Sediment supply from lateral moraines to a debris-covered glacier in the Himalaya

Abstract

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.

Unravelling the evolution of Zmuttgletscher and its debris cover since the end of the Little Ice Age

“…The observed temporal variations in ice flow and thickness on the main glacier tongue of Zmuttgletscher also closely re-flect variations in climate as exemplified by the acceleration and thickening in the period of more positive mass balance in the 1970s and 1980s. Positive mass balances impacting flow velocities were also observed at debris-covered Glacier de Tsarmine (Capt et al, 2016) and a number of other debrisfree glaciers in Switzerland (Glacier de Giétro, Glacier de Corbassière, Mattmark; Bauder, 2017), Austria (Hintereisferner, Kesselwandferner; Stocker-Waldhuber et al, 2018), and France (Glacier d' Argentière; Vincent et al, 2009). Also at Glacier de Miage, a kinematic wave migrating downglacier was observed between the 1960s and 1980s that led to a small terminus advance in the late 1980s (Thomson et al, 2000).…”

Supraglacial ice cliffs and ponds on debris-covered glaciers: spatio-temporal distribution and characteristics

“…Debris controls the surface ablation of the debris-covered tongues and a thin layer of debris enhances the melt rate by lowering the albedo, whereas a layer thicker than a few centimetres insulates the ice and reduces melt (Østrem, 1959; Mattson and others, 1993; Mihalcea and others, 2006; Nicholson and Benn, 2006; Evatt and others, 2015). Recent studies have since attempted to increase our understanding of debris-covered glaciers, from the meteorology (Collier and others, 2014; Shaw and others, 2015; Steiner and Pellicciotti, 2016; Steiner and others, 2018) to the actual mechanisms of mass loss and gain (Pellicciotti and others, 2015; Ragettli and others, 2016) to the evolution and changes in the thickness and properties of debris (Shukla and others, 2009; Shukla and Qadir, 2016; Gibson and others, 2017a,b; Anderson and Anderson, 2018; Woerkom and others, 2019).…”

GERALDINE (Google Earth Engine supRaglAciaL Debris INput dEtector): a new tool for identifying and monitoring supraglacial landslide inputs

“…The expansion of supraglacial debris cover is due to (i) glaciological and climatological controls such as thrusting and meltout of sub-and en-glacial sediment onto the surface (e.g. Kirkbride and Deline, 2013;Mackay et al, 2014;Wirbel et al, 2018); (ii) debris input from surrounding valley walls through bedrock mass movements (Deline et al, 2015;Porter et al, 2010); (iii) dispersion of medial moraines (Anderson, 2000); and (iv) remobilization of debris stores, particularly lateral moraines (Van Woerkom et al, 2019). The relative contributions of "glacially" derived sediment, which may in fact be the re-emergence of glacially modified mass movements (Mackay et al, 2014), as compared to direct subaerial inputs, are highly variable and there is complex coupling between hillslopes and glaciers that varies with relief (Scherler et al, 2011a).…”