7. Periglacial Processes - Permafrost

Question 1

Briefly explain Permafrost.

Answer 1

Where subsoil temperatures remain below zero for at least 2 consecutive years, permafrost will occur. Today, it is estimated that permafrost covers around a quarter of the Earth’s surface. When summer temperatures rise above freezing, the surface layer thaws from the surface downwards to form an active layer. The thickness of this layer depends upon local conditions, but may extend to 4m.

Question 2

There are three kinds of permafrost. Discuss Continuous Permafrost.

Answer 2

Areas of permafrost can be **continuous (all **the ground is frozen). For continuous permafrost to form the mean annual temperature needs to be **below -5°C for at least 2 consecutive years. Continuous permafrost **is found in the coldest regions, reaching deep into the surface layers. In Siberia today, it is estimated that the permafrost can reach down over 1,500m. In the very coldest areas, there is hardly any melting of the uppermost layer.

Question 3

There are three kinds of permafrost. Discuss Discontinuous Permafrost.

Answer 3

Areas of permafrost can be discontinuous (only **patches **of the ground are frozen). For discontinuous permafrost to form the mean annual temperature needs to be **below 0°C **for at least 2 consecutive years. Discontinuous permafrost occurs in regions that are slightly warmer, where the ground is not frozen to such great depths. On average the frozen area will extend 20-30m below the ground surface, although it can reach 45m. There are also gaps in the permafrost under rivers, lakes and near the sea.

Question 4

There are three kinds of permafrost. Discuss Sporadic Permafrost.

Answer 4

**Sporadic Permafrost **is found where mean annual temperatures are around or just below freezing point (0°C for at least 2 consecutive years). In these places, permafrost occurs only in isolated spots where the local climate is cold enough to prevent complete thawing of the soil during the summer.