An integrated assessment of landslide: Type, causes, pre-post scenario and risk impact of the Pettimudi incident in Idukki District, India

Abstract

Landslides are devastating and create an immense challenge for human life in mountainous terrain. The recent landslide occurred on August 06, 2020, at Pettimudi, Idukki District of Kerala, in the Western Ghats. The event was caused by prolonged rainfall. Consequently, there was a massive debris flow, the destruction of numerous settlements and vehicles, and the fatalities of around 70 people. In this scenario, this study focused on understanding (investigating) the nature, causes and impact of current landslides and their risk. A pre and post-assessment of the landslide was conducted. Available secondary datasets like the digital elevation model, local soil, slope, geology, rainfall, and landuse were utilized to comprehend the nature and stability of the landslide area. Ground Penetrating Radar (GPR) was carried out during the post-assessment in the field. The primary data was utilized to find out the buried human bodies and other materials and assess the depth of debris. Advanced technology like GPR helped in rescue missions to detect human bodies and buried houses in the suspected locations. The significant findings of this study expose the causes, i.e., triggered rainfall, slope failure, flash flood-induced landslides, and debris flow through the assessment of Hydro-Meteorological (Rainfall runoff); morpho-tectonic (Drainage Density, Length of Overland flow, Valley flower width to height etc.), topographic signature and debris flow spatial susceptibility. The quantification of loaded debris and sediment depositions are identified as 2–6 ft at various locations. The landslide risk assessment is based on the comprehensive susceptibility, hazard and vulnerability index. Also, this study reveals that the study area is highly susceptible to landslide and its risk. The result depicts that 33.5 % of the total geographic area has a very high to high-risk zone and 42.3 % of the area belongs to moderate risk zone. The integrated assessment of landslide is highly beneficial for administrative authorities and the scientific community in making the right decisions and taking immediate action.