Landslide: Types, Causes, Impact & Remedial steps

Introduction to Natural Hazards

• A hazard is a dangerous condition or threat, natural or man-made that can cause injury, loss of life, or damage to property, livelihood, and environment.
• Natural Hazards may be grouped under the following 2 major categories
  1. Geological Hazards – Earthquakes, Volcanoes, Tsunami, Landslides, and Avalanches.
  2. Weather associated Hazards – Cyclones, Thunderstorms, Droughts, Floods and epidemics.
• It has been estimated that the world endures on an average about lakhs of thunderstorms, thousands of floods, hundreds of landslides and earthquakes, and scores of the cyclone and volcanic eruptions every year.
• Natural Disaster versus Natural Hazard:
  • A natural hazard is a threat of a naturally occurring event that will have a negative effect on humans. This negative effect is what we call a natural disaster.
    • In other words, when the hazardous threat actually happens and harms humans, we call the event a natural disaster.

Landslides

• Landslide is a rapid movement of rock, soil, and vegetation down the slope under the influence of gravity. It may be induced by natural agencies, e.g., heavy rain, earthquake, or it may be caused by human over- interference with the slope – stability.
• Man breaks rocks for constructing roads, railways, buildings, tunnels, etc. In such cases rocks become loose and landslide occurs.
• Earth flow, mass movement, mudflow, rotational slip, and avalanches are all examples of landslides.
• Landslides are rarely on a scale comparable to seismic or volcanic events. The intensity and magnitude of the landslide, however, depends on the geological structure, angle of dip of the slope, nature of sedimentary rocks, and the human interaction with the slope.

Landslide Dam

• When landslides occur on the slopes of a river valley, the sliding mass may reach the bottom of the valley and cause partial or complete blockage of the river channel. This accumulated mass of landslide debris resulting in the blockage of a river is commonly termed as a Landslide dam.

Types of landslides

1. Falls: It happens due to the abrupt movements of masses of geologic materials, such as rocks and boulders that become detached from steep slopes or cliffs.
2. Topples: It happens due to the forward rotation of a unit or units about some pivotal point, below or low in the unit, under the actions of gravity and forces exerted by adjacent units or by fluids in cracks
3. Slides: In this types, rocks, debris or soil slide through slope forming material.
4. Spread: It usually occur on very gentle slopes or flat terrain.

Causes of Landslides

• The major causes of landslides are:
• Rainfall and Snowfall-
  • The occurrence of heavy or continuous rainfall may lead to heavy landslides in the areas of steep slopes where National Highways and roads have been constructed.
  • The Nashri area between BatoteRamban- Ramsu, and Banihal (Jammu and Kashmir) is frequently subjected to landslides. The landslides in this region are particularly severe during the rainy and winter seasons when the vehicular traffic is disturbed for several days.
• Earthquakes and Volcanic Eruptions-
  • Earthquakes are the most important cause of landslides in the folded mountainous areas. In India, Landslides are more frequent in the folded mountains of the Tertiary Period, like the Himalayas.
  • In the Kashmir valley, the earthquake of 1905 resulted into landslides in the lesser and the Greater Himalayas in which several thousand people lost their lives.
  • Volcanic eruptions also trigger landslides in the mountainous regions.
• Mining, Quarrying and Road cutting-
  • The continuous extraction of coal, minerals, and stones from the mines and quarries and the development of roads by cutting the steep slopes in the folded mountains create conducive conditions for the occurrence of landslides.
  • Such landslides may be observed throughout the Himalayas and in the Eastern and Western Ghats.
• Loading by construction of houses-
  • The unplanned growth of towns and cities in the hilly areas without testing soil and rocks in also an important cause of landslides.
  • The eastern slope of Nanital (Uttarakhand) is sinking because of the heavy load of hotels and residential structures.
• Deforestation-
  • Deforestation and other human activities also induce landslides. Most of the landslides are small involving some blocks up to a few meters across. But some are large enough to cause a catastrophe. They may bury roads, buildings, and other structures.
  • The adverse effect of landslides can be reduced by checking deforestation on mountain slopes, following building codes for such areas, and by avoiding the construction of buildings on steep slopes.

Impact of Landslides

Vulnerability Profile of India

• In India, this hazard affects at least 15% of the land area of the country ( approx 0.49 million square Km.)
• It is very frequent in geodynamical active domains in the Himalayan and Arakan- Yoma belt of the Northeastern parts of the country as well as in the relatively stable domains of the Meghalaya Plateau, Western Ghats, and Nilgiri Hills.
• The Nilgiri Hills located at the convergence of Eastern and the Western Ghats bear the innumerable scars of the landslides due to their location in a zone of high intensity and protracted rainfall where the overburden is sensitive to over-saturation.

Landslides Mitigation Strategy

• Hazard zones have to be identified and specific slides to be stabilized and managed in addition to monitoring and early warning systems to be placed at selected sites.
• Hazard mapping should be done to locate areas commonly prone to landslides. It is always advisable to adopt area-specific measures to deal with landslides.
• Restriction on the construction and other developmental activities such as roads and dams, limiting agriculture to valleys and areas with a moderate slope, and control on the development of large settlements in high vulnerability zones, should be enforced.
• NDMA Guidelines for Landslides –
  • Landslide Hazard, vulnerability and Risk Assessment
  • Multi – Hazard Conceptualisation
  • Landslide Remediation practice
  • Research and Development, monitoring, and early warning
  • Knowledge network and management
  • Capacity building and Training
  • Public awareness and Education
  • Emergency preparedness and response
  • Regulation and Enforcement

What Measures should be taken?  

