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In 2021 a catastrophic flood occurred in the Melamchi Valley of Nepal, causing widely distributed erosion in Himalayan headwaters and mobilizing a large sediment volume. As the flood progressed downstream it induced an erosional cascade, producing 100m deep incisions into high- elevation valley fills, generating new landslides, and burying the lower reaches in alluvium. This event demonstrated the destructive impact of cascading processes and their potential for reshaping the landscape. 

The data were collected in the Helambu region of central Nepal as part of the "Nepal-FRES" (Frontier Research in Earth Sciences) project to document the impacts of the 2021 Melamchi Flood, aiming to understand its cascading nature, the legacy of the 2015 Gorkha earthquake, and fluvial adjustment to such an extreme sediment transporting event. Polygon KML files of landslides, active river channels, and river terraces were mapped using 50 cm-resolution pre- and post-event Pléiades stereo satellite imagery. This data package comprises:  Melamchi Khola Catchment (study area)  Landslides before the 2015 Gorkha earthquake, between 2015 and 2020, between Nov 2020 and Oct 2021 (Melamchi Flood), and between Oct 2021 and Dec 2023  Obscured areas in which landslide mapping is incomplete due to the existence of clouds and shadow  River channel of Melamchi Khola in Nov 2020 and Oct 2021 (w/ the thalweg line in Oct 2021)  River terraces in Oct 2021  Forested areas in Nov 2020 and Dec 2023 

Abstract Wildfire alters the hydrologic cycle, with important implications for water supply and hazards including flooding and debris flows. In this study we use a combination of electrical resistivity and stable water isotope analyses to investigate the hydrologic response during storms in three catchments: one unburned and two burned during the 2020 Bobcat Fire in the San Gabriel Mountains, California, USA. Electrical resistivity imaging shows that in the burned catchments, rainfall infiltrated into the weathered bedrock and persisted. Stormflow isotope data indicate that the amount of mixing of surface and subsurface water during storms was similar in all catchments, despite higher streamflow post-fire. Therefore, both surface runoff and infiltration likely increased in tandem. These results suggest that the hydrologic response to storms in post-fire environments is dynamic and involves more surface-subsurface exchange than previously conceptualized, which has important implications for vegetation regrowth and post-fire landslide hazards for years following wildfire. 

This multi-disciplinary project is a collaboration of USA, Nepal, and U.K. scientists to investigate the multi-scale relationships between tectonic uplift, topographic evolution, chemical weathering, and seismicity. The Himalayan orogen in central Nepal is the representative study site. The seismic experiment is a set of high resolution dense arrays to image the near surface to hundreds of meters depth. The experiment used 309 three-component 5-Hz nodes at nominal 100 m spacing, deployed and recorded for one month. 21 of these nodes were arranged in a local 2D array. Circle array collection was also carried out targeting shallow fracture anisotropy.