Polar desert

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Polar deserts are areas with annual precipitation less than 250 millimetres and a mean temperature during the warmest month of less than 10° C. Polar deserts on Earth cover nearly 5 million square kilometres and are mostly bedrock or gravel plains. Sand dunes are not prominent features in these deserts, but snow dunes occur commonly in areas where precipitation is locally more abundant. Temperature changes in polar deserts frequently cross the freezing point of water. This "freeze-thaw" alternation forms patterned textures on the ground, as much as 5 metres in diameter.

The Dry Valleys of Antarctica have been ice-free for thousands of years.

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