Lateral moraine failure in the valley of the Djankuat Catchment (Central Caucasus) and subsequent morphodynamics

Abstract

Moraine failures are severe events in proglacial areas that lead to major surface changes. On July 1, 2015, a lateral moraine collapsed within the 9.1 km2 glacierized Djankuat Catchment in the Northern Caucasus. This study quantifies the surface changes over a 7-year period after the collapse and proposes the main event triggers using hydrometeorological measurements and remote sensing data. Digital Elevation Models (DEMs), derived from Unmanned Aerial Vehicle (UAV) surveys and satellite images for the 2010–2022 period, were used to estimate erosion/deposition associated with the event and further surface changes in several zones: the breach, the fan, the headward erosion area and gully erosion on lateral moraine slopes. The failure occurred due to an extreme precipitation event (7-day cumulative sum: 227 mm, 24 h prior: 60 mm), simultaneous snowmelt within the whole upstream catchment, and continuous positive temperatures. During the 2015 event, approximately 200,000 m3 of material was instantly eroded, corresponding to a surface lowering of 1.91 m a−1 (over 52,227 m2). Only 25 % of the eroded material redeposited on the fan. Later in 2017–2019, the breach underwent infilling with a 10 m deposition layer in the bottom (net change ca. 14,600 m3), while the stream in the headward erosion area continued to incise (ca. −12,900 m3). From 2019 to 2022, the dynamics decreased, and a positive sediment budget was assessed for all zones except the intensive local erosion on the fan in 2021–2022 (ca. −15,200 m3). Gully changes suggested a constant erosion of 90–100 mm a−1. Based on daily rainfall measurements for the 2008–2022 period, we proposed a 3-day and prior 15-day cumulative precipitation threshold that outlines major erosional events in the Djankuat River valley. A cumulative 3-day precipitation of 100 mm could be a sufficient but not necessary condition since some significant sediment export was recorded below that threshold.