Author(s)

S. Sreekumar & A. Aslam

Abstract

The Western Ghats, the main peninsular hill range in India, is prone to several types of slope failures, of which debris flows are most common. Kerala has a total area of 38863 km2 and 47% of the state lies on the western slopes of the Western Ghats. The average annual rainfall in the highranges is 500 cm. The state has a population density of 819 per km2. The volumes of hectic anthropogenic activities are bringing the slopes to the geotechnical threshold of failure. The field investigation carried out indicates that the natural instabilities are accentuated by anthropogenic factors, such as deforestation, contour terracing, obstruction of the natural drainage, artificial loading of water on the steep slopes and cultivation of shallow rooted crops. A strong relationship between slope failure and rainfall could be established in all paleoslide events. The rainfall induced pore pressure acted as the trigger force for the onset of debris flow, landslide and slump along the slopes, which were already at the threshold of failure. It is concluded that it is not the rainfall on the day of occurrence of the incidence that counts, but rainfall received a few days before the event is more decisive in causing landslides. The failures are observed in hills with gradients >20°, both in highland and midland regions. This paper presents the cause and mechanism of ten major landslide events in the state. Keywords: landslide, Western Ghats, Kerala, land use, debris flow, slump, rainfall, pore pressure. 1 Introduction Slope failures are among the major geohazards that effect large parts of India, especially in the Himalayas, which forms the most prominent mountain range

Keywords

landslide, Western Ghats, Kerala, land use, debris flow, slump, rainfall, pore pressure