Expansion and hazard risk assessment of glacial lake Jialong Co in the central Himalayas by using an unmanned surface vessel and remote sensing.

Glacial lake outburst floods (GLOFs) are a severe hazard in the Himalayas. Glacial lake expansion and the corresponding volume increase play major roles in GLOFs as well as climate change. Furthermore, mass movement and dam conditions play a major role in the GLOF initiation process. Recently, because of global warming, glacial lakes in the central Himalayas have been expanding rapidly. Owing to a lack of systematic assessment and meticulous field surveys, people living downstream are at great risk of GLOFs. Comprehensive investigations and assessment of the relationships among lake expansion, lake dam conditions, and GLOF risk are urgently needed. In this study, we surveyed Jialong Co, a typical end-moraine dammed lake in Poiqu River in the central Himalayas by using Landsat and Sentinel satellite images from the past 32 years, field work, and depth measurements using an unmanned surface vessel on August 28, 2020. The results showed that Jialong Co had experienced slow-quick-slow expansion, increasing in area from 0.13 ± 0.03 to 0.60 ± 0.02 km. The lake bathymetric map revealed that the lake volume was (3.75 ± 0.38) × 10 m in 2020. Lake expansion occurred in the area from which the mother glacier retreated, indicating a close connection between the lake and its mother glacier and revealing that topography controlled the lake expansion process. Furthermore, thorough field work revealed that outlet dynamics and external water erosion are vulnerable elements in the disaster chain that initiate and affect the GLOF hazard of Jialong Co. Overall, this case study could help scholars understand the expansion mechanism of end-moraine dammed lakes and aid in hazard assessment of glacial lakes in the central Himalayas.