Role of debris flow on the change of ^10Be concentration in rapidly eroding watersheds： a case study on the Seti River, central Nepal

• Published in: Journal of mountain science Vol. 14; no. 4; pp. 716 - 730
• Main Authors: Kim, Dong Eun, Seong, Yeong Bae, Choi, Kwang Hee, Yu, Byung Yong
• Format: Journal Article
• Language: English
• Published: Heidelberg Science Press 01.04.2017
• Subjects: Earth and Environmental Science; Earth Sciences; Ecology; Environment; Geography; SETI; 剥蚀速率; 多普勒雷达; 尼泊尔; 河流沉积物; 泥石流; 流域侵蚀; 混合均匀; Be; Debris flow; Episodic erosional processes; Seti River; Catchment-wide denudation rate (CWDR); Beryllium-10
• ISSN: 1672-6316; 1993-0321
• DOI: 10.1007/s11629-016-4282-y

The concentration of cosmogenic loBe in riverine sediments has been widely used as a proxy for catchment-wide denudation rate （CWDR）. One of the key assumptions of this approach is that sediments originating from sub-basins with different erosional histories are well mixed. A tragic debris flow occurred in the Seti River watershed, central Nepal, on May 5, 2012. This catastrophic debris flow was triggered by slope failure on the peak of Annapurna IV and resulted in many casualties in the lower Seti Khola. However, it provided an opportunity to test the assumption of equal mixing of sediments in an understudied rapidly eroding watershed. This study documents the CWDR of ^10Be to evaluate the extent of the influence of episodic erosional processes such as debris flow on the spatio-temporal redistribution of loBe concentrations. Our data show that the debris flow caused little change in CWDR across the debris flow event. In addition to isotopic measurement, we calculated denudation rates by using the modeled concentrations in pre- and post-landslide sediments based on the local ^10Be production rate. The modeled result showed little change across the event, indicating that the debris flow in May 2012 played a minor role in sediment evacuation, despite the rapid erosion in the catchment. Our study concludes that although the 2012 event caused many casualties and severe damage, it was a low-magnitude, high frequency event.