Our Changing Earth

1. What are lithospheric plates?

• The lithosphere is broken into numerous pieces.

• These big pieces are called lithospheric plates.

• The earth’s crust consists of several large and small, rigid, irregularly shaped plates/pieces.

• The movement of these plates causes changes on the surface of the earth.

2. Why do the lithospheric plates move slowly?

The lithospheric plates move slowly because of the slow movement of molten magma inside the earth in a circular manner.

3. What are the two types of the earth’s forces?

• The earth’s movements are divided on the basis of the forces which cause them.

• The forces which act in the interior of the earth are called endogenic forces.

• The forces that work on the surface of the earth are called exogenic forces.

• Endogenic forces sometimes produce sudden movements.

• At other times they produce slow movements.

• Sudden movements are earthquakes and volcanoes.

• They cause mass destruction over the surface of the earth.

4. Define a volcano.

A volcano is a vent or a hole in the earth’s crust through which molten material erupts suddenly.

5. What are earthquakes? Define focus and epicentre.

Earthquake

• When the lithosphere plates move, the surface of the earth vibrates.

• The vibrations travel all around the earth.

• These vibrations are called earthquake.

Focus:

The place or point in the crust where the movement starts is called Focus.

Epicentre:

The place or the surface above the focus is called Epicentre.

• Vibrations travel outwards from the epicentre as waves.

• Greatest damage occurs closest to the epicentre.

• The strength of the earthquake decreases, going away from the centre.

6. What are three types of earthquake waves?

There are three types of earthquake waves:

• P waves or longitudinal.

• S waves or transverse waves.

• L waves or surface waves.

7. How can we minimise the impact of an earthquake?

• Earthquakes cannot be predicted.

• Their impact can certainly be minimised if we are prepared before hand.

8. Give an account of some common earthquake prediction methods adopted locally by people.

Some of the common earthquake prediction methods adopted locally by people are:

• Wild animal behaviour.

• Agitated fish in the ponds.

• Snakes coming out to the surface from their holes.

• Animals trying to untie themselves and run away.

• Birds leaving their nests and beginning to chatter loudly.

• Aborigines beginning to run to higher grounds.

9. What is seismograph? How is the magnitude of earthquake measured?

• An earthquake is measured with a machine.

• It is called a seismograph.

The magnitude of the earthquake is measured on Richter scale.

• An earthquake of 2.0 or less is felt only a little.

• An earthquake over 5.0 causes damage from things falling.

• A 6.0 or higher magnitude is considered very strong and 7.0 is classified as a major earthquake.

10. Explain Earthquake preparedness.

Earthquake Preparedness:

When an earthquake strikes we should do the following:

• We should be in a safe spot like: under a kitchen counter, table or desk.

• We should stand against an inside comer or wall.

• We should stay away from fire places, areas around chimneys, windows that shatter including mirrors and picture frames.

• We should be prepared by arousing awareness amongst our friends and family members.

• We should face any disaster confidently.

11. What are the two processes which continuously wear away the landscape? Explain them.

The Processes:

The landscape is continuously worn away by two processes.

They are:

• Weathering and erosion.

• Weathering is the breaking up of rocks on the earth’s surface.

• Erosion is the wearing away of the landscape by different agents like water, wind and ice.

• The eroded material is carried away or transported by water, wind etc.

• They deposit material eventually.

• This process of erosion and deposition creates different landforms on the surface of the earth.

Work of a River

12. What is a waterfall? Explain with example.

When the rivers tumble at steep angle over the hard rocks of a deep steep valley it forms a waterfall.

For example: Victoria waterfalls or Niagara waterfall.

13. Describe the work of a river.

Work of a River:

• Running water in the river erodes the landscape.

• When the river tumbles at steep angle over very hard rocks or down a steep valley side, it forms a waterfall.

• When the river enters the plain it twists, turns and forms large bends. These bends are known as meanders.

Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer.

• In due course of time the meander loop cuts-off from the river and forms a cut-off lake.

• It is called an ox-bow lake.

• At times the river overflows its banks.

• This leads to the flooding of the neighbouring areas.

• The flood water deposits layers of fine soil and other material.

• They’are called sediments, along its banks.

• This leads to the formation of a flat fertile land called a flood plain.

• The raised banks are called levees.

As the river approaches the sea, the speed of the running water decreases.

• The river begins to break up into a number of streams. They are called distributaries.

• Now the river becomes so slow that it begins to deposit its load.

• Each distributary forms its own mouth.

• The collection of sediments from all the mouths forms a delta, the triangular shaped land mass.

14. Write a note on the work of sea-waves.

Work of Sea Waves

• Erosion and deposition of the sea waves form coastal land forms.

• Sea waves continuously strike at the rocks.

• Cracks develop.

• In course of time they become larger and wider.

• Hollow like caves are formed on the rocks.

• They are called sea caves.

• As caves become bigger and bigger only the roofs of the caves remain. This leads to formation of Sea arches.

• Continuous erosion breaks the roofs and only walls are left.

• These wall-like features are called stacks.

• The steep rocky coast rising almost vertically above sea water is called sea cliff.

• The sea waves deposit sediments along the shores.

• This leads to formation of sea beaches.