Pingos can only form in a permafrost environment. Evidence of collapsed pingos in an area suggests that there was once permafrost.
Pingos usually grow only a couple centimetres per year, with Ibyuk Pingo growing at a rate of 2 centimetres (0.79 in) a year,[4] and the largest take decades or even centuries to form. The process that creates pingos is believed to be closely related to frost heaving.
Hydrostatic (closed-system) pingos form as a result of 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. 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.[citation needed]
GOD BLESS WIKIPEDIA!
http://en.wikipedia.org/wiki/Pingo
, Fossils, Ecology, Microbe Mission, Dynamic Planet
