A final class of deserts is the polar desert, found principally in the Dry Valleys and other parts of Antarctica, parts of Greenland, and northern Canada. Approximately 3 million square miles (7.8 million km2) on Earth consists of polar desert environments. in these places cold downwelling air lacks moisture, and the air is so dry that the evaporation potential is much greater than the precipitation. Temperatures do not exceed 50°F (10°C) in the warmest months, and precipitation is less than one inch (2.5 cm) per year. There are places in the Dry Valleys of Antarctica that have not been covered in ice for thousands of years.
Polar deserts are generally not covered in sand dunes but are marked by gravel plains or barren bedrock. The landforms of polar deserts are shaped by frost wedging, where alternating freeze-thaw cycles allow small amounts of water to seep into cracks and other openings in rocks. When the water freezes it expands, pushing large blocks of rock away from the main mountain mass. in polar deserts and other regions affected by frost wedging, large talus slopes may form adjacent to mountain fronts, and these are prone to frequent rock falls from frost wedging.
Continue reading here: Desert drainage systems
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