Permafrost is a layer of permanently frozen soil beneath the tundra. Plants that grow here grow in the thinnest top layer of soil which thaws for a short time in the summer. Permafrost prevents drainwater above it from seeping into the ground, causing the water to accumulate in the tundra above, and so the ground remains somewhat soggy on the surface.

In parts of northern Russia, the permafrost is over 1,800 feet deep.

ASCII Art diagram of permafrost:

                I'm cold! --  o/
                             /Y
 ,  ,,, ,, , ,,,,   surface  / \  ,  ,, ,,,,, <-- some small plant life
  `. ,' `- ^ ~'` ^  tundra  ' o `.' - `~. '   <-- soggy
 OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
 OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO | can be
 OOOOOOOOOOOOOOOO permafrost OOOOOOOOOOOOOOOO | 100's of
 OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO | feet deep 
 OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO V
 OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

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