What is the X in X-mas?
Plural pingos or pingoes
A large mound or dome of ice covered with soil. Pingos are about 30 to 50 m (98 to 164 ft) high and up to 400 m (1,312 ft) in diameter and are found in Arctic regions. They are believed to form in basins (such as drained lake beds) as a result of the freezing and upward expansion of water held in subsurface soil, which initiates the doming, as well as by the rising and freezing of water trapped beneath or within the permafrost, as a result of hydrostatic pressure.
dome-shaped hill formed in a permafrost area when the hydrostatic pressure of freezing groundwater causes the upheaval of a layer of frozen ground. Pingos may be up to 90 metres (300 feet) high and over 800 metres (12 mile) across and are usually circular or oval. The core, which may be only slightly smaller than the pingo itself, consists of a lens of clear, injected ice. Modern pingos occur in the continental tundras and are generally restricted to latitudes of 65 to 75 N. Rupture of the overlying material at the top of the pingo exposes the ice to melting and may create a smaller crater and lake. Two types are recognized, the open-system pingo and the closed-system pingo.