Sunday, April 25, 2010

Permafrost

Permafrost is permanently frozen ground. It is found beneath permanent ice and snow. It is also found in large area around the Arctic Ocean where the snow melts in summer but only the top few centimetres of the soil thaw.

Permafrost covers the whole of Antarctica. In the Arctic, permafrost is shallowest near the coast and deepest inland where the weather is coldest. Permafrost 4,495 feet deep has been found in Siberia.

In summer, when the snow melts and the topsoil thaws, water cannot drain into the frozen ground below. The whole surface is marshy.

It is difficult to build on permafrost. Heated buildings have to be insulated from the ground beneath, else they defrost the soil and sink into the mud. Permafrost is also a great hindrance to oil-drilling and mining. But is has preserved the remains of ancient animals, such as woolly mammoths.

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