How do pingos form in periglacial landscapes?

Pingos form in periglacial landscapes due to the freezing and expansion of subterranean water, creating a mound of earth-covered ice.

Pingos are a unique geological feature found in periglacial environments, which are areas adjacent to glaciers or ice sheets. They are essentially large mounds or hills that can reach up to 70 metres in height and 600 metres in diameter. The formation of pingos is closely linked to the freezing and expansion of water beneath the ground surface, a process that is facilitated by the extremely cold temperatures in these regions.

The process begins when a body of subterranean water starts to freeze. As water freezes, it expands. This expansion exerts pressure on the surrounding soil and rock, causing it to be pushed upwards. Over time, this upward movement of the ground surface results in the formation of a mound or hill, which is what we refer to as a pingo. The core of a pingo is made up of a large mass of ice, while its outer layer consists of soil and rock that has been pushed up from the ground.

There are two types of pingos: closed-system pingos and open-system pingos. Closed-system pingos form in areas where the ground is permanently frozen, or permafrost. Here, the water source is often a buried body of unfrozen ground or talik. As the talik freezes and expands, it pushes up the overlying permafrost and soil to form a pingo.

Open-system pingos, on the other hand, form in areas where there is a continuous supply of groundwater. This water seeps up into the permafrost, where it freezes and expands to form a pingo. This type of pingo is often larger than closed-system pingos, as the continuous supply of water allows them to keep growing for as long as the conditions remain favourable.

In summary, the formation of pingos in periglacial landscapes is a fascinating process that involves the freezing and expansion of subterranean water. This process results in the creation of large mounds or hills, which are a distinctive feature of these cold and icy environments.