Surging Processes and Mechanisms at Small Glaciers in the Qilian Mountains, Northwestern China, Revealed by Long-Term, Temporally Dense Remote Sensing Observations

A glacier surge, an exceptional phenomenon of mass redistribution, is one of the least understood dynamic processes in cryospheric science. Long-term detailed changes in glacier elevation and flow velocity are crucial for assessing surge dynamics. However, capturing complex changes during surges through traditional methods, especially on small and narrow valley glaciers, is often hampered by the limitations in spatiotemporal resolution of available satellite records. In this study, we investigated the long-term changes of small surging glaciers in the Qilian mountains whose dynamics remain poorly understood. Using ASTER and Landsat imagery, we employed the two newly developed methods specifically designed for surging glaciers to derive long-term monthly flow velocity and elevation time series. Combing with historical morphological analysis, our results successfully captured the detailed surging process of five glaciers. One glacier (GLIMS ID: G097781E38470N) experienced a major surge during 2002–2008, characterized by abrupt acceleration and mass transfer during 2002–2005. One glacier (G097762E38509N) underwent a surge with terminus advance prior to 2000. Two glaciers (G097722E38519N and G097681E38536N) experienced gradual surges that lasted over 10 years. The fifth glacier (G097731E38477N) shows early surge initiation, characterized by recent acceleration and thickening in its middle trunk. Considering the long duration, glacier surges in this region appear primarily thermal-controlled. However, the pre-surge stage and sudden mass release suggest a possible impact from saturated soft sediment failure. This research demonstrates the potential of advanced time-series methods for revealing diverse surge patterns and surge evolution of small glaciers, and provides new insights into the surge dynamics in this region.