| dc.description.abstract | Mountain glaciers in High Mountain Asia have experienced rapid shrinking and thinning in recent
decades through global warming. In addition, more and more glaciers are developing massive lakes at
their front, mainly forming in overdeepenings as glaciers retreat. These proglacial lakes have the ability
to rapidly accelerate glacier melt as glaciers actively calve into the lake. The formation and expansion
of these proglacial lakes heavily affect downstream regions as the water supply is reduced, and the risk
for glacial lake outburst floods (GLOFs) increases. It is therefore crucial to study the development of
these glacial lakes and to increase our understanding of the influence that these lakes exert on glacier
dynamics. This study shows how glacial lake development has affected glacier flow velocities and
thinning rates in the Bhutanese Lunana region over the past two decades. Five glaciers were selected
from this region, among which one land-terminating glacier and four lake-terminating glaciers. The
development of the lakes in this region was mapped using Landsat, RapidEye and PlanetScope imagery
to calculate the NDWI. By applying a newly developed feature tracking tool, GIV, the flow velocities
were derived over five selected periods from the past two decades. The thinning rate and mass loss
from 1975 to 2022 were estimated by combining existing data with data obtained from DEM
differencing. The results showed that the glacial lakes have experienced rapid expansion over the past
two decades, heavily affecting the flow velocity and thinning rates of glaciers. Some lake-terminating
glaciers in the region were characterized by significantly higher flow velocities and thinning rates,
mainly at the glacier front compared to land-terminating glaciers, which are mainly influenced by
supraglacial lake development and rising air temperatures. The dominant processes at lake-terminating
glaciers, causing these high velocities and thinning rates, are dynamic thinning and buoyant uplift which
reduce basal stress, causing an acceleration of the terminus and consequently buoyancy-induced
calving through a positive feedback. Other lake-terminating glaciers in the region were less affected by
their lakes as their fronts were only subjected to subaqueous melt and thermal-notching. For these
glaciers, the velocities were decreasing, caused by a decrease in driving stresses by increased glacier
thinning. It is estimated that proglacial lakes are likely to expand in the future, and new lakes will form
through increased global warming and the presence of large overdeepenings underneath the glaciers.
However, many aspects of these lakes, including lake bathymetry and temperature, remain unknown,
while playing an important role in glacier-lake interactions. | |
