Search for: All records

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. 

This Review synthesizes progress and outlines a new framework for understanding how land surface hazards interact and propagate as sediment cascades across Earth’s surface, influenced by interactions among the atmosphere, biosphere, hydrosphere, and solid Earth. Recent research highlights a gap in understanding these interactions on human timescales, given rapid climatic change and urban expansion into hazard-prone zones. We review how surface processes such as coseismic landslides and post-fire debris flows form a complex sequence of events that exacerbate hazard susceptibility. Moreover, innovations in modeling, remote sensing, and critical zone science can offer new opportunities for quantifying cascading hazards. Looking forward, societal resilience can increase by transforming our understanding of cascading hazards through advances in integrating data into comprehensive models that link across Earth systems. 

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. 

Abstract On August 14, 2021, aMw7.2 earthquake struck the Tiburon Peninsula of western Haiti triggering thousands of landslides. Three days after the earthquake on August 17, 2021, Tropical Storm Grace crossed shallow waters offshore of southern Haiti triggering more landslides worsening the situation. In the aftermath of these events, several organizations with disaster response capabilities or programs activated to provide information on the location of landslides to first responders on the ground. Utilizing remote sensing to support rapid response, one organization manually mapped initiation point of landslides and three automatically detected landslides. The 2021 Haiti event also provided a unique opportunity to test different automated landslide detection methods that utilized both SAR and optical data in a rapid response scenario where rapid situational awareness was critical. As the methods used are highly replicable, the main goal of this study is to summarize the landslide rapid response products released by the organizations, detection methods, quantify accuracy and provide guidelines on how some of the shortcomings encountered in this effort might be addressed in the future. To support this validation, a manually mapped polygon-based landslide inventory covering the entire affected area was created and is also released through this effort. 

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. 

Abstract Shallow bedrock strength controls both landslide hazard and the rate and form of erosion, yet regional patterns in near‐surface mechanical properties are rarely known quantitatively due to the challenge in collectingin situmeasurements. Here we present seismic and geomechanical characterizations of the shallow subsurface across the central Himalayan Range in Nepal. By pairing widely distributed 1D shear wave velocity surveys and engineering outcrop descriptions per the Geological Strength Index classification system, we evaluate landscape‐scale patterns in near‐surface mechanical characteristics and their relation to environmental factors known to affect rock strength. We find that shallow bedrock strength is more dependent on the degree of chemical and physical weathering, rather than the mineral and textural differences between the metamorphic lithologies found in the central Himalaya. Furthermore, weathering varies systematically with topography. Bedrock ridge top sites are highly weathered and have S‐wave seismic velocities and shear strength characteristics that are more typical of soils, whereas sites near valley bottoms tend to be less weathered and characterized by high S‐wave velocities and shear strength estimates typical of rock. Weathering on hillslopes is significantly more variable, resulting in S‐wave velocities that range between the ridge and channel endmembers. We speculate that variability in the hillslope environment may be partly explained by the episodic nature of mass wasting, which clears away weathered material where landslide scars are recent. These results underscore the mechanical heterogeneity in the shallow subsurface and highlight the need to account for variable bedrock weathering when estimating strength parameters for regional landslide hazard analysis.