Pingo

In 1825, John Franklin made the earliest description of a pingo when he climbed a small pingo on Ellice Island in the Mackenzie Delta. However, it was in 1938 that the term pingo was first borrowed from the Inuvialuit by the Arctic botanist 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. The term pingo, which in Inuvialuktun means conical hill, has now been accepted as a scientific term in English-language literature. == Formation ==

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). Hydrostatic pingos Closed systems, also known as hydrostatic pingos, are formed as a result of hydrostatic pressure that has built up within the core of pingos due to water. They occur in regions of continuous permafrost where there is an impermeable ground layer. 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. 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. The height of pingos can range anywhere from and their diameters range from . 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. == 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 Mesters Vig. 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 wide and high, taking the shape of a semicircle. This pingo is still active, meaning it is increasing in elevation over time. Canada Tuktoyaktuk Peninsula pingos polygons and a growing pingo, August 1987 The Tuktoyaktuk Peninsula is an area with a marine 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 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. The height of pingos in Alaska ranges from in height and in width. The world's tallest pingo is located in Alaska, known as the Kadleroshilik Pingo. The Kadleroshilik Pingo is in height, but is continuing to rise in elevation by a few centimeters a year. 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 cold periods of the last deglaciation. United Kingdom Evidence of collapsed pingos formed in the last ice age are to be found in a number of locations in the United Kingdom, notably Thompson Common near Thetford managed by the Norfolk Wildlife Trust and designated as a Site of Special Scientific Interest for its collection of approximately 400 pingo ponds. The Rockingham Anomaly in Elephant and Castle, London, with its well-preserved peat, has also been interpreted as a relict pingo. Mars Although no pingos have been confirmed to be located on Mars, there are signs of pingo-like features (PLFs). 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. == Effects of climate change ==

Global warming is causing Arctic temperatures to rapidly rise, causing permafrost to thaw. For this reason, permafrost environments are extremely vulnerable to 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. The interchange between permafrost degradation and aggradation shapes sub-Arctic and Arctic lowland landscapes, and therefore contain records of past climate and landscape development. Pingos are vulnerable to surface disturbance given the considerable amount of ground ice stored within them. Abrupt permafrost thaw processes can cause ice wedges within pingos to melt, which can result in increased pingo collapse and the formation of remnant lakes. However, there are currently few studies investigating how climate change could affect formation and growth of pingos. == See also ==