Landslides: Causes, Types, Effects, Mitigation Strategies & UPSC Notes

A landslide is when much rock, soil, and other materials quickly move down a slope or hill. It can happen after heavy rain, earthquakes, or when the land is disturbed. Landslides can be dangerous because they destroy homes, block roads, and hurt people. It's essential to stay safe and know what to do if a landslide happens nearby. Understanding landslides helps us protect ourselves and the environment.

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Landslides are part of Geography under Geophysical Phenomena in GS Paper 1 for UPSC. They are also relevant to Disaster Management in GS Paper 3, linking to environmental conservation, risk reduction, and climate-related challenges. This article is a significant part of the UPSC IAS exam. Take your UPSC preparation further by enrolling in UPSC coaching.

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What is a Landslide?

A landslide is the movement of rock, earth, or debris down a slope, occurring either abruptly or gradually over an extended duration—the occurrence of a landslide results from the force of gravity surpassing the resisting forces of a hill. Various external factors contribute to landslides, such as Intense rainfall causing ground saturation, Erosion at the base of a mountain, Changes in the slope, and strength due to weathering.

India's Vulnerability to Landslides

A landslide refers to the downward movement of rock, soil, or other debris under the force of gravity—often triggered by rainfall that saturates and destabilizes slopes. The Geological Survey of India (GSI) estimates that approximately 12.6 % of India's land area—or around 0.42 million sq km—is prone to landslides.

Regional Hotspots

• Himalayan Region: The most vulnerable territory, with ~0.14 million sq km in the Northwest Himalaya (including Uttarakhand, Himachal Pradesh, Jammu & Kashmir) and ~0.18 million sq km in the Northeast Himalaya (like Sikkim and Darjeeling).
• Western Ghats & Konkan Hills: Covers approximately 0.09 million sq km across Maharashtra, Goa, Karnataka, Kerala, and Tamil Nadu.
• Eastern Ghats (Araku region): Around 0.01 million sq km in Andhra Pradesh faces vulnerability.

High-Resolution Susceptibility Insights

Recent high-resolution modeling—the India Landslide Susceptibility Map (ILSM), developed using big data and machine learning—indicates that 13.17 % of India's area is landslide-prone, with 4.75 % categorized as highly susceptible.

Key findings include:

• Sikkim: Around 57.6 % of its land is at risk.
• Arunachal Pradesh: Records the largest absolute prone area.
• Kerala: Among non-Himalayan states, it exhibits the highest landslide susceptibility.
• The Eastern Ghats, particularly in Odisha and Tamil Nadu, have surfaced as new risk areas in this updated mapping.

Primary Drivers of Landslide Risk

• Rainfall variability—especially sudden, intense monsoon downpours—is the leading catalyst of landslides across India, notably in the Himalayas and Western Ghats.
• Geological features—steep slopes, fragile soils, high seismicity—further destabilize vulnerable regions.
• Human activities, including deforestation, road construction, unscientific hill cuts, and urban expansion, exacerbate vulnerability.

Climate change intensifies heavy rain events, amplifying landslide hazards in areas like Kerala's Wayanad.

Why India Stands Out Globally?

India ranks among the top five landslide-prone nations, experiencing at least one landslide-related fatality per 100 sq km each year. Hotspots within the ISRO-prepared Landslide Atlas emerged in Uttarakhand, Kerala, Jammu & Kashmir, Mizoram, Tripura, Nagaland, and Arunachal Pradesh.

Strategies

• Susceptibility mapping, like the ISRO Landslide Atlas and ILSM, offers critical data for targeted action.
• Early warning systems—GSI has piloted rain-based alerts in regions such as Darjeeling and the Nilgiris.
• Policy frameworks, such as the National Landslide Risk Management Strategy (2019), emphasize risk mapping, warning systems, and mountain zone regulations.
• Mitigation efforts, including slope reinforcement, afforestation, and land-use regulation, help improve hill-slope stability.
• Climate adaptation, better infrastructure planning, and sustainable development are crucial to reducing future landslide risk.

