Velocity variations and hydrological drainage at Baltoro Glacier, Pakistan

Kurzfassung

Surface meltwater directly influences glacier velocity, as liquid water at the bed allows the glacier to slide. However, prolonged discharge of water at the bed increases the efficiency of the drainage system and decreases the amount of sliding. Due to the presence of an insulating debris mantle, debris-covered glaciers respond in a more complex way to changes in climate than those that are debris-free. The influence of higher temperatures on melt processes and, subsequently, supraglacial lake formation, and the triggers of basal sliding have not yet been sufficiently analyzed and understood. We present a spatio- temporal analysis of key glacier characteristics for the Baltoro Glacier in the Karakoram, from October 2016 to September 2022 based from Earth Observation data and climate parameters extracted from the High Asia Refined analysis (HAR) data set. For the glacier variables, we used surface velocity, supraglacial lake extent, snowmelt, and runoff derived from Earth Observation data. For climate variables, we focused on air temperature and precipitation. The relationship and dependency between the variables were examined with Pearson correlation and linear regression, respectively. Additionally, the temporal delay between snowmelt peak and glacier flow acceleration was determined. The surface velocity of the Baltoro Glacier was characterized by a spring speed-up, summer peak, and fall speed-up with the largest increase in spring of 1.0–1.7 m d-1 triggered by the onset or an increase of basal sliding. Snowmelt has the largest impact to the spring speed-up, summer velocity peak, and to the transition from inefficient to efficient drainage. The temporal delay between the initial peak of seasonal snowmelt and the first relative velocity maximum seems to decrease during the observation period. Drainage from supraglacial lakes contributed to the fall speed-up, which showed a lower magnitude by 0.1–0.2 m d-1 than the summer velocity peak. Wet snow covered up to 64 % (353 km2) of the complete Baltoro Glacier and reached up to to 4700 m a.s.l. during the first melt peak and up to 5600 m a.s.l. during summer. In comparison, the supraglacial lake area ranged between 3.6–5.9 km2. Most of the runoff can be attributed to snowmelt. However from mid-June onwards, the lakes play an increasing role, even though their contribution is estimated to be only about half of that of the snowmelt. The observed increase in summer temperatures influences the magnitude of snowmelt, as well as the formation of supraglacial lakes. This tendency is expected to intensify in the future.