Echo dunes are one of the important anchored dune types and they can form in front of various obstacles due to the deposition of blowing sands. Our field investigations illustrate that the echo dunes show similar shapes to barchan dunes, their stoss slopes range from 2° to 18° while the steep lee slopes reach 21°-31°. Both the dune height and the sand-free distance (i.e. the distance from lee slope base to the obstacle) are affected by the height of obstacle，the higher the obstacle means the higher dune and the longer sand-free distance. The relationships can be described with linear functions. The grain size characteristics strongly imply that the dune sands are composed of local deposit. The saltating particles and even the granular materials could be transported and deposited in front of obstacle to form an echo dune. The comparisons of grain size and sorting parameters between echo and barchan dunes indicate that the surface sands over a echo dune experience more intensive winnowing processes. The finer and better sorted as well as the more positive skewness and leptokurtic distribution of the sediments over an echo dune reflect the influences of reversing airflow formed in front of obstacle.

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Comparison of grain size parameters between echo dunes and barchan dunes in the east edge of the Badain Jaran Desert