Deserts

Deserts are places where it rarely rains. Many are hot, but one of the biggest deserts is Antarctica. Deserts cover about ont-fifth of the Earth's land.

Hamanda is desert that is strewn with boulders. Reg is desert that is blanketed with gravel. About one-fifth of all deserts are seas of sand dunes. these are known as ergs in Sahara. The type of sand dune depends on how much sand there is, and how changeable the wind is.

Barchans are moving, crescent-shaped dunes that form in sparse sand where the wind direction is constant.

Seifs are long dunes that form where sand is sparse and the wind comes from two or more directions.

Most streams in deserts flow only occasionally, leaving dry stream beds called wadis or arroyos. These may suddenly fill with a flash flood after rain.