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Quantifying ice cliff evolution with multi-temporal point clouds on the debris-covered Khumbu Glacier, Nepal

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<mark>Journal publication date</mark>10/2017
<mark>Journal</mark>Journal of Glaciology
Issue number241
Volume63
Number of pages15
Pages (from-to)823-837
Publication statusPublished
Early online date7/09/17
Original languageEnglish

Abstract

Measurements of glacier ice cliff evolution are sparse, but where they do exist, they indicate that such areas of exposed ice contribute a disproportionate amount of melt to the glacier ablation budget. We used Structure from Motion (SfM) photogrammetry with Multi-View Stereo (MVS) to derive 3D point clouds for nine ice cliffs on Khumbu Glacier, Nepal (in November 2015, May 2016 and October 2016). By differencing these clouds, we could quantify the magnitude, seasonality, and spatial variability of ice cliff retreat. Mean retreat rates of 0.30 to 1.49 cm d-1 were observed during the winter interval (November 2015 to May 2016) and 0.74 to 5.18 cm d-1 were observed during the summer (May 2016 to October 2016). Four ice cliffs, which all featured supraglacial ponds, persisted over the full study period. In contrast, ice cliffs without a pond or with a steep back-slope degraded over the same period. The rate of thermo-erosional undercutting was over double that of subaerial retreat. Overall, 3D topographic differencing allowed an improved process-based understanding of cliff evolution and cliff−pond coupling, which will become increasingly important for monitoring and modelling the evolution of thinning debris-covered glaciers.