Maharashtra Board Class 8 Science Chapter 9 Disaster Management PDF Download

9. Disaster Management

What do you mean by disaster?

What are the different types of disaster?

Last year we have introduced various natural calamities and disasters. This year we are going to study about earthquake and some other natural calamities.

What is an earthquake? What are the effects of earthquake?

Earthquake

Sudden vibrations on the earth and shaking of the earth surface or ground is called an earthquake. These cause seismic waves leading to movements of the earth's surface like tremors, shaking or it goes up-down.

The shocks and waves formed in the interior of the earth spread on the surface in all directions. The central point of earthquake is the point above the epicenter on the earth surface. Strong convulse or waves at first reach to the epicenter, therefore major loss occurs near to that area.

Shocks occurred due to an earthquake can be mild or intensified (acute). On the earth mild earthquakes occur in a larger number than the intensified ones.

Everyday, earthquakes are noticed at some or the other places on the earth. According to the observation of National Earthquakes information center every year nearly 12,400 to 14,000 earthquakes occur on the earth. From this it is noticed that earth is continuously vibrating.

The machine or instrument which records the earthquakes is called Seismograph or Seismometer, and the accentuation (intensity) is measured in Richter Scale. This is one of the mathematical measuring unit.

Effects of earthquakes are mentioned below. Study them carefully.

Teacher's Note

Earthquakes happen suddenly and shake the ground. In India, cities like Delhi and Mumbai sometimes feel small earthquakes. It is important to know how to stay safe during an earthquake.

Exam Trick

Remember: Seismograph records earthquakes like a camera records videos. Richter Scale measures how strong the earthquake is. Higher number means stronger earthquake.

Points to Remember

Earthquake is sudden shaking of the ground caused by movement inside the earth.
Seismograph is the machine that records earthquakes.
Richter Scale measures the strength of earthquakes.
Mild earthquakes happen more often than strong ones.
About 12,000 to 14,000 earthquakes happen on earth every year.

9.2 Focal Point And Epicenter Of Earthquake

The machine or instrument which records the earthquakes is called Seismograph or Seismometer, and the accentuation (intensity) is measured in Richter Scale. This is one of the mathematical measuring unit.

Effects of earthquakes are mentioned below. Study them carefully.

Teacher's Note

The focal point is deep inside the earth where the earthquake starts. The epicenter is the point on the surface above the focal point. In India, the epicenter of the 2001 Gujarat earthquake was near Bhuj city.

Exam Trick

Remember: Focal point is inside the earth. Epicenter is on top of the earth, just like how an island is on top of water. The epicenter is always above the focal point.

Points to Remember

Focal point is the place inside the earth where earthquake starts.
Epicenter is the point on the earth surface above the focal point.
Strongest shaking happens near the epicenter.
Seismic waves spread out from the focal point in all directions.
More damage occurs near the epicenter because waves reach there first.

9.3 Seismometer

The machine or instrument which records the earthquakes is called Seismograph or Seismometer. There are two types of seismometers: vertical seismometer and horizontal seismometer.

Teacher's Note

A seismometer works like a bell that rings when there is an earthquake. Scientists use these machines to know where earthquakes happen and how strong they are. India has many seismometers to watch earthquakes.

Exam Trick

Remember: Seismometer detects earthquakes like a smoke detector detects fire. It shakes when the ground shakes and records the movement on paper or computer.

Points to Remember

Seismometer is a machine that records earthquakes and shakes of the ground.
Vertical seismometer records up and down movements.
Horizontal seismometer records side to side movements.
Both types of seismometers help scientists study earthquakes.
Richter Scale uses seismometer readings to measure earthquake strength.

Causes Of An Earthquake

Volcanic eruption

Stress of big dams on the earth

Mining

Underground atomic tests

Water percolates through the cracks of the earth. Due to tremendous heat, the water converts into steam. The steam formed tries to come out from the loosened earth surface causing earthquakes

Effects Of An Earthquake

Loss of human beings, wild animals and pets

Economic loss at large scale such as electric poles, pipelines, houses, buildings, roads and railway tracks are destroyed

Ecosystem destruction due to the loss of biodiversity

Direction of flow of rivers and streams changes

Possibility of fire in cities increases

If there is earthquake at the bottom of ocean, it may create tsunami waves and thereby large scale destruction of coastal region

Level of water-table changes

Teacher's Note

Earthquakes cause very big problems in India. In 2001, Gujarat had a bad earthquake that destroyed many houses and buildings. Many people died and lost their homes.

Exam Trick

Remember: Five main causes of earthquakes are volcanoes, big dams, mining, atom bombs, and water turning to steam. Five main effects are loss of people, money loss, ecosystem damage, river changes, and tsunami waves.

Points to Remember

Earthquakes can be caused by volcanoes pushing rocks up.
Big dams can cause small earthquakes because of their weight.
Mining removes rocks which weakens the earth.
Underground atom tests shake the earth.
Water turning to steam inside the earth can cause earthquakes.

