Morphological changes and dynamic mechanism of blowouts on fixed dunes in the Otingdag sandy land, China

Abstract

<p indent="0mm">Blowouts are a major indicator of fixed dune reactivation, and their continuous occurrence and expansion aggravate the process of regional desertification. Therefore, research on the morphological evolution and dynamic processes of blowouts is paramount not only to understanding reactivation processes in stabilized and semistabilized dune fields but also to accurately assessing regional desertification trends. At present, much research has focused on blowouts in coastal dunes and flat grasslands, and little research has focused on the evolution mode of blowouts that have developed on fixed dunes in semiarid inland areas. Moreover, the morphological changes and airflow dynamics of blowouts are usually analyzed separately, and research integrating the two is still insufficient. In this paper, a fixed dune on the southern edge of the Otingdag sandy land was selected as the research object. A high precision real-time kinematic global positioning system (RTK-GPS) and 17 2D ultrasonic anemometers were used to measure the topography and airflow of four blowouts with different morphologies on the fixed dunes, and the multiperiod imaging data and multiyear meteorological data were used to monitor the morphological changes of each type of blowout and the regional meteorological conditions. The goal of this research is to reveal the morphological evolution, erosion-accumulation characteristics and airflow distribution patterns of each type of blowout and to discuss the relationship among the topography of fixed dunes, morphology of various blowouts and airflow variation. The results showed that the length, width and area of each type of blowout continued to increase from 2010 to 2021, and the overall shapes of each type of blowout tend to be oval or trough-shaped. The expansion direction of the blowout shape has a general corresponding relationship with the erosion-accumulation pattern in the deflation basin. The eastern and southeastern edges of the deflation basins are the most severely eroded, and their overall shapes expand from west to east. Relative to the wind direction of the field reference station, the approaching wind direction of the blowouts hardly deflects at the foot of the windward slope of the fixed dune, while it deflects significantly at the middle and top of the fixed dune, and the deflection angle changes with the regional wind direction. Both the blowout shapes and the approaching wind directions determine the airflow pattern within the blowouts. Based on a detailed analysis of both the regional climate and the morphological changes in blowouts, this study considered that the effect of the topography of fixed dunes on regional airflow could be the fundamental reason for the morphological differences in blowouts. The shape of blowouts determines the airflow pattern in the deflation basin, and the change in the wind speed and wind direction in turn affects the erosion-accumulation pattern and finally changes the evolution direction of blowouts. The research results can act as a good supplement for studying blowouts in semiarid inland areas.