Structure and composition of debris flows in the Eastern Sayan

Based on the catastrophic June 28, 2014, Arshan debris flows in the Eastern Sayan Mountains, the structure and lithological composition of the debris are studied and a debris flow defense system is proposed. Among five debris flows in this region, two flows 4.1 and 5.6 km long are scrutinized. The grain size and mineral composition of fans and mudflows, as well as their evolution scenario are studied. The paper also examines the engineering-geological features of debris flow sediments and their textural-structural and physical alterations in the course of settling. Specific attention is devoted to the lithological and climatic constraints of debris flows. It is noted that sediments of recent mudflows are characterized by a high underconsolidation and deliquescence, promoting the formation of high-plastic and fluidal zones that can migrate actively. The approach proposed for debris flow defense measures lies in the construction of flow diversion dams designed for orienting the debris flows toward the "debris dump site."