View source for Pingo

{{Other}}
{{short description|Mound of earth-covered ice}}
[[File:Ibyuk - Canada's Tallest Pingo.jpg|thumb|Ibyuk pingo near Tuktoyaktuk, northern Canada]]
[[File:Mackenzie Delta, Pingo, Tuktoyaktuk.jpg|thumb|View from top of a pingo towards another, within a partly drained lake, the Arctic Ocean in the background (near Tuktoyaktuk). July 20, 1975.]]

'''Pingos''' are intrapermafrost ice-cored hills,   {{convert|3|-|70|m|abbr=on|0}} high and {{convert|30|-|1000|m|abbr=on}} in diameter.<ref name=":52">{{cite web|title=Periglacial Processes and Landforms|url=http://www.physicalgeography.net/fundamentals/10ag.html|last=Pidwirny|first=M|year=2006|work=Fundamentals of Physical Geography}}</ref> They are typically conical in shape and grow and persist only in [[permafrost]] environments, such as the [[Arctic]] and [[subarctic]].<ref name=":62">{{Cite journal|last=Mackay |first=J. Ross |date=2 October 2002 |title=Pingo Growth and collapse, Tuktoyaktuk Peninsula Area, Western Arctic Coast, Canada: a long-term field study |journal=Géographie Physique et Quaternaire |volume=52 |issue=3 |pages=271–323 |doi=10.7202/004847ar |issn=1492-143X |doi-access=free}}</ref> A pingo is a [[Periglaciation|periglacial]] landform, which is defined as a non-glacial landform or process linked to colder climates.<ref name=":25">{{Cite book|author-last=Harris |author-first=Stuart A. |title=Glossary of permafrost and related ground-ice terms |year=1988 |isbn=0-660-12540-4 |oclc=20504505}}</ref> It is estimated that there are more than 11,000 pingos on Earth,<ref>{{cite journal|author-last1=Grosse |author-first1=G. |author-last2=Jones |author-first2=B.M. |year=2011 |title=Spatial distribution of pingos in northern Asia |url=http://www.the-cryosphere.net/5/13/2011/tc-5-13-2011.html |journal=The Cryosphere |volume=5 |issue=1 |pages=13–33 |bibcode=2011TCry....5...13G |doi=10.5194/tc-5-13-2011 |doi-access=free}}</ref> with the [[Tuktoyaktuk]] peninsula area having the greatest concentration at a total of 1,350.<ref name=":0">{{cite journal|author-last=Mackay |author-first=J. Ross |year=1998 |title=Pingo Growth and Collapse, Tuktoyaktuk Peninsula Area, Western Arctic Coast, Canada: A Long-Term Field Study |url=http://www.erudit.org/revue/gpq/1998/v52/n3/004847ar.pdf |journal=Géographie Physique et Quaternaire |publisher=University of Montreal |volume=52 |issue=3 |page=311 |doi=10.7202/004847ar |access-date=23 June 2012 |doi-access=free}}</ref> 

== History ==
[[File:Mackenzie Delta, Pingo, Tuktoyaktuk (3).jpg|thumb|left|Collapsed pingo in the Mackenzie Delta. The outline of the previously drained lake can be seen. August 8, 1987.]]
In 1825, [[John Franklin]] made the earliest description of a pingo when he climbed a small pingo on Ellice Island in the [[Mackenzie River|Mackenzie Delta]].<ref name="Mackay"/> However, it was in 1938 that the term ''pingo'' was first borrowed from the [[Inuvialuit]] by the Arctic botanist [[Erling Porsild|Alf Erling Porsild]] in his paper on Earth mounds of the western Arctic coast of Canada and Alaska. Porsild Pingo in [[Tuktoyaktuk]] is named in his honour.<ref name=":13">{{Cite journal|author-last=Mackay |author-first=J. Ross |date=1 January 1988 |title=The Birth and Growth of Porsild Pingo, Tuktoyaktuk Peninsula, District of Mackenzie |journal=Arctic |volume=41 |issue=4 |doi=10.14430/arctic1731 |issn=1923-1245|doi-access=free }}</ref> The term pingo, which in [[Inuvialuktun]] means conical hill, has now been accepted as a scientific term in English-language literature.<ref name=":13"/>

