From an overall standpoint, sand movement in this region belongs to the category of sand flow from the Gobi Desert. Specifically, intense saltation of sand grains raises the height of sand transport and makes the amounts
Of sand carried in the upper and lower layers relatively uniform. Under such conditions, sand is transported and tends not to accumulate. However, winds from different directions, of different frequencies and different intensities, alter the characteristics of the sand movement, making it more complex. For example, there can be sands of different granularity accumulated in different shapes in different directions around a plant (Fig. 4). Accumulation of sand can only undergo changes in shape but cannot continuously increase in volume. Sand ripples and dunes are no exception to this. There are also severe limitations imposed by multiple changes of wind direction. In Figure 4, the formation of coarse sand ripples at the leeward side under the action of the strong west wind can clearly be seen. The sand was from a sand and gravel surface. Not only is the area of accumulation large but the height and width of the ripples are also large. Sand formed by southerly winds is very fine-grained and displays a small area of accumulation, and the height and width of the ripples are small. This sand originates from drifting sand dunes. The east wind has a reverse transport capacity in respect to sand accumulated at the tops and sides of the cliffs and can form accumulations of sand behind vegetation. The scale and granularity of the sand deposits are smaller than those deposited by the west wind but larger than those deposited by the south wind. There are clear seasonal variations in the shape of sand accumulation, and the changes are completely congruent with the pattern of changes in average flow fields.
Figure 4
Patterns of sand accumulation in different directions around a plant.
World History
