LAUSR

Abstract A landslide-dam break flood can cause great damage to the downstream area in a mountainous watershed. The analysis of quartz sand surface textures is a valid microscale method by which to study the genetic mechanisms of flood deposits. However, previous studies have not considered the microstructures of dam-break outburst deposits. In this research, samples from 24 sites along the Diexi dam-break flood deposits in southwestern China were examined and analyzed using scanning electron microscopy (SEM) photomicrographs. In addition, the frequency statistical results of quartz sand microtextures were also compared in different sedimentary environments. On one hand, the upstream end of dam-break flood deposits contained quartz grains with breakage blocks and inherited microtextural characteristics, while the downstream quartz sands are characterized by v-shaped and small conchoidal fractures. The different combinations of quartz sand surface textures indicate the transformation process changing from high energy collisions to low energy collisions over a short distance. On the other hand, the results exhibit the difference between dam-break flood deposits and other sediments such as debris-flow deposits or normal flood deposits, which reveals the potential of this microscopy method for recognition of dam-break flood deposits. The features of quartz sand microtextures also indicate that channel topography, sediment concentration and other factors may play important roles in routing of dam-break flood events, thus we suggest that the quartz sand microtextures can be used as a complementary method rather than the only identification criterion of dam-break flood deposits.