9.4 Precautions To Be Taken

Precautions To Be Taken At The Time Of Earthquake

If you are at home, then, do not get scared and instead of running here and there, stand still at one place. Either sit on the floor or below the bed or any other furniture and cover yourself until the movement of earth stops. If there is no table or any other shelter then sit in any corner of the room and cover your head by folding your hands around it.

If you are in the vehicle or outside the house, then park your vehicle at a safe place and sit inside it. Do not wait near or below tall building, trees or electric pole.

Avoid Doing Following Things During Earthquake

Avoid using lift in the multistoried building, instead use staircase

Do not sit in discomfort for long. Do some physical movements

After the earthquake there is a possibility of fire, hence, to avoid it carefully switch off the main electric supply. Do not use candles, lantern, or matchbox, instead use torch or battery

Earthquake Resistant and Proof Buildings

The constructions which do not get damaged due to earth movements upto a certain limit, are called earthquake resistant buildings. To construct tall buildings, Indian Standard Institute has made some code of conduct. Buildings are constructed as per I.S. 456 and earthquake resistant constructions are performed as per IS 1893 (Criteria for earthquake resistant design of structure) and IS 13920 (Ductile detailing of reinforced concrete structures subjected to seismic forces). Advanced technology is used for earthquake resistant construction.

To get prior intimation about earthquake, modern equipments like laser ranging very long baseline, geiger counter, creep meter, strain meter, tide gauge, tilt meter, volumetric strain gauge etc. are used.

Teacher's Note

When an earthquake comes, the safest place is under a strong table or bed. This protects you from falling objects. In India, new buildings are made earthquake-proof so they do not fall down easily.

Exam Trick

Remember: DROP, COVER, and HOLD ON. Drop to the ground, cover your head with your hands, and hold on to something. Never use lifts during earthquake because they can get stuck.

Points to Remember

Do not run out of the building during an earthquake.
Hide under a strong table or bed to protect yourself.
Switch off gas and electricity after the earthquake stops.
Do not use lifts, always use stairs.
Earthquake-proof buildings are made with special technology so they do not break easily.

Fire

Is fire a natural calamity or man made calamity?

Types Of Fire

Class A Fire (Solid substances): Commonly flammable materials are their fuel source such as wood, clothes, coal and papers. This fire can be put out with water.

Class B Fire (Liquid substances): Fires caused due to flammable liquid substances such as petrol, oil, varnish, solvents, cooking oil and paints. All these substances are lighter than water, therefore, fire extinguishers can be used to extinguish fire.

Class C Fire (Gaseous Substances): Fires caused due to acetylene and household gas (L.P.G.)

Class D Fire (Chemical substances): Fires caused due to combustible metals like potassium, sodium and calcium, which react with water at normal room temperature. Magnesium, aluminum and zinc react with water at high temperature. When both these groups combine with water, it explodes.

Class E Fire (Electrical): A fire caused due to electrical components is class E fire. To extinguish such fire, power is cut off and non-conductive fire extinguishers like carbon dioxide are used.

Methods Of Fire Extinction

There are 3 main methods to stop the spreads of fire or to control the fire.

Cool Out (Use of Water): To extinguish fire water is most common and effective solution which is easily available everywhere. If you spray water on the fire or around the fire it creates cooling effect and helps to control the fire.

Suppress the Fire: To control the fire which is caused due to electricity or oil, sand or soil can be used. If we spread a froth like substance on the fire, it cuts off the contact between air and fire. This method is more useful to extinguish the fire spread due to oil.

Keep Away Flammable Substances: In this method, all flammable substances are kept away from the fire. Any wooden article or flammable substances must be kept away so that no source is left for the fire to spread. Stirr up pump is the best device to put off small fires. It sprays water in all directions around the fire.

Precautions And Safety Measures

Develop the habit of switching off the gas regulator when not in use specially during night. Switch off the electrical appliances when you are going out of the house.

To make others alert and call them for help, shout loudly.

Call fire brigade.

Provide information how to use fire extinguishers.

First Aid

Let the patient sit or sleep in a comfortable position and call the doctor immediately.

Teacher's Note

Fire spreads very fast and can burn down houses and forests. In India, many fires happen in cities because of careless use of gas stoves and electricity. Always check that gas is turned off before you sleep.

Exam Trick

Remember: Five types of fire need different ways to put them out. Class A = water, Class B = foam or extinguisher, Class C = special powder, Class D = sand, Class E = carbon dioxide. Do not use water on electrical fires.

Points to Remember

Class A fire comes from solid things like wood and paper and can be put out with water.
Class B fire comes from liquids like oil and petrol and needs special foam.
Class C fire comes from gases like cooking gas and LPG.
Class D fire comes from chemicals and reacts badly with water.
Class E fire comes from electricity and needs special extinguishers.

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