, and often forms specifically in shaded (and therefore cooler and darker) areas, i.e. beneath overpasses.[117]

Whenever there is freezing rain or snow which occurs at a temperature near the melting point, it is common for ice to build up on the windows of vehicles. Often, snow melts, re-freezes, and forms a fragmented layer of ice which effectively "glues" snow to the window. In this case, the frozen mass is commonly removed with ice scrapers.[118] A thin layer of ice crystals can also form on the inside surface of car windows during sufficiently cold weather. In the 1970s and 1980s, some vehicles such as Ford Thunderbird could be upgraded with heated windshields as the result. This technology fell out of style as it was too expensive and prone to damage, but rear-window defrosters are cheaper to maintain and so are more widespread.[119]

1943 US propaganda film explaining how the ice of Lake Ladoga became the Road of Life during WWII

In sufficiently cold places, the layers of ice on water surfaces can get thick enough for ice roads to be built. Some regulations specify that the minimum safe thickness is 4 in (10 cm) for a person, 7 in (18 cm) for a snowmobile and 15 in (38 cm) for an automobile lighter than 5 tonnes. For trucks, effective thickness varies with load - i.e. a vehicle with 9-ton total weight requires a thickness of 20 in (51 cm). Notably, the speed limit for a vehicle moving at a road which meets its minimum safe thickness is 25 km/h (15 mph), going up to 35 km/h (25 mph) if the road's thickness is 2 or more times larger than the minimum safe value.[120] There is a known instance where a railroad has been built on ice.[121]

The most famous ice road had been the Road of Life across Lake Ladoga. It operated in the winters of 1941–1942 and 1942–1943, when it was the only land route available to the Soviet Union to relieve the Siege of Leningrad by the German Army Group North.[122] : 76–80  The trucks moved hundreds of thousands tonnes of supplies into the city, and hundreds of thousands of civilians were evacuated.[123] It is now a World Heritage Site.[124]

Water-borne travel

Channel through ice for ship traffic on Lake Huron with ice breakers in background

For ships, ice presents two distinct hazards. Firstly, spray and freezing rain can produce an ice build-up on the superstructure of a vessel sufficient to make it unstable, potentially to the point of capsizing.[125] Earlier, crewmembers were regularly forced to manually hack off ice build-up. After 1980s, spraying de-icing chemicals or melting the ice through hot water/steam hoses became more common.[126] Secondly, icebergs – large masses of ice floating in water (typically created when glaciers reach the sea) – can be dangerous if struck by a ship when underway. Icebergs have been responsible for the sinking of many ships, the most famous being the Titanic.[127]

For harbors near the poles, being ice-free, ideally all year long, is an important advantage. Examples are Murmansk (Russia), Petsamo (Russia, formerly Finland), and Vardø (Norway). Harbors which are not ice-free are opened up using specialized vessels, called icebreakers.[128] Icebreakers are also used to open routes through the sea ice for other vessels, as the only alternative is to find the openings called "polynyas" or "leads". A widespread production of icebreakers began during the 19th century. Earlier designs simply had reinforced bows in a spoon-like or diagonal shape to effectively crush the ice. Later designs attached a forward propeller underneath the protruding bow, as the typical rear propellers were incapable of effectively steering the ship through the ice [128]

Air travel

Rime ice on the leading edge of an aircraft wing. When the build-up is too large, the black deicing boot inflates to shake it off [129][130]

For aircraft, ice can cause a number of dangers. As an aircraft climbs, it passes through air layers of different temperature and humidity, some of which may be conducive to ice formation. If ice forms on the wings or control surfaces, this may adversely affect the flying qualities of the aircraft. In 1919, during the first non-stop flight across the Atlantic, the British aviators Captain John Alcock and Lieutenant Arthur Whitten Brown encountered such icing conditions – Brown left the cockpit and climbed onto the wing several times to remove ice which was covering the engine air intakes of the Vickers Vimy aircraft they were flying.[131]

One vulnerability effected by icing that is associated with reciprocating internal combustion engines is the carburetor. As air is sucked through the carburetor into the engine, the local air pressure is lowered, which causes adiabatic cooling. Thus, in humid near-freezing conditions, the carburetor will be colder, and tend to ice up. This will block the supply of air to the engine, and cause it to fail. Between 1969 and 1975, 468 such instances were recorded, causing 75 aircraft losses, 44 fatalities and 202 serious injuries.[132] Thus, carburetor air intake heaters were developed. Further, reciprocating engines with fuel injection do not require carburetors in the first place.[133]

Jet engines do not experience carb icing, but they can be affected by the moisture inherently present in jet fuel freezing and forming ice crystals, which can potentially clog up fuel intake to the engine. Fuel heaters and/or de-icing additives are used to address the issue.[134]

