Structural and Climatic Control of Mass Movements Along the Karakoram Highway

Abstract

The Karakoram Highway (KKH) connects Pakistan and China by traversing through rapidly rising mountainous Karakoram area, which is the junction between the Indian and Eurasian plates including the Kohistan Island Arc. Being a plate boundary, the area is highly prone to active tectonics. The Main Mental Thrust, Main Karakorum Thrust, Main Continental Thrust and Panjal Thrust are the major fault systems operating in the region. The area is seismically active and various major earthquakes (Muzaffarabad Oct, 2005: M = 7.6, Afghanistan Oct, 2015: M = 7.5) have occurred. The geology of the area primarily consists of rocks including sedimentary, metamorphic and plutonic rocks. Granite and ultramafic rocks, slates and quartzites are the dominant lithologies of the area. Alterations of these rocks result in a large amount of incompetent and weak lithologies. The KKH passes through some of the world’s deepest gorges with high relief. The floor of these gorges is filled by glacial deposits (moraines). Since its construction in 1979, it has been damaged at various locations by a number of mass movements. In our study, data of mass movement events was acquired from Frontier Works Organisation. Then a spatial distribution map was prepared along KKH using ArcGIS. Furthermore, this mass movement distribution data was correlated with active faults, seismic information and rainfall data aiming to quantify the regression of mass movements and individual distance to active faults in the study area. Moreover, the impact of rainfalls on slope stabilities in the region is investigated. The active faults in this area have caused brittle deformation of crystalline rocks. This has resulted into poor to fair rockmass close to faults with densely populated joints having low shear strength. As a result, distances from active faults have inverse effects on mass movement events. Furthermore, rockmass quality close to the active faults is very poor having multiple joint sets. In addition, during heavy rainfall water seeps down into these joint which results in further decrease of shear strength and increase of pore water pressure, ultimately resulting in mass movements. Mass movements in Hassan Abdal-Gilgit Section showed dependence on rainfall intensity, whereas, mass movements in Gilgit-Khunjrab Pass section are function of temperature and rainfall intensity.