== Formation ==
{{Main|Permafrost}}
Pingos can only form in a [[permafrost]] environment. Evidence of collapsed pingos in an area suggests that there was once permafrost. Pingos can collapse due to the melting of the supporting ice and give rise to a depression in the landscape showing an inverse shape (horizontal mirror).<ref>{{Cite web |title=Six bizarre landforms created by global warming |url=https://www.newscientist.com/gallery/climate-landforms/ |access-date=2022-11-09 |website=New Scientist |language=en-US}}</ref>

=== Hydrostatic pingos ===
[[File:Closed pingos diagram.jpg|thumb|upright=1.35|Diagram showing how closed system (hydrostatic) pingos are formed]]
Closed systems, also known as hydrostatic pingos, are formed as a result of [[Hydrostatics#Hydrostatic pressure|hydrostatic pressure]] that has built up within the core of pingos due to water.<ref name=":32">{{Cite journal |date=2013 |title=Pingos |journal=Treatise on Geomorphology |volume=8 |pages=274–297 |doi=10.1016/B978-0-12-374739-6.00212-8 |isbn=9780080885223 |author-last=Yoshikawa |author-first=K.}}</ref> They occur in regions of [[Permafrost#Continuous permafrost|continuous permafrost]] where there is an impermeable ground layer.<ref name=":32" /> These pingos are found in flat, poorly drained areas with limited groundwater available such as shallow lakes and river deltas.<ref name=":25"/> The formation of these landforms occurs when layers of permafrost generate an upwards movement or pressure, resulting in masses of confined soil freezing, which pushes material upwards due to expansion.<ref name=":32" />

The figure illustrates this process and the changes that occur throughout the year.<ref name=":4">{{Cite web|title=Formation of Closed System Pingos |url=http://physgeog.blogspot.com/2013/02/formation-of-closed-system-pingos.html |language=en-GB |access-date=25 April 2020}}</ref> This type of closed system pingos is formed in an area where a lake has been infilled with sediment. This indicates that the ground is insulated, allowing liquid water to collect underneath the sediment.<ref name=":4" /> In winter months this sediment begins to freeze which leads to expansion of sediment, confining the water and increasing the pressure.<ref name=":4" /> This results in the formation of a mound due to the upwards pressure. However, during summer months the ice core of the pingo begins to melt which causes the mound to cave in.<ref name=":4" />

=== Hydraulic pingos ===
[[File:Pingos.png|thumb|Diagram showing how open system (hydraulic) pingos are formed]]
Hydraulic (open-system) pingos result from groundwater flowing from an outside source, i.e. sub-permafrost or intra-permafrost [[aquifer]]s. Hydrostatic pressure initializes the formation of the ice core as water is pushed up and subsequently freezes.<ref name=":32" /> Open-system pingos have no limitations to the amount of water available unless the aquifers freeze. They often occur at the base of slopes and are commonly known as Greenland type.<ref name=":62"/> The [[groundwater]] is put under [[Artesian aquifer|artesian]] pressure and forces the ground up as it makes an expanding ice core.<ref name=":52"/> It is not the artesian pressure itself that forces the ground up, but rather the ice core that is being fed the water from the aquifer. These are often formed in a thin, discontinuous permafrost. These conditions allow an ice core to form, but also provide it with a supply of artesian ground water. If water pressure entering an artesian pingo is strong enough, it can lift the pingo up allowing a sub-pingo water lens to form underneath. However, if the water lens starts to leak water it can cause subsidence which can compromise the structure.<ref name="Mackay">{{cite journal|author-last=Mackay |author-first=Ross |title=Pingos of the Tuktoyaktuk Peninsula Area, Northwest Territories |journal=Géographie Physique et Quaternaire |year=2011 |volume=33 |pages=3–61 |publisher=Department of Geography University of British Columbia |doi=10.7202/1000322ar|doi-access=free }}</ref> These pingos are often oval or oblong shaped. It is still not entirely understood why open system or hydraulic pingos normally occur in unglaciated terrain.<ref name=":25"/>

