Landslides in India
Landslides in India
The term’ landslide’ includes all varieties of mass movements of hill slopes and can be defined as the downward and outward movement of slope forming materials composed of rocks, soils, artificial fills or combination of all these materials along surfaces of separation by falling, sliding and flowing, either slowly or quickly from one place to another.
Although the landslides are primarily associated with mountainous terrains, these can also occur in areas where an activity such as surface excavations for highways, buildings and open pit mines takes place.
The materials may move by falling, toppling, sliding, spreading, or flowing. Some landslides are rapid, occurring in seconds, whereas others may take hours, weeks, or even longer to develop.
Areas effected in India
Landslides are one of the natural hazards that affect at least 15 per cent of the land area of our country—an area which exceeds 0.49 million km2.
Landslides of different types are frequent in geodynamically active domains in the Himalayan and Arakan-Yoma belt of the North-Eastern parts of the country as well as in the relatively stable domains of the Meghalaya Plateau, Western Ghats and Nilgiri Hills.
In all, 22 states and parts of the Union Territory of Pudducherry and Andaman & Nicobar Islands are affected by this hazard. The phenomenon of landslides is pronounced during the monsoon period.
Causes of Landslides
Gravity: Gravity works more effectively on steeper slopes, but more gradual slopes may also be vulnerable.
Geological factors: Many slides occur in a geologic setting that places permeable sands and gravels above impermeable layers of silt and clay, or bedrock.
Heavy and prolonged rainfall: Water is commonly the primary factor triggering a landslide. Slides often occur following intense rainfall, when storm water runoff saturates soils on steep slopes or when infiltration causes a rapid rise in groundwater levels.
Earthquakes: Seismic activities have always been a main cause of landslides throughout the world. Any time plate tectonics move the soil that covers moves with it.
Waves: Wave action can erode the beach or the toe of a bluff, cutting into the slope, and setting the stage for future slides.
Inappropriate drainage system: Natural drainage lines on slopes are blocked by terracing/ contour bounding adopted to prevent soil erosion and to enhance percolation during dry season for cultivation, without adequate provision for surface drainage of excess storm water during high intensity rains increase the landslide vulnerability.
Cutting & deep excavations on slopes for buildings, roads, canals & mining: Developmental activities like construction of buildings, road cutting, embankments, cut and fill structures causes modification of natural slopes, blocking of surface drainage, loading of critical slopes and withdrawal to toe support promoting vulnerability of critical slopes.
Change in slope/land use pattern, deforestation, agricultural practices on steep slopes: Deforestation and cultivation of seasonal crops and increase in settlements. Improper land use practices such as heavy tilling, agricultural practices and settlement patterns have contributed to creep and withdrawal of toe support in many cases
Effects of landslides
- In hilly terrains of India, Himalayan mountains, western ghats and northeastern part, landslides have been a major natural disasters that strike life and property almost perennially.
- These landslides, year after year, bring about untold misery to human settlements apart from causing devastating damages to transportation and communication network.
- Landslides cause property damage, injury and death and adversely affect a variety of resources. For example, water supplies, fisheries, sewage disposal systems, forests, dams and roadways can be affected for years after a slide event.
- The negative economic effects of landslides include the cost to repair structures, loss of property value, disruption of transportation routes, medical costs in the event of injury, and indirect costs such as lost timber and lost fish stocks.
- Water availability, quantity and quality can be affected by landslides. Geotechnical studies and engineering projects to assess and stabilize potentially dangerous sites can be costly.
- Large, infrequent landslides contribute less to personal and property losses than do the smaller, more frequent slides and debris torrents in populated areas.
Drainage Corrections: The most important triggering mechanism for mass movements is the water infiltrating into the overburden during heavy rains and consequent increase in pore pressure within the overburden. Hence the natural way of preventing this situation is by reducing infiltration and allowing excess water to move down without hindrance.
As such, the first and foremost mitigation measure is drainage correction. This involves maintenance of natural drainage channels both micro and macro in vulnerable slopes.
Proper land use measures: Adopt effective land-use regulations and building codes based on scientific research.
Afforestation: The afforestation programme should be properly planned so the little slope modification is done in the process. Bounding of any sort using boulders etc. has to be avoided.
Awareness generation: Educate the public about signs that a landslide is imminent so that personal safety measures may be taken.
Financial Mechanisms: Support the establishment of landslide insurance\
Legal and Policy: legislation to direct a governmental or private program to reduce landslide losses should be strengthened