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alas

Overview page. Subjects: Earth Sciences and Geography — Ecology and Conservation.

In a periglacial landscape, a large, steep-sided, flat-bottomed depression which can be several kilometres across. Lakes often occur in alases, which may then develop into pingos.

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frost heave

Overview page. Subjects: Earth Sciences and Geography.

Upward movement of the ground surface or of individual particles, due to the formation of lenses of ice up to 30 mm thick in the regolith. It reaches its maximum in silt-dominated material,...

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ice mound

Overview page. Subjects: Earth Sciences and Geography.

In a periglacial landscape, a swelling in the ground due to the expansion of an underground ice lens. Solifluction displaces the material at the top of the mound, so that when the ice lens...

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palsa

Overview page. Subjects: Plant Sciences and Forestry — Ecology and Conservation.

A mound or ridge, largely made from peat, that contains a perennial ice lens and is found in the damper sites of mires in periglacial areas. Widths are in the range 10–30 m, lengths 15–150...

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permafrost

Overview page. Subjects: Earth Sciences and Geography.

Permanently frozen ground which occupies some 26% of the Earth's land surface under thermal conditions where temperatures below 0 °C have persisted for at least two consecutive winters and...

See overview in Oxford Index