Maharashtra Board Class 11 Environmental Science Chapter 5 Disasters PDF Download

5. Disasters

5.1 Understanding disasters

5.2 Types of disasters

5.3 Natural disasters

5.4 Man made disasters

5.5 Effects of disasters

5.6 Disaster emergency kit

5.7 Activity

5.1 Understanding Disasters

A disaster is "a sudden accident or a natural catastrophe that causes great damage or loss of life". A disaster is an event or series of events, which gives rise to casualties and damage or loss of property, infrastructure, essential environmental services, or means of livelihood.

Disasters threaten sustainable economic development worldwide. In the past twenty years, earthquakes, floods, tropical storms, droughts and other calamities have killed around three million people, inflicted injury, disease, homelessness, and misery on one billion people, and caused damage worth millions of rupees. Disasters destroy decades of human effort and investments, thereby placing new demands on society for reconstruction and rehabilitation.

Teacher's Note

Disasters can happen anytime and anywhere. Just like when heavy rain floods your street, we need to be prepared and safe always.

Exam Trick

Remember: Disaster = sudden damage to many people. Just like when a heavy storm breaks your house, disasters break many houses at one time.

Points to Remember

A disaster is a sudden accident that causes great damage.
Disasters harm many people and destroy their homes and property.
Disasters destroy roads, buildings and other things we need.
We need money and help to build things again after a disaster.
Disasters can happen in any place at any time.

5.2 Types Of Disasters

We shall discuss some of the disasters as follows;

Features Of Disasters

It disrupts the normal functioning of society.

It affects large number of people.

It causes large scale loss to life and property.

It affects a community which requires external aid to cope with the losses.

Teacher's Note

There are two types of disasters - natural and man made. Natural disasters happen because of nature like earthquakes. Man made disasters happen because of human mistakes like factory fires.

Exam Trick

Remember: Natural = Nature made (earthquake, flood). Man made = Human made (fire, accident). Think - what did humans do to cause it?

Points to Remember

Natural disasters are caused by nature and we cannot stop them.
Man made disasters happen because of human mistakes or carelessness.
Both types of disasters hurt many people and destroy property.
Disasters disrupt our daily life and work.
We need help from the government and others after a disaster.

5.3 I. Natural Disasters

A) Earthquakes

Earthquakes cause the shaking, rolling or movement of the earth's surface. Earthquakes happen along cracks (called fault lines) in the earth's surface. Earthquakes can be felt over large areas, although they usually last less than one minute. Earthquake is a sudden geological event below the surface of the earth which results in generation of shock waves that travel far and wide and cause vertical and horizontal vibrations. These consequential motions cause destructions of infrastructure. The severity of the impact depends on the magnitude of the earthquake, which in turn depends on the amount of energy released at the spot where the geological event takes place below the surface of the earth. Scientific study of earthquakes is called seismology. Therefore, earthquake activity is also referred to as seismic activity.

Earthquakes are considered to be one of the most dangerous and destructive natural hazards. The impact of this phenomenon is sudden with very little warning or without any warning. Large number of earthquakes occur every year all-round the earth but only a limited number of them are centered near populated areas or are having sufficient strength to cause damage to the environment. It can destroy buildings and infrastructure in seconds, killing or injuring the inhabitants. Earthquakes not only destroy the entire habitation but may destabilize economy and social structure of the region.

Teacher's Note

An earthquake is when the ground shakes very fast. It happens in a few seconds but can cause big damage like in Nepal earthquake in 2015.

Exam Trick

Remember: Seismic = Shaking. Earthquake activity = Seismic activity. Just remember "Seismic" means the earth is shaking below.

Points to Remember

Earthquakes happen suddenly with little or no warning.
They are caused by movement of rock layers below the earth.
Strong earthquakes can destroy buildings and kill people.
The strength of an earthquake is measured on the Richter Scale.
We must know how to stay safe during an earthquake.

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