Variable evolution of debris-covered glaciers in High Mountain Asia during the last several decades

Debris-covered glaciers (DCG) are common in most parts of High Mountain Asia (HMA). Existing studies show that DCG have been losing mass at similar or even higher rates than debris-free glaciers (DFG). However, the process driving the response of DCG to climate change are much more heterogenous than those of DFG. Understanding the evolution of DCG is further complicated by the development glacial lakes which have significant impacts on glacier dynamics.

To investigate the characteristics and development of the DCG a long time series of observations is beneficial. Here, we present the mass balance and surface evolution of selected DCGs located in different parts of HMA since the last 60 years using historical KH-4 and KH-9 stereo imagery and contemporary high-resolution stereo images such as Pléiades. In addition, we analyse their velocity changes since the 1980s using available data from ITS_Live and calculated annual and seasonal velocities from Sentinel-1 and 2 data.

Our results show that DCGs have slowed-down on average and the surface of DCGs have become rougher indicating the evolution of ice cliffs and supra-glacial lakes. Most DCG have large stagnant tongues, a reverse elevation change gradient at the distal part of the tongue and no visible signs of retreat (“Khumbu type”). In contrast, others show flow activity throughout the tongue and are retreating. Their surface elevation change gradient is similar to DFG (“Kangshung type”). The lake-terminating DCG are also active throughout, have the highest velocity at the end of the tongue and show the highest mass loss. We found topography to be one of the main drivers of heterogeneity. Work is ongoing to analyse various climate parameters to better understand the reasons for the heterogeneity and investigate the similarities and differences in the seasonal velocity of DCGs.