Abstract
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 83×106 m3 and ran out up to 7 km in horizontal distance, killing nine people. The only similar event currently documented is the 130×106 m3 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.
Highlights
In the Aru Mountain range on the western Tibetan Plateau, the entire ablation zone of an unnamed glacier spontaneously collapsed on 17 July 2016
Through the more accurate bedrock topography derived in this study and the 3-D approach, we show here that the temperate zones likely extended into significantly larger areas beneath the detachments than previously thought
Sensitivity tests show that the temperate area remains stable for a basal heat flux between 6.0 × 10−2 and 1.2 × 10−1 W m−2 and disappears only at ≤ 2.0 × 10−2 W m−2
Summary
In the Aru Mountain range on the western Tibetan Plateau, the entire ablation zone of an unnamed glacier (termed here Aru-1) spontaneously collapsed on 17 July 2016. A. Gilbert et al.: Mechanisms leading to the 2016 giant twin glacier collapses with speeds exceeding 200 km h−1, spread over a 7 km long and 3 km wide deposit, and killed nine herders and hundreds of their animals (Kääb et al, 2018). Gilbert et al.: Mechanisms leading to the 2016 giant twin glacier collapses with speeds exceeding 200 km h−1, spread over a 7 km long and 3 km wide deposit, and killed nine herders and hundreds of their animals (Kääb et al, 2018) This event was followed by the collapse of the adjacent glacier south of Aru-1 2 months later, on 21 September 2016, producing a similar low-angle giant avalanche (see Fig. 1b). The collapses raise the question of whether similar future events affecting other glaciers might be influenced by ongoing climate change
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
