Abstract: Blowout is the driving factor of sandy desertification in alpine meadow region. The sediment within deflation basin which is eroded, transported, and deposited by airflow provides a dominant source material for desertification. This study focuses on the different blowouts under different developmental stages which formed in alpine meadow region on the terrace of Yellow River upper reaches of Longyangxia Dam in Gonghe basin, and its aim is to investigate the variation of grain-size associated with topography, morphology and its dynamical significance by comparing the particle size distribution of surface sands. The result indicates that surface sediment of blowout mainly provenances from paleo-sediments. Although the sampling blowouts show considerable differences in sizes and shapes, grain-size characteristics remain constant in macroscale because of the similar al process operative within the blowout. With the increase of the blowout area, significant increasing rate of coarse and very coarse sand is found on the middle-lower windward slope and deflation basin. In addition, the surface sediments tend to be less well sorted and varied to multimodal distribution; the variation scale of the grain size parameter also became wider with the increase of the blowout size. The effect of the slope aspect and the prevailing wind from northwest leads to the preferential erosion and better sorting on northeast wall compared to opposing wall. The grain size analysis of blowout surface sediments as the base research of aeolian geomorphology provides the primary datum for the following study to clarify the development and dynamical evolution process of blowouts in alpine meadow regions.

Key words: blowout, particle size distribution, alpine meadow, desertification, aerodynamics