Consecutive Glacier Sub-Surge Events Within Five Years Were Identified in an Unexplored Glacier of the Karakoram

Abstract

In order to monitor the dynamic changes of an unnamed glacier (called G1 Glacier) located in the Karakoram in detail, glacier surface velocities were extracted from 165 Sentinel-1 SAR images with 12-day and 24-day time intervals from 2014 to 2020, glacier elevation changes were obtained from four ASTER stereo images, and glacier terminus evolutions were derived from four Landsat 8 images. Based on the high-density glacier surface velocity results, four consecutive glacier sub-surge events of the G1 Glacier ranging from 6 months to 1 yr between 2015 and 2019 were confirmed for the first time, accompanied by sporadic pulse events before and after the four sub-surges. The velocity changes and impact range of the four glacier sub-surges showed a trend of first increasing, then stabilizing and finally decreasing. At the same time, the accelerating area gradually moved downstream of the glacier. The changes in glacier elevation and the evolutions in the glacier terminus also proved the occurrence of glacier acceleration events. Sentinel-1 SAR images with shorter time intervals could be used to identify multiple sub-surge events and pulse events within a complete surge. Combining four sub-surges and multiple pulse events, a complete chain of glacier large-scale acceleration events from pulse to surge and then to pulse could be summarized, which might mean that the effective identification of pulse events provides the possibility for the early warning of glacier surge events.