Causes and processes of sandy desertification in Guinan County, Qinghai-Tibet Plateau

摘要

By means of field investigations, interpretation of remote sensing images, analysis of a digital elevation model, and grain-size tests, we analyzed the causes and processes responsible for sandy desertification in Guinan County, on the Qinghai-Tibet Plateau. The desertified land is mainly distributed on the Mugetan region and covered 566 km 2, about 96.1 % of which distributed on the sandy hills. We found that reactivation of the underlying fossil dunes supplied the sand that contributed to modern sandy desertification. The surface turf, which supports a dense growth of grass and its matted roots, covers the underlying cohesive silty sands in the sandy hills, and both layers protect the dunes against erosion. Mechanical destruction of the protective shell leads to exposure of fossil dune sands. The exposed loose fossil sands are then carried away by the wind, creating scarps, followed by lateral recession at the bottom of the scarp, leading to its collapse. The process then repeats. With the expansion of recession caused by wind erosion, abundant sands are supplied and aeolian activity intensifies. Repetition of this process expands the blowouts, leading to merger of the blowouts and the evolution of mobile dunes. Similar processes occur at the top of cliffs above the Yellow River and Mangla River.