LANDSLIDES

31.05.2024

LANDSLIDES

Why in the news?

Cyclone rain-triggered landslides in the Northeast spotlights need for building resilience to multi-hazard disasters.

Key Points

• About 13% of India’s area, spread over 15 states and four Union Territories, is prone to landslides.
• Cyclone-triggered landslides have hit Northeastern states on earlier occasions as well. Cyclone Aila had caused landslide events in this region in May 2009.
• The latest episode spotlights the need for building resilience to multi-hazard disasters. One event can trigger another, and can lead to multiple disasters simultaneously.
• Over the last few years, India has witnessed events in which heavy rainfall has resulted in a breach of glacial lakes, causing flash floods that have resulted in landslides and flooding.
• Although India has done well to prepare and safeguard itself against certain natural events such as cyclones, landslides remain a weak point.

What are Landslides?

• It is defined as the movement of a mass of rock, debris, or earth down a slope.
• These are a type of “mass wasting,” which denotes any down-slope movement of soil and rock under the direct influence of gravity.
• The term “landslide” encompasses five modes of slope movement: falls, topples, slides, spreads, and flows.
• These are further subdivided by the type of geologic material (bedrock, debris, or earth). Debris flows (commonly referred to as mudflows or mudslides) and rock falls are examples of common landslide types.
• Almost every landslide has multiple causes. Slope movement occurs when forces acting down-slope (mainly due to gravity) exceed the strength of the earth materials that compose the slope. Causes include factors that increase the effects of down-slope forces and factors that contribute to low or reduced strength.
• Landslides can be initiated in slopes already on the verge of movement by rainfall, snowmelt, changes in water level, stream erosion, changes in groundwater, earthquakes, volcanic activity, disturbance by human activities, or any combination of these factors.
•  Earthquake shaking and other factors can also induce landslides underwater. These landslides are called submarine landslides. Submarine landslides sometimes cause tsunamis that damage coastal areas.

Landslide vulnerability: India’s Case

• About 0.42 million square km of India’s landmass, or about 13% of its area, spread over 15 states and four Union Territories, is prone to landslides, according to the Geological Survey of India (GSI).
• This covers almost all the hilly regions in the country. About 0.18 million square km, or 42% of this vulnerable area is in the Northeastern region, where the terrain is mostly hilly.This area is also prone to earthquakes, which too, are a major trigger for landslides.
• Government data show that between 2015 and 2022, the eight states in this region, including Sikkim, recorded 378 major landslide events which resulted in loss of life or damage to property. In the country as a whole, Kerala saw the largest number of landslides  2,239 most of which occurred after the disastrous 2018 floods in the state.
• The National Disaster Management Authority (NDMA) has been working with GSI and other agencies to mitigate and manage the risks from landslides.
• A National Landslide Risk Management Strategy was finalized in 2019, which talked about vulnerability mapping, identifying the most vulnerable locations, development of an early warning system, and preparation of mountain zone regulations. But most of the work still remains to be done.

Early warning for landslides:

• Some early warning systems have been developed and deployed on a trial basis at a few locations. These warning systems are linked to rainfall forecasts from IMD. The rainfall prediction is combined with soil and terrain information to calculate whether it is likely to result in displacement of land.
• Most landslides in the hilly regions are caused by heavy rainfall. Earthquakes can trigger landslides too. Since earthquakes themselves cannot be predicted, we cannot have a landslide early warning based on earthquakes. But rainfall-based early warning systems for landslides seem to work well.
• Rainfall forecasts, on the other hand, come quite early. Reliable location-specific predictions are available at least a day in advance. Scientists create a rainfall threshold for land movement and soil displacement at each landslide-prone location. If the rainfall forecast is higher than the threshold, an early warning for landslides is issued.

Human pressure for landslides:

• The risk from landslides has been exacerbated by the failure to remain mindful of the terrain’s ability to withstand the load. Many hilly areas do not have building regulations. Often, regulations are not implemented effectively.
• New constructions, infrastructure development, and even agricultural practices can increase the risk of landslides.
• Every mountainous area has a carrying capacity. Sustainability has to be factored in, so that the load does not exceed the carrying capacity.

                                                                      Source: Indian Express

Question :- Consider the following statements with reference to the Landslide:

1.It is defined as the movement of a mass of rock, debris, or earth down a slope.

2. In India 13% of its area, spread over 15 states and four Union Territories, is prone to landslides.

3.Assam saw the largest number of landslides 2,239 most of which occurred after the disastrous 2018 floods in the state.

How many of the above statements is/are correct?

A)  only one

B)  only two

C)  All three

D) None

Answer B