Natural Hazards & Disasters

• Difference between a hazard and a disaster.
• Earthquakes: causes, measurement, India's earthquake zones.
• Volcanoes: types of eruptions, famous examples.
• Floods in India — causes, effects, management.
• Cyclones — how they form, India's vulnerable coastline.
• Disaster management in India.

Hazard vs Disaster

Not all hazards become disasters — a powerful earthquake in an uninhabited desert causes little disaster; the same earthquake under a city is catastrophic.

Earthquakes

Cause

• Earth's crust is broken into tectonic plates floating on the mantle.
• Plates move slowly; at plate boundaries, friction builds up.
• When stress releases suddenly → ground shakes = earthquake.
• Focus (hypocentre): point underground where quake originates.
• Epicentre: point on the surface directly above the focus.
• Seismic waves travel outward from the focus.

Measurement

• Seismograph: instrument that records earthquake waves.

India's earthquake zones

India divided into 5 seismic zones (Zone I = least risk to Zone V = most risk):

• Zone V (highest risk): J&K, Himachal Pradesh, Uttarakhand, northeast states, Andaman & Nicobar.
• Zone IV: Delhi, parts of UP, Bihar, West Bengal.
• Zone II: Southern peninsular India (generally stable).

Recent major earthquakes: Bhuj (Gujarat, 2001) — 7.7 magnitude; ~20,000 deaths.

Effects and safety

• Ground shaking → building collapse → fires → landslides → tsunamis (if undersea).
• Do: Drop, Cover, Hold; move away from windows; if outdoors, move away from buildings.
• Don't: Use lifts; run outside during shaking.

Volcanoes

Cause

• Magma (molten rock) beneath Earth's crust rises through vents → erupts as lava.
• Mostly at plate boundaries or "hot spots" (e.g., Hawaii).

Types of eruptions

Volcanoes in India

• Barren Island (Andaman & Nicobar) — India's only active volcano.
• Narcondam Island (Andaman) — dormant volcano.

Floods

Causes in India

• Heavy monsoon rainfall — rivers overflow banks.
• Deforestation — less absorption of rainwater; rapid runoff.
• Dam failure or release.
• Encroachment on floodplains — people build on land that naturally floods.
• Poor drainage in cities — heavy rain → urban flooding.

States most affected

Bihar, Assam, UP, West Bengal, Odisha — rivers like Ganga, Brahmaputra, Kosi flood regularly.

Effects

• Crop loss, property damage, displacement, spread of waterborne disease (cholera, malaria).
• Kosi River called "Sorrow of Bihar" — floods almost every year.

Management

• Embankments (dams along river banks) — reduce flooding but can cause worse floods if they break.
• Early warning systems.
• Flood-resistant housing; elevated roads.
• Wetland conservation — natural sponges for floodwater.

Cyclones

What is a cyclone?

• Cyclone = a large rotating storm with very low pressure at the centre.
• Form over warm ocean water (26°C+) — heat evaporates water → rising air → rotation due to Earth's spin (Coriolis effect).
• Called hurricane (Atlantic), typhoon (Pacific), cyclone (Indian Ocean).

How cyclones affect India

• Bay of Bengal: most cyclones form here; hit Odisha, AP, TN, WB coasts.
• Arabian Sea: fewer but intense cyclones; hit Gujarat, Maharashtra, Kerala coasts.
• Cyclone season: October–December (northeast monsoon, Bay of Bengal) and May–June (pre-monsoon).

Famous cyclones

• Odisha Super Cyclone (1999): 10,000+ deaths; 15 million affected.
• Cyclone Fani (2019, Odisha): massive early warning → only ~89 deaths despite being Category 5.

Disaster management improvement

• India Meteorological Department (IMD): issues 3–7 day cyclone warnings.
• NDMA (National Disaster Management Authority): coordinates response.
• Cyclone shelters built along coast; evacuation drills.
• Fani example: 1.2 million people evacuated in 48 hours → proof that early warning saves lives.

Disaster Management in India

• National Disaster Management Act, 2005.
• NDMA: headed by PM; sets policies.
• NDRF (National Disaster Response Force): trained rescue teams; deployed during disasters.
• State Disaster Management Authorities (SDMAs): state-level coordination.

• What is the difference between a natural hazard and a disaster?
• What causes earthquakes? What is the difference between focus and epicentre?
• Name India's five seismic zones and give one state in Zone V.
• How do cyclones form? Which coast of India is most vulnerable?
• What steps did India take before Cyclone Fani that saved lives?

Open the Practice tab for graded questions on Natural Hazards & Disasters.