Pingos usually grow only a couple of centimetres per year, with Ibyuk Pingo growing at a rate of {{convert|2|cm|abbr=on}} a year,<ref name="pcl">{{cite web|url=http://www.pc.gc.ca/docs/v-g/pingo/index_e.asp |title=Pingo Canadian Landmark |archive-url=https://web.archive.org/web/20070603210903/http://www.pc.gc.ca/docs/v-g/pingo/index_e.asp |archive-date=3 June 2007}}</ref> and the largest take decades or even centuries to form. The process that creates pingos is believed to be closely related to [[frost heaving]]. The base of the pingo tends to reach its maximum diameter in its early youth. This means pingos tend to grow higher rather than growing in diameter and height at the same time.<ref name="Mackay" /> The height of pingos can range anywhere from {{convert|3|to|70|m|abbr=on}} and their diameters range from {{convert|30|to|1000|m|abbr=on}}.<ref name=":52"/> The shape of pingos is usually circular. Smaller pingos tend to have curved tops whereas larger pingos usually have collapsed mounds or craters due to the melting of exposed ice.<ref name=":52"/>

== Locations ==
=== Greenland ===
The landscape of [[Greenland]] contains many pingos and other glacial landforms. In western Greenland it is estimated that there are 29 pingos, whilst in eastern Greenland it is estimated there are 71 pingos. The majority of pingos in Greenland are located within [[Disko Bay]] and [[Nuussuaq Peninsula]] within western Greenland as well as some in eastern Greenland in [[Mestersvig|Mesters Vig]].<ref name=":32" /> The thickness of the permafrost at Disko Bay is around {{convert|150|m|abbr=on}} deep, providing for ideal conditions for the development of closed system pingos. There are 20 pingos located on Disko Island, with the largest located on Kuganguaq alluvial plain at {{convert|100|m|abbr=on}} wide and {{convert|15|m|abbr=on}} high.<ref name=":7">{{Cite journal |date=1996 |title=Growth and collapse history of pingos, Kuganguaq, Disko island, Greenland |journal=Polarforschung |volume=64 |issue=3 |pages=109–113 |author-last1=Yoshikawa |author-first1=K. |author-last2=Nakamura |author-first2=T. |author-last3=Igarashi |author-first3=Y.}}</ref>

In eastern Greenland, pingos are found in [[Nioghalvfjerdsfjorden]]. They are well known because they are the northernmost pingos of eastern Greenland. The largest of these pingos is {{convert|100|m|abbr=on}} wide and {{convert|8|m|abbr=on}} high, taking the shape of a semicircle. This pingo is still active, meaning it is increasing in elevation over time.<ref name=":8">{{Cite journal |date=1998 |title=Pingos at Nioghalvfjerdsfjorden, eastern North Greenland. |journal=Geology of Greenland Survey Bulletin |volume=180 |pages=159–162 |doi=10.34194/ggub.v180.5101 |doi-access=free |author-last=Bennike |author-first=O}}</ref>

