The changes of Hailuogou Glacier in the Southeastern Tibetan Plateau and the impacts on glacier dynamics from the mechanical ablation

Glaciers in the Tibetan Plateau are melting at an unprecedented rate in the context of global warming. Hailuogou (HLG) Glacier, a rapidly receding temperate land-terminating glacier in the southeastern Tibetan Plateau, has been observed to lose mass partly through ice frontal mechanical ablation (i.e., ice collapse).

In this study, we present analysis from Uncrewed Aerial Vehicles (UAV) surveys conducted over nine field campaigns to the HLG Glacier, providing evidence of glacier change and frontal ice collapse between 2017 and 2021. Structure from Motion with Multi-View Stereo was applied to produce multi-temporal Digital Surface Models (DEMs) and orthophoto mosaics, from which geomorphological maps and DEMs of Difference were derived to quantify the changes of the glacier snout and the ice loss from frontal ice collapse. Based on that, a linear correlation of Area-Volume for frontal ice collapse was subsequently built. Planet images were used to identify additional ice collapse events (i.e., 2017 to 2021) and to extract time-sequenced glacier extents. ASTER-derived DEMs generated by NASA Ames Stereo Pipeline (ASP) were then differenced to calculate the ice volume changes in the period. Combined with frontal ice collapse events identified from Planet, the contribution of that to the glacier mass balance can be estimated from the established Area-Volume correlation.

These analyses reveal that at the margins of the glacier terminus retreated 132.1 m over the period of analysis, and that in the area specifically affected by collapsing (i.e., the glacier collapsed terminus), it retreated 236.4 m. Overall the volume lost in the terminal area was of the order of 184.61 ± 10.32 x 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. The contribution to the mass balance change of the entire glacier that is attributed to frontal ice collapse is limited (i.e., ranges from 0.48% to 1.12% from 2017 to 2021). However, the mechanical ablation (e.g., frontal ice collapse and subglacial/englacial conduit’s roof collapse) has probably changed the way of losing ice mass to some extent.

Our results suggest that the evolution of the HLG Glacier terminus is dominantly controlled by the frontal ice collapse. The projection of the recession rate of the HLG Glacier may well be underestimated if based on surface mass balance alone, as the frontal ice collapsing might be more frequent and larger under the context of warming. 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.