Aeolian landscape

The dry regions of the Earth are the most exposed to wind action, which blows in a regular way and with a speed that can range from few kilometres an hour to 200 kilometres an hour in case of a hurricane or a typhoon. Compared to water, the wind transports lighter fragments: sands and silts are transported by wind that exceeds 30-40 kilometres an hour. Trees, bushes and grass create obstacles to the wind. Also the presence of water makes soil particles heavy and hinders their transport.
Very fine particles are kept in continuous suspension by the wind that lift them very high and keeps them high for days, weeks or months and then deposits them far away. Saharan fine sands are transported by the wind towards the Mediterranean Sea until they fall down on the Plain of the Po when it rains.  The result of this process is the red sand that falls on cars. Sand, silt and clay particles are dragged and rolled by the wind, that makes them jump 1-2 metres high.
When the wind removes fine materials from the soil surface, this results in gravel deserts, made of gravel, stones and big blocks. These materials together form the desert floor.
Wind erosion
The sandy particles that are more easily transported are those made of quartz minerals. Quartz is a very hard mineral, which erodes the rocks close to the ground and the materials it encounters (for example telephone and electric poles). The result is the creation of grooves and slots on clay rocks, while rocky walls and soil blocks are smoothed.
Particles deposited by the wind
When the wind stops or reduces its speed, the transported material is deposited. The sands pile up as dunes, which can be 10-100 metres high. Dunes are never isolated, but they are grouped and form dune fields that move as the wind pushes them. When, as a consequence of environmental and climatic change, dunes are covered by vegetation, they acquire a fixed shape and position.
Thin sands are transported by the wind from desert regions to far away places. They deposit onto several layers and form the loss. Deposits of loss can be found in central-northern Europe, Chile and North America.
Deserts and desert regions
Desert regions are characterized by draught, and water streams are called uadi: they are almost always dry, because the water evaporates or filters into the subsoil before reaching the sea. When the water collects into a depression, it evaporates and leaves layers of evaporitic rock sediments. In this way the chotts form. They are “salt deserts”, located in Tunisia. Or the playa of California desert is formed. Or a black layer is created due to water evaporation and oxidation of the salts that are contained in the desert minerals. This is called desert paint.
A desert cannot be completely flat. It can have heights and steep slopes, with a debris base, without vegetation. Characteristic of desert landscapes are the wide plateaux called mesa or meseta (what is left of a wide eroded flat area) and buttles (tower-shaped heights).

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