• Resilience Building: To address these challenges, it’s important to develop resilience against geo-hazards caused by natural processes, environmental degradation, and human activities. This involves implementing a network of sensors for real-time monitoring and data collection. 
• Leveraging Technology for Effective Monitoring:  
  • Web-based sensors such as rain gauges, piezometers, inclinometers, extensometers, InSAR (Interferometric Synthetic Aperture Radar), and total stations can help monitor vulnerable areas. Monitoring should be prioritized in densely populated and built-up zones. 
  • Integrated Early Warning System (EWS): The development of an integrated Early Warning System (EWS) using AI and Machine Learning (ML) algorithms is crucial. Such a system could help predict and alert communities about impending hazards, giving them valuable time to take preventive measures. 
• Formation of Himalayan States Council: Establishing a collaborative platform that brings together the disaster management authorities from different states in the Himalayan region is a strategic move. This centralized council would enable the sharing of knowledge, experiences, and resources to effectively assess and manage the impacts of various stressors on the region.
  • Simulation and Hazard Assessment: The council should focus on simulating and assessing hazard scenarios resulting from natural processes, environmental degradation, climate-induced phenomena, and anthropogenic activities. This will help in understanding potential risks and formulating appropriate mitigation strategies. 
  • Knowledge Dissemination: While the Himalayan region is diverse and varied, sharing the findings of assessments across different states is essential. Collaborative efforts and shared knowledge can lead to a more comprehensive understanding of the challenges and potential solutions. 
  • Ecosystem Protection: Protecting the region’s ecosystems is a priority. By promoting sustainable practices and responsible resource use, the council can help safeguard the natural environment. 
• Sustainable Socio Economic Development: Recognizing the valuable natural resources present in the region, such as glaciers, springs, minerals, energy sources, and medicinal plants, offers the potential for sustainable socio economic development. However, it’s crucial to strike a balance between resource exploitation and ecological preservation to ensure long-term viability. 
• Environmental Considerations: Proper town planning that accounts for the unique characteristics of mountainous terrain is vital. Restricting heavy construction, implementing effective drainage systems, scientifically managing slope cutting, and using retaining walls are important aspects of environmentally conscious development.
  • Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides. 
• Building Codes and Assessment: High-resolution mapping of towns and assessing their load-bearing capacity are essential components in creating effective building codes. This approach ensures that construction is safe and resilient, especially in regions prone to natural hazards like landslides and earthquakes. 
• Sustainable Tourism: Sustainable tourism can reduce landslides by promoting environmental awareness, conservation and protection of natural resources, and respect for biodiversity and ecosystems.  
  • It can also provide economic incentives and social benefits for local communities, which can enhance their resilience and adaptive capacity to cope with natural hazards. 
• Building Sustainable Govt Projects: To ensure responsible development in the Himalayan region, key measures include conducting environmental assessments, using eco-friendly technologies, involving local communities, increasing stakeholder awareness, and promoting coordination among governmental sectors. 

Initiatives taken by the Government to mitigate the risk of landslides 

• National Landslide Risk Management Strategy (2019): 
  • This is a comprehensive document that addresses all the components of landslide disaster risk reduction and management, such as hazard mapping, monitoring, early warning system, awareness programs, capacity building, training, regulations, policies, stabilization and mitigation of landslides, etc 
• National Landslide Risk Mitigation (NLRM) Project:
  • In 2021, Central Government had constituted National Disaster Mitigation Fund (NDMF) under Disaster Management Act, 2005 based on recommendation of 15th Finance Commission.
  • It shall be applied by National Disaster Management Authority (NDMA).
  • It is exclusively for purpose of mitigation projects in respect of disasters.
• Landslide Risk Mitigation Scheme (LRMS): 
  • This is a scheme under preparation that envisages financial support for site specific landslide mitigation projects recommended by landslide prone states, covering disaster prevention strategy, disaster mitigation and R&D in monitoring of critical landslides, thereby leading to the development of early warning system and capacity building initiatives. 
• Flood Risk Mitigation Scheme (FRMS): 
  • This is another scheme under preparation that covers activities like pilot projects for development of model multi-purpose flood shelters and development of river basin specific flood early warning system and digital elevation maps for preparation of inundation models for giving early warning to the villagers for evacuation in case of flood. 
• National Guidelines on Landslides and Snow Avalanches: 
  • These are guidelines prepared by the National Disaster Management Authority (NDMA) to guide the activities envisaged for mitigating the risk emanating from landslides at all levels. The guidelines cover aspects such as hazard assessment, vulnerability analysis, risk management, structural and non-structural measures, institutional mechanisms, financial arrangements, community participation, etc. 
• Landslide Atlas of India: 
  • The Landslide Atlas of India is a document that provides the details of landslides present in landslide provinces of India, including damage assessment of specific landslide locations. It is prepared by the National Remote Sensing Centre (NRSC), one of the centers of ISRO. 
• National Landslide Susceptibility Mapping Program initiated by Geological Survey of India in 2014-15.