Map India 2000 - Poster :Landslide Hazard Zonation Mapping Using GIS Technique - A Case Study from Nilgiri District Tamil Nadu

Landslide is a common natural hazard that usually occurs in mountainous areas. They are the most devastating and frequently occurring environmental hazards landslide is a common term generally used for all forms of rapid mass environment.

In general landslide activity is related to the following factors. Slope, geology, structure, lineament, geomorphology, climate, rainfall and landuse. The principal factors that initiate landslides are heavy and prolonged rainfall, cutting and deep excavations on slopes for buildings, earthquake shocks and tremors widespread deforestation and population pressure.

In this paper an attempt has been made to prepare a land slide hazard zonation mass of Nilgiri districts covering far of Conoor and Kotagiri, Ooty taluks using GIS systems. A study has been made on the extent to which some important factors like slope land use lineament density rainfall and geomorphology exert this control over triggering of land slopes various thematic maps were prepared and these were ranked bases on frequently of occurrence of past landslides for the case of certain factor such as slope and lineament density the ranking does not appear to follow conventional geology, relatively low slope percentage were given like ranking, origin high lineament density regions were given low ranking become of frequency of past landslides. Therefore a second landslide zonation map was prepared by modifying the rank. High slopes were given a high rank. The same procedure was also followed into the case of lineament density map and drainage density map.

GIS is a very fast and accurate methods by which large volume of the integrating of various landslide triggering factors has resulted in a map which in a certain extent a is ale to predict the susceptibility of an area of landslides and a regional scale. The software IDRISI was used for the work.

Description Of The Study Area
The study area is located in Nilgiri district a mountainous terrain in the NW part of Tamil Nadu state the study area covers part of Ooty Coonoor and Kotagiri taluks. The area is between 11 15' to 11 30' N latitude and 76 45' to 76 55' East. Longitude. The study area covers about 500 sq. kilometers. Physiographically the Nilgiri hills rise abruptly form the plains to an average elevation of 1370 m above MSL. Many of the hill peaks have steep rocky escarpment with or without soil cover around which radial drainage pattern are seen.

The Nilgiri ranges comprise archaen metamorphic rocks which include quartzite, biotite gneiss, magnetite quartzite, hornblende granulite, pegmatite, dolerite and quartz veins. Charnockite forms the bulk of the rock units in the study area.

The Nilgiri hills is a plateau sloping steeply into the Mysore plateau towards north and merging gradually with the western ghats in the NW west and SW. The plateau is divided into a highly dissected plateau and a less dissected undulating plateau.

Nilgiri plateau has been formed by three systems of faults along the peripherals namely a E-NE fault, a North-West fault and a third fault along the northern boundary of the platea. The regional foliation is towards E-NE. Most of the lineament may represent fractures along which there may or may not have been movement. Many of the lineaments represent faults.

The major area in the Nilgiri is either under vegetation or is used for plantation. The reserves forest area have over the years has reduced and more and more thick woods have turned into vegetated scrub lands.