When the Earth Moves: Earthquakes, Tsunamis, Landslides, Volcanoes

Geo-disasters are disasters driven by the solid Earth and the ocean: earthquakes, tsunamis, landslides and volcanoes. Unlike slow-onset hazards, they strike with little warning, so the decisive question for UPSC is never whether the hazard can be stopped, it is whether human systems can absorb the shock. India is one of the most exposed countries in the world: about 59 per cent of its landmass faces moderate to severe seismic hazard, about 12.6 per cent is landslide-prone, and its 11,098 km coastline faces both cyclones and tsunamis.

This article maps each geo-disaster: what causes it, where India is vulnerable, what the state has built to manage it, and what UPSC has actually asked. Definitions are kept complete, because mains answers are graded on precision, not on name-dropping.

Earthquakes: the sudden release of tectonic stress

An earthquake is a phenomenon that occurs without warning and involves violent shaking of the ground and everything over it. It results from the release of accumulated stress of the moving lithospheric or crustal plates, and that energy radiates outward as seismic waves. India recorded 159 earthquakes between November 2024 and February 2025, a reminder that the hazard is continuous even when it is not in the headlines.

Seismologists classify earthquakes by what sets them off. Five types matter for the exam:

Reservoir-induced seismicity is the triggering of earthquakes by the filling of a large reservoir behind a dam. The water load changes stress and pore pressure in the underlying rocks, reactivating old faults. The textbook Indian case is the Koyna earthquake of 10 December 1967: the Koyna Dam's reservoir had been filling since 1962, and the resulting M6.3 shock, the largest induced earthquake ever recorded, destroyed Koynanagar township, killed around 180 to 200 people and damaged the dam itself. Tremors have continued in the Koyna-Warna region for nearly sixty years, proving that induced seismicity is a long-lived legacy, not a one-time event.

India's exposure is structural, not accidental. Under the in-force IS 1893:2016 seismic-zoning framework, about 59 per cent of India's land faces moderate to severe seismic hazard (MSK VII and above): roughly 11 per cent lies in the most vulnerable Zone V, 18 per cent in Zone IV and 30 per cent in Zone III. The Himalayan belt can produce great earthquakes of magnitude 8 and above, as in 1934 Bihar-Nepal (M8.3) and 1950 Assam-Tibet (M8.6). Worryingly, intraplate regions once considered safe, like peninsular India after Koyna, now face damaging quakes, so no part of the country is outside the preparedness question.

Preparedness, not prediction, is the strategy, because earthquakes cannot be predicted with useful lead time. The National Centre for Seismology (NCS) under the Ministry of Earth Sciences is the nodal monitoring agency; seismic observatories grew from 80 in 2014 to 168 by February 2025, and the BhooKamp app gives real-time updates. NDMA's approach rests on six pillars: seismic-resistant construction and retrofitting of lifeline buildings, strict adherence to the National Building Code, risk-informed urban planning and land-use zoning, stronger monitoring and early dissemination, public awareness and mock drills, and functional Emergency Operations Centres with community participation through PRIs and local bodies.

• Bhuj 2001
• Latur 1993
• Secondary disasters
• Japan's practice

Tsunamis: when the sea floor moves

A tsunami (Japanese for harbour waves) is a series of large waves of extremely long wavelength and period, generated by a sudden large-scale disturbance of the sea floor or the water column. The 2004 Indian Ocean tsunami, which killed over 2.3 lakh people across 14 countries, is the defining modern example and the event that forced India to build a warning system.

What makes a tsunami different from an ordinary wave is its physics:

The primary cause is an undersea earthquake with vertical movement of the sea floor, generally of magnitude 6.5 or more. Other triggers are underwater landslides, volcanic eruptions (the 1883 Krakatoa eruption killed over 36,000 people through its tsunamis), and atmospheric disturbances that produce meteotsunamis, rapid sea-level oscillations driven by sudden air-pressure changes during squalls or cyclones.

India's vulnerability is concentrated on the east. The long, densely settled coastline, the proximity of the Andaman-Sumatra trench, the Makran subduction zone in the Arabian Sea, and the location of the Andaman and Nicobar Islands almost on top of major seismic zones mean minimal warning time for islanders. About 13 tsunamis are recorded in the Indian Ocean over the past 300 years. Mangroves are the natural defence: they are natural shock absorbers that can reduce wave energy by 70 to 90 per cent.

