Runout Characteristics and Grain Size Distribution of Large-scale Debris Flows Triggered by Deep Catastrophic Landslides

Abstract

Deep catastrophic landslides (DCLs) sometimes lead to large-scale debris flows with serious impacts on human life and infrastructure. However, no adequate information about DCL-triggered debris flows, such as the topography of eroded and deposited areas or the grain size distribution, exist. We compiled published data and obtained additional new data for the topographic characteristics and grain size distributions of 10 recent DCL-triggered debris flows in Japan. We compared these data with previously published data of small-scale debris flows, steep-slope failures, and large-scale debris flows. We examined the effects of topography and DCL volume on erosion and deposition due to debris flow as well as on grain size distribution. The longitudinal gradient of the lower end of the deposited area decreased with increasing landslide volume, and about half of DCL-triggered debris flows deposited material where the longitudinal gradient of the lower end of the deposited area was less than 2°. However, the minimum longitudinal gradient of the eroded section due to debris flow was not affected by the landslide or the debris flow volume. We found that the travel distance of debris flow, including DCL-triggered debris flow, might also be a function of landslide and/or debris flow volume and that the grain size of debris flows triggered by DCLs spanned more than eight orders of magnitude.