185:‘Epigenetic’ in geological terms refers to geological features that formed after the formation of the surrounding materials. In relation to ice wedges, this means that epigenetic ice wedges are found to form in preexisting permafrost, and are not formed at the same time as the permafrost meaning they are much younger than the surrounding material. An ice wedge being epigenetic also refers to the fashion in which they grow. These types of ice wedges grow considerably wider over their lifetime, but rarely any deeper or taller. This means that epigenetic ice wedges can grow to at most 3–5 meters in width, but stay roughly the same depth/height as when they had formed. Typically, the sediments on either side of an epigenetic ice wedge, adjacent to the edges of the wedge exhibit upward bending. In an epigenetic ice wedge, the age of the ice on the periphery changes little from top to bottom.
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ground surface. This allows syngenetic ice wedges to grow very deep, as the surface around them rises with the accumulation of alluvium (in floodplains), peat (in tundra), and gelifluction deposits (at the bottom of a slope), among other materials. Syngenetic ice wedges may only form if the thermal contraction and subsequent ice-veinlet growth can keep pace with the addition of new material. If this is the case, the ice wedge can reach depths of 25 meters, but the average is much less. In a syngenetic ice wedge, the age of the ice on the periphery decreases upwards.
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of material. Anti-syngenetic ice wedges only form on slopes, where there is a net loss of materials erosion. Similar to syngenetic ice wedges, anti-syngenetic ice wedges can only occur if the rate of thermal contraction cracking and ice-veinlet growth keeps pace with the removal of active material. Anti-syngenetic ice wedges therefore only grow downwards, penetrating deeper into the soil only as the upper layers are removed by mass wasting and erosion. In an anti-syngenetic ice wedge, the age of the ice on the periphery increases upwards.
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distinctly classified types of ice wedges observed in nature. The differences among the growth patterns of epigenetic, syngenetic and anti-syngenetic wedges then depend upon ground surface conditions, i.e. whether the ground level remains essentially unchanged or whether there is addition or loss of material.
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Ice wedges have historically been classified into two main categories: epigenetic and syngenetic. The type of an ice wedges refer to the way in which the wedge grows over time. Relatively recent field studies have revealed a new type of ice wedge: anti-syngenetic. Currently, these are the only three
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Ice wedge exposed by erosion along the
Beaufort Sea coast, Canada. The wedge formed by thermal contraction of the ground which opened a crack in winter. The crack filled with meltwater in the spring which then froze in the permafrost, causing the thin vertical lines of ice and sediment that form the
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Anti-syngenetic ice wedge were first observed in 1990 during the fieldwork of J. Ross Mackay. Mackay found that anti-syngenetic grew in conditions opposite to those of syngenetic ice wedges in that the anti-syngenetic variety required the removal of material instead of the accumulation and addition
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Active ice wedges are those that are still evolving and growing. During each year, a layer of ice will be added if cracking occurs, but cracking need not occur every year to be considered active. The area in which most ice wedges remain active is along the permafrost zone. The number of active ice
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produces upturning of the frozen sediment by plastic deformation. The next winter the cold refreezes and cracks the already forming ice wedge, opening a way for the melting snow of spring to fill the empty crack. The mean annual air temperature thought needed to form ice wedges is −6° to −8 °C
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Syngenetic ice wedges, like the epigenetic variety, find their roots in the geological term syngenetic, which means forming at the same time as the surrounding material. This is because syngenetic ice wedges grow as the upper permafrost surface rises in response to the addition of material on the
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that measures up to 3–4 meters in length at ground level and extends downwards into the ground up to several meters. During the winter months, the water in the ground freezes and expands. Once temperatures reach −17 degrees
Celsius or lower, the ice that has already formed acts like a solid and
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The thermal contraction theory posits that during the winter months, thermal contraction cracks form only a few cm wide and a couple of metres deep because of the extreme cold weather. Over the next few months, the snow melts and the remaining water fills the cracks and the
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Hariprasad C. (2011) Epigenetic Ice. In: Singh V.P., Singh P., Haritashya U.K. (eds) Encyclopedia of Snow, Ice and
Glaciers. Encyclopedia of Earth Sciences Series. Springer, Dordrecht
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There are many theories that attempt to explain the origin of ice wedges but only one has been consistently supported by most prominent scientists: the thermal contraction theory.
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Inactive ice wedges are wedges that are no longer cracking and growing. Throughout the winter months, the wedge does not split and therefore in the summer no new water is added.
