permafrost


permafrost

Perennially frozen earth, with a temperature below 32 °F (0 °C) continuously for two years or more. Permafrost is estimated to underlie 20% of the Earth's land surface and reaches depths of 5,000 ft (1,500 m) in northern Siberia. It occurs in 85% of Alaska, more than half of Russia and Canada, and probably all of Antarctica. Permafrost has a significant effect on plant and animal life, and it presents special problems in engineering projects. All land use in permafrost environments must take into account the terrain's special sensitivity; if the delicate natural balance is not maintained, extensive degradation and ecological damage may result.

This entry comes from Encyclopædia Britannica Concise.
For the full entry on permafrost, visit Britannica.com.

Seen & Heard

What made you look up permafrost? Please tell us what you were reading, watching or discussing that led you here.