Articles | Volume 12, issue 1
https://doi.org/10.5194/esurf-12-135-2024
https://doi.org/10.5194/esurf-12-135-2024
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16 Jan 2024
Research article | Highlight paper |  | 16 Jan 2024

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

Emma L. S. Graf, Hugh D. Sinclair, Mikaël Attal, Boris Gailleton, Basanta Raj Adhikari, and Bishnu Raj Baral

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Latest update: 20 Nov 2024
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Do earthquakes result in higher levels of sediment in rivers in the years following the event? There are several reasons to believe this could be the case. Previous studies have even provided evidence of increased sediment loads in mountainous areas after major earthquakes. However, a study by Graf et al. challenges this perspective. They demonstrate that despite the thousands of landslides triggered by the 2015 Gorkha Earthquake in Nepal, there were only minimal increases in coarse sediment in river channels during the subsequent years. Instead, the study reveals a different story. In June 2021, a single, exceptionally heavy rainfall event mobilized large volumes of sediment, leading to riverbed elevation by as much as 12 meters. This effect greatly overshadowed any sedimentary impact left by the earthquake along the river corridor. The study underscores that earthquake evidence may not always be found in the sedimentary records of alluvial areas. In high-mountainous regions, records of riverbed elevation may be strongly influenced by unique and localized events.
Short summary
Using satellite images, we show that, unlike other examples of earthquake-affected rivers, the rivers of central Nepal experienced little increase in sedimentation following the 2015 Gorkha earthquake. Instead, a catastrophic flood occurred in 2021 that buried towns and agricultural land under up to 10 m of sediment. We show that intense storms remobilised glacial sediment from high elevations causing much a greater impact than flushing of earthquake-induced landslides.