Initial Screening of Regional Landslide Hazards in the Hunza River Watershed, Gilgit Baltistan, Pakistan

Abstract

Landslides pose a significant hazard to life and property in areas vulnerable to mass movements. Qualitative landslide susceptibility maps offer a preliminary means of screening locations likely susceptible to slope instability. In this study, attempts have been made to identify various landslide hazard zones within the Hunza River watershed (varying from very high to low hazards) by considering geomorphic and geological conditions and employing common trigger factors into GIS data layers. Three different approaches were selected: the weighted overlay, fuzzy logic, and analytical hierarchy processes. These approaches allowed the compilation of preliminary landslide hazard maps for the 8,000 km2 Hunza River watershed area. This study utilizes the information layers related to geomorphological and geological risk factors such as elevation, slope angle, slope aspect, curvature, the normalized difference vegetation index (NDVI), lithology, distance to major faults, and drainage. Assumed triggering factors included seismic excitation and precipitation, expressed in raster files. These thematic map overlays were employed as input layers to compile landslide hazard maps. Each of the methods used to construct hazard maps produced satisfactory results when compared with existing landslide inventories, even those accompanied by field validation surveys. For the very high hazard zones in Chalt and the upper Hunza Valley, the trigger variable appears to be the Main Karakorum Thrust (MKT), where shattered lithologic units are most susceptible to landslides. These comparisons suggest that majority of documented rockslides fall in high and very hazard zones in the Hunza River watershed. Our findings also suggest that the employment of off-the-shelf GIS software may become a cost-effective means of assembling similar hazard maps on a regional scale elsewhere.