Recreation and sports

Skating fun by 17th century Dutch painter Hendrick Avercamp

Ice plays a central role in winter recreation and in many sports such as ice skating, tour skating, ice hockey, bandy, ice fishing, ice climbing, curling, broomball and sled racing on bobsled, luge and skeleton. Many of the different sports played on ice get international attention every four years during the Winter Olympic Games.[135]

Small boat-like craft can be mounted on blades and be driven across the ice by sails. This sport is known as ice yachting, and it had been practiced for centuries.[136][137] Another vehicular sport is ice racing, where drivers must speed on lake ice, while also controlling the skid of their vehicle (similar in some ways to dirt track racing). The sport has even been modified for ice rinks.[138]

Other uses

As thermal ballast

  • Ice is still used to cool and preserve food in portable coolers.[110]
  • Ice cubes or crushed ice can be used to cool drinks. As the ice melts, it absorbs heat and keeps the drink near 0 °C (32 °F).[139]
  • Ice can be used as part of an air conditioning system, using battery- or solar-powered fans to blow hot air over the ice. This is especially useful during heat waves when power is out and standard (electrically powered) air conditioners do not work.[140]
  • Ice can be used (like other cold packs) to reduce swelling (by decreasing blood flow) and pain by pressing it against an area of the body.[141]

As structural material

Ice pier during 1983 cargo operations. McMurdo Station, Antarctica.
  • Engineers used the substantial strength of pack ice when they constructed Antarctica's first floating ice pier in 1973.[142] Such ice piers are used during cargo operations to load and offload ships. Fleet operations personnel make the floating pier during the winter. They build upon naturally occurring frozen seawater in McMurdo Sound until the dock reaches a depth of about 22 feet (6.7 m). Ice piers are inherently temporary structures, although some can last as long as 10 years. Once a pier is no longer usable, it is towed to sea with an icebreaker.[143]
An ice-made dining room of the Kemi's SnowCastle ice hotel in Finland
  • Structures and ice sculptures are built out of large chunks of ice or by spraying water[121] The structures are mostly ornamental (as in the case with ice castles), and not practical for long-term habitation. Ice hotels exist on a seasonal basis in a few cold areas.[144] Igloos are another example of a temporary structure, made primarily from snow.[145]
  • Engineers can also use ice to destroy. In mining, drilling holes in rock structures and then pouring water during cold weather is an accepted alternative to using dynamite, as the rock cracks when the water expands as ice.[9]
  • During World War II, Project Habbakuk was an Allied programme which investigated the use of pykrete (wood fibers mixed with ice) as a possible material for warships, especially aircraft carriers, due to the ease with which a vessel immune to torpedoes, and a large deck, could be constructed by ice. A small-scale prototype was built,[146] but it soon turned out the project would cost far more than a conventional aircraft carrier while being many times slower and also vulnerable to melting.[147]
  • Ice has even been used as the material for a variety of musical instruments, for example by percussionist Terje Isungset.[148]

Impacts of climate change

Historical

Earth lost 28 trillion tonnes of ice between 1994 and 2017, with melting grounded ice (ice sheets and glaciers) raising the global sea level by 34.6 ±3.1 mm.[149] The rate of ice loss has risen by 57% since the 1990s−from 0.8 to 1.2 trillion tonnes per year.[149]
On average, climate change has lowered the thickness of land ice with every year, and reduced the extent of sea ice cover.[149]

Greenhouse gas emissions from human activities unbalance the Earth's energy budget and so cause an accumulation of heat.[150] About 90% of that heat is added to ocean heat content, 1% is retained in the atmosphere and 3-4% goes to melt major parts of the cryosphere.[150] Between 1994 and 2017, 28 trillion tonnes of ice were lost around the globe as the result.[149] Arctic sea ice decline accounted for the single largest loss (7.6 trillion tonnes), followed by the melting of Antarctica's ice shelves (6.5 trillion tonnes), the retreat of mountain glaciers (6.1 trillion tonnes), the melting of the Greenland ice sheet (3.8 trillion tonnes) and finally the melting of the Antarctic ice sheet (2.5 trillion tonnes) and the limited losses of the sea ice in the Southern Ocean (0.9 trillion tonnes).[149]

Other than the sea ice (which already displaces water due to Archimedes' principle), these losses are a major cause of sea level rise (SLR) and they are expected to intensify in the future. In particular, the melting of the West Antarctic ice sheet may accelerate substantially as the floating ice shelves are lost and can no longer buttress the glaciers. This would trigger poorly understood marine ice sheet instability processes, which could then increase the SLR expected for the end of the century (between 30 cm (1 ft) and 1 m (3+12 ft), depending on future warming), by tens of centimeters more.[151]: 1302 

Ice loss in Greenland and Antarctica also produces large quantities of fresh meltwater, which disrupts the Atlantic meridional overturning circulation (AMOC) and the Southern Ocean overturning circulation, respectively.[152] These two halves of the thermohaline circulation are very important for the global climate. A continuation of high meltwater flows may cause a severe disruption (up to a point of a "collapse") of either circulation, or even both of them. Either event would be considered an example of tipping points in the climate system, because it would be extremely difficult to reverse.[152] AMOC is generally not expected to collapse during the 21st century, while there is only limited knowledge about the Southern Ocean circulation.[151]: 1214 

