Slope mass movements and debris flow activity in the Geysernaya River valley (Kamchatka, Russia)

A detailed analysis of remote sensing data (1964–2024) and field surveys were used to classify and trace the dynamics of exogenous slope processes in the Geysernaya River valley over 60 years. Repeated low-altitude Unmanned Aerial Vehicle (UAV) surveys and comparison of Digital Elevation Models (DEMs) revealed that landslides and/or rock/debris collapses deliver material into channels, where it is pulsationally transported by debris flows. The formation of large debris flows in the Geysernaya River valley is associated with the collapse of significant fragments of its left side and outburst of dammed lakes. Debris flows from the right side of the valley are associated with the release of cold groundwater, heavy precipitation, and periods of snowmelt, while on the left side they may have a non-seasonal character, as they are formed within the thermal fields under conditions of constant heating and gas-hydrothermal manifestations. The study of endogenous process manifestations (areas of thermal anomalies, current uplifts, faults, epicenters of local earthquakes) and areas of exogenous movements (landslides, debris flow (mudflow) basins, fluvial erosion and accumulation) in the valley allowed identify a zone of potential activation of slope and debris flow processes. The zone covers the left side of the Geysernaya River valley, its bottom, and the basin of the Lavoviy Creek. The action of these processes on the left side of the valley is attributed to a combination of endogenous factors, including the crushing of rocks, their transformation into clays due to gas-hydrothermal impact, as well as heating and increased wetting of the slopes. These findings are crucial for understanding the activity of slope and debris flow processes in geothermal regions. They provide valuable insights that can be applied to other volcanic and hydrothermally active regions, such as the Kuril Islands and other parts of the Pacific Ring of Fire.