Geomorphological mapping in the Khumbu region using UAV and its application in engineering geology, Nepal

Abstract:

The global temperature rise has largely impacted the Himalayan glaciers (Immerzeel et al., 2010; Xu et al., 2009). In the Khumbu region this effect has been manifested through increasing number of supraglacial lakes above the terminal moraines (Bajracharya et al., 2018). This accelerated melting depletes the water sources as well as poses immediate natural hazards, mostly glacial lake outburst flood (GLOF). In an effort to understand these hazards, we applied the structure-from-motion (SfM) technique to construct a geomorphological map of the Khumbu Glacier moraine deposits around the Lobuche area. Geotechnical properties of the moraine deposits were quantified for slope stability analysis. The geomorphological map of this region reveals several rotational slides along the ice contact slope of lateral moraine, with recent fluvial breaches and numerous supraglacial lakes. Particle size within these moraines varies greatly. The hydrometer analysis for the fine dominated sediments relatively suggests higher fraction of silt particles and trace amount of clay. The fines have very low plasticity index with low liquid and plastic limit. The internal friction angle (f) ranges from 34.22º to 37.14º with zero cohesion. These values were input in Slope/W (GeoStudio v8.15.6.13446) to estimate slope stability analysis, the result of which have shown that most of the slopes are unstable. This study concludes that coupling morphological mapping and geotechnical characterization can help us identify processes like glacier shrinking, debris movement and meltwater ponding, which serves as a tool in locating places of future hazards to improve the safety of disaster resilient in a comprehensible way.

Key words: SfM, geomorphological mapping, geotechnical characterization, slope modelling, natural hazards.