Historical evolution and controls on mega-blowouts in northeastern Qinghai-Tibetan Plateau, China

Abstract

Mega-blowouts are very large-scale deflationary landforms, formed by wind erosion. They are abundant in the Gonghe basin, northeast margin of the Qinghai-Tibet Plateau (QTP) and little is known about the evolution, dynamics or controls on the mega-blowout development. Here we report on mega-blowouts' morphodynamic expansion rates based on 4 years of monitoring. Also presented is a remotely sensed longer-term (48 years) morphologic change record which is used to understand the initiation, growth and evolution of mega-blowouts in alpine grasslands. Links between the morphodynamics and blowout-controlling factors are analysed. The expansion rates of the monitored blowouts vary according to blowout area, with different parts of the blowouts expanding at different rates. Generally longitudinal (downwind) mega-blowout expansion is greatest, with upwind headwall expansion via collapse being particularly significant. The growth of depositional lobes downwind of mega-blowouts tends to be faster than growth of the deflation basins. Merging of adjacent blowouts is one of the key mechanisms for mega-blowout development and extension. Sediment characteristics, wind erosion, water erosion, and freeze-thaw processes also all play a part in mega-blowout initiation and expansion. However, the relative roles that these factors play may differ according to a blowout's evolutionary stage. Due to an almost unlimited depth of sand, very low water table, and short grass vegetation cover, evolution into parabolic dunes is limited. A large proportion of sand patches and small blowouts around the mega-blowouts are still developing in the Gonghe basin proving that land degradation is still ongoing. Future work will focus on the feedback mechanisms between the blowout morphodynamics, climate change and anthropogenic impacts.