Class 9 Science Note

Natural Disasters

The natural events that cause loss of life and properties and sometimes disturb the ecosystem are called natural disasters.


The overflow of the dry land when mixed with water from the river or streams is called flood.


Causes of flood

Heavy rainfall



Destruction of dam

The effects of flood are as follows:

It causes pollution in the sources of water and rivers.

It may create a vicious cycle of hunger.

It causes loss of lives of human beings, animals and lands as well.


The ways of controlling flood are:

Management of watershed

Use of engineering technology

Preparation of flood hazard map





Earthquake is the vibration of the surface of the earth caused due to the sudden release of stored energy beneath the surface of the earth.

The causes of earthquake are as follows:

Tectonic cause: The movement of tectonic plates creates pressure, which generates energy and stores in different places beneath the earth surface. This energy creates faults of rocks. In this process of creation of faults, seismic wave are produced and come out which vibrate the earth. This vibration of the earth is called earthquake.

Volcanic cause:  Volcanic activities are also responsible for the creation of earthquake. During volcano, the hot gases and magma are trying to come out of the earth. So, when magma erupts using gases on the surface of the earth, it generates seismic waves which vibrate the surface of the earth due to which earthquake is experienced.

Other cause: Human activities also cause the shaking of the earth surface in limited area. The underground detonation of the rock while 

using name the mine, constructing tunnels or the blasting of rocks in road construction, testing nuclear bombs disturbs the position of inner part of the earth surface as well as the position of the rocks. Such disturbance creates vibration on the surface of the earth and we experience earth quaking. Likewise land sliding, movement of the trains and heavy vehicles on the highway also cause the earthquake locally.


The effects of earthquake on environment are as follows:

The earthquake may bring changes on the form of earthquake. Like, plain surface of the earth may change into hills and mountains. Similarly, hills and mountains may change into plain surface.

It may bring serious problems in communication, transportation and supply of daily needs to human beings, because it destroys the underground communication cables, water supply pipe lines, oil pipe lines, gas pipelines, drainage system, roads and bridges.

It may cause land sliding which makes the agricultural land useless. It may also cause the disappearance of springs from a place and there may appear similar new spring water in new places due to the result of sizzling, extend and creating fractures on the earth surface.

It may cause firing which may cause air pollution. Similarly it may cause leakage of radiation from nuclear furnace that results the pollution of environment. Eventually, it brings deterioration of human health.



The sudden fall of the piece of land due to the force of gravity on mountain, hillside is called landslide.

Causes of landslide

Heavy rainfall


Soil erosion

Extraction of metals


The ways of controlling landslides are as follows:

a. Use of appropriate agricultural system: Nepal is an agricultural country, So, most of the people depend on agriculture. Therefore, it is very necessary to preserve the agricultural land from landslide. For this, scientific agricultural technology should be implemented. Terrace farming method is a proper way of cultivation in sloping land.

b. Use of Bioengineering: Generally, erosion occurs at the sides of small streams and rivers of hilly regions where geo-structure of the land is 

week. Due to this, the breadth of such streams and rivers are increasing each year. This process can be controlled by making check dam with retaining wall, using bamboos, wood etc on either sides of the streams and rivers. Besides this, the landslide can be controlled by planting deep rooted plants or other green grasses on either side. Thus the way of controlling landslide with the help of physical construction and green plants is known as bio-engineering technology.


Volcano: A volcano is a place through which molten rocks and gases escape into the surface of the earth or into the atmosphere.

The effects of volcano eruption are as follows:

During the volcano eruption, hot lava, volcano ash, and toxic gasses escape out on the surface of the earth. These things bring tremendous damage to the life of living organism.

The ash and other substances cover up the crops and fertile land.

Volcano substances bury and destroy the human made physical infrastructure.

Explosion of volcano near the ocean or on the surface of the ocean creates tsunami. It causes tremendous damage to the life of human beings as well as loss of property.

Safety measures of volcano

Warning should be given to the public who lives nearby the volcano active region.

New construction should not be made without studying the physical and chemical attributes in the belt of volcanic area.

Protection should be made from the toxic gas emitting from the volacano.




Cyclone is a very powerful and special type of storm formed in big seas or oceans growing upwards forcefully with rotated core of clouds.

Some of the precautions that should be taken against cyclone are as follows:

a. Shelter/houses should be constructed for the victims of cyclone.

b. Buildings in coastal areas should be constructed using safety measures or using cyclone resistant technology.

c. People should remain informed of the notice, warnings and instructions given by the government in different media and they should act accordingly.

d. Publics should be made aware of the safety Volcano


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