Permafrost is one of the main components of the Earth’s cryosphere, which is a word indicating all the ice existing on Earth. It is defined as “any subsurface material which remains at or below a temperature of 0°C for at least two consecutive years” and mainly occurs in high-latitude areas of the northern hemisphere (look at its distribution map here).

Permafrost may also exist at high altitude areas of the mid- and low-latitudes, such as the Alps