Different Types of Landslides

• Rock Falls: This is the most common and easily identifiable form of landslide, called rock falls. They are due to the detachment of individual rocks or boulders on steep slopes and falling freely down. These landslides commonly occur as a result of weathering, earthquakes or erosion. The sediment substances (in this case, the falling stones) can lead to massive destruction and directly endanger human lives and infrastructures in the affected area.
• Slides: Slide-type slides are characterized as the down-slope flow of consolidated rock or soil simply times along a well-marked failure plane. One would usually believe that slides occur in slopes, which are composed of loose materials in the form of rocks or soil loosened up by the rolling force of gravity, among others. They can also be classified into rotational, translational and compound slides depending on the pattern of movements.
• Rotational Slides: Rotational slides, also termed as slumps, occur when a mass experiences down and outward movement, along a curved plane of failure. These landslides generally happen in cohesive materials like clay or silt, and there is a curved failure plane where it moves in rotation.
• Translational Slides: Translational slides happen when a mass travels alongside a planar failure surface parallel to the slope. They tend to occur due to weak or saturated soil (clay or silt) whose failure plane is relatively flat.
• Compound Slides: These slides have the properties of both rotational and translational slides. They have complicated movements, at every point of the mass motion along a curved surface, and another part along a plane.
• Flows: Landslides,s which can be broken into as flows consist of a mass of uncoherent material being moved along a slope, e.g., soil, debris and mud. Flows commonly occur following intense rainstorms, snow melt, and volcanoes. The flow landslides are of three primary kinds, which are:
  • Debris Flows: Debris flows are represented by soil, rock and fragments, water and organic materials. They tend to be in regions with mountains, and may move very fast, making them like fast rivers. Debris flows are very destructive as they can carry high volumes of materials and debris with them.
  • Mudflows: Mudflows or mudslides resemble debris flows, with mudflows comprising more fine-grained materials like clay and silt. They frequently occur in places with heavy precipitation or where wildfires have recently occurred, the vegetation is burned away, and the soil is more prone to erosion.
• Lahars: Lahars are particular mudflows that occur due to volcanic activity. They come as a result of a combination of volcanic ash, debris and water, which creates a high velocity slurry that can extend long distances away from the origin of the volcano. Lahars are a significant threat to people inhabiting the areas around volcanoes.
• Complex Landslides: They combine at least two types; hence, it is difficult to segregate, study and predict them. Such landslides are characterized by cascades of movements, such as rock falls, slides, and flows that may happen together or one after another. Multifaceted landslides will have extensive destruction and are harder to alleviate since they are complex.

Causes of Landslides

Several factors, including natural or human causes, can cause landslides. They are divided into categories.

Natural Causes

• Gravity: Gravity is the primary reason for the landslides. Steeper slopes coupled with gravitational force can trigger a massive landslide.
• Climate: A general precipitation or ground saturation increase drastically raises groundwater levels.
• When slopes become entirely saturated with water, landslides can occur. If mechanical root support is absent, the soils start to run off.
• Earthquakes: When earthquakes strike regions with steep slopes, the soil often slips, resulting in landslides.
• Ashen debris flows produced by earthquakes can also cause significant soil movement.
• Weathering: Weathering causes inundation and weakens rocks. Landslides are triggered when the stones become too weak and begin to slide away.
• Erosion: It is caused by periodic running water, such as streams, rivers, wind, currents, ice, and waves, which remove latent and lateral slope support, allowing landslides to develop more easily.
• Volcanoes: Volcanic eruptions can trigger landslides. If an eruption happens in moist conditions, the soil will flow downhill, resulting in a landslip.

Man-made Causes

• Mining: Mining activities that utilise blasting techniques contribute to landslides. Vibrations from the blasts can degrade soils in the locations prone to landslides, such as in the Himalayas.
• A landslip can occur at any time due to soil deterioration.
• Clear-cutting: A timber harvesting practice involves removing all old trees from the area. This practice is risky since it destroys the area's current mechanical root structure, allowing landslides.
• Unsustainable Tourism: The unregulated tourism in Uttarakhand and other Himalayan States exceeds the region's carrying capacity, causing disastrous impacts, including landslides. Religious tourism sites like Char Dham have been hugely commercialised and exploited to become unsustainable.
• Example: In 2013, around 5000 people were killed in a massive flood and landslide in Kedarnath. In 2011, around 25 million tourists visited the region, despite its vulnerability to natural disasters such as earthquakes, landslides, and flash floods.
• Unplanned infrastructure: The Himalayas are the world's most densely populated and rapidly urbanising mountain ecosystem.
• Urban encroachment into forests, disturbance of natural drainage, and cutting and deep excavations on hill slopes to develop buildings and infrastructure have contributed to a massive increase in landslides in Uttarakhand.
• Example: The land subsidence incident of Joshimath in 2023 was mainly due to a lack of infrastructure for drainage, an increase in human population, and rapid expansion of infrastructure to cater to the tourism potential.
• Climate change: The intense and sudden rainfall due to climate change and the melting of the glaciers in the Himalayas have aggravated the problems of landslides in India.

Effects of Landslides

Landslides have enormous implications for different areas, including lives, infrastructures and the environment. Knowing these impacts provides differential disaster management policies.

