NATURAL DISASTER

Earthquake

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. The earth’s crust is divided into seven major plates, about 50 miles thick, that move slowly and continuously over the earth’s interior. Earthquakes are tectonic in origin, and their occurrence in populated areas may cause numerous casualties and injuries, as well as extensive property damage.

The Earthquake Risk in India

India’s increasing population and widespread unscientific constructions—multistoried apartments, factories, malls, and warehouses—put the country at high seismic risk. In the last 15 years, India has experienced 10 major earthquakes causing over 20,000 deaths. Over 59% of India’s land area is under moderate to severe seismic hazard (IS 1893: 2002).

Historically, the Himalayan belt has experienced several major earthquakes: 1897 Shillong (M8.7), 1905 Kangra (M8.0), 1934 Bihar-Nepal (M8.3), and 1950 Assam-Tibet (M8.6). Other non-Himalayan regions have also seen significant quakes such as the Koyna earthquake in 1967 and the Killari earthquake in 1993, prompting revisions to India’s seismic zoning maps.

The North-Eastern region and the Andaman and Nicobar Islands frequently experience damaging earthquakes. Urbanization and high-tech industries also increase the risk of severe economic loss in events affecting mega-cities like Delhi or Mumbai.

Resources and Initiatives:

• Shillong 1897 Earthquake Scenario
• Seismic Vulnerability Assessment
• Earthquake Disaster Awareness Resources
• Disaster Resistant Construction Practices
• Techno-Legal Frameworks for Safe Construction
• Past Projects and Risk Management Material
• Post-Earthquake Reconnaissance Reports
• Homeowner Safety Guidelines

Floods

India is highly vulnerable to floods. Out of 329 million hectares of geographical area, more than 40 million hectares are flood-prone. Floods cause huge losses to lives, property, livelihoods, and infrastructure. Annual average flood damage rose from ₹1805 crore (before 1996) to ₹4745 crore (1996–2005).

Each year, about 75 lakh hectares of land are affected, 1600 lives are lost, and damage amounts to ₹1805 crores. In 1977 alone, 11,316 people lost their lives. Floods have occurred even in non-traditional flood-prone areas, emphasizing the need for robust flood management strategies.

Most rainfall occurs during the monsoon (June–September), and heavy sediment loads, inadequate drainage, cyclones, and cloudbursts are key flood causes. Many rivers causing floods originate in neighboring countries, adding to the complexity.

Landslide

India’s mountainous regions—especially the Himalayas, Northeastern hills, Western Ghats, Nilgiris, Eastern Ghats, and Vindhyans—are landslide-prone. The northward movement of the Indian plate causes continuous stress on rocks, making them weak and landslide-susceptible.

Landslides in areas like Darjeeling, Sikkim, Mizoram, Meghalaya, Assam, and the Western Ghats cause recurring losses. The Nilgiris and the Konkan coast also face high landslide risk due to their geological makeup.

Notable Landslide Events:

• Varnavat, Uttarkashi District
• Malpha, Pithoragarh District
• Okhimath, Chamoli District
• Paglajhora, Darjeeling
• Aizawl Sports Complex, Mizoram

Management includes hazard zone mapping, stabilization, monitoring, and early warning systems.

Cyclones

Cyclones are atmospheric disturbances around low-pressure areas, accompanied by strong winds and storms. Air circulation is anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Types of Cyclones:

• Extra Tropical Cyclones (Temperate zones)
• Tropical Cyclones (Develop in tropical/subtropical regions)

Tropical cyclones are powered by sea heat and trade winds, and they are classified in India by:

• Wind strength
• Storm surge
• Rainfall

Worldwide Terminology:

• Typhoons – China Sea and Pacific Ocean
• Hurricanes – Caribbean Sea and Atlantic Ocean
• Tornadoes – USA and West Africa
• Willy-willies – Australia
• Tropical Cyclones – Indian Ocean

Indian Meteorological Department (IMD)

The IMD classifies low-pressure systems in the Bay of Bengal and Arabian Sea based on potential to cause damage. These criteria are adopted by the World Meteorological Organization (WMO).