Class 7,
Subject. Social Science, Chapter -3(Geo). Name of Chapter: -Our Changing Earth.
Name of teacher: Atul Kumar Rai.
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Exercise:
A. Choose the correct option:
1. 2. Earthquakes.
2. 3. 100 KM.
3. 3. Both 1&2.
4. 1. Focus.
5. 2. Igneous rocks.
6. 3. River valleys.
7. 3. Collision of lithospheric plates.
8. 4. Stack
9. 3. Deserts.
10. 4. All of the above.
B. Fill in the blanks: 1. 20.
2. Tectonic
3. epicentre.
4. Richter scale.
5. Vulcan.
6. Plate.
7. meanders.
8. wave.
9. moraine.
10. mushroom rocks.
E. Match The following:
Column A. Column B.
Falling of water vertically down the steep slope Waterfall
Glacier Frozen river.
A vent through which molten material erupts Volcano.
Removal of sediments due to action of wind and water Erosion.
Landform created at mouth of river Delta.
Large bend in the course of river Meanders.
Vertical column of rock Stack.
C. Distinguish between the following:
1. Endogenic and exogenic forces.
Ans. Endogenic forces: The Phenomena that occur beneath the surface of the earth or any other celestial body.
Exogenic forces: The phenomena that occur over the earth surface.
2. Sea caves and Sea Arches. Ans. Sea caves: A sea cave is a type of cave formed primarily by the wave action of the sea.
Sea arches: A sea arch is a natural arch or bridge made of stone that has been created through the process of land wind and water erosion.
D. Give reason for:
1. The formation of mushroom rock in desert:
Ans. The sand particles blown along by the wind being heavier remain close to the surface and as the wind passes along the rocks the sand particles in the wind keep eroding the portion of the rock closer to the surface while the upper portion is not affected as much. This gives the rocks a mushroom like shape.
2. The surface of earth not being in a consistent state:
Ans. Two types of forces , endogenic and exogenic forces , are continuously acting on earth, There fore the surface of earth not being in a consistent state.
F. answer the following questions briefly.
1. What cause tsunami?
Ans. Tsunami is caused by volcanic eruption or earthquake below or very close to the sea floor.
2. List two causes of earthquakes.
Ans. 1. Earthquake can occur due to volcanic eruption.
2. earthquake can be triggered by tectonic activity associated with plates margins and faults.
3. What is volcano?
Ans. A volcano is an opening or rupture on the Earth’s surface or crust , which allows hot , molten rocks, ash and gases to escape from below the surface.
4. What are the exogenic forces?
Ans. The phenomena /external processes that occur over the earth surface.
5. When and where the ox-bow lake formed?
Ans. An ox-bow lake is a shallow U-shaped or C-shaped body of water formed when a wide meander from the main stream of river is cut off to create a lake.
It is formed in Middle or lower course of river.
6. How are sea arches formed? Ans. A sea arch is a natural arch or bridge made of stone that has been created through the process of land wind and water erosion.
7. How are sand dunes formed?
Ans. In desert , sand is transported by wind and where ever wind losses its velocity the sand gets deposited and forms a hillock of sand called Dune.
G. Answer the following questions in detail.
1. How are Sea caves and Arches formed?
Ans. Sea caves: A sea cave is a type of cave formed primarily by the wave action of the sea. The primary process involved is erosion in the rocky faces on the seashore.
Sea arches: A sea arch is a natural arch or bridge made of stone that has been created through the process of land wind and water erosion.
2. How is Delta formed? Draw a neat and labelled diagram of delta.
Ans. A delta is a landform that is created at the mouth of a river where the slope of the river bed becomes too shallow before it enters the seashore and speed of water losses speed. This causes it to lose the sediments it had carried earlier. As the river flows in a relatively flat area it forms large number of distributaries or streams and sediments keep collecting between these streams and forms shallow islands . This whole area is called a delta.
3. Explain the depositional work of Glacier.
Ans. Moraines. Moraine is any glacially formed accumulation of unconsolidated glacial debris ( soil and rock) which can occur in glaciated regions.
As the mass of ice forming a glacier slides down it erodes the soil and rock on the side of the valley through which it passes. These soil and rock debris keep collecting and moving along with the mass of the ice and is called glacial moraine.
4. Explain the erosional and depositional work of wind.
Erosional work. Mushroom Rocks are formed. The sand particles blown along by the wind being heavier remain close to the surface and as the wind passes along the rocks the sand particles in the wind keep eroding the portion of the rock closer to the surface while the upper portion is not affected as much. This gives the rocks a mushroom like shape.
Depositional work : Sand dunes are formed. In desert , sand is transported by wind and where ever wind losses its velocity the sand gets deposited and forms a hillock of sand called Dune.