Grain size characteristics of aeolian sands and their implications for the aeolian dynamics of dunefields within a river valley on the southern Tibet Plateau: A case study from the Yarlung Zangbo river valley

Authors: ZHOU, NA - Beijing Normal University; LI, QING - Institute Of Geographic Sciences And Natural Resources; ZHANG, CHUN-LAI - Beijing Normal University; Huang, Chi Hua; WU, YANBING - Beijing Normal University; ZHU, BINGQI - Institute Of Geographic Sciences And Natural Resources; CEN, SONGBO - Beijing Normal University; HUANG, XIAOQI - Beijing Normal University

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2020
Publication Date: 7/31/2020
Citation: Zhou, N., Li, Q., Zhang, C., Huang, C., Wu, Y., Zhu, B., Cen, S., Huang, X. 2020. Grain size characteristics of aeolian sands and their implications for the aeolian dynamics of dunefields within a river valley on the southern Tibet Plateau: A case study from the Yarlung Zangbo river valley. Catena. 196:104794. https://doi.org/10.1016/j.catena.2020.104794.
DOI: https://doi.org/10.1016/j.catena.2020.104794

Interpretive Summary: Sand dunes are common features at the Tibetan Plateau of China. Formation and movement of the sand dunes can take away valuable farm lands and affect the livelihood of residents in the region. One way to understand how the dunes were formed is to examine the grain size characteristics of the dune surface. In the dynamics of aeolian processes, different source material and strength of the wind field controls how particles are transported and deposited during the formation of the dunes. Once the dunes are formed, the shape and height of the dune further affect the wind strength at both windward and leeward faces of the dune. The research was conducted to analyze the grain size of dunes in three regions along a river at the Tibetan Plateau. Dunes with grains become finer toward the top of the dune on the windward face indicates the weakening of the wind field while ascending. The interdune area is where fine grains are deposited as the wind field is further weakened. Dunes formed with river deposits as the source material are usually having coarser grains. By understanding how the dunes are formed, conservationist can plan suitable control measures to minimize hazards from the sand dunes.

Technical Abstract: Typical aeolian landforms have developed in China’s Yarlung Zangbo River valley, which is on the Qinghai–Tibet Plateau. Fully understanding the grain size characteristics of these dune fields is the first step to reveal the region’s aeolian dynamics. We selected three distinctive dune fields for grain size analysis: the Maquan, Shannan, and Mainling valley dune fields. At the scale of individual dunes, we found a trend for sands on the dune surface, with the sediments gradually becoming finer towards the crest, gradually becoming coarser, or exhibiting an asymmetric M-shaped distribution. In Maquan valley, these patterns resulted from interactions between the local airflow and local sands with a diameter of 2.0 to 2.5 F. The asymmetric M-shaped distribution in the Shannan valley was mainly controlled by dune height and valley winds. The gradually coarser sands with increasing height on the dune surface in Mainling valley were controlled by sands that are easily entrained by the wind (1.99 to 2.74 F) and that undergo saltation. At a dune field scale, strong winds that entrained medium sands cause these sands to accumulate downwind in Maquan valley. Multi-directional winds combined with a limited sand supply (1.74 to 2.30 F) favored a stable aeolian environment in Shannan valley. The saltating sands produced by these winds build dunes under a constantly erosive wind regime in Mainling valley. Wind transported interdune sediments to accumulate on dunes, following a McLaren Case IIIB or Case I transportation path. The gradual evolution of grain sizes moving downstream suggests the existence of a spatial connection among dune sands along the main stream of the Yarlung Zangbo River.