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Subcommittee, P., 1988. Glossary of permafrost and related ground-ice terms. Associate
Committee on Geotechnical Research, National Research Council of Canada, Ottawa, 156.
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There are three different forms of ice wedges: active, inactive and casts. All three forms are prevalent today and can be found in different parts of the world.
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Peninsula at the coast of the Arctic Ocean in the
Mackenzie Delta area showing well developed ice-wedge polygons. A Caribou herd is grazing on it.
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expands to form cracks in the surface known as ice wedges. As this process continues over many years ice wedges can grow, up to the size of a
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from the surrounding walls. These are called ice wedge casts and can be used to estimate the climate of hundreds of thousands of years ago.
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Mackay, J. Ross (1990). "Some observations on the growth and deformation of epigenetic, syngenetic and anti-syngenetic ice wedges".
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below the surface freezes it. These tiny cracks turn into permafrost. Once the summer months arrive, the permafrost expands;
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Lakes in the
Mackenzie delta. In the foreground, a drained lake shows large, low-centered ice-wedge polygons
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wedges that are cracking yearly is consistently declining as they become inactive.
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In areas of past permafrost, ice wedges have melted and are no longer filled with
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227:. U.S. Fish & Wildlife Service - Alaska. 2006-02-14. Archived from
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85:. Ice wedges usually appear in a polygonal pattern known as ice wedge
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274:"Permafrost: Active wedges, inactive wedges, and ice-wedge casts"
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is a crack in the ground formed by a narrow or thin piece of
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Crack in the ground formed by a narrow vertical block of ice
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55:with surrounding ice wedge polygons near
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309:Permafrost and Periglacial Processes
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698:Montane grasslands and shrublands
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221:"Ice wedges, polygons and pingos"
276:. Britannica Online Encyclopedia
252:. Britannica Online Encyclopedia
225:Arctic National Wildlife Refuge
762:Category:Periglacial landforms
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505:Solifluction lobes and sheets
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590:Syngenetic permafrost growth
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105:Thermal contraction theory
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641:Stratified slope deposit
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393:Periglacial environment
550:Fluvio-thermal erosion
329:10.1002/ppp.3430010104
116:horizontal compression
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788:Periglacial landforms
712:Massenerhebung effect
417:Cryoplanation terrace
250:"Permafrost: Origins"
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595:Zero-curtain effect
321:1990PPPr....1...15M
604:Soils and deposits
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793:Patterned grounds
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767:Template:Glaciers
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708:Alpine tree line
693:Antarctic tundra
678:Arctic tree line
560:Frost weathering
487:Patterned ground
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457:Protalus rampart
447:Periglacial lake
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198:Anti-Syngenetic
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23:Ice wedges in
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545:Cryoturbation
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510:Sorted stripe
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231:on 2008-05-18
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83:swimming pool
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68:wedge itself.
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25:Sprengisandur
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611:Active layer
585:Solifluction
565:Gelifluction
462:Rock glacier
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315:(1): 15–29.
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278:. Retrieved
254:. Retrieved
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233:. Retrieved
229:the original
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555:Frost heave
540:Cryosuction
477:Thermokarst
472:Glaciokarst
119:or colder.
91:sand wedges
57:Tuktoyaktuk
798:Permafrost
782:Categories
636:Permafrost
515:Stone ring
495:Frost boil
467:Strandflat
407:Blockfield
280:2008-05-26
256:2008-05-26
235:2008-05-26
207:References
189:Syngenetic
181:Epigenetic
112:permafrost
51:A melting
621:Ice wedge
528:Processes
412:Bratschen
400:Landforms
97:Formation
74:ice wedge
27:, Iceland
749:Subpolar
665:ecotones
616:Gelisols
580:Nivation
500:Polygons
432:Lithalsa
162:sediment
140:Inactive
87:polygons
59:, Canada
732:Climate
317:Bibcode
739:Alpine
688:Golets
661:Biomes
651:Yedoma
156:. The
131:Active
744:Polar
718:Taiga
646:Talik
626:Loess
452:Pingo
442:Palsa
427:Kurum
172:Types
158:wedge
148:Casts
123:Forms
53:pingo
663:and
631:Peat
437:Paha
166:dirt
164:and
325:doi
154:ice
78:ice
72:An
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346:^
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289:^
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93:.
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720:(
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710:(
385:e
378:t
371:v
331:.
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313:1
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