=== Canada ===
==== Tuktoyaktuk Peninsula pingos ====
[[File:Mackenzie Delta Ice-Wedge Tuktoyaktuk Pingo.jpg|left|thumb|Mackenzie delta with drained lake (foreground), [[Ice wedge|ice-wedge]] polygons and a growing pingo, August 1987]]
[[File:Pingo in the Mackenzie delta area.jpg|thumb|left|Pingo in the Mackenzie delta area]]
[[File:Injection ice in a pingo.jpg|thumb|left|Injection ice in a pingo, Mackenzie delta area]]
The [[Tuktoyaktuk]] Peninsula is an area with a marine [[Canadian Arctic tundra|tundra]] environment on the shores of the [[Arctic Ocean]] in the [[Northwest Territories]], Canada. This peninsula is covered in thick permafrost, which is known to be more than 50,000 years old. There are many pingos within the [[Pingo Canadian Landmark]] area, all ranging in size and diameter. The most well known pingo in this area is Ibyuk Pingo, which is the tallest pingo in Canada. The height of this pingo is {{convert|50|m|abbr=on}} above sea level, but the pingo is still increasing in height by a few centimetres every year. This pingo is one of the younger pingos in the area, estimated at around 1,000 years old.<ref name=":62"/> Since about 1990, several larger pingos have started to melt out as the injection ice of the core is exposed.

=== Alaska ===
[[File:Mackenzie Delta, Pingo, Tuktoyaktuk (4).jpg|thumb|Collapsed pingo in the Mackenzie Delta with thick injection ice. The outline of the previously drained lake can be seen. August 8, 1987.]]
[[File:Mackenzie Delta, Pingo, Tuktoyaktuk (5).jpg|thumb|Detail of pingo in the Mackenzie Delta with massive injection ice. August 8, 1987.]]
[[File:Melting pingo wedge ice.jpg|thumb|Melting pingos near Tuktoyaktuk, Northwest Territories, Canada]]

Approximately 80% of [[Alaska]] is covered in permafrost, with 29% of this continuous permafrost, 35% discontinuous permafrost and the rest sporadic or isolated permafrost. Throughout Alaska, there are more than 1,500 known pingos with the majority being open system pingos.<ref name=":9">{{Cite journal |date=2008 |title=Permafrost characteristics in Alaska |journal=Proceedings of the Ninth International Conference on Permafrost |volume=3 |pages=121–122 |author-last1=Jorgenson |author-first1=M.T. |author-last2=Yoshikawa |author-first2=K. |author-last3=Kanevskiy |author-first3=M. |author-last4=Shur |author-first4=Y. |author-last5=Romanovsky |author-first5=V. |author-last6=Marchenko |author-first6=S. |author-last7=Grosse |author-first7=G. |author-last8=Brown |author-first8=J. |author-last9=Jones |author-first9=B.}}</ref> The height of pingos in Alaska ranges from {{convert|3|to|54|m|abbr=on}} in height and {{convert|15|to|450|m|abbr=on}} in width.<ref>{{Cite journal|author-last1=Holmes |author-first1=G.W. |author-last2=Hopkins |author-first2=D.M. |author-last3=Foster |author-first3=H.L. |date=1968 |title=Pingos in central Alaska |journal=US Government Printing Office |pages=1–40|doi=10.3133/b1241H |bibcode=1968usgs.rept....6H }}</ref> The world's tallest pingo is located in Alaska, known as the [[Kadleroshilik Pingo]]. The Kadleroshilik Pingo is {{convert|54|m|abbr=on}} in height, but is continuing to rise in elevation by a few centimeters a year.<ref name=":9" />

=== Siberia ===
In [[Siberia]], an area containing a high density of close system pingos can be found near [[Yakutsk]] located on the [[Lena River]]. In this area there are more than 500 pingos next to the Lena River. The area consists of [[alluvial plain]]s areas of thick permafrost, allowing pingos to form and develop.<ref name=":32" />

=== Central Asia ===
Areas of [[Central Asia]] are known to have pingos at the highest elevations in the world.<ref name=":32" /> For example, the [[Tibetan Plateau]] has pingos at above {{convert|4000|m|abbr=on}} in elevation due to its permanently frozen terrain. This environment is perfect for pingo production, and the cold, dry permafrost along with cold temperatures deters pingo collapse.<ref name=":10">{{Cite journal |date=2009 |title=Pingos on Earth and Mars |journal=Planetary and Space Science |volume=57 |issue=5 |pages=541–555 |bibcode=2009P&SS...57..541B |doi=10.1016/j.pss.2008.11.003 |author-last1=Burr |author-first1=D.M. |author-last2=Tanaka |author-first2=K.L. |author-last3=Yoshikawa |author-first3=K.}}</ref>

