Permafrost and Active Layer

A key characteristic of periglacial areas is permafrost or permanently frozen ground. The depth and continuity of the permafrost vary with latitude, altitude and ocean currents.

Active Layer

In Northern Canada continuous permafrost extends down to depths of around 700 metres. Mean annual air temperatures is below -5°C and winter temperatures may fall to -50°C. In summer only the top of the ground will thaw.

This unfrozen surface layer is known as the active layer.

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The active layer varies from a few centimetres to about 5 metres and even on gentle slopes this saturated layer can become very mobile.

Below the active layer, ground temperatures fluctuate but remain below freezing point. The unfrozen layer beneath the active layer is known as talik. The lower limit of the talik (permafrost base) is determined by geothermal heat rising up from the mantle.

Permafrost distribution

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