ИСТИНА

During field campaign 2017 initial stages and consequences of a complex debris flow event occurred on July 3 were observed in the Sengisjok valley. One of the largest valleys dissecting the western slope of Lovozerskiye Mountains was investigated immediately before the event and repetitively after providing a unique dataset of valley bottom morphology sediment composition and vegetation changed by the incident. The post-event field survey and remote sensing data analysis have established the limits of all morphodynamic zones of the flow and helped identifying some specifics of its origin. It apparently have started as a slushflow on a steep step of the stream channel profile, immediately downstream of the vast flattened surface of the glacial cirque. Downstream it transformed into a granular debris flow. Maximum splash levels were determined by the debris traces and large plant remnants about 2 m above the channel for the deposition zone. Detailed sketches of valley floor morphology and vegetation change patterns and lithological map for the runout zone were compiled. Additionally, sampling of fresh debris flow deposits and large-scale aerial photography of four key sections of its floor using the UAV were accomplished for further monitoring. All that allows approximating a volume of transported sediment load, water-snow budget and depositional rates and evaluating the event magnitude.