ИСТИНА

Proglacial zones are unstable and are prone to transformation by intensive geomorphic processes. This study is dedicated to a quantitative assessment of two different-scale impulsive geomorphic events. The study site is the Djankuat river catchment (Total areas 9,1 km2) in the Caucuses. The first area is a buried ice outcrop. We conducted repeated UAV surveys with an annual interval (September 2019 yr. – August 2020 yr.) and a two-day interval (August 18 – 20, 2020 yr.). For a 3,950 m2 area, the defined material (both sediment +melting ice) transfer in two days was 1,880 m3, while the annual interval was 6,330 m3. The event contribution associated with the ice-wall collapse is almost 1/3 of the total annual change. The second event is the lateral moraine breakthrough that happened in July 2015 yr. due to the preceding 227 mm precipitation per week. The evaluation was based on DEMs obtained from satellite image stereo pairs. It was found, that about 134 thousand m3 of material was removed with the formation a cone in the valley bottom with total volume 101 thousand m3. Another 81 thousand m3 was transported to the Djankuat River during the following 2 years due to active erosion of new formed tributary channel. The volume of material removed from the Dzhankuat River catchment as a result of this extreme 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 and necessity of the individual extreme events assessment since they determine the primary changes in the proglacial terrain.