Permafrost

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An illustration of the range in temperatures experienced at different depths in the ground during the year. The active layer (shown in grey) thaws each summer and freezes each winter, while the permafrost layer remains below 0°C.
An illustration of the range in temperatures experienced at different depths in the ground during the year. The active layer (shown in grey) thaws each summer and freezes each winter, while the permafrost layer remains below 0°C.

The extent of permafrost can vary as the climate changes. Today, a considerable area of the Arctic is covered by permafrost (including discontinuous permafrost).

Overlying permafrost is a thin active layer that seasonally thaws during the summer.

Plant life can be supported only within the active layer since growth can occur only in soil that is fully thawed for some part of the year. Thickness of the active layer varies by year and location, but is typically 0.6–4 m (2.0–13 ft) thick.

Permafrost will typically form in any climate where the mean annual air temperature is less than the freezing point of water.

Permafrost or permafrost soil is soil at or below the freezing point of water (0 °C or 32 °F) for two or more years.

Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material.

Typically, the below-ground temperature will be less variable from season to season than the air temperature, with temperatures tending to increase with depth. Thus, if the mean annual air temperature is only slightly below 0 °C (32 °F), permafrost will form only in spots that are sheltered — usually with a northerly aspect.

This creates what is known as discontinuous permafrost. Usually, permafrost will remain discontinuous in a climate where the mean annual soil surface temperature is between -5 and 0 °C (23 and 32 °F).

In the moist-wintered areas mentioned before, there may not be even discontinuous permafrost down to −2 °C (28.4 °F).

Discontinuous permafrost is often further divided into extensive discontinuous permafrost, where permafrost covers between 50 and 90 percent of the landscape and is usually found in areas with mean annual temperatures between -2 and -4 °C (28 and 25 °F), and sporadic permafrost, where permafrost cover is less than 50 percent of the landscape and typically occurs at mean annual temperatures between 0 and -2 °C (32 and 28 °F).

Permafrost or permafrost soil is soil at or below the freezing point of water (0 °C or 32 °F) for two or more years.
Permafrost or permafrost soil is soil at or below the freezing point of water (0 °C or 32 °F) for two or more years.


[edit] Also see;


[edit] Reference

  • See Wikipedia Permafrost [1]
  • See Geological Survey of Canada [2]
  • See International Permafrost Association [3]

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