===Scandinavia===
Despite its high latitude and the occurrence of permafrost, no modern pingos are known from [[Scandinavia]]. [[Palsa]] mounds in Scandinavia have been mistaken for pingos. Some depressions found in [[Jutland]], and some circular lakes in the [[Finnmarksvidda]] plateau may be remnants of collapsed pingos. The possible Jutland pingos could have developed during the [[Weichselian glaciation]] and the possible Finnmarkvidda pingos during [[stadial|cold periods]] of the last [[deglaciation]].<ref name="Svensson1976">{{Cite journal |last=Svensson |first=Harald |year=1976 |title=Pingo problems in the Scandinavian countries |journal=[[Biuletyn Peryglacjalny]] |volume=26 |pages=33–40}}</ref>

=== England ===
The [[Rockingham Anomaly]] in [[Elephant and Castle]], [[London]], with its well-preserved [[peat]], has been interpreted as a relict pingo.<ref>https://bsky.app/profile/londongeology.bsky.social/post/3lkzzr2kdhc2g</ref><ref>https://londongeopartnership.org.uk/wp/wp-content/uploads/2019/07/Rockingham-Street-Anomaly-Report-2019_reduced.pdf</ref>

=== Mars ===
Although no pingos have been confirmed to be located on [[Mars]], there are signs of pingo-like features (PLFs).<ref name=":32" /> PLFs are periglacial features that are not classed as pingos. This is usually because they are not large enough or there is not enough evidence to class them as pingos.<ref name=":10" />

== Effects of climate change ==
[[Global warming]] is causing [[Arctic]] temperatures to rapidly rise, causing [[permafrost]] to thaw.<ref>{{Cite journal|author-last1=Schuur |author-first1=Edward A. G. |author-last2=Abbott |author-first2=Benjamin |date=30 November 2011 |title=High risk of permafrost thaw |journal=Nature |volume=480 |issue=7375 |pages=32–33 |doi=10.1038/480032a |pmid=22129707 |s2cid=4412175 |issn=0028-0836 |url=https://digital.library.unt.edu/ark:/67531/metadc836756/|doi-access=free }}</ref> For this reason, permafrost environments are extremely vulnerable to [[Climate of the Arctic|climate change in the Arctic]]. Permafrost degradation caused by climate warming is indicated by increased mean annual ground temperature, increased [[active layer]] thickness, [[talik]] and [[thermokarst]] development and disappearance of permafrost islands.<ref>{{Cite journal|author-last1=Cheng |author-first1=Guodong |author-last2=Wu |author-first2=Tonghua |date=8 June 2007 |title=Responses of permafrost to climate change and their environmental significance, Qinghai-Tibet Plateau |journal=Journal of Geophysical Research |language=en |volume=112 |issue=F2 |pages=F02S03 |doi=10.1029/2006JF000631 |bibcode=2007JGRF..112.2S03C |issn=0148-0227 |citeseerx=10.1.1.730.9627}}</ref> The interchange between permafrost degradation and aggradation shapes sub-Arctic and Arctic lowland landscapes, and therefore contain records of past climate and landscape development.<ref>{{Cite journal|author-last1=Wetterich |author-first1=Sebastian |author-last2=Schirrmeister |author-first2=Lutz |author-last3=Nazarova |author-first3=Larisa |author-last4=Palagushkina |author-first4=Olga |author-last5=Bobrov |author-first5=Anatoly |author-last6=Pogosyan |author-first6=Lilit |author-last7=Savelieva |author-first7=Larisa |author-last8=Syrykh |author-first8=Liudmila |author-last9=Matthes |author-first9=Heidrun |author-last10=Fritz |author-first10=Michael |author-last11=Günther |author-first11=Frank |date=July 2018 |title=Holocene thermokarst and pingo development in the Kolyma Lowland (NE Siberia) |journal=Permafrost and Periglacial Processes |language=en |volume=29 |issue=3 |pages=182–198 |doi=10.1002/ppp.1979 |bibcode=2018PPPr...29..182W |s2cid=135299374 |url=https://epic.awi.de/id/eprint/47847/1/PPP1979.pdf}}</ref>

