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A westerly wind was blowing sand up the dunes through saltation. The vegetation slows the wind, causing deposition of the sand in the dunes but they were already at the critical angle of repose for dry sand so it had to fall back down again in these mini 'sand avalanches'. These lobes were active, with frequent earth flows returning sand back down the face of the dunes. It is unusual for mass movement processes to occur with dry material, more normally the trigger for movement is water saturation reducing coherence or erosion removing removing the base rather than deposition increasing the angle. See [[3163204]].