Investigating seasonal velocity variations of selected glaciers in high mountain asia

Glacier velocity is a sensitive indicator of mass balance and is key to understanding how glaciers respond to climate change. Monitoring glacier velocity at high temporal resolutions enables a better understanding of the drivers of glacier dynamics. Previous studies have found that the glaciers in High Mountain Asia (HMA) tend to slow down concomitant to losing mass at an accelerating rate on decadal timescales. However, few studies have explored seasonal variations in glacier velocities and have typically focused on large, fast-flowing glaciers. We select one debris-covered glacier, and four clean-ice glaciers in HMA. Sentinel-1 and -2 images are used to calculate the glacial velocities using the feature tracking module provided by the Cryosphere And Remote Sensing Toolkit (CARST). We develop a novel, regularised linear inverse model to extract the seasonally resolved glacial velocity time series (6-day intervals) with rigorous uncertainty estimates. Our results show that three of the five glaciers have strong seasonal signals in velocities, with faster velocities in spring and/or summer compared to winter. We also find an up-glacier propagation of the late spring and/or summer accelera- tions and a down-glacier propagation of the autumn accelerations. We suggest that changes in the subglacial hydrology efficiency drive the observed seasonal variations in velocities. We also highlight that icefalls may alter the glacier flow response by blocking the development of subglacial drainage channels and thus the seasonal propagation of velocities. Our methodol- ogy enables us to successfully extract seasonal signals in glaciers that flow slowly and provide a further understanding of glacier dynamics. • Seasonal signals in glacier velocities were detected using a novel optimization method alongside a classical feature tracking technique. • Changes in the subglacial hydrology system are likely driving the observed seasonal signals in velocities. • Icefalls may stop the propagation of the glacier seasonal dynamics by blocking the development of the subglacial drainage channels.