The institutional answer is the Indian Tsunami Early Warning Centre (ITEWC), established in 2007 by the Indian National Centre for Ocean Information Services (INCOIS), Hyderabad, under the Ministry of Earth Sciences. It issues real-time alerts within 10 to 15 minutes of an undersea earthquake, and UNESCO-IOC recognised it in 2011 as a Regional Tsunami Service Provider serving 28 Indian Ocean rim countries. The system is being upgraded with Tarang, a next-generation HPC-based warning platform, while the Tsunami Ready programme certifies resilient coastal communities (Odisha led with 26 certified villages) and NavIC satellites now push tsunami alerts directly to fishermen's handheld devices.

Landslides: when slopes fail

A landslide is the geological phenomenon in which masses of rock, soil or debris move down a slope under gravity. It is a form of mass wasting, encompassing falls, topples, slides, spreads and flows. About 12.6 per cent of India's land area is susceptible, and recent events from Wayanad (2024) to Himachal Pradesh (2023) keep pushing the hazard up the policy agenda.

Two very different landslide regimes operate in India:

Natural triggers are intense rainfall (which raises pore pressure and lowers slope stability), seismic activity and soil erosion; the human triggers are deforestation, unregulated quarrying and road-cutting, and unplanned construction on fragile slopes. The 2023 Joshimath land subsidence in Uttarakhand is the cautionary tale: the Mishra Committee (2023) identified unregulated development, hydropower tunnelling and overburdened infrastructure as the causes, and recommended halting major construction, enforcing land-use planning and zoning, and ecological restoration.

The policy backbone is the National Landslide Risk Management Strategy (2019), NDMA's comprehensive plan covering hazard mapping, monitoring, early warning, capacity building, public awareness, policy reform and mitigation. It is operationalised through the National Landslide Forecasting Centre (NLFC) inaugurated by the Geological Survey of India at Kolkata on 19 July 2024 for real-time forecasting using rainfall thresholds, remote sensing and geospatial tools, and through the Landslide Atlas of India (2023) prepared by NRSC-ISRO, which mapped about 80,000 landslide events between 1998 and 2022 across 147 districts in 17 states and 2 Union Territories. The Bhusanket portal and Bhooskhalan app crowdsource reports and push alerts, and the National Landslide Risk Mitigation Project (NLRMP), worth Rs 1,000 crore under the National Disaster Mitigation Fund for 15 states, funds structural mitigation.

For UPSC, remember the 2019 question's core: hazard zonation mapping classifies terrain into high, moderate and low hazard zones using topography, geology, soil and rainfall data, which then guides land-use regulation (as in the Nilgiris), safe alignment of roads and tunnels, placement of monitoring instruments, and targeted funding for slope treatment. Macro-scale mapping at 1:50,000 already covers 4.3 lakh sq km, and NDMA guidelines push for 1:10,000 micro-zonation in the most vulnerable towns.

• Engineering fixes
• Wayanad SOP
• Char Dham lesson

Volcanoes: Barren Island and the Ring of Fire

Barren Island in the Andaman and Nicobar Islands, about 135 km northeast of Port Blair, hosts India's only active volcano. It is a stratovolcano, a steep cone built of alternating layers of lava and ash, formed where the Indo-Australian plate subducts beneath the Eurasian plate. First recorded erupting in 1787, it has shown near-continuous activity since 2008, with its most recent significant eruption in January 2017 producing ash plumes and lava flows, and minor eruptive activity reported again in September 2025.

Globally, some 1,350 to 1,500 volcanoes are potentially active, and roughly 75 per cent ring the Pacific in the Ring of Fire, the belt of subduction zones where most convergent-boundary volcanism occurs. Volcanoes also form at divergent boundaries and over mantle-plume hotspots such as Hawaii, and eruptions are typically preceded by earthquakes as magma fractures rock on its way up.

