LANDSLIDES AND LAND SUBSIDENCE

Published on 23 Feb 2025

Landslides are geological phenomena where masses of rock, soil, or debris rapidly move down slopes, triggered by heavy rainfall, earthquakes, volcanic activity, or human activities, posing a significant threat to life, property, and infrastructure.

Land subsidence refers to the gradual sinking or settling of the Earth's surface due to various factors such as excessive groundwater extraction, mining activities, natural compaction of sediments, or the collapse of underground cavities, leading to potential damage to life and infrastructure.

Vulnerability of India

• Physiographic features: Around 15% of the country’s region is prone to landslides. The Himalayas and the Western Ghats are two regions of high vulnerability.

• Tectonically active Himalayas: The convergence of two tectonic plates in the area raises the likelihood of earthquakes, which, in turn, can lead to a higher occurrence of landslides.

• Heavy Monsoon Rains: India’s monsoon season from June to September, bringing heavy rainfall and triggering landslides, especially in hilly regions and areas with poor drainage.

• Example: Kerala recorded 3782 landslides (highest in the country) from 2015-2022. (Ministry of Earth Sciences data)

• Nature of Rivers: Mighty and youthful Himalayan rivers do a lot of downcutting, which enhances the occurrence of landslides.

• Example: The Kali Gandaki River in Nepal.

• Climate change: Global warming is expected to increase glacier melt and more water would flow over the steep slopes, thereby generating more landslides.

• Example: Chamoli disaster of 2021 triggered by a glacier break in the Nanda Devi region led to mud flow and landslides.

• Population Pressure: High population density calls for creating more infrastructure in the fragile ecosystems.

Anthropogenic causes

• Deforestation: Clearing large areas of forests for agriculture, logging, or urbanization reduces the binding effect of tree roots, leading to increased soil erosion and slope instability. 

• Example: Shifting cultivation practices in N-E hills increasing landslide vulnerability in the region.

• Urbanization and Construction: Poorly planned urban development, construction of roads, buildings, and infrastructure on steep slopes without proper engineering measures can disturb the natural balance, triggering landslides.

• Example: Mushrooming of tourist structures in Himalayan states.

• Mining and Quarrying: Unregulated mining and quarrying activities can alter the natural topography and weaken slopes, making them susceptible to landslides.

• Example: Landslides in the Western Ghats intensified by quarrying of stone.

• Slope Modification: Altering the natural slope angle or cutting slopes for landscaping or engineering purposes without proper stabilization measures can trigger landslides.

• Example: Flattening of hills to promote paddy cultivation reportedly contributed to the deadly 2014, Malin Landslide of Pune. 

• Hydroelectric Projects: The construction and operation of large-scale hydroelectric projects can alter the hydrological regime, leading to changes in groundwater levels and slope stability.

• Example: Joshimath land subsidence is linked to Tapovan Vishnugad hydropower projects.

Effects of Landslide

• Social Effects

• Loss of Lives and Injuries: Landslides can result in the loss of human lives and cause injuries, affecting families and communities emotionally and economically.

• Example: 2018 Kedar Nath Landslide, Uttarakhand.

• Displacement and Homelessness: Landslides can force people to evacuate their homes and communities, leading to temporary or long-term displacement and homelessness.

• Health and Public Health Concerns: Health hazards includes water contamination, vector-borne diseases, and mental health issues arising from the trauma of the disaster.

• Economic Effects

• Infrastructure Damage: Roads, bridges, buildings, and other critical infrastructure can be damaged by landslides, disrupting transportation and services, and incurring substantial repair costs.

• Example: 2018 Kerala Floods lead to numerous landslides in Idukki district.

• Business and Tourism Impact: Businesses and tourism in landslide-prone areas may suffer due to damages, reduced accessibility, and safety concerns.

• Example: 2023 Landslide on Gap Road in Munnar led to traffic ban, impacting tourism.

• Agricultural Losses: Landslides can devastate agricultural lands, leading to crop failure and loss of livelihoods for farmers and agricultural workers.

• Increased Costs of Disaster Response: Landslide events demand emergency response efforts, which can strain government resources and budgets.

• Environmental Effects

• Habitat Destruction: Landslides can destroy natural habitats and disrupt ecosystems, leading to loss of biodiversity and impacts on wildlife.

• Example: Malin Landslides, Pune.

• Soil Erosion: Landslides can contribute to soil erosion, affecting soil fertility and the ability to support vegetation.

• Water Quality Impact: Sediment and debris from landslides can enter water bodies, impacting water quality and aquatic ecosystems.

• Example: Darjeeling Landslides, West Bengal

• Natural Hazards: Landslides can create secondary hazards such as debris flows and damming of rivers, posing additional risks to downstream communities.

• Example: Rishiganga hydroelectric power project was almost completely buried under ice and mud post Chamoli disaster of 2021.

Effects of Land Subsidence

• Damage to Infrastructure: Land subsidence can harm essential infrastructure like roads, buildings, bridges, and pipelines, resulting in costly repairs and jeopardizing their safety and functionality.

• Example: Joshimath land subsidence, Uttarakhand.

• Increased Flooding Risk: Subsidence can alter natural drainage patterns, leading to increased flooding in low-lying areas, especially during heavy rainfall or storm events.

• Groundwater Contamination: As the land sinks, it can alter the movement of underground water, potentially causing changes in water quality and increased risk of contamination.