• Social and Economic consequences: Landslides may produce significant social and economic impacts, including:
• Damage to Life and Injuries: Landslides are extremely dangerous to human existence, resulting in loss of life and injuries, especially when there are high population densities or when there is poor infrastructure.
• Displacement and Migration: Displaced people have been exposed to the problems of relocation, loss of livelihoods, and the breaking of social contacts, which require long rehabilitation efforts.
• Economic Losses: Landslides cause buildings, roads and other structures to be ruined or even destroyed, which causes significant financial losses to the local communities and governments.
• Environmental implications: The effects of landslides have ecological implications and an adverse impact on the environment:
• Vegetation Loss: Substantial vegetation cover is also removed in the process of landslides, meaning that the soil is exposed, exposing it to the elements and loss of biodiversity. This hurts the ecology in the long run.
• Soil Erosion and Sedimentation: Landslides may cause the soil to enter a river or a water body, and therefore, block its flow, which causes disruption of the ecosystem of the water bodies and makes it prone to flooding due to the blockage.
• Habitat Destruction: Landslides can destroy an entire natural habitat, either stranding or threatening to extinguish the animal and bird population, and upsetting otherwise delicate ecosystems.

Understanding Landslide Mechanisms and Triggers

To understand the nature of landslides in depth, it is vital to appreciate the mechanics and the stimuli that lead to the occurrence of landslides.

Mechanisms of Slope Failure. Landslides occur in numerous ways depending on the soil and the slope's nature. Dominant mechanisms are:

• Sliding: In this, the soil or mass of rocks slides along a plane of reasonably well-defined failure, the plane commonly being in distinct layers or zones of relatively weak material.
• Flowing: On a wet surface, the falling debris may have a fluid character to the extent that it moves like a fluid or, somewhat, downwards like a fluid in a reduced friction state.
• Falling: Any rock or boulder may break loose on a slope and fall freely, damaging buildings or threatening human life.
• Rainwater and Saturation: With a larger water proportion, soil and rocks are weakened, less frictional, and weaker. Severe or extensive rains may serve as landslide triggers.
• Earthquakes: Shaking around during earthquakes may cause landslides by subjecting slopes to increased stress or reintroducing previously existing weaknesses to failure.
• Human Activities: Human activities like deforestation, construction, orchard drainage systems, etc., can cause instability on natural slopes, creating conditions for landsliding.

Mitigation Strategies for Landslides

A set of dry early warning systems involving land-use planning and community participation needs to be implemented to avoid and minimize the risk of landslides.

Early Warning Systems 

The impact of landslides can be mitigated by enhancing early warnings that can keep the communities informed in time and give them adequate landslide preparedness. Such systems mainly comprise:

• Monitoring: Placing the sensors and the instrumentation to determine the change in slope stability, rainfall intensity and the groundwater level.
• Risk Assessment: Evaluation of landslide-prone areas to determine susceptibility and vulnerability of the areas under threat of landslides and therefore rank regions of high risk in the mitigation process.
• Communication and Response: Setting up communication links that will help spread concerns and organize emergency responses in coordination with the local organizations.

Land-Use Planning and Regulation 

Proactive land-use planning is essential to minimize the exposure of vulnerable areas to landslides. This includes:

• Zoning: Identifying and mapping areas with high landslide susceptibility to restrict or regulate construction and human activities in these regions.
• Building Codes: Enforcing stringent building codes and guidelines to ensure structures are designed and constructed to withstand potential landslide impacts.
• Afforestation and Soil Conservation: Promoting afforestation, implementing erosion control measures, and maintaining the natural stability of slopes through sustainable land management practices.

Community Awareness and Preparedness

 Empowering communities with knowledge and skills is crucial for effective disaster management:

• Education and Training: Conducting awareness programs to educate individuals about the risks associated with landslides, safe evacuation procedures, and early warning signs.
• Community Participation: Encouraging community involvement in planning, preparedness, and response activities to enhance the overall resilience of vulnerable areas.

Read the Article Landforms here!

About Landslide Prediction Mapping

• Mapping and landslide hazard analysis help minimize devastating losses and establish the basis of planning guidelines on land use on a sustainable basis.
• The landslide-related factors in the analysis include how to identify factors related to landslides, the approximate significance of these factors to landslides along slopes, the relationship, and the forecasting of the landslide hazards in the future.
• Factors for analysis include geomorphology, geology, land use/land cover, and hydrogeology.
• GIS (Geographic Information System) is ideal for landslide hazard mapping due to its capacity for efficiently collecting, storing, manipulating, displaying, and analyzing spatially referenced data.
• Cardenas highlights the extensive use of GIS alongside uncertainty modeling tools for comprehensive landslide mapping.
• Remote sensing techniques, using before and after aerial photographs and satellite imagery, aid in gathering information on landslide characteristics, distribution, classification, and factors like slope, lithology, and land use/land cover.
• Such imagery helps predict future events, understand landscape changes post-landslide, identify triggers, and observe the regeneration and recovery process.

Conclusion

A landslide conclusion happens when someone makes a quick judgment without enough proof. It's like jumping to an answer too soon, which can lead to mistakes or misunderstandings. Always check facts before deciding.

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