Volcanic hazards split into primary and secondary effects. Primary effects are lava flows (slow but destructive), pyroclastic flows (fast, extremely hot clouds of gas and ash; the 1902 Mount Pelee eruption killed about 28,000 people) and ash fall (which disrupts aviation, agriculture and health). Secondary effects include lahars (volcanic mudflows; the 1985 Nevado del Ruiz lahar killed about 23,000 people in Colombia), climate cooling from stratospheric aerosols (Mount Pinatubo, 1991, cooled the globe by about 0.5 degrees C) and volcanic tsunamis such as the one from Anak Krakatau in 2018.

Management follows a standard chain: seismic monitoring, satellite imagery and gas-emission studies for early warning; hazard maps and zonation to keep settlements out of lava-flow and ash-fall paths; community awareness and evacuation drills; and engineering measures such as diversion barriers used in Iceland and Italy. For India, the mainland risk is minimal, but ash, toxic gases and distant eruptions triggering meteotsunamis in the Indian Ocean keep Barren Island on the watch list.

• Pinatubo lesson
• India's monitoring gap

Comparing early warning across geo-hazards

No geo-hazard can be prevented, so the policy question is always about detection speed and last-mile delivery. The systems differ sharply in lead time:

Reading seismic risk: zones, swarms and sequences

India's seismic zoning, prepared by the Bureau of Indian Standards on the basis of historical seismic activity, divides the country into four zones. Zone V is the most seismically active and Zone II the least; there is no Zone I, because no part of India is considered free of earthquake risk.

Three sequence terms complete the vocabulary. Foreshocks are small earthquakes that occur before a major earthquake in the same area and are recognised as foreshocks only after the main shock happens. Aftershocks are smaller earthquakes that follow the main earthquake as the crust adjusts to a new balance. An earthquake swarm is a sequence of mostly small earthquakes with no identifiable main shock, occurring in a localised region over days to weeks.

Tsunami warning: the ITEWS and the twenty-year turnaround

The 2004 Indian Ocean tsunami, generated by a magnitude 9.1 submarine earthquake, exposed the absence of any Indian Ocean warning system. India's answer was the Indian Tsunami Early Warning System (ITEWS), established in 2007 at INCOIS, Hyderabad. It functions as a Tsunami Service Provider for 28 Indian Ocean rim countries, and India now ranks among the five countries with advanced tsunami warning systems. Globally, sea-level monitoring stations have grown from about 1,000 in 2004 to over 14,000, which is why a comparable tsunami today meets a warned coastline rather than an unwarned one.

Mapping landslide susceptibility: the IIT Delhi atlas layer

Landslide science in India has recently gained a national picture. A team at IIT Delhi built the first high-resolution landslide susceptibility map for India at 100 metre resolution, confirming high susceptibility across the Himalayan foothills, the Assam-Meghalaya region and the Western Ghats, and revealing previously under-recognised risk in parts of the Eastern Ghats north of Andhra Pradesh. Such maps convert the National Landslide Risk Management Strategy, 2019 from policy text into district-level planning evidence.

UPSC and this topic: PYQ weightage

Geo-disasters are a recurring mains theme. The actual questions UPSC has asked:

• 2015 (12.5 marks): The frequency of earthquakes appears to have increased in the Indian subcontinent. However, India's preparedness for mitigating their impact has significant gaps. Discuss various aspects.
• 2017 (15 marks): In December 2004, a tsunami brought havoc on 14 countries including India. Discuss the factors responsible for the occurrence of Tsunami and its effects on life and economy. In the light of the guidelines of NDMA (2010) describe the mechanisms for preparedness to reduce the risk during such events.
• 2019 (15 marks): Disaster preparedness is the first step in any disaster management process. Explain how hazard zonation mapping will help disaster mitigation in the case of landslides.
• 2021 (15 marks): Describe the various causes and the effects of landslides. Mention the important components of the National Landslide Risk Management Strategy.
• 2021 (GS-3, 10 marks): Discuss about the vulnerability of India to earthquake related hazards. Give examples including the salient features of major disasters caused by earthquakes in different parts of India during the last three decades.
• 2026 (GS-3, 10 marks): Discuss how the contradiction between 'rapid infrastructure development' and 'disaster-risk reduction' in ecologically-sensitive areas of India can be managed, with suitable examples.

