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Volume 12, issue 9 | Copyright
The Cryosphere, 12, 2883-2900, 2018
https://doi.org/10.5194/tc-12-2883-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Sep 2018

Research article | 07 Sep 2018

Mechanisms leading to the 2016 giant twin glacier collapses, Aru Range, Tibet

Adrien Gilbert1, Silvan Leinss2, Jeffrey Kargel3, Andreas Kääb1, Simon Gascoin4, Gregory Leonard5, Etienne Berthier6, Alina Karki7, and Tandong Yao8 Adrien Gilbert et al.
  • 1Department of Geosciences, University of Oslo, Oslo, Norway
  • 2Institute of Environmental Engineering, ETH Zurich, Zurich, Switzerland
  • 3Planetary Science Institute, Tucson, Arizona, USA
  • 4CESBIO, CNES, CNRS, IRD, UPS, Université de Toulouse, Toulouse, France
  • 5Department of Planetary Sciences, University of Arizona, Tucson, USA
  • 6LEGOS, CNES, CNRS, IRD, UPS, Université de Toulouse, Toulouse, France
  • 7Society for Ecological Restoration-Nepal, Kathmandu, Nepal
  • 8ITP-CAS, Beijing, China

Abstract. In north-western Tibet (34.0°N, 82.2°E) near lake Aru Co, the entire ablation areas of two glaciers (Aru-1 and Aru-2) suddenly collapsed on 17 July and 21 September 2016. The masses transformed into ice avalanches with volumes of 68 and 83×106m3 and ran out up to 7km in horizontal distance, killing nine people. The only similar event currently documented is the 130×106m3 Kolka Glacier rock and ice avalanche of 2002 (Caucasus Mountains). Using climatic reanalysis, remote sensing, and three-dimensional thermo-mechanical modelling, we reconstructed the Aru glaciers' thermal regimes, thicknesses, velocities, basal shear stresses, and ice damage prior to the collapse in detail. Thereby, we highlight the potential of using emergence velocities to constrain basal friction in mountain glacier models. We show that the frictional change leading to the Aru collapses occurred in the temperate areas of the polythermal glaciers and is not related to a rapid thawing of cold-based ice. The two glaciers experienced a similar stress transfer from predominant basal drag towards predominant lateral shearing in the detachment areas and during the 5–6 years before the collapses. A high-friction patch is found under the Aru-2 glacier tongue, but not under the Aru-1 glacier. This difference led to disparate behaviour of both glaciers, making the development of the instability more visible for the Aru-1 glacier through enhanced crevassing and terminus advance over a longer period. In comparison, these signs were observable only over a few days to weeks (crevasses) or were absent (advance) for the Aru-2 glacier. Field investigations reveal that those two glaciers were underlain by soft, highly erodible, and fine-grained sedimentary lithologies. We propose that the specific bedrock lithology played a key role in the two Tibet and the Caucasus Mountains giant glacier collapses documented to date by producing low bed roughness and large amounts of till, rich in clay and silt with a low friction angle. The twin 2016 Aru collapses would thus have been driven by a failing basal substrate linked to increasing pore water pressure in the subglacial drainage system in response to increases in surface melting and rain during the 5–6 years preceding the collapse dates.

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In Tibet, two glaciers suddenly collapsed in summer 2016 and produced two gigantic ice avalanches, killing nine people. This kind of phenomenon is extremely rare. By combining a detailed modelling study and high-resolution satellite observations, we show that the event was triggered by an increasing meltwater supply in the fine-grained material underneath the two glaciers. Contrary to what is often thought, this event is not linked to a change in the thermal condition at the glacier base.
In Tibet, two glaciers suddenly collapsed in summer 2016 and produced two gigantic ice...
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