Morphological characteristics and evolution processes of the blowouts on fine-grain armored paleodunes in the eastern Qaidam Basin, Tibetan Plateau

Abstract

Blowouts are essential wind-erosion landforms, representing the reactivation of fixed dunes and initiation of desertification. Blowouts occurring on stabilized paleodunes have received less attention than the more common, smaller and shallower blowouts within loose sand surfaces. We explored the geomorphic characteristics, evolutionary processes, and influencing factors of a unique type of blowout in the eastern Qaidam Basin, Tibetan Plateau that forms on paleodunes armored with thick crusts of fine-grained loess or fluvial sediments. Altogether, 1569 blowouts were mapped and analyzed on Google Earth and 24 blowouts were studied in the field. The presence of hard crusts, along with associated undercutting-collapsing expansion model, contributes to their distinct morphological features such as steep sidewalls, sharp rims, irregular shapes, and diverse sand lobe types. These blowouts, with prolonged evolutionary cycles at centennial to millennial scales, are significantly larger sizes than active dune blowouts and generate substantial dust emissions. Blowout shapes gradually become more regular approaching ellipticity with their orientations progressively aligning with the prevailing sand-driving wind direction. Blowout lengths were found to extend faster than their widths that in turn widen faster than their depths. In addition, their areas and lengths altogether increase faster than those of their deposition lobes. The formation and evolution of this special type of blowout are mainly attributed to climatic, sedimentological, and morphological factors which are associated with the destruction of the crusts and release of paleodune sand. Beyond providing new insight into the broader mechanisms of wind erosion and desertification in the Tibetan Plateau, this study appears relevant for many terrestrial and planetary aeolian environments.