Comprehensive interpretation of the Sedongpu glacier-related mass flows in the eastern Himalayan syntaxis

Glacier-related mass flows (GMFs) in the high-mountain cryosphere have become more frequent in the last decade, e.g., the 2018 Sedongpu (SDP) GMFs in the Himalayas. Seismic forcing, thermal perturbation and heavy rainfall are common triggers of the GMFs. But the exact role of seimic forcing in the GMF formation is poorly known due to scarity of observational data of real cases. Here the evolution processes of the GMFs and the detachment of the trunk glacier in SDP are reconstructed by using remote sensing techniques, including feature-tracking of multi-source optical satellite imagery and visual interpretation. The reconstruction demonstrates that the high frequency of GMF events in SDP after the Milin earthquake on 18 November 2017 was mainly attributed to the earthquake-induced glacial stress changes and destablisation. The post-earthquake velocity of the trunk glacier is about three times of that in December 2016 and December 2017. The median glacier-surface velocity raised to 0.32 m d−1 between November 2017 and June 2018, being 14%–77% higher than that of pre-earthquake, which is initiated by the seismic forcing and then aggravated by additional loading of ice/rock avalanches, infiltration of liquid water, progressively crevassed glacier, and local compressional deformation. Ensuing surge motion of the trunk glacier resulted from high temperature and heavy precipitation between July and September 2018. We infer that the trunk glacier is more sensitive to the thermal perturbation after the Milin earthquake, which is the predominant cause in sudden surge movement. These findings reveal comprehensive mechanisms of quake-induced, low-angle, glacial detachment and multisource-driven GMF in the Himalayas.