Geomorphological and hydrological controls on sediment export in earthquake-affected catchments in the Nepal Himalaya

IF 2.8 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL
Emma L. S. Graf, Hugh D. Sinclair, Mikaël Attal, Boris Gailleton, Basanta Raj Adhikari, Bishnu Raj Baral
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Abstract

Abstract. Large earthquakes can contribute to mountain growth by building topography but also contribute to mass removal from mountain ranges through widespread mass wasting. On annual to decadal or centennial timescales, large earthquakes also have the potential to significantly alter fluvial sediment dynamics if a significant volume of the sediment generated reaches the fluvial network. In this contribution, we focus on the Melamchi–Indrawati and Bhote Koshi rivers in central Nepal, which have both experienced widespread landsliding associated with the 2015 Gorkha (Nepal) earthquake. Using a time series of high-resolution satellite imagery, we have mapped exposed sediment along the rivers from 2012–2021 to identify zones of active channel deposition and document changes over time. Counter to expectations, we show negligible increases in coarse-sediment accumulation along both river corridors since the Gorkha earthquake. However, an extremely high-concentration flow event on 15 June 2021 caused an approximately 4-fold increase in exposed sediment along a 30 km reach of the channel with up to 12 m of channel aggradation in the Melamchi–Indrawati rivers; this event was localised and did not impact the neighbouring Bhote Koshi catchment. Based on published reports, new helicopter-based photography, and satellite data, we demonstrate that this event was sourced from a localised rainfall event between 4500 and 4800 m and that a significant fraction of the sediment was supplied from sources that were unrelated to the landslides generated by the Gorkha earthquake.
尼泊尔喜马拉雅山脉受地震影响流域沉积物输出的地貌和水文控制因素
摘要大地震可以通过塑造地形促进山脉的增长,但也会通过大范围的物质流失造成山脉的物质流失。在每年到十年或百年的时间尺度上,如果大地震产生的大量沉积物进入河流网络,那么大地震也有可能极大地改变河流沉积物动力学。在本文中,我们重点研究了尼泊尔中部的 Melamchi-Indrawati 河和 Bhote Koshi 河,这两条河流都经历了与 2015 年尼泊尔高尔察地震相关的大范围山体滑坡。利用高分辨率卫星图像的时间序列,我们绘制了 2012-2021 年沿河裸露沉积物的地图,以确定河道沉积活跃的区域,并记录随时间推移发生的变化。与预期相反,我们发现自廓尔喀大地震以来,两条河流走廊沿线的粗沉积物累积量增加微乎其微。然而,2021 年 6 月 15 日发生的一次高浓度水流事件导致梅拉姆齐-印德拉瓦提河 30 公里河道沿线裸露沉积物增加了约 4 倍,河道最深的地方水位上升了 12 米;这次事件是局部性的,并未对邻近的博特甲子河流域造成影响。根据已发表的报告、新的直升机摄影和卫星数据,我们证明了这次事件的源头是海拔 4500 到 4800 米之间的局部降雨事件,而且很大一部分沉积物的来源与廓尔喀地震引发的山体滑坡无关。
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来源期刊
Earth Surface Dynamics
Earth Surface Dynamics GEOGRAPHY, PHYSICALGEOSCIENCES, MULTIDISCI-GEOSCIENCES, MULTIDISCIPLINARY
CiteScore
5.40
自引率
5.90%
发文量
56
审稿时长
20 weeks
期刊介绍: Earth Surface Dynamics (ESurf) is an international scientific journal dedicated to the publication and discussion of high-quality research on the physical, chemical, and biological processes shaping Earth''s surface and their interactions on all scales.
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