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The evolution of supraglacial ponds and ice cliffs on Himalayan debris-covered glaciers

Watson, Cameron Scott (2017) The evolution of supraglacial ponds and ice cliffs on Himalayan debris-covered glaciers. PhD thesis, University of Leeds.

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Abstract

The widespread negative mass balance of debris-covered glaciers in the central Himalaya is expressed through, and influenced by, glacier surface morphology, including the spatio-temporal dynamics of supraglacial ponds and ice cliffs. These features form a relatively unknown component of the overall melt budget but are thought to be key contributors to a debris-cover anomaly, whereby the insulating effect of debris is offset by enhanced melt at supraglacial ponds and ice cliffs. In this thesis we revealed the role of ice cliff evolution and supraglacial pond dynamics at seasonal to annual timescales using extensive fieldwork and assessments of remotely sensed satellite imagery from the Everest region of Nepal. Supraglacial pond dynamics were assessed over the last decade using multitemporal fine-resolution satellite imagery (~0.5−2 m), revealing a net increase in pond area but large inter-annual and seasonal variability. Coalescing and persistent ponds on Khumbu Glacier suggested that a trajectory towards large lake development was underway. Additionally, we revealed that the size distribution of ponds on debris-covered glaciers potentially leads to large classification omissions in studies using medium-resolution (e.g. 30 m) satellite imagery, on the order of 15–88% of ponded area. Instrumentation of ponds on Khumbu Glacier revealed seasonal expansion and drainage, and water temperatures conducive to englacial ablation. We surveyed 24 ponds with an unmanned surface vessel to derive their bathymetry and an empirical area-volume relationship, which can now be used to predict glacier-scale water storage fluxes. A remote sensing assessment of ice cliffs revealed that on average 49% of cliffs were associated with a supraglacial pond, and that cliff density was positively correlated with glacier mass loss. We presented the first application of 3D point cloud differencing to multi-temporal ice cliff point clouds to quantify the magnitude and spatio-temporal variation in cliff retreat, and revealed the role of ponds and local topography on controlling cliff persistence. We observed mean retreat rates of 0.30–1.49 cm d−1 during the winter interval (November 2015–May 2016) and 0.74–5.18 cm d−1 during the summer (May 2016–October 2016). Overall, by coupling remote sensing and field-based observations we produced a holistic assessment of ice cliffs and supraglacial ponds. This assessment has improved our process-based understanding of debris-covered glacier evolution and has provided the foundations for better consideration of surface processes in studies modelling glacier evolution.

Item Type: Thesis (PhD)
Keywords: debris-covered glaciers, supraglacial ponds, ice cliffs, Khumbu Glacier, Nepal, Himalaya, Everest
Academic Units: The University of Leeds > Faculty of Environment (Leeds) > School of Geography (Leeds)
Identification Number/EthosID: uk.bl.ethos.731496
Depositing User: Mr Cameron Scott Watson
Date Deposited: 24 Jan 2018 15:37
Last Modified: 25 Jul 2018 09:56
URI: http://etheses.whiterose.ac.uk/id/eprint/18964

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