Contribution of the extreme events to the surface transformation in proglacial areas (the Djankuat River catchment case study, Caucasus)

This study is dedicated to a quantitative assessment of two different-scale impulsive geomorphic events in proglacial areas. The study site is the Djankuat River catchment in the Caucuses. The first event is an ice-wall collapse of a buried ice outcrop. We conducted a repeated UAV survey with an annual interval (September 2019 – August 2020) and a two-day interval (August 18 – 20, 2020). For a 3,950 m2 area, the defined material (both sediment and melting ice) transfer in two days was 1,880 m3, while for the annual interval was 6,330 m3. The event contribution is almost 1/3 of the total annual change. The second event is the lateral moraine breakthrough that happened in July 2015 due to the preceding 227 mm precipitation per week. The evaluation was based on DEMs obtained from satellite image stereo pairs. About 134 thousand m3 of material was removed with the formation a cone in the valley bottom (volume ≈ 101 thousand m3). Another 81 thousand m3 was transported to the Djankuat River during the following 2 years due to active erosion of the new-formed channel. The volume of material removed from the Djankuat River catchment due to the event is at least 20 times higher than the average annual sediment runoff in years with the usual formation of sediment runoff. This research illustrates the importance of the individual extreme events assessment since they determine the primary changes in the proglacial terrain. The study was supported by the Russian Science Foundation (project No. 19-17-00181).