Relevance:

GS-1 Geography: geographical features and their location-changes in critical geographical features (including water-bodies and ice-caps) and in flora and fauna and the effects of such changes.

Introduction

• India, is vulnerable to different types of landslides which cause significant destruction in terms of loss of lives and property. As per GSI, about 0.42 million km 2 covering nearly 12.6% of land area of our country is prone to landslide hazards. Mountainous region of the North-Western Himalayas, the Sub-Himalayan terrain of the North-East, the Western and Eastern Ghats are prone to landslides covering 22 States and 2 Union Territories.

  

• During the monsoon, these areas witness frequent landslides. Some of the major recent incidents are:
  • Kerala (2018), Himachal Pradesh (2018), Uttarakhand (2018), Tamenglong-Manipur (2018), Kalikhola, Manipur (June, 2017); Laptap, Pampare-Arunachal Pradesh (July, 2017); Malpa, Uttarakhand (August, 2017); Kotropi, Himachal Pradesh (August, 2017); Malin, Pune (July, 2014); Mirik, West Bengal (June, 2015) etc. causing huge loss to life and property. Most of the landslides occur due to heavy rainfall.
• Majority of landslide prone areas are located in the earthquake prone seismic Zone-IV and V. Thus these areas are also prone to earthquake-triggered landslides e.g. Sikkim Earthquake (2011), Kashmir Earthquake (2005), Chamoli Earthquake (1999), Uttarkashi Earthquake (1991) etc.
• In recent years, the incidences of landslides have increased due to extreme weather events, environmental degradation due to human interference and other anthropogenic activities resulting in heavy losses of human lives, livestock and property.
• In-depth information regarding landslides is provided in this article.

What is a landslide?

• According to the United States Geological Survey (USGS), a landslide is defined as the movement of a mass of rock, debris, or earth down a slope. Landslides are a type of “mass wasting,” which denotes any down-slope movement of soil and rock under the direct influence of gravity.
• Landslide is a physical phenomenon when a part of rock, and/or debris/ soil fall due to the action of gravity.
• It is caused by a set of terrain-specific geofactors (e.g., slope, lithology, rock structure, land use/ cover, geomorphology etc.) and in general is triggered by heavy rainfall or earthquake tremors.

  

Landslides in the Indian Context:

• Landslides account for considerable loss of life and damage to communication routes, human settlements, agricultural fields and forest lands in India.
• Based on the general experience with landslides, a rough estimate of monetary loss is of the order of Rs. 100 crore to Rs. 150 crore per annum at the 2011 prices for the country as a whole (Disaster Management in India, MHA, Govt. of India, 2011).
• In India, excluding the permafrost regions in the north, about 0.42 Million km2 areas of the landmass (12.6%) is landslide-prone which are spread over 19 odd numbers of States/Union
  Territories and are spreading over more than 65,000 villages in hilly/ mountainous areas (Fig. 1).

  

• Major parts of the northern states of India namely Jammu & Kashmir, Himachal Pradesh, Uttarakhand and north-eastern states of the country viz. Sikkim, Arunachal Pradesh, Mizoram, Nagaland, Manipur, Meghalaya, Assam and Tripura are vulnerable to landslides due to fragile geology, active tectonics, high relief, critical slopes, intense rainfall as well as anthropogenic activities at various locations of these states.
• Western parts of Maharashtra, Karnataka, Goa and Kerala covering parts of Western Ghats and eastern parts of Andhra Pradesh and Tamil Nadu in Eastern Ghats are also vulnerable to landslides.
• Hence, there is an urgent need for holistic approach to landslide mitigation and management on the basis of region and area specific landslide hazard information with structural and non structural mitigation as the core theme.

What Causes a Landslide in India?

• Deforestation
  • Landslides due to human intervention is one of the causes of landslides in India. One such is deforestation. For example, the Himalayan region has become more vulnerable to landslides due to the indiscriminate cutting of trees.
  • Removal of trees reduces the binding properties of soil and rocks. This enables the water to seep into the sub-surface, making the topsoil vulnerable. Even GSI confirmed that increased deforestation is one of the reasons for landslides in Western Maharashtra and the Konkan region.
• Heavy Rainfall and Earthquakes
  • Above 40% of the Kumaon Himalayan region are vulnerable to landslides due to earthquakes. Additionally, heavy rainfall often causes landslides. For example, heavy rain caused landslides in Talai village of Maharashtra in 2021.
• Mining
  • Human activities like mining or quarrying remove the vegetation cover and soil gravel. This lowers the groundwater retention capacity. Also, it increases the risk of flooding. Therefore, landslides occur due to loose debris or excess floods during an earthquake and heavy rainfall, respectively.
• Shifting Cultivation
  • Shifting cultivation is common in hilly regions and Northeast areas. Every year, residents burn the forests for cultivation purposes. However, this deteriorates the quality of topsoil, causing erosion during heavy rainfall. This makes such regions more vulnerable to landslides.
• Urbanisation
  • Increasing population pressure in few regions of India is alarming. For example, Dharamshala is prone to landslides. It is one of the fastest developing cities in the Himalayan region. Here, intensive urbanisation activities such as establishing commercial housing projects and road construction reduce the vegetation cover. This leads to an increasing frequency of landslides in this region.

