The landslides are simply defined as the mass movement of rock, debris or earth down and have to include a broad range of motions whereby falling, sliding and flowing under the influence of gravity dislodges earth material. They often take place in conjunction with earthquakes, floods and volcanoes. The Himalayan Mountain, the north-east hill ranges and the Western Ghats and the Nilgiris experience considerable landslide activities of varying intensities.
Causes of Landslides:
There are several factors which lead to the occurrence of landslides. Seismic activity, intensity of rainfall, steep slopes, rigidity of slopes, highly weathered rock layers, soil layers formed under gravity, poor drainage these all are natural factors that cause the landslides. Not only this there are many man-made factors also which contribute to the occurrence of landslides. These are land use pattern, non-engineered construction, mining and quarrying, non-engineered excavation and deforestation leading to soil erosion.
Generally landslides happen where they have already occurred in the past, or in identifiable hazard locations.
Following are the areas that are distinctly considered safe from landslides:
I. Areas that have not moved in the past
II. Relatively flat areas away from sudden changes in slope
III. Areas at the top of or along ridges but set back from the edge of slopes. However, the homes built at the toe of steep slopes are frequently vulnerable to slides and debris flows that originate on property controlled by others.
Adoption of slope stabilizing methods and professional site investigations by an engineering geologist and a technical Engineer has shown to reduce the landslide damage to over 95%. But in many situations preventing landslides may be impractical.