Aeolian processes and landforms
Aeolian processes play an integral role in the evolution of our landscape through the entrainment, transportation, and deposition of fine grained sediments by the wind. They may be triggered by both natural and human-induced forcings, including climate change that leads to aridity, or daily weather phenomena such as fohn wind storms, thunderstorm outflows, and whirlwinds that produce favourable conditions for the entrainment of fine-grained sediments by the wind. Human-induced forcings are many and varied, and include any activity that results in the exposure of surface sediments to the wind. Two dramatic examples of such activities have been the widespread cultivation of the prairie grasslands in the American and Canadian Midwest that lead to the Dust Bowl period of the 1930s (Figure 18.1), and the abstraction of water from the Amudar'ya and Syrdar'ya Rivers, which flow into the Aral Sea. T his has resulted in a 50% decrease in size of what was once the world's fourth-largest lake, thereby exposing more than a million hectares of lake bed to aerial processes. The resulting dust storms laden with salts, pesticides, radio-nucleides, and industrial pollutants now affect the health and livelihoods of over 50 million people (Barrow 1995). Such dust storms contribute to the estimated annual global dust emissions of 1000-3000 Tg (Li et al. 1996), which look certain to rise as the rate of vegetation clearance due to cultivation and overgrazing, particularly in arid and semi-arid regions, continues to increase. Of recent concern is the role of tropospheric dust load in global climate dynamics, particularly climate change through modification of the radiation budget and energy balance, while dust transport is fundamental to many biogeochemical and photo-oxidant cycles.