Editing Permafrost (section)

=== Landforms ===
{{See also|Patterned ground}}
Permafrost processes such as [[thermal contraction]] generating cracks which eventually become [[ice wedge]]s and [[solifluction]] – gradual movement of soil down the slope as it repeatedly freezes and thaws – often lead to the formation of ground polygons, rings, steps and other forms of [[patterned ground]] found in arctic, periglacial and alpine areas.<ref>{{cite journal |last1=Black |first1=Robert F. |year=1976 |title=Periglacial Features Indicative of Permafrost: Ice and Soil Wedges |journal=Quaternary Research |volume=6 |issue=1 |pages=3–26 |doi=10.1016/0033-5894(76)90037-5 |bibcode=1976QuRes...6....3B |s2cid=128393192 }}</ref><ref>{{cite journal |last1=Kessler |first1=M. A. |last2=Werner |first2=B. T. |title=Self-organization of sorted patterned ground |journal=Science |volume=299 |issue=5605 |pages=380–383 |date=17 January 2003 |pmid=12532013 |doi=10.1126/science.1077309 |bibcode=2003Sci...299..380K |s2cid=27238820 }}</ref> In ice-rich permafrost areas, melting of ground ice initiates [[thermokarst]] landforms such as [[thermokarst lake]]s, thaw slumps, thermal-erosion gullies, and active layer detachments.<ref>{{cite journal |last1=Li |first1=Dongfeng |last2=Overeem |first2=Irina |last3=Kettner |first3=Albert J. |last4=Zhou |first4=Yinjun |last5=Lu |first5=Xixi |title=Air Temperature Regulates Erodible Landscape, Water, and Sediment Fluxes in the Permafrost-Dominated Catchment on the Tibetan Plateau |journal=Water Resources Research |date=February 2021 |volume=57 |issue=2 |pages=e2020WR028193 |doi=10.1029/2020WR028193 |bibcode=2021WRR....5728193L |s2cid=234044271 }}</ref><ref>{{cite journal |last1=Zhang |first1=Ting |last2=Li |first2=Dongfeng |last3=Kettner |first3=Albert J. |last4=Zhou |first4=Yinjun |last5=Lu |first5=Xixi |title=Constraining Dynamic Sediment-Discharge Relationships in Cold Environments: The Sediment-Availability-Transport (SAT) Model |journal=Water Resources Research |date=October 2021 |volume=57 |issue=10 |pages=e2021WR030690 |doi=10.1029/2021WR030690 |bibcode=2021WRR....5730690Z |s2cid=242360211 }}</ref> Notably, unusually deep permafrost in Arctic [[moorland]]s and [[bog]]s often attracts meltwater in warmer seasons, which pools and freezes to form [[ice lense]]s, and the surrounding ground begins to jut outward at a slope. This can eventually result in the formation of large-scale land forms around this core of permafrost, such as [[palsa]]s – long ({{cvt|15|-|150|m|abbr=on|0}}), wide ({{cvt|10|-|30|m|abbr=on|0}}) yet shallow (<{{cvt|1|-|6|m|abbr=on|0}} tall) [[peat]] [[mound]]s – and the even larger [[pingo]]s, which can be {{cvt|3|-|70|m|abbr=on|0}} high and {{cvt|30|-|1000|m|abbr=on}} in [[diameter]].<ref>{{cite web|last=Pidwirny|first=M|title=Periglacial Processes and Landforms|url=http://www.physicalgeography.net/fundamentals/10ag.html|work=Fundamentals of Physical Geography|year=2006}}</ref><ref>{{Cite journal|last1=Kujala|first1=Kauko|last2=Seppälä |first2=Matti|last3=Holappa|first3=Teuvo|date=2008|title=Physical properties of peat and palsa formation |url=http://www.sciencedirect.com/science/article/pii/S0165232X07001644 |journal=Cold Regions Science and Technology|language=en|volume=52|issue=3|pages=408–414|doi=10.1016/j.coldregions.2007.08.002|bibcode=2008CRST...52..408K |issn=0165-232X}}</ref>

<gallery mode="packed" heights="150px">
File:Palsaaerialview.jpg|A group of [[palsa]]s, as seen from above, formed by the growth of ice lenses.
File:Injection ice in a pingo.jpg|Injection ice in a pingo, Mackenzie delta area.
File:Pingos near Tuk.jpg|[[Pingo]]s near [[Tuktoyaktuk]], [[Northwest Territories]], Canada
File:Permafrost - polygon.jpg|[[Patterned ground#Polygons|Ground polygons]]
File:Permafrost stone-rings hg.jpg|[[Patterned ground#Circles|Stone rings]] on [[Spitsbergen]]
File:Polygons in Padjelanta.jpg|[[Helicopter]] view of ground polygons and ice lenses at [[Padjelanta National Park]], Sweden
File:Ice-wedge hg.jpg|[[Ice wedge]]s seen from top
File:Permafrost soil-flow hg.jpg|[[Solifluction]] on [[Svalbard]]
File:Permafrost pattern.jpg|Contraction crack ([[ice wedge]]) polygons on Arctic sediment.
</gallery>