What is a Landslide?

Neelima saw a slope full of boulders and debris from the window of Himsutra AC bus run by Himachal Pradesh Road Transport Corporation (HRTC) along Chandigarh-Mandi route.  She asked her friend who was sitting next to her what was that. The friend, replied that it was a landslide. Neelima asked what landslide was and why it happened. The friend replied irritatingly why tsunami came. I am sure that the answer did not satisfy Neelima’s curiosity.

A first time trekker also posed the same question to her weekend trek team. But she also did not get a clear answer like Neelima. So I thought of defining the word landslide because visitors to the mountains should understand it because landslides could be deadly. For example, in April 2017, a gigantic landslide took hundreds of lives in Colombia, a South American country. Landslides are quite common in the Himalayas especially during rainy season.

First Look at Landslide

Debris, earth, rocks, and / or soil running down the slopes recklessly are dubbed as a landslide. Why are they able to run recklessly? When a slope’s resistance to deformation is lower than the gravitational and other forces attacking the slope along its planes and trying to deform it, even a solid slope breaks and its constituents roll down.

How do the forces develop, break apart the slope, and push down the material?

A number of factors can reduce the resistance of the slope and contribute to the development of the forces that weaken the slope. These factors attack the cohesive (binding ability) and frictional (resistance to movement) strength of the constituents. For example, the following activities can destroy the slope(s) and trigger landslides:

  • Earthquakes
  • Ongoing erosion of the slope by natural forces, including rain, water, and wind
  • Overloading due to excessive waterlogging
  • Unmindful cutting of the slope to lay down roads

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