Assessing the evolution of hanging glacier: multi-method monitoring of the Mallory glacier (Mont-Blanc massif, France)

Hanging glaciers remain poorly understood despite the significant hazards they pose to alpinists, infrastructure and downstream valleys. This study investigates the recent evolution of the Mallory hanging glacier (Mont-Blanc massif, France) using a multi-method monitoring approach. We characterize morphological, thermal and dynamic changes and their implications for glacier stability and risks for alpinists. Results indicate different glacier evolutions. The glacier front remained relatively stable between 2000 and 2023 despite episodic collapses; 3D analyses reveal an average thickness reduction of 1.61 m between 2022 and 2025. GPR measurements show a mean glacier thickness of about 20.5 m, with a maximum of 27 m in the central flow channel and only 5.6-15 m remaining in the upper part. Borehole temperatures highlight contrasting thermal regimes, with persistently cold ice (<0°C) in the upper part of the glacier and a polythermal regime in the lower part, where ice becomes temperate (0°C) during summer following meltwater infiltration triggered when mean daily air temperature exceeds +2°C at the Aiguille du Midi. Despite this thermal evolution, no clear signs of large-scale destabilization have been detected up to now. The study concludes that continued glacier thinning and morphological change may alter alpinism practices in this area.