Geomorphological Evolution of the Terminus Area of the Hailuogou Glacier, Southeastern Tibetan Plateau

Hailuogou (HLG) Glacier, a rapidly receding temperate glacier in the southeastern Tibetan Plateau, has been observed to lose mass partly through ice frontal mechanical ablation (i.e., ice collapse). These events are difficult to quantify using current satellite-based monitoring techniques due to their small scale and frequent nature. However, recent developments in Uncrewed Aerial Vehicles (UAV) have provided a possible approach to track their spatiotemporal variation and their impact on the geomorphological evolution of the glacier terminus area. Here, we present analysis from UAV surveys conducted over eight field campaigns to the HLG Glacier, providing evidence of glacier change between October 2017 and November 2020. Structure from Motion with Multi-View Stereo (SfM-MVS) was applied to produce multi-temporal Digital Surface Models (DSMs) and orthophoto mosaics, from which geomorphical maps and DEMs of Difference (DoDs) were derived to quantify glacier changes. These analyses reveal that the glacier terminus retreated 132.1 m over the period of analysis, and that in the area specifically affected by collapsing, it retreated 236.4 m. Overall the volume lost was of the order of 184.5 ± 10.29×104 m3, within which the volume change due to observed collapsing events comprises approximately 28%. We show that ice volume changes at the terminus due to a single ice collapse event may exceed the interannual level of volume change, and the daily volume of ice loss due to ice calving exceeds the seasonal and interannual level by a factor of ~2.5 and 4. Our results suggest that the evolution of the HLG Glacier terminus is dominantly controlled by the frontal ice-water interactions. If the future evolution of glaciers such as HLG Glacier is to be robustly predicted, the contribution of mechanical ablation should be accounted for by numerical models.