The Surge of the Hispar Glacier, Central Karakoram: SAR 3‐D Flow Velocity Time Series and Thickness Changes

Abstract

Abstract The Hispar Glacier is a useful site for studying surge mechanisms. Prior to this study, only two‐dimensional (2‐D) flow velocities having low temporal resolution were available for this glacier, providing inadequate information about its surge evolution. In this study, 139 synthetic aperture radar (SAR) images from Sentinel‐1A were used to obtain 3‐D flow velocity time series for the Hispar Glacier during the recent surge (2014–2016). The 3‐D flow velocities were sampled at an interval of 11 days, which is much greater than in previous studies. Besides, the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) and two TanDEM‐X images were used to determine glacier thickness changes prior to and following the recent surge. Combining the results and geomorphologic features, we deduced that the recent surge was because of saturated basal water pressure in the Yutmaru tributary. The mass from the Yutmaru tributary squeezed into the trunk and rapidly flowed downslope along the northern margin, generating strong normal pressure to the trunk mass. Pushed by the Yutmaru tributary, the trunk began to surge in September 2014. The flow velocity reached a first peak in May 2015 and then decreased in October 2015, as part of the basal meltwater ran off. However, basal meltwater accumulated again during the following 4 months, and correspondingly, the trunk accelerated again after October 2015. Finally, as kinetic energy was released and resisting force increased, the trunk became almost stagnant in August 2016. The surge mass was blocked downstream in the trunk by the mass transferred from the Kunyang tributary, and consequently, the glacier did not advance.