Vol 5 Life in the Desert ... Introduction ... Desert sand and rock
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Introduction

Desert sand and rock

Much of the sand that makes sandy deserts was originally eroded from mountains and highlands, and was carried by rivers or floods to lowland regions, where it was picked up by winds and dropped in the desert.
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Although many desert areas are rocky, most people think of vast landscapes of sand when they think of deserts. Desert sand begins life as rock, which is weathered down over the ages to form fine particles which we call sand. Much of the huge quantity of sand that makes sandy deserts was originally eroded from mountains and highlands, and was carried by rivers or floods to lowland regions, where it was picked up by winds and dropped in the desert. Some desert sand also comes from the shores of lakes and seas. In many areas, the sand is blown away by winds so that only solid rock and stone remains. In other regions, the sand builds up into giant sand dunes that may be hundreds of feet high. Some sand is coarse, while the sand from other deserts may be very fine. Desert sands may be black, red, yellow or brown in color. Sandstone is made of grains of sand which cement together under pressure, making the sand hard and rock-like. Wind erosion also smooths the surface of the sandstone.

Strong winds are characteristic of deserts, because there are few plants or buildings to provide resistance. Dry sand is whipped into dust or sandstorms: the whirling sand can be so thick that the sky darkens, making it hard to see more than few paces ahead. The Sahara Desert often produces over a hundred million tons of sand each year – this desert may be the world’s largest source of dust. Some regions of Iran and the south of the CIS (formerly called the Soviet Union) have duststorms on more than 100 days each year.