Landforms in semiarid deserts are often carved by sudden torrential rains and flash flooding.
Each climatic region has its own landforms, or rock and dirt formations. Semiarid deserts experience scant rainfall measuring a few inches a year at best. When rain does come, it often unleashes torrential floods, which carve the landscape and give semiarid areas their particular landforms. Earthquakes also play a role in the development of some semiarid landforms.
Inselbergs
Inselberg means "island mountain" in German. These small hills, ridges or mountains, also called mesas, rise suddenly from otherwise flat land. They develop from debris left in the wake of tectonic activity, and they have their own related landforms. Pediments, or thin layers of rocky, sandy debris, gather at the bases of inselbergs as the hills slowly erode. And talus cones are larger piles of rocks that build up around inselbergs. Talus cones result from the dramatic temperature differences in semiarid environments. Temperature swings force disintegration of the inselbergs' rocks and result in the cone-shaped debris piles.
Alluvial Fans
These landforms begin in mountain foothills and spread out, fanlike, into lower elevations. Alluvial fans form when water from heavy rain or snowmelt rushes down the mountainside through a narrow canyon or cut in the slope. The flood carries with it sand, gravel, rocks and boulders, and the water surge spreads the debris across a broad plain. Larger boulders typically remain at the mouth of the fan, while smaller pieces of rock and gravel are pushed to the fan's periphery. Newer fans, which may indicate recent flash-flood activity, are generally lighter in color, while fans that have been water-free for many years take on a darker hue.
Wadis
Wadi is an Arabic word for "valley." Many wadis began as rivers during the Holocene era, about 10,000 years ago. Today, wadis typically run dry unless heavy rains fall. Some wadis see water only once in a few years. During that rare flash flood, wadis act as washes that channel the water and collect rocky debris from the torrent. Many wadis connect to playas, or dry lakebeds. The swiftly moving water in wadis can be very dangerous to humans and animals in the path of the flow.
Playas
Playas are dry lakebeds covered in minerals left behind after water evaporation. They begin as low-lying basins that capture water from flash floods. In basins with no outlet, the water will sit until it evaporates. When the lakebed dries completely, a film of salts forms. Common playa salts include calcite, dolomite and gypsum. The U.S. inland, particularly in southwestern states, such as Arizona, Nevada, California and Utah, is home to thousands of playas, many of them formed around 10,000 years ago as healthy, life-laden lakes.
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