Another example of ice-related tipping point is permafrost thaw. While the organic content in the permafrost causes CO2 and methane emissions once it thaws and begins to decompose,[152] ice melting liqufies the ground, causing anything built above the former permafrost to collapse. By 2050, the economic damages from such infrastructure loss are expected to cost tens of billions of dollars.[153]

Predictions

Potential regional warming caused by the loss of all land ice outside of East Antarctica, and by the disappearance of Arctic sea ice every year starting from June.[154] While plausible, consistent sea ice loss would likely require relatively high warming,[155] and the loss of all ice in Greenland would require multiple millennia.[156][157]

In the future, the Arctic Ocean is likely to lose effectively all of its sea ice during at least some Septembers (the end of the ice melting season), although some of the ice would refreeze during the winter. I.e. an ice-free September is likely to occur once in every 40 years if global warming is at 1.5 °C (2.7 °F), but would occur once in every 8 years at 2 °C (3.6 °F) and once in every 1.5 years at 3 °C (5.4 °F).[155] This would affect the regional and global climate due to the ice-albedo feedback. Because ice is highly reflective of solar energy, persistent sea ice cover lowers local temperatures. Once that ice cover melts, the darker ocean waters begin to absorb more heat, which also helps to melt the remaining ice.[158]

Global losses of sea ice between 1992 and 2018, almost all of them in the Arctic, have already had the same impact as 10% of greenhouse gas emissions over the same period.[159] If all the Arctic sea ice was gone every year between June and September (polar day, when the Sun is constantly shining), temperatures in the Arctic would increase by over 1.5 °C (2.7 °F), while the global temperatures would increase by around 0.19 °C (0.34 °F).[154]

Possible equilibrium states of the Greenland ice sheet in response to different equilibrium carbon dioxide concentrations in parts per million. Second and third states would result in 1.8 m (6 ft) and 2.4 m (8 ft) of sea level rise, while the fourth state is equivalent to 6.9 m (23 ft).[160]

By 2100, at least a quarter of mountain glaciers outside of Greenland and Antarctica would melt,[161] and effectively all ice caps on non-polar mountains are likely to be lost around 200 years after global warming reaches 2 °C (3.6 °F).[156][157] The West Antarctic ice sheet is highly vulnerable and will likely disappear even if the warming does not progress further,[162][163][164][165] although it could take around 2,000 years before its loss is complete.[156][157] The Greenland ice sheet will most likely be lost with the sustained warming between 1.7 °C (3.1 °F) and 2.3 °C (4.1 °F),[166] although its total loss requires around 10,000 years.[156][157] Finally, the East Antarctic ice sheet will take at least 10,000 years to melt entirely, which requires a warming of between 5 °C (9.0 °F) and 10 °C (18 °F).[156][157]

If all the ice on Earth melted, it would result in about 70 m (229 ft 8 in) of sea level rise,[167] with some 53.3 m (174 ft 10 in) coming from East Antarctica.[56] Due to isostatic rebound, the ice-free land would eventually become 301 m (987 ft 6 in) higher in Greenland and 494 m (1,620 ft 9 in) in Antarctica, on average. Areas in the center of each landmass would become up to 783 m (2,568 ft 11 in) and 936 m (3,070 ft 10 in) higher, respectively.[168] The impact on global temperatures from losing West Antartica, mountain glaciers and the Greenland ice sheet is estimated at 0.05 °C (0.090 °F), 0.08 °C (0.14 °F) and 0.13 °C (0.23 °F), respectively,[154] while the lack of the East Antarctic ice sheet would increase the temperatures by 0.6 °C (1.1 °F).[156][157]

Non-water

The solid phases of several other volatile substances are also referred to as ices; generally a volatile is classed as an ice if its melting or sublimation point lies above or around 100 K (−173 °C; −280 °F) (assuming standard atmospheric pressure). The best known example is dry ice, the solid form of carbon dioxide. Its sublimation/deposition point occurs at 194.7 K (−78.5 °C; −109.2 °F).[169]

A "magnetic analogue" of ice is also realized in some insulating magnetic materials in which the magnetic moments mimic the position of protons in water ice and obey energetic constraints similar to the Bernal-Fowler ice rules arising from the geometrical frustration of the proton configuration in water ice. These materials are called spin ice.[170]

See also

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Further reading

  • Brady, Amy. Ice: From Mixed Drinks to Skating Rinks--A Cool History of a Hot Commodity (G. P. Putnam's Sons, 2023).
  • Hogge, Fred. Of Ice and Men: How We've Used Cold to Transform Humanity (Pegasus Books, 2022)
  • Leonard, Max. A Cold Spell: A Human History of Ice (Bloomsbury, 2023) online review of this book