Natural Hazards And Disasters Class 11 Notes Geography Chapter 6 - CBSE

Chapter : 6

What Are Natural Hazards And Disasters ?

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A Disaster is an undesirable occurrence resulting from forces that are largely outside human control, strike quickly with little or no warning, cause or threaten serious disruption of life and property, including death and injury to a large number of people, and requires, therefore, mobilisation of efforts in excess of that which are normally provided by statutory emergency services.
Disasters are also caused by some human activities. There are some activities carried by human beings that are directly responsible for disasters. Bhopal Gas tragedy, Chernobyl nuclear disaster, wars, release of CFCs (Chlorofluorocarbons) and increase of green house gases, environmental pollutions such as noise, air, water,
and soil are some of the examples.
Geological Survey of India, Department of Meteorology, Government of India, along with the recently formed National Institute of Disaster Management, have divided India into the following five earthquake zones:
- Very high damage risk zone
- Moderate damage risk zone
- Very low damage risk zone
- High damage risk zone
- Low damage risk zone

Cyclones originate between 10°–15° north latitudes during the monsoon season. In Bay of Bengal, cyclones mostly develop during the months of October and November. Here, they originate between 16°–2°N latitudes and to the west of 92°E. By July, the place of origin of these storms shifts to around 18°N latitude and west of 90°E near the Sunderban Delta. A tropical cyclone or hurricane: It is like a heat engine that is energised by the release of latent heat on account of the condensation of moisture that the wind gathers after moving over the oceans and seas.
Drought: The term ‘drought’ is applied to an extended period when there is a shortage of water availability due to inadequate precipitation, excessive rate of evaporation, and over utilisation of water from the reservoirs and other storages, including the ground water.
On the basis of severity of droughts, India can be divided into the following regions:
- Extreme Drought Affected Areas
- Severe Drought Prone Area
- Moderate Drought Affected Area
Flood: When a river bursts, its banks and the water spills out onto the floodplain which is termed flood. Floods occur commonly when water in the form of surface run-off exceeds the carrying capacity of the river channels and streams and flows into the neighbouring low-lying flood plains.
Landslide: It refers to a form of mass movement in which rock and debris moves rapidly downslope under the
influence of gravity as a result of failure along a shear plane.
Tsunamis: Earthquakes and volcanic eruptions cause the sea floor to move abruptly resulting in sudden
displacement of ocean water in the form of high vertical waves called tsunamis (harbour waves) or seismic sea waves.