Abstract. Debris-covered glaciers in the Himalaya play an important role in
the high-altitude water cycle. The thickness of the debris layer is a key
control of the melt rate of those glaciers, yet little is known about the
relative importance of the three potential sources of debris supply: the
rockwalls, the glacier bed and the lateral moraines. In this study, we
hypothesize that mass movement from the lateral moraines is a significant
debris supply to debris-covered glaciers, in particular when the glacier is
disconnected from the rockwall due to downwasting. To test this hypothesis,
eight high-resolution and accurate digital elevation models from the
lateral moraines of the debris-covered Lirung Glacier in Nepal are used.
These are created using structure from motion (SfM), based on images captured
using an unmanned aerial vehicle between May 2013 and April 2018. The
analysis shows that mass transport results in an elevation change on the
lateral moraines with an average rate of -0.31±0.26 m year−1 during
this period, partly related to sub-moraine ice melt. There is a higher
elevation change rate observed in the monsoon (-0.39±0.74 m year−1)
than in the dry season (-0.23±0.68 m year−1). The lower debris aprons
of the lateral moraines decrease in elevation at a faster rate during both
seasons, probably due to the melt of ice below. The surface lowering rates of
the upper gullied moraine, with no ice core below, translate into an annual
increase in debris thickness of 0.08 m year−1 along a narrow margin of the
glacier surface, with an observed absolute thickness of approximately 1 m,
reducing melt rates of underlying glacier ice. Further research should focus
on how large this negative feedback is in controlling melt and how debris is
redistributed on the glacier surface.
Post-LGM glacial retreat and Early Holocene monsoon intensification drives aggradation in the interiors of the Kashmir Himalaya