Landslides:

Landslides occur when a mass of rock, earth, or debris slides down a slope. Landslides are a type of “mass wasting”, which refers to any down-slope movement of soil and rock that is directly affected by gravity. The term “landslide” encloses five modes of slope movement: falls, topples, slides, spreads, and flows. Additionally, there are subcategories based on the type of geological material (bedrock, debris, or earth). There are various types of landslides, including debris flows, mudslides, and rockfalls.

Causes: Most landslides are caused by multiple factors.

• The movement of slopes occurs due to forces acting downward (primarily gravity).
• The factors that may contribute to these effects include those that increase the effects of downhill forces and those that contribute to low or decreased strength.
• Rainfall, melting snow, stream erosion, changing groundwater levels, earthquakes, volcanic activity, human activities, or any combination of these factors may cause landslides to occur on slopes on the verge of moving.
• Other factors such as earthquake shaking can also cause underwater landslides. These landslides can cause tsunamis that cause damage to coastal areas. These landslides are called submarine landslides.

Effects:

• A landslide can cause death, infrastructure destruction, land damage and natural resources loss and can result in extensive damage.
• As a result of landslide material, rivers can be blocked, and floods can be exacerbated. Deep landslides caused by earthquakes or volcanoes can destroy thousands of square kilometers of land and kill thousands of people.
• Farmers’ livelihoods are at risk from landslides as they can hinder access to land for years, destroy seed and food stocks, and cause livestock and crops to be lost.

Landslides can happen anywhere in the world and are more common than any other geological occurrence. The Himalayas can claim to have experienced landslides of every kind—large and small, swift and slow, old and recent. The NRSC (National Remote Sensing Center) Atlas on selected corridors of Uttarakhand and Himachal Pradesh has been very useful in minimising the damage. As part of a parallel subject on landslide mitigation, Geographic Information System (GIS) and Remote Sensing applications are being employed by NRSC at NDMA through database gathering from all related departments and being stored through the good offices of GIS and other agencies, CSIR labs, DST, etc.