Intensified paraglacial slope failures due to accelerating downwasting of a temperate glacier in Mt. Gongga, southeastern Tibetan Plateau

[摘要] Topographic development via paraglacial slope failure(PSF) represents a complex interplay between geological structure, climate,and glacial denudation. Southeastern Tibet has experienced amongst thehighest rates of ice mass loss in High Mountain Asia in recent decades, butfew studies have focused on the implications of this mass loss on thestability of paraglacial slopes. We used repeat satellite- and unpiloted aerialvehicle (UAV)-derivedimagery between 1990 and 2020 as the basis for mapping PSFs from slopesadjacent to Hailuogou Glacier (HLG), a 5 km long monsoon temperate valleyglacier in the Mt. Gongga region. We observed recent lowering of the glaciertongue surface at rates of up to 0.88 m a −1 in the period 2000 to 2016,whilst overall paraglacial bare ground area (PBGA) on glacier-adjacentslopes increased from 0.31  ±  0.27 km 2 in 1990 to1.38  ±  0.06 km 2 in 2020. Decadal PBGA expansion rates were ∼  0.01 km 2  a −1 , 0.02 km 2  a −1 , and 0.08 km 2 in theperiods 1990–2000, 2000–2011, and 2011–2020 respectively, indicating anincreasing rate of expansion of PBGA. Three types of PSFs, includingrockfalls, sediment-mantled slope slides, and headward gully erosion, weremapped, with a total area of 0.75  ±  0.03 km 2 in 2020. South-facingvalley slopes (true left of the glacier) exhibited more destabilization(56 % of the total PSF area) than north-facing (true right) valley slopes(44 % of the total PSF area). Deformation of sediment-mantled moraineslopes (mean 1.65–2.63  ±  0.04 cm d −1 ) and an increase inerosion activity in ice-marginal tributary valleys caused by a drop in localbase level (gully headward erosion rates are 0.76–3.39 cm d −1 ) haveoccurred in tandem with recent glacier downwasting. We also observedeformation of glacier ice, possibly driven by destabilization of lateralmoraine, as has been reported in other deglaciating mountain glaciercatchments. The formation, evolution, and future trajectory of PSFs at HLG(as well as other monsoon-dominated deglaciating mountain areas) are relatedto glacial history, including recent rapid downwasting leading to theexposure of steep, unstable bedrock and moraine slopes, and climaticconditions that promote slope instability, such as very high seasonalprecipitation and seasonal temperature fluctuations that are conducive tofreeze–thaw and ice segregation processes.

[学科分类] 土壤学