Class 11 Geography Chapter 6: Natural Hazards and Disasters Notes in English

1What Is a Hazard? What Is a Disaster?

Change never stops. Some changes are slow, like a river carving a valley over thousands of years. Some are sudden, like an earthquake. Nature does not call any of these “good” or “bad”, they just happen. It is only from a human point of view that a change becomes something to fear, because it threatens our lives and property.

Students often use “hazard” and “disaster” as if they mean the same thing. The book treats them as two related but different ideas, and this exact difference is a favourite one-line exam question.

Not every disaster is natural. Some are entirely man-made: the Bhopal Gas Tragedy and the Chernobyl nuclear disaster happened because of human error, not nature; wars, the release of CFCs (chlorofluorocarbons), and noise, air, water and soil pollution are also directly caused by people. Other disasters are natural but made worse by human activity: deforestation and unscientific land use turn an ordinary rainy season into a flood or a landslide.

The world’s understanding of disasters has changed too. Earlier, people simply avoided living in disaster-prone areas, so the damage stayed limited. Today, technology has given humans the power to build almost anywhere, so cities and ports have grown right inside disaster-prone zones, for example the colonisation of river flood plains and port cities like Mumbai and Chennai along the coast. This is exactly why the scale of damage from disasters has increased even though our ability to predict them has also improved.

1.2 Classification of Natural Disasters

To manage disasters scientifically, they first have to be identified and classified. The book sorts every natural disaster into four broad groups, based on which part of the environment it disturbs.

India experiences almost every disaster on this list, every year, losing thousands of lives and property worth millions of rupees. This is because of its sheer size and diversity, which is why scholars call it the Indian subcontinent and the land of unity in diversity. A vast geographical area, many different climates and cultures, a long colonial past, and a very large population all add up to make India more vulnerable, not less, to natural disasters.

2Earthquakes and Tsunami

2.1 Earthquakes

Earthquakes are the most unpredictable and the most destructive of all natural disasters. The most damaging ones come from tectonic activity, movements deep inside the earth’s crust, while earthquakes caused by volcanic eruptions, rockfalls, landslides, mining subsidence, or the weight of a new dam and reservoir affect a much smaller area.

Some of the most vulnerable states and union territories are Jammu and Kashmir, Ladakh, Himachal Pradesh, Uttarakhand, Sikkim, the Darjeeling area of West Bengal, and all seven north-eastern states. Even parts of the old, stable Peninsular block have had severe earthquakes, Gujarat in 1819, 1956 and 2001, and Maharashtra in 1967 and 1993. Scientists have proposed a new fault-line theory along the Bhima (Krishna) river near Latur and Osmanabad in Maharashtra, suggesting the Indian Plate itself may be breaking there.

After studying more than 1,200 past earthquakes, the National Geophysical Laboratory, the Geological Survey of India, the Department of Meteorology and the National Institute of Disaster Management divided India into five earthquake damage-risk zones, in order: Very High, High, Moderate, Low and Very Low damage risk. The book describes the areas under each of the first three separately, then groups the safest, low-risk parts of the country together, so the table below follows the same grouping.

An earthquake in a densely populated area becomes a calamity: it destroys homes, factories, roads and communication links all at once, which is exactly what makes relief work so difficult afterwards. It can also trigger surface fissures through which water and gases escape and flood nearby land, and it can cause landslides that block rivers, sometimes forming new lakes or changing a river’s course entirely.

2.2 Tsunami

A tsunami behaves very differently in the open ocean and near the coast, which is exactly why ships far out at sea barely notice one passing under them.

Tsunamis occur most often along the Pacific “Ring of Fire”, off Alaska, Japan, the Philippines, Indonesia, Malaysia, Myanmar, Sri Lanka and India. The most devastating one in living memory struck on 26 December 2004, killing more than 300,000 people across the Indian Ocean rim. India joined the International Tsunami Warning System after this disaster.

3Tropical Cyclones

A cyclone’s force decreases the further it travels from the sea, since its energy comes from the latent heat of warm, moist sea air. Along the Indian coast, cyclonic storms average 180 km/h. Their most damaging effect is the storm surge, an abnormal rise in sea level caused by very strong winds and low pressure pushing sea water inland along with heavy rain, flooding settlements, farmland and destroying structures.

4Floods

Unlike most other disasters, floods are slow to build up and occur in well-known regions at a fairly predictable time of year. They can be triggered by heavy surface run-off, a cyclone’s storm surge, unusually long spells of heavy rain, melting snow and ice, poor infiltration into the soil, or extra silt from soil erosion clogging up river channels. Floods are especially frequent and damaging across South, South-east and East Asia, particularly China, India and Bangladesh.

Human activity plays a big part too: deforestation, poor farming practices, disturbing natural drainage, and building homes and farms right on flood plains and river beds all make floods worse. The Rashtriya Barh Ayog (National Flood Commission) has identified 40 million hectares of Indian land as flood-prone.

5Droughts

Drought is not a single, simple thing, it is a complex mix of rainfall, evaporation, soil moisture, farming practices and socio-economic conditions. The book names four distinct types.

Along with these, droughts kill large numbers of cattle, force people and their livestock to migrate, and push people to drink contaminated water, spreading diseases like gastro-enteritis, cholera and hepatitis.

6Landslides

Landslides are much more localised than earthquakes or cyclones, which are controlled by large, regional factors. A landslide instead depends on very local conditions, geology, slope, land-use, vegetation cover and human activity right at that one spot, which is exactly why gathering information about them is both difficult and expensive.

Even though the direct area affected is small, a landslide’s effects can spread far: it can block roads and railway lines, and it can dam or divert a river, causing floods somewhere else entirely. It also makes travel and trade in the area riskier and more expensive, which slows down development.

7Disaster Management

Cyclones are actually easier to manage than earthquakes, tsunamis or volcanic eruptions, because modern tracking can predict their time, place, direction and intensity reasonably well. This lets governments build cyclone shelters, embankments, dykes and reservoirs, and plant trees to slow down the wind, in advance. Even so, countries like India, Bangladesh and Myanmar keep losing lives because so many people live right on the vulnerable coast.

Every disaster, whatever its cause, is handled in three stages.

The Disaster Management Bill, 2005 and the founding of the National Institute of Disaster Management are the Government of India’s two clearest steps in this direction.