The southern boundary of the Mu Us Sand Sea and its controlling factors

Abstract

Boundaries are important spatial attributes of sand seas. Recognizing the accurate location of these boundaries forms not only the basis of regional aeolian geomorphological research but also the premise of quantifying spatial changes in typical climatic epochs. Identifying the factors controlling boundary locations is beneficial for understanding their formation and evolution. While the boundary of sand seas was an ambiguous concept in previous studies, few studies have posed extraction rules and presented the definite position of a given sand sea. Based on the geomorphic map of Mu Us, which has a scale of 1:250,000, and according to the ‘50% sand cover’ principle, this study quantitatively extracted the southern boundary of the Mu Us Sand Sea and investigated its controlling factors by analysing the geomorphology and grain size change along the margin and the history of aeolian activities outside of Mu Us from two sites. The results reveal the following: climatic features of northern China determine the spatial extent to which sand seas can occur, while the location of the Mu Us Sand Sea southern boundary is mainly controlled by topography. Dune construction occurred outside of the Mu Us Sand Sea under suitable topography, and the outside response of aeolian activity to climate change was also similar to that in the inner Mu Us. The southern and southeastern Mu Us is bounded by river valleys and loess landforms. Deeply incised and high-density gullies effectively limit sand transport, and the topography of loess landforms is unsuitable for aeolian sand preservation. In the southwestern Mu Us, outcropping groundwater at the edge of the alluvial fan at the Baiyu Mountain front impedes the downwind transport of saltating sand. As a consequence, the Sand Sea terminates at the extensive lacustrine landform in this area. In addition, the distribution of the localized dune provenance from immediate sources in margin areas may cause slight boundary location changes.