Topographic barriers play an important role in the development process of pyramidal mega-dunes. Pyramid mega-dunes usually develop in front of mountains, and they belong to dunes controlled by topography. Firstly, vertical airflow is a main characteristic of airflow in mountain front wind shadow area. The lower, middle, and top locations of the east-oriented side corresponded to the vertical airflow initiation, development, and recession zones, respectively. Vertical airflow is the main driving mechanism of the upward growth of mega-dunes. Secondly, pyramidal dunes usually develop in areas with strong local air circulation. Local air circulation and regional wind regime consist of three wind directions which contribute to the maintenance and development of complex dunes (pyramidal dunes). The local air circulation-southerly wind in the study area has high frequency and long duration, and the downhill flow is strong. Thirdly, microreliefs, such as unaka soils and bench terraces, are similar to a "rock core", serving as the function of "minimum survival size". When the dune body reaches the so-called "minimum survival size", the vertical airflow begins to develop, making pyramidal dunes to develop to a certain height with a large volume and the end result is a pyramidal mega-dune. Our results also indicate that pyramidal mega-dunes develop from liner dunes controlled by topography.
Zhang Weimin
,
Tan Lihai
,
Bian Kai
,
Niu Qinghe
. The Role of Topographic Barriers in Pyramidal Mega-dune Development: a case study in Mingsha Mountain, Dunhuang, China[J]. Journal of Desert Research, 2016
, 36(5)
: 1207
-1215
.
DOI: 10.7522/j.issn.1000-694X.2015.00268
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