Hazards — Class 8 Social Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 8 Social Science, Geography — Chapter 5. Natural and human-made dangers, and how we manage them.
1. About this lesson
This lesson explains hazards and disasters, the types of hazards, the main natural disasters, and disaster management.
2. Hazard and disaster
- A hazard is a natural process or event that threatens human life and property.
- A disaster is a hazardous event in a limited area and time that causes great loss of life and property and needs outside help.
3. Natural and human-made hazards
- Natural hazards result from natural processes with no human role — earthquakes, floods, cyclones, volcanic eruptions, droughts.
- Human-made hazards are caused by human activity — chemical leaks, oil spills, pollution and wars.
4. Major natural disasters
| Disaster | Cause |
|---|---|
| Earthquake | a violent tremor in the Earth's crust sending out shock waves |
| Cyclone | intense low-pressure storm with very high winds |
| Flood | land submerged by heavy rainfall or large sea waves |
| Drought | failure of the monsoon rains |
| Tsunami | giant sea waves from an undersea earthquake |
- India's flood-prone areas include Punjab, Haryana, Uttar Pradesh, North Bihar, West Bengal, the Brahmaputra valley, coastal Andhra Pradesh and Odisha.
- The Indian Ocean tsunami of 26 December 2004 (a magnitude 9.1 quake off Sumatra) killed about 2,25,000 people across many countries.
5. Disaster management
- Prevention — actions to stop a hazard harming people or property.
- Mitigation — actions to reduce the effects of a disaster (e.g. strong buildings, embankments).
- Preparedness — early-warning systems, mock drills and relief plans.
6. Worked examples
Example 1. Differentiate a hazard and a disaster. A hazard is a threatening event; a disaster is when it actually causes great loss and needs help.
Example 2. What causes a drought? The failure of the monsoon rains.
Example 3. What is mitigation? Activities that reduce the effects of a disaster.
7. Book-back questions (Samacheer Kalvi)
I. Choose the correct answer
- An earthquake is a violent tremor in the Earth's — (a) crust / (b) atmosphere. Ans: (a) crust.
- A drought is caused by the failure of the — (a) monsoon / (b) rivers. Ans: (a) monsoon.
- A giant sea wave caused by an undersea earthquake is a — (a) tsunami / (b) cyclone. Ans: (a) tsunami.
- An oil spill is an example of a — (a) natural / (b) human-made hazard. Ans: (b) human-made.
- Activities that reduce the effects of a disaster are called — (a) mitigation / (b) prevention. Ans: (a) mitigation.
II. Fill in the blanks 6. A hazardous event causing great loss of life and property is a disaster. 7. The Indian Ocean tsunami occurred on 26 December 2004. 8. The Brahmaputra valley is a major flood-prone area.
III. Answer briefly 9. Differentiate natural and human-made hazards. 10. What is the difference between prevention and mitigation?
8. Common mistakes
- Mistake: Using "hazard" and "disaster" interchangeably. Fix: A hazard is a threat; a disaster is the actual damaging event.
- Mistake: Calling an oil spill a natural hazard. Fix: Oil spills and chemical leaks are human-made hazards.
- Mistake: Mixing up prevention and mitigation. Fix: Prevention stops harm; mitigation reduces the effects.
9. Quick revision
- Geography Ch 5 · hazards and disasters.
- Hazard = threatening event; disaster = great loss needing help.
- Natural (earthquake, flood, cyclone, drought, tsunami) vs human-made (oil spill, pollution, war).
- 2004 Indian Ocean tsunami (mag 9.1, ~2,25,000 deaths); Brahmaputra valley flood-prone.
- Disaster management: prevention, mitigation, preparedness.