What Are the Different Types of Landslides?

Landslides in India are divided into four categories –

1. Topples: This occurs due to fracture in rocks. It causes tilting for gravitational pull without collapsing.
2. Falls: This involves the collapse of rocks or debris from a cliff or slope. It results in the collection of debris at the base of a hill.
3. Spread: It occurs in gentle slopes where soft debris or other materials are widely available
4. Slides: It occurs when debris, rocks or soil slide through a slope.

   

Impacts of Landslides in India:

• Mud, debris and rocks slide from the slope during landslides. This restricts human movement and creates a traffic barrier on highway and railway lines. For example, the recent landslide blocked the national highway-5 at Badhal district.
• Loss of human lives is one of the severe effects. On 11th August 2021, a landslide at Kinnaur district killed approximately 28 people.
• It damages houses, roads and buildings. This further creates a financial burden for rebuilding infrastructure to rehabilitate the masses.
• The debris sliding down from slopes block the river channel fully or partially. This makes it difficult
• Landslides also increase the risk of floods. It is because the debris increases the river sediment. As a result, irregular course rivers become frequent, resulting in floods.

Why landslides are so frequent in the monsoon:

Context:

• A landslide in Manipur late-last month (June 2022) has so far claimed 47 lives, while in another instance in Karnataka three people died. Experts believe most landslips occur during the monsoon because of geologically weak soil, deforestation and careless infrastructure projects.
• Every year as the monsoon covers the country, landslides at several places become almost regular. While some places like Assam face nature's wrath more severely, others are saved by a whisker from major damage to life and property.

Reasons for frequent landslides in the monsoon:

• Monsson's Nature – concentrated rainfall in short timeframe:
  • One of the foremost reasons is concentrated rainfall due to climate change, experts say. In Assam’s case this year (2022), the state received 65 per cent excess rain from 1 March to 20 May.
  • The neighbouring state of Meghalaya recorded an even greater excess of 137 per cent.
  • We can attribute the changes in rainfall intensity, arrival and departure times to climate change.
  • It is due to such heavy rains and flooding that landslides and mudslides occur. Several incidents of landslides were reported from south Assam’s Dima Hasao and Cachar districts.
• Unplanned Urbanization and Deforestation:
  • When heavy rains meet “undesirable, unpragmatic, unplanned structural intervention on the fragile landscape of hills”, it can cause landslide.
  • Deforestation for public and private infrastructure projects leaves the soil weak and vulnerable to spate of water coming from a higher level. Whether it is an extension of a railway line, or construction of a bridge or roads, the fragile ecosystem of mountainous areas is disturbed.
• Geological Factors and Anthropogenic Modifications:
  • Similarly in Manipur, experts believe the geological weakness of the soil, lack of vegetation, prolonged human pressure and incessant rain are the major factors for the landslide.
  • Apart from weakness of the soil due to prolonged exposure, rainfall and anthropogenic (human) pressure factors, the way the people used the land is also responsible for this tragedy.
  • Almost all landslides in the hilly states of North East India have been caused due to weak lithology, intense fracturing of rocks, steep slopes, thick mantle of waste and excessive rainfall in short duration.

NDMA guidelines on Landslides:

• The main objectives of the NDMA guidelines are to institutionalise the landslide hazard mitigation efforts, to make society aware of the various aspects of landslide hazard in the country and to prepare the society to take suitable action to reduce both risks and costs associated with this hazard.
• The recommendations include:
  • Continuously updating the inventory of landslide incidences affecting the country.
  • Landslide hazard zonation mapping in macro and meso scales after consultation with the Border Roads Organization, state governments and local communities.
  • Pilot projects to be taken up in different regions of the country to carry out detailed studies and monitoring of select landslides to assess their stability status and estimate risk.
  • Setting pace setter examples for stabilization of slides and also setting up early warning systems depending on the risk evaluation and cost-benefit ratio.
  • Completion of site specific studies of major landslides and plan treatment measures, and encourage state governments to continue these measures.
  • Institutional mechanisms have to be set up for generating awareness and preparedness about landslide hazard among various stakeholders.
  • Training and capacity building measures to be taken up for professionals and organizations working in the field of landslide management.
  • New codes and guidelines to be developed on landslide studies and existing ones have to be revised.
  • An autonomous national centre for landslide research, studies and management has to be established.
• Implementation of above action points would increase efficacy in management of landslides and avalanches in the country. The above measures should be duly backed by requisite operational, legal, institutional, and financial support.