My Science School

The glowing sun glares down on a vast sea of sand. As far as the eye can see, sand stretches in great brown ripples. The air is so hot it seems to shimmer as it rises from the sand. Not even the tiniest green plant is in sight.

Most people picture this endless, hot sandy land when they think of a desert. But there are many kinds of deserts. Some deserts are sandy places with very few plants. Others are flat plains with many kinds of plants. Some deserts are bare spots near seashore, while others are rocky areas high in the mountains. Some deserts are hot all year round. Others are hot or warm only in summer.

But one thing that is true of all deserts is that they are places where little rain falls. It does rain in deserts, but usually not much. Some parts of deserts get just a sprinkle every few years. Sometimes a desert is so hot that the rain dries up before it reaches the ground! In some deserts, heavy rain can cause sudden floods because the earth can’t soak up water fast enough.

Scientists say that some deserts were once green and fertile. Changes in climate made the rains stop and turned the land to desert.

The dry wind whispers as it passes over high, rocky deserts. Here there is little change. The rocks look the same year after year. But in a sandy desert, you might have a hard time finding the same spot from one year to the next. Hills of sand, called dunes, shift and change shape.

There are two kinds of dunes in the desert. One is usually crescent-shaped. A crescent is like a half circle. This dune builds up gradually into a long slope on the side from which the wind comes. It then drops steeply on the other side.

The second type of dune takes shape along the same direction that the wind blows. It has long, wavy ridges with the same kind of slopes on both sides.

Winds shift the sand from one shape to another. As desert sands shift, the dunes move. As the dunes move, they can cause a lot of damage to any buildings in their path. Desert towns sometimes disappear under shifting sand.