Quantification and classification of grainflow morphology on natural dunes

Grainflows (or avalanches) are fundamental mechanisms associated with the evolution and migration of dunes. This study addresses grainflow morphology on the 21.3 m and 54.5 m high slipfaces of two barchans. A series of metrics to characterize shape developed with the perspective that this approach may provide a key to recognizing different grainflow morphodynamic regimes. We provide the first detailed and objective measurements of grainflow morphometry based on terrestrial laser scanning and subsequent image analysis of 1243 grainflows on the larger dune and 1609 from the smaller dune. Grainflow shape was classified based on five representative morphometric attributes: average length, average width, rectangularity, triangularity, and elongation. Cluster analysis indicated three recognizable grainflow types: elongated, narrow grainflows (Type 1); long, triangular grainflows (Type 2); and short, rectangular grainflows (Type 3). The distributions of grainflow types were substantially different on the larger and smaller dune, and different from distributions found on smaller dunes in other studies.