Valley blocking landslides in the Nepal Himalaya: database and analysis

Abstract:

Hydroclimatic, tectonic and anthropogenic factors interact with the fragile geology in the Himalaya causing frequent mass movements. These landmass movements into the narrow V-shaped valleys result in the formation of landslide dams. Despite the multiple cascading consequences like outburst floods, barrier lakes, aggradation, and channel instability, a comprehensive database of the past and present landslide dams in the region is not available. Furthermore, their stability criteria are still not fully understood. Lack of these has made it complicated to quantify the associated risks in this region.

Here, we have prepared a database of 150 landslide dams in the Nepal Himalaya, documenting all recorded events between 2009 to 2019 and some additional historical events. The database encompasses geotechnical (e.g. bulk density, soil texture, soil water content, etc.) and geometric (e.g. height, length, width) features of landslide dams. Morphological features (e.g. longitudinal slope, catchment area) of the river valley and geometric features (e.g. impoundment area, volume) of the barrier lakes formed due to landslide dams are calculated. The database is compiled from media reports, articles, global datasets, researches, and satellite images from Landsat, Sentinel-1, Google Earth, and Bing Maps. Dams are classified based on trigger mechanisms, lithology, geology, and landslide movement. The formation and stability of dams are studied based on geomorphic indices defined in previous researches. Furthermore, relationships of the landslide area, elevation, and side slopes of the valley are derived.

This inventory is comprehensive database of landslide dams in the Nepal Himalaya covering 10-years multi-temporal documentation and characterization of morphological parameters for stability analysis. The geomorphological parametrization will provide a basis for future research on the longevity analysis, susceptibility, early warning and more advanced studies on landslide dams in this region. In addition, it contributes to the global database allowing the comparative study of landslide dams throughout the world.