Key Terms

• National Landslide Risk Management Strategy (2019): The National Landslide Risk Management Strategy (2019) is NDMA's national strategy for reducing landslide risk through hazard zonation, early warning, land-use regulation and community awareness. It set the framework for state landslide plans. Example: the strategy underpins the National Landslide Forecasting Centre's operations
• Indian Tsunami Early Warning Centre (ITEWC): The Indian Tsunami Early Warning Centre, operated by INCOIS in Hyderabad, is India's 24x7 tsunami warning system established after the 2004 tsunami. It can detect tsunamigenic earthquakes and issue bulletins within minutes, serving India and other Indian Ocean countries. Example: ITEWC issues tsunami advisories for the entire Indian Ocean region
• Koyna earthquake of 10 December 1967: The Koyna earthquake of 10 December 1967 was the magnitude 6.3 earthquake near the Koyna dam in Maharashtra that killed about 180 people. It is the world's most cited case of reservoir-induced seismicity, occurring just years after the reservoir filled. Example: Koyna remains a permanent field laboratory for studying reservoir-triggered earthquakes
• National Landslide Forecasting Centre (NLFC): The National Landslide Forecasting Centre, inaugurated on 19 July 2024 at the GSI's Dharitri Campus in Kolkata, is India's dedicated centre for issuing landslide forecasts and early warnings. It runs the Bhusanket portal and Bhooskhalan app. Example: NLFC issues regional landslide bulletins for vulnerable Himalayan and Western Ghats districts during the monsoon
• National Centre for Seismology (NCS): The National Centre for Seismology, under the Ministry of Earth Sciences, is India's nodal agency for earthquake monitoring, operating the national seismological network. It reports earthquake parameters in near real time. Example: the NCS issues earthquake alerts within minutes through its website and the BhooKamp app
• Landslide Atlas of India (2023): The Landslide Atlas of India (2023) is the NRSC/ISRO atlas mapping about 80,000 landslides across India between 1998 and 2022. Released in early 2023, it is the most comprehensive national inventory of landslide occurrence. Example: the atlas shows the Himalaya and Western Ghats as the densest landslide zones
• Induced (anthropogenic) earthquakes: Induced or anthropogenic earthquakes are earthquakes triggered by human activities such as reservoir impoundment, mining, fracking or geothermal extraction. Example: the Koyna earthquake of 1967 is attributed to reservoir-induced seismicity from the Koyna dam
• Joshimath land subsidence: Joshimath land subsidence is the sinking of the Uttarakhand town that cracked hundreds of buildings in January 2023, caused by construction on an old landslide mass, overloaded infrastructure and tunnelling for the Tapovan-Vishnugad project. The response included evacuation and compensation. Example: the crisis forced a national rethink of carrying capacity in Himalayan towns
• hazard zonation mapping: Hazard zonation mapping is the division of territory into zones of high, medium and low hazard susceptibility, guiding where construction is allowed, restricted or prohibited. It is the basis of land-use regulation in landslide and seismic areas. Example: landslide hazard zonation maps of Uttarakhand mark slopes where new construction needs geotechnical clearance
• Makran subduction zone: The Makran subduction zone is the tectonic boundary off Pakistan and Iran where the Arabian plate dives beneath the Eurasian plate, capable of generating tsunamis that threaten India's west coast. It produced the 1945 Balochistan tsunami. Example: ITEWC's warning system specifically models Makran-zone tsunami scenarios for Gujarat and Maharashtra
• Ring of Fire: The Ring of Fire is the horseshoe-shaped belt around the Pacific Ocean where most of the world's earthquakes and volcanic eruptions occur, driven by subduction zones. Example: the 2004 Sumatra earthquake that caused the Indian Ocean tsunami occurred on the Ring of Fire
• Reservoir-induced seismicity: Reservoir-induced seismicity is earthquake activity triggered by the filling of large reservoirs, where water pressure seeps into faults and lubricates them. It is a recognised induced hazard of big dams. Example: the Koyna earthquake of 10 December 1967 (magnitude 6.3) is the classic Indian case linked to the Koyna reservoir

Practice questions