Pingo Canadian Landmark
The Pingo Canadian Landmark is a unique geographical area located within the highest concentration of pingos in the world. Ibyuk Pingo, which is among the world's largest pingos, is the most prominent pingo within the landmark.
Pingos are ice-cored hills that form in recently drained lakes. The unfrozen ground directly beneath the lake, called “talik,” is surrounded by permanently frozen ground called permafrost. After the lake drains and the water-saturated sediment at the bottom of the lake bed becomes exposed, its surface begins to freeze. Without a source of latent heat provided by the lake, the permafrost begins to encapsulate the unfrozen sediments of the lakebed.
Water in the saturated sediment expands as it freezes, pushing excess water inwards toward the centre of the lakebed. The area of encapsulated water and unfrozen ground comes under increasing pressure as the surrounding sediments continue to freeze. The pressurized water pushes upwards, lifting up a thin layer of ground above it. The pingo continues to grow until its entire core becomes ice, marking the end of a pingo’s vertical growth.
|How Pingos Grow|
|A layer of unfrozen ground lies beneath most arctic lakes,since the are often too deep to freeze through to the bottom in winter. This year-round presence of water thaws the permafrost.|
|When a lake drains, a shallow residual pond is often left behind. The former lake bed begins to freeze, but the remaining water slows the development of permafrost around it. As the lake bed freezes, the water in the ground turns to ice and expands. The extra water cannot escape,so it pushes inward toward the centre, ahead of the freezing front. (see arrows)|
|The freezing front advances inward, placing the encapsualted "lens" of water under pressure. The thin layer of permafrost above the lens is pushed upward and the pingo begins to grow.|
|The pingo is fuly formed and stops growing when it is frozen solid. The unfrozen ground becomes permafrost. Now the pingo's core is almost pure ice.|
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