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

Perennially frozen ground. Enormous amounts of permafrost are found across Canada, Alaska, northern Europe and Asia, and Antarctica. Greenland is almost totally covered with permafrost. Pockets of permafrost are found as far south as the 50th parallel in Canada and the 45th parallel in Siberia. No one knows exactly how long permafrost has been around, but clues to the age of the permafrost in the northern hemisphere lie in the numerous discoveries of mammoth remains embedded in the frozen ground. Mammoths became extinct about 10,000 to 15,000 years ago, around the same time as the end of the last Ice Age.

In any case, permafrost is an important aspect of the tundra biome. And I love the ASCII art above! Golden. And a great example of permafrost.