1887

Abstract

Summary

Although the topographic evolution and erosion dynamics of the Himalayan range have been extensively documented, it is not known how the very high Himalayan peaks erode. Some conceptual models assume that intense periglacial processes involve regressive erosion of high peak headwall at rates dictated by valley-floor downcutting of glaciers. However, recent data indicate that frost-cracking intensity decreases with elevation, suggesting instead that highest Himalayan peaks are free of erosion, raising the question of their long-term evolution.

Here, we report geological evidence for a giant rockslide that occurred around 1190 AD (14C burial age, 36Cl exposure age, and IRSL dating) in the Annapurna Massif (central Nepal), involving a total rock volume of ∼23km3, and that filled a wide glacial cirque (Sabche cirque) and the Seti valley farther downstream with a rock-avalanche deposit up to 1km thick, made of finely-crushed breccia. On the basis of an original reconstruction of the geometry of the collapsed volume, based on an estimate of the average cohesion of the rock mass at high altitude, we propose that this giant rockslide decapitated a paleosummit, the paleo-Annapurna IV, culminating most probably above 8000m of altitude. Giant rockslides have major implications for landscape evolution: the massive supply of finely-crushed sediments can fill the valleys over >150km further downstream and saturate the Himalayan rivers with sediments for a century or longer time periods. This raises the crucial question of natural hazards associated with such high-magnitude events in the Himalayan regions.

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/content/papers/10.3997/2214-4609.2023500048
2023-09-18
2025-07-19
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