Our Changing Earth



--> The lithosphere is broken into a number of plates known as the Lithospheric plates.

-->The forces which act in the interior of the earth are called as Endogenic forces and the forces that work on the surface of the earth are called as Exogenic forces.

--> A volcano is a vent (opening) in the earth’s crust through which molten material erupts suddenly.

--> when the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all round the earth. These vibrations are called earthquakes.

--> The place in the crust where the movement starts is called the focus.

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

--> There are three types of earthquake waves:

1. P waves or longitudinal waves
2. S waves or transverse waves
3. L wave or surface waves

--> An earthquake is measured with a machine called a seismograph. The magnitude of the earthquake is measured on the Richter scale. An earthquake of 2.0 or less can be felt only a little. An earthquake over 5.0 can cause damage from things falling. A 6.0 or higher magnitude is considered very strong and 7.0 is classified as major earthquake.

--> The landscape is being continuously worn away by two processes – weathering and erosion. Weathering is the breaking up of the rocks on the earth’s surface. Erosion is the wearing away of the landscape by different agents like water, wind and ice.

--> The highest waterfall is Angel Falls of Venezuela in South America. The other waterfalls are Niagara falls located on the border between Canada and USA in North America and Victoria Falls on the borders of Zambia and Zimbabwe in Africa.

-->As the river enters the plain it twists and turns forming large bends known as meanders.

--> The collection of sediments from all the mouths forms a delta.

--> The erosion and deposition of the sea waves gives rise to coastal landforms. Sea waves continuously strike at the rocks. Cracks develop. Over time they become larger and wider. Thus, hollow like caves are formed on the rocks. They are called sea caves.

--> Glaciers are “rivers” of ice which too erode the landscape by bulldozing soil and stones to expose the solid rock below.

--> Tick the correct answer.

(i) Which is not an erosional feature of sea waves?
(a) Cliff
(b) Beach
(c) Sea cave

(ii) The depositional feature of a glacier is:
(a) Flood plain
(b) Beach
(c) Moraine

(iii) Which is caused by the sudden movements of the earth?
(a) Volcano
(b) Folding
(c) Flood plain

(iv) Mushroom rocks are found in:
(a) Deserts
(b) River valleys
(c) Glaciers

(v) Ox bow lakes are found in:
(a) Glaciers
(b) River valleys
(c) Deserts

--> Match the following.

(i) Glacier              (a) Sea shore
(ii) Meanders              (b) Mushroom rock
(iii) Beach              (c) River of ice
(iv) Sand dunes              (d) Rivers
(v) Waterfall              (e) Vibrations of earth
(vi) Earthquake              (f) Sea cliff
                         (g) Hard bed rock
                         (h) Deserts