Seasonal speedup of glacier in the southeastern Tibetan Plateau

Most glaciers around the world are slowing down, but some marine-terminating outlet glaciers occur and trigger seasonal or shorter-term accelerations (up to 100% greater than the annual mean), and the speedup events of glaciers cause accelerated glacier loss. Although some speedup events have been observed in the Greenland and Antarctica, limited observed in the Tibetan Plateau and the trigger mechanism is also poorly understood. In this study, we used the high-frequency Global Navigation Satellite System (GNSS) observations collected on the Parlung No.4 Glacier in southeastern Tibetan Plateau in 2022 to characterize the seasonal dynamics of glacier velocity and analyze its mechanism. The results show that the velocity has a distinct seasonal variation, with highly fast in summer (1.42 times as fast as winter flow). A total of 9 speedup events were observed in spring and summer, with 3 GNSS stations simultaneously generating 5 acceleration events; the glacier accelerated frequently from 25 June to 3 July, with a total of 3 speedup events; with the maximum intensity occurred at the end of July, which was about 10 times as fast as others. In addition, we find that the speedup of the glacier is mainly consistent with precipitation and the glacial runoff, and we suggest that the speedup of the glacier is mainly due to enhanced meltwater leading to glacier basal motion.