Cosmogenic dating of two rock avalanches in the Ama Drime Range, Central Himalayas

Abstract

The Himalayan region, shaped by active tectonics and complex geomorphological processes, is highly susceptible to avalanches. Among various avalanche types, rock avalanches—recognized as the most prevalent failure pattern—have been extensively studied in the western Himalayan orogen, whereas research on its central segment remains limited. In this study, two newly discovered rock avalanches, located on the eastern and western sides of the Ama Drime range in the central Himalayan region, were investigated and dated using cosmogenic ¹⁰Be exposure ages. The results show that the Pengqu (PQ) rock avalanche, situated on a river terrace, was dated to 120.0 ± 13.0 ka, and the Xiaerqu (XRQ) rock avalanche, located in a glacial valley, occurred between 5.8 ± 0.5 and 4.4 ± 0.5 ka. Considering geological, climatic and seismic factors, we propose that the PQ rock avalanche was primarily caused by prolonged warm and humid conditions during the MIS 5e period, which induced internal deformation of the Kartha gneiss. In contrast, the XRQ rock avalanche was mainly driven by glacial debuttressing, which reduced the stability of the underlying rock. Ultimately, both the PQ and XRQ avalanches were triggered by fault activity, specifically the Khatar and Dinggye faults, respectively. These findings are crucial for understanding the driving mechanisms of rock avalanches in the central Himalayan region and offer valuable insights into fault activity and geomorphological evolution.