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Current Affairs

Triggering of landslides

Date: 19 August 2020 Tags: Climate Change

Issue

The toll in the landslide in Kerala’s Idukki district rose to 58 even as 12 others remained buried under debris over two weeks after the incident at a settlement of tea estate workers.

 

Background

A landslide also called a landslip, is a slow or rapid movement of a large mass of earth and rocks down a hill or a mountainside. 

 

Details

  • The location where the landslide was triggered, according to the Kerala Geology Department, has a 40° slope, and any slope above 20° is vulnerable to slipping during heavy rain.

  • The soil has a high content of sand, which absorbs more water, takes a loose form, and is at risk of slipping down.

 

 Mass movement

  • Mass wasting, also known as slope movement or mass movement, is the geomorphic process by which soil, sand, regolith, and rock move downslope typically as a solid, continuous or discontinuous mass, largely under the force of gravity, frequently with characteristics of a flow as in debris flows and mudflows.

  • Types of mass wasting include creep, slides, flows, topples, and falls, each with its own characteristic features, and taking place over timescales from seconds to hundreds of years. Mass wasting occurs on both terrestrial and submarine slopes.

  • When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs.

  • The slope material's strength and cohesion and the amount of internal friction within the material help maintain the slope's stability and are known collectively as the slope's shear strength. 

  • Mass wasting may occur at a very slow rate, particularly in areas that are very dry or those areas that receive sufficient rainfall such that vegetation has stabilized the surface. It may also occur at very high speed, such as in rockslides or landslides.

 

Reason for landslides

  • Earthquakes

  • Increased overburden from structures

  • Increased soil moisture

  • Reduction of roots holding the soil to bedrock

  • Undercutting of the slope by excavation or erosion

  • Weathering by frost heave or chemical dissolution

 

Mitigation

  • Afforestation

  • Re-Afforestation

  • Terracing steps on slopes or, more generally, re-modeling its shape

  • Slope stabilization