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Sand dunes. Aerial photograph of sand dunes in the Namib Desert, Namibia. This is one of the driest deserts in the world. The rainfall is kept low by the presence of a very cold current of water (the Benguela current), which flows northwards along the nearby coast (not seen). The sand dunes in the Namib Desert are among the largest in the world, reaching upwards of 350 metres in height. (KEYSTONE/SCIENCE PHOTO LIBRARY/Bernhard Erdmaier) === ===