Deflation, Blowouts, and Desert Pavement
One way that wind erodes is by deflation (de = out, flat = blow), the lifting and removal of loose material. Because the competence (ability to transport different-sized particles) of moving air is low,
it can suspend only fine sediment, such as clay and silt. Larger grains of sand are rolled or skipped along the surface (a process called saltation) and comprise the bed load. Particles larger than sand are usually not transported by wind. Deflation sometimes is difficult to notice because the entire surface is being lowered at the same time, but it can be significant.
The most noticeable results of deflation in some places are shallow depressions called blowouts (Figure 6.34). In the Great Plains region, from Texas north to Montana, thousands of blowouts can be seen. They range from small dimples less than 1 meter deep and 3 meters wide to depressions that are over
45 meters deep and several kilometers across.
In portions of many deserts, the surface is characterized by a layer of coarse pebbles and cobbles that are too large to be moved by the wind. This stony veneer, called desert pavement, may form
as deflation lowers the surface by removing sand and silt from poorly sorted materials. As Figure GJSA illustrates, the concentration of larger particles at the surface gradually increases as the finer particles are blown away. Eventually, a continuous cover of coarse particles remains.
Studies have shown that the process depicted in Figure 6.34A is not an adequate explanation for all environments in which desert pavement exists. As a result, an alternate explanation was formulated and is illustrated in Figure 6.353. This hypothesis suggests that pavement develops on a surface that initially consists of coarse pebbles. Over time, protruding cobbles trap fine wind-blown grains
Deflation, Blowouts, and Desert PavementOne way that wind erodes is by deflation (de = out, flat = blow), the lifting and removal of loose material. Because the competence (ability to transport different-sized particles) of moving air is low,it can suspend only fine sediment, such as clay and silt. Larger grains of sand are rolled or skipped along the surface (a process called saltation) and comprise the bed load. Particles larger than sand are usually not transported by wind. Deflation sometimes is difficult to notice because the entire surface is being lowered at the same time, but it can be significant. The most noticeable results of deflation in some places are shallow depressions called blowouts (Figure 6.34). In the Great Plains region, from Texas north to Montana, thousands of blowouts can be seen. They range from small dimples less than 1 meter deep and 3 meters wide to depressions that are over45 meters deep and several kilometers across. In portions of many deserts, the surface is characterized by a layer of coarse pebbles and cobbles that are too large to be moved by the wind. This stony veneer, called desert pavement, may formas deflation lowers the surface by removing sand and silt from poorly sorted materials. As Figure GJSA illustrates, the concentration of larger particles at the surface gradually increases as the finer particles are blown away. Eventually, a continuous cover of coarse particles remains. Studies have shown that the process depicted in Figure 6.34A is not an adequate explanation for all environments in which desert pavement exists. As a result, an alternate explanation was formulated and is illustrated in Figure 6.353. This hypothesis suggests that pavement develops on a surface that initially consists of coarse pebbles. Over time, protruding cobbles trap fine wind-blown grains
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