Tracking mass‐wasting sediments in the large Brahmaputra River system

Abstract The impact of mass‐wasting events on river systems is typically studied in the immediate aftermath and within close proximity to the source area. However, basin‐wide hydro‐geomorphic responses in large river systems, beyond the immediate postdisaster context, remain poorly understood. In this study, we examine the Eastern Himalayan Syntaxis in the Brahmaputra basin, where the Sendongpu glacier valley has undergone rapid erosion due to major mass‐wasting events in 2017, 2018 and 2021. A nearby large‐scale event also occurred in 2000 along the Yigong River. We assess the river's response to these events using satellite‐derived water turbidity indices, water surface elevation, sandbar area and flood extent, at the finest temporal and spatial resolution available through Google Earth Engine's database. Our time series analysis reveals that, following the 2017 event, fine suspended sediment signals can be traced more than 1000 km downstream to the delta, while coarser sediments primarily affect river morphology within approximately 100 km of the mountain front. In this zone, we observed a notable increase in sandbar area and water surface elevation, indicating extensive deposition and channel infilling. Comparison with the 2000 Yigong outburst highlights the differing geomorphic effects of rapid, high‐magnitude events versus slower, more sustained sediment inputs. These findings highlight the need to integrate mass‐wasting‐driven sediment processes into flood risk assessments and hydropower planning in Himalayan river systems, particularly as such landscapes are increasingly subject to both natural and anthropogenic pressures.