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A pingo, also called a hydrolaccolith, is a mound of earth-covered ice found in the Arctic and subarctic that can reach up to in height and up to in diameter. The term originated as the Inuvialuktun word for a small hill. The plural form is "pingos". A pingo is a periglacial landform, which is defined as a nonglacial landform or process linked to colder climates. "Periglacial" suggests an environment located on the margin of past glaciers. However, freeze and thaw cycles influence landscapes outside areas of past glaciation. Therefore, periglacial environments are anywhere that freezing and thawing modify the landscape in a significant manner. They are essentially formed by ground ice which develops during the winter months as temperatures fall.〔(Pingos Jennifer Vinck, Geology 495, University of Regina, 2006 )〕〔(Hydrogeology )〕〔(Periglacial Landforms 1 )〕 == Formation == (詳細はhydrostatic pressure on water from permafrost, and commonly form in drained lakes or river channels. Permafrost rises to the drained body's former floor. Pore water is expelled in front of the rising permafrost, and the resulting pressure causes the frozen ground to rise and an ice core to form. The shape and size of a hydrostatic or closed system pingo is often similar to the body of water that it originated from. They can vary from symmetrical conical domes to asymmetric, elongate hills. Hydraulic (open-system) pingos result from groundwater flowing from an outside source, i.e. subpermafrost or intrapermafrost aquifers. Hydrostatic pressure initializes the formation of the ice core as water is pushed up and subsequently freezes. 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. The groundwater is put under artesian pressure and forces the ground up as it makes an expanding ice core. 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. 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. Pingos usually grow only a couple centimetres per year, with Ibyuk Pingo growing at a rate of a year,〔 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pingo」の詳細全文を読む スポンサード リンク
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