CBSE Class 5 Science – 9. Volcanoes, Earthquakes and Tsunamis (Notes)

Introduction:

Our earth is a beautiful and safe place for all living beings.

It provides shelter to all. But sometimes it becomes furious and shows its anger through natural disasters such as volcanoes, earthquakes and tsunamis.

These cause great damage of life and property on the earth.

These are caused by the natural forces.

All these natural activities take place due to movement of molten materials within the earth.

 

Volcanoes – A vent in the earth crust through which molten materials irrupts suddenly are called volcano.

A volcano an opening in the earth’s crust that allows molten rocks or magma, ash or gases to reach the earth’s surface.

The magma that reaches the earth’s surface is called lava and the passage through which it travels is called vent.

Volcanoes are usually in the form of conical mountains.

 

 

There are three types of volcano:-

 Active volcano

 Dormant volcano

 Extinct volcano

 

Active volcano – Type of volcano that erupted regularly is called active volcano.

Example – Mount Vesuvius, Mount Fuji and Mount Erebus are some active volcanoes.

 

Dormant volcano – Type of volcano that has not erupted for a long time but can erupt any time is called dormant volcano. Example – Chile, Sitick and Alaska

 

Extinct volcano – Type of volcano that has not erupted for a long time in recorded history is called extinct volcano. Example – Mount Egneont in New Zealand, and Mount Kilimanjaro in Tanzania

 

Hot springs – Water from the ground gets heated in the volcanic rocks and comes out from the ground in the form of fountains of hot water. These are called hot springs or geysers.

 

Earthquake – The vibrations caused on the surface of the earth when the Lithospheric plates move are called earthquakes.

These vibrations can travel all around the earth.

The place in the earth where the movement starts is called the focus.

It is the origin of the seismic energy.

The place on the surface above the focus is called the epicentre.

Vibrations travel outwards from the epicentre as waves.

The strength of the earthquake decreases away from the epicentre.

In other words, the greatest damage is usually closest to the epicentre.

 

Seismograph – An instrument that records the size, force and direction of earthquakes is called Seismograph.

 

Richter scale – A scale on which the magnitude/strength of an earthquake is represented is called Richter scale.

 

Some areas on the earth’s surface are more prone to the earthquakes. In India the Himalayan region and the Ganga-Brahmaputra valley are prone to earthquakes. A large number of people lost their lives in massive earthquakes that occur in Uttarkashi in 1991, Chamoli in 1999, Gujarat in 2001 Jammu & Kashmir in 2005, China in 2008, Japan in 2011 and Nepal in 2015.

 

Measuring Earthquakes:

An earthquake generates waves that travel all over the earth.

These are called seismic waves.

Seismic waves are recorded by an instrument called seismograph.

The magnitude of an earthquake is measured on Richter scale.

The numbers on this scale range from 1 to 10.

Earthquakes below 6 are considered as moderate and mild and those above 6 are considered as severe.

 

Effects of an Earthquake:

An earthquake always causes destruction of lives and property.

The undersea earthquakes can cause disasters like tsunami.

They cause harm to the lives in the water.

The earthquakes also cause landslides and fires.

They disrupt the transport and communication system.

 

Tsunami – A series of waves caused by earthquakes or undersea volcanic eruptions is called tsunami.

The word tsunami is of the Japanese origin meaning “harbour wave”.

Tsunamis used to be called tidal waves, but they actually have nothing to do with the tides.

A tsunami is a huge wave in the ocean that develops as a result of an earthquake, volcanic eruption, undersea landslides or nuclear strike.

It can reach about a height of 100 feet (or 30 meters) with a great speed.

It can travel even faster than a commercial jet.

This powerful wall of water reaches the coast and causes a lot of damage to lives and property.

The undersea earthquake occurred in the Indian Ocean caused the tsunami of December, 2004 in which thousands of people from India, Sri Lanka and Indonesia lost their lives and property worth crores was damaged.

 

                         

 

It is important to know about tsunami because it causes a major damage and loss of life in the areas along coastlines which are affected by it. Its knowledge serves several interests.

 

Scientific interest – Measuring tsunami may help to understand the structure and nature of earth’s oceans,

 

Cultural interest – The major devastation sometimes caused by tsunami has an impact on lives for a long time.

 

Technological interest –  By studying tsunami, early warning sensor systems could be put into place to provide advance notice of when a tsunami is coming, although they travel at very fast pace.