Permafrost underlies more than 50% of the ground surface of Canada. The two major divisions of permafrost are continuous permafrost and discontinuous permafrost. In the continuous permafrost zone, permafrost occurs everywhere beneath the ground surface except large bodies of water. In the far north, it may be more than 500 m thick. The discontinuous permafrost zone is broken into two other divisions: the widespread permafrost zone, where permafrost underlies 50-90% of the land area, and the sporadic permafrost zone, where it occurs mostly in peatlands and underlies 10-50% of the land area. Permafrost can also occur in localized areas, where it is found in small isolated lenses in peat and affects less than 10% of the land area.

Technically speaking, permafrost is ground that remains below 0°C for two summers and an intervening winter. In practical terms, however, permafrost may be thought of as frozen ground, because it is ice in the ground that creates most of the challenges associated with permafrost. In many ways permafrost defines the North - it is the ground on which plants and animals must survive. It has also determined the way people live in the North - buildings, roadways and other facilities must handle the distinct conditions associated with "frozen ground".

The GSC maintains national databases on both permafrost temperatures and permafrost thickness (figure below). These data sets have been compiled largely from borehole observations, ground temperature measurements and geophysics soundings obtained at GSC study sites and from other published sources. Information from over 500 sites has been entered into the temperature database and from over 1000 sites in the thickness database.

[Click on an image thumbnail to view a larger image, notice]

Permafrost thickness.	Permafrost thickness.
Permafrost thickness.	Permafrost thickness.

• National Permafrost Database Online
  (a component of the National Arctic Geoscience Databases)