Causes and Mechanism of Amboori Landslide of 9^th November, 2001, Thiruvananthapuram District, Kerala

Abstract

Amboori landslide, one of the worst natural disasters of Kerala, had taken a toll of 38, besides exposing the vulnerability of the hilly state to such mishaps. The failed slope located in Kurisumalai hill, was fairly steep at 32° and was covered by overburden consisting of colluvial deposits, boulders and weathered rock. Its contact with the underlying migmatised garnet-Biotite gneiss and garnetiferous quartzofeldspathic gneiss was marked by a thin layer of lithomargic clay which represented a weak plane. While cultivation on the slope blocked the drainage course, road cutting undermined the toe support. Rainfall during the monsoon was above average. It culminated in a heavy downpour of 82.4 mm in a short span of less than 2 hours on a delicate slope and triggered a planar failure between the bed rock and overburden. Corroborative evidences are lacking to the media claims that linked the slide to earthquake, lightning, thunder etc.

Several settlements in the area are facing imminent danger from unstable slopes and precariously perched boulders. Identification of such spots by carrying out detailed survey and taking preventive measures are considered a priority requisite. Future development based on Landslide Hazard Zoning and enforcing of housing codes are recommended for the Amboori area.