• Loss of Agricultural Productivity: Subsidence can affect the fertility of agricultural lands, leading to reduced crop yields and economic losses for farmers.

• Loss of Ecosystem Services: Land subsidence can impact natural ecosystems, wetlands, and coastal areas, leading to habitat loss and disrupting the balance of local flora and fauna.

• Example: Gulf of Khambhat, Gujarat, excessive groundwater extraction for agriculture, industrial use, and domestic needs has contributed to land subsidence.

Challenges in mitigation of Landslides

• Lack of Data and Monitoring: Adequate data on landslide-prone areas, historical events, and real-time monitoring are often lacking, hampering accurate risk assessment and early warning systems.

• Rapid Urbanization: Urban expansion into landslide-prone areas without proper planning can increase the exposure of vulnerable populations and infrastructure to landslide hazards.

• Existing Infrastructure: Retrofitting or upgrading existing infrastructure to withstand landslide impacts can be costly and logistically challenging.

• Long Response Time: Landslide events can occur suddenly, leaving limited time for response and evacuation, especially in remote or densely populated areas.

• Policy and Regulatory Gaps: Inconsistent or inadequate regulations related to land-use planning, construction, and environmental protection can exacerbate landslide vulnerability.

India’s current preparedness

• NDMA guidelines

• 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 landslide prone area to estimate risk.

• Setting pace setter examples for stabilization of slides and 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.

• National Landslide Risk Management Strategy (2019): Addresses all the components of landslide disaster risk reduction and management, which includes,

• Hazard mapping, monitoring, and early warning system, awareness programs, 

• Capacity building, training, regulations, and policies, stabilization and mitigation of landslides, etc.

• Generation of User-Friendly Landslide Hazard Maps

• Development of Landslide Monitoring and Early Warning System

• Stabilisation and Mitigation of Landslides and Creation of Special Purpose Vehicle (SPV) for Landslide Management.

• Technological measures:

• Hazard zone mapping: Many Indian states have undertaken hazard zone mapping projects which provides valuable insights into local landslide risks and help in formulating targeted strategies.

• Remote Sensing and GIS: Satellite imagery, aerial surveys, and ground-based monitoring are employed to assess landscape changes, slope movements, and potential landslide-prone areas.

• Wireless sensor-based landslide detection system:  Establishment of such system in the Western Ghats of Kerala has delivered multiple successful warnings.

Implementation gaps

• Long-term Maintenance: Some engineering measures, such as retaining walls and drainage systems, require regular maintenance to remain effective.

• Technological Barriers: Limited access to advanced technology and remote areas may restrict the implementation of modern landslide monitoring and forecasting techniques.

• Limited Inter-Agency Coordination: Inadequate collaboration and coordination among different government departments and agencies can lead to fragmented efforts and duplication of tasks.

• Lack of community-based disaster management: Communities are the first responders during the disaster, thus communities become significant in disaster response, mitigation, and management interventions.

Best practices from aboard

• Brazil - “Paranhana River Basin Landslide Early Warning System”: This system integrates rainfall data, geotechnical monitoring, and slope stability analysis to provide real-time early warnings for landslides. It has reduced landslide impact by enabling timely evacuation and proactive response, safeguarding lives and minimizing property damage.

• Hong Kong: Hong Kong's Geotechnical Engineering Office (GEO) has implemented various landslide mitigation measures such as installing retaining walls, rockfall barriers, and soil nailing. Along with the Landslip Warning System, this has significantly reduced the frequency and impact of landslides. 

Case Studies/ Strategies for landslide management

• Uttarakhand: Both Integrated Watershed Management Program and afforestation is used to promote sustainable land use and prevent soil erosion. 

• Darjeeling: The Darjeeling district administration collaborated with geotechnical experts and engineers to implement a landslide risk reduction plan. The plan involved slope stabilization measures, such as construction of retaining walls and drainage systems, to mitigate the impact of landslides.

• Early Warning Systems: Implementing real-time monitoring systems for rainfall, slope stability, and other relevant factors to provide early warnings to vulnerable communities. 

• Land Use Planning and Regulations: Enforcing land use planning regulations to prevent construction in high-risk landslide areas. 

• Slope Stabilization and Engineering Measures: Engineering solutions for slope stability and landslide prevention include building retaining walls, installing drainage systems, using soil reinforcement techniques, and constructing rockfall barriers.

Way Forward

• There should be proper implementation of Environmental impact assessment norms before initiating mining or dam construction in the high-risk zones.

• The adoption of landslide micro zoning procedures for mountainous and other highly vulnerable regions.

• More funding should be given to Landslide planning and mitigating agencies to improve disaster management potential.

• There should be involvement of locally available trained manpower to intensify the hazard reduction and public awareness programs.

• Mitigation strategies like limiting agriculture to valleys and areas with moderate slopes, promoting large-scale afforestation programs, and construction of bunds to reduce the flow of water, etc. should be encouraged.

Tags:
Disaster Management

Keywords:
LANDSLIDES LAND SUBSIDENCE disaster disaster management landslide Vulnerability of India Anthropogenic causes for landslide and land subsidence Effects of Landslide Effects of Land Subsidence Challenges in mitigation of Landslides India’s current

Syllabus:
General Studies Paper 3

Topics:
Disaster and Disaster Management