Approximately 25 % of the glacierized area in the Everest region is covered by debris, yet the surface mass balance of debris-covered portions of these glaciers has not been measured directly. In this study, ground-based measurements of surface elevation and ice depth are combined with terrestrial photogrammetry, unmanned aerial vehicle (UAV) and satellite elevation models to derive the surface mass balance of the debris-covered tongue of Changri Nup Glacier, located in the Everest region. Over the debris-covered tongue, the mean elevation change between 2011 and 2015 is -0.93 m year-1 or -0.84 m water equivalent per year (w.e. a-1). The mean emergence velocity over this region, estimated from the total ice flux through a cross section immediately above the debris-covered zone, is +0.37 m w.e. a-1. The debris-covered portion of the glacier thus has an area-averaged mass balance of -1.21 ± 0.2 m w.e. a-1 between 5240 and 5525 m above sea level (m a.s.l.). Surface mass balances observed on nearby debris-free glaciers suggest that the ablation is strongly reduced (by ca. 1.8 m w.e. a-1) by the debris cover. The insulating effect of the debris cover has a larger effect on total mass loss than the enhanced ice ablation due to supraglacial ponds and exposed ice cliffs. This finding contradicts earlier geodetic studies and should be considered for modelling the future evolution of debris-covered glaciers.
Bibliographical noteFunding Information:
This work has been supported by the French Service d'Observation GLACIOCLIM, the French National Research Agency (ANR) through ANR-09-CEP-005-01-PAPRIKA and ANR-13-SENV-0005-04-PRESHINE and has been supported by a grant from Labex OSUG@2020 (Investissements d'avenir - ANR10 LABX56). This study was carried out within the framework of the Ev-K2-CNR Project in collaboration with the Nepal Academy of Science and Technology as foreseen by the Memorandum of Understanding between Nepal and Italy, and thanks to contributions from the Italian National Research Council, the Italian Ministry of Education, University and Research and the Italian Ministry of Foreign Affairs. Funding for the UAV survey was generously provided by the United Kingdom Department for International Development (DFID) and by the Ministry of Foreign Affairs, Government of Norway. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 676819). EB acknowledges support from the French Space Agency (CNES) through the TOSCA Top Glaciers project. SPOT5 HRG images were obtained thanks to ISIS-CNES project #510. This work was supported by public funds received in the framework of GEOSUD, a project (ANR-10-EQPX-20) of the program "Investissements d'Avenir" managed by the French National Research Agency. The International Centre for Integrated Mountain Development is funded in part by the governments of Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal and Pakistan. The views expressed are those of the authors and do not necessarily reflect their organizations or funding institutions. We thank the French private company SINTEGRA for its useful support. We thank J. O. Hagen Editor, J. Steiner, and an anonymous reviewer whose thorough comments improved the quality of the manuscript.
© 2016 Author(s).