Articles | Volume 10, issue 5
The Cryosphere, 10, 2075–2097, 2016
The Cryosphere, 10, 2075–2097, 2016

Research article 14 Sep 2016

Research article | 14 Sep 2016

Heterogeneous glacier thinning patterns over the last 40 years in Langtang Himal, Nepal

Silvan Ragettli1,2, Tobias Bolch2,3, and Francesca Pellicciotti4 Silvan Ragettli et al.
  • 1Institute of Environmental Engineering, ETH Zürich, Zurich, Switzerland
  • 2University of Zurich, Department of Geography, Zurich, Switzerland
  • 3Institute for Cartography, Technische Universität Dresden, Dresden, Germany
  • 4Northumbria University, Department of Geography, Newcastle upon Tyne, UK

Abstract. This study presents volume and mass changes of seven (five partially debris-covered, two debris-free) glaciers in the upper Langtang catchment in Nepal. We use a digital elevation model (DEM) from 1974 stereo Hexagon satellite data and seven DEMs derived from 2006–2015 stereo or tri-stereo satellite imagery (e.g., SPOT6/7). The availability of multiple independent DEM differences allows the identification of a robust signal and narrowing down of the uncertainty about recent volume changes. The volume changes calculated over several multiyear periods between 2006 and 2015 consistently indicate that glacier thinning has accelerated with respect to the period 1974–2006. We calculate an ensemble-mean elevation change rate of –0.45 ± 0.18 m a−1 for 2006–2015, while for the period 1974–2006 we compute a rate of −0.24 ± 0.08 m a−1. However, the behavior of glaciers in the study area is heterogeneous, and the presence or absence of debris does not seem to be a good predictor for mass balance trends. Debris-covered tongues have nonlinear thinning profiles, and we show that recent accelerations in thinning correlate with the presence of supraglacial cliffs and lakes. At stagnating glacier areas near the glacier front, however, thinning rates decreased with time or remained constant. The April 2015 Nepal earthquake triggered large avalanches in the study catchment. Analysis of two post-earthquake DEMs revealed that the avalanche deposit volumes remaining 6 months after the earthquake are negligible in comparison to 2006–2015 elevation changes. However, the deposits compensate about 40 % the mass loss of debris-covered tongues of 1 average year.

Short summary
This study presents a multi-temporal dataset of geodetically derived elevation changes on debris-free and debris-covered glaciers in the Langtang valley, Nepalese Himalaya. Overall, we observe accelerated glacier wastage, but highly heterogeneous spatial patterns and temporal trends across glaciers. Accelerations in thinning correlate with the presence of supraglacial cliffs and lakes, whereas thinning rates remained constant or declined on stagnating debris-covered glacier areas.