Pingos are vulnerable to surface disturbance given the considerable amount of ground ice stored within them. Abrupt permafrost thaw processes can cause [[ice wedge]]s within pingos to melt, which can result in increased pingo collapse and the formation of remnant lakes.<ref>{{Cite journal|author-last1=Grosse |author-first1=G. |author-last2=Jones |author-first2=B. M. |date=7 January 2011 |title=Spatial distribution of pingos in northern Asia |url=https://www.the-cryosphere.net/5/13/2011/ |journal=The Cryosphere |language=en |volume=5 |issue=1 |pages=13–33 |doi=10.5194/tc-5-13-2011 |bibcode=2011TCry....5...13G |issn=1994-0424 |doi-access=free}}</ref> However, there are currently few studies investigating how climate change could affect formation and growth of pingos.

== See also ==
*[[Gas hydrate pingo]] - Submarine dome structure formed by the accumulation of [[Clathrate hydrate|gas hydrates]] under the seafloor that resembles a pingo
*{{annotated link|Cryovolcano}}
*{{annotated link|Frost heaving}}
*{{annotated link|Kettle (landform)}}, some are known as ''pingo ponds'' especially in Norfolk, England.<ref>{{cite web|accessdate=7 April 2021 |title=Ponds and pingos |url=https://www.norfolkwildlifetrust.org.uk/wildlife-in-norfolk/habitat-explorer/ponds-and-pingos |website=Norfolk Wildlife Trust}}</ref>
*{{annotated link|Laccolith}}
*{{annotated link|Palsa}}, a low oval elevation in areas with [[permafrost]], frequently [[peat bog]]s, where a perennial ice lens has developed within the soil.
*{{annotated link|Periglacial lake}}

== References ==
{{reflist}}

== Bibliography ==
* Easterbrook, Don J. (1999) ''Surface Processes and Landforms'' Second Edition, Prentice-Hall, Inc., pp.&nbsp;412–416, {{isbn|0-13-860958-6}}.
* {{Cite journal|author-last1=Burr |author-first1=Devon M. |author-first2=Kenneth L. |author-last2=Tanaka |author-first3=Kenji |author-last3=Yoshikawa | year = 2009| title = Pingos on Earth and Mars| journal = Planetary and Space Science| volume = 57| issue = 5–6| pages = 541–555| issn = 0032-0633| doi = 10.1016/j.pss.2008.11.003| bibcode=2009P&SS...57..541B}}

==External links==
{{Commons category|Pingos}}
{{wiktionary}}
*{{Cite web| author = National Snow and Ice Data Center (NSIDC)| title = All about frozen ground: How does it affect land?| access-date = 29 December 2010| url = http://nsidc.org/frozenground/how_fg_affects_land.html| archive-url = https://web.archive.org/web/20101218080832/http://nsidc.org/frozenground/how_fg_affects_land.html| archive-date = 18 December 2010| url-status = dead}}

{{Periglacial environment}}

[[Category:Geomorphology]]
[[Category:Glaciology]]
[[Category:Ground freezing]]
[[Category:Palsas]]
[[Category:Patterned grounds]]
[[Category:Periglacial landforms]]
[[Category:Soil]]
[[Category:Geologic domes]]
[[Category:Geography of the Arctic]]
[[Category:Geography of the Inuvialuit Settlement Region]]