Our Changing Earth Class 7 Worksheet Geography Chapter 3

Q.1. How do glacial moraines form?

The material carried by the glacier such as rocks big and small, sand and silt gets deposited. These deposits form glacial moraines.

Q.2. What is a volcano?

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

Q.3. What are Lithospheric plates?

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

Q.4. What is erosion?

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

Q.5. Why do the plates move?

Plates move because of the movement of the molten magma inside the earth.

Q.6. What is the name of the scale used to measure earthquakes?

The magnitude of the earthquake is measured on the Richter scale.

Q.7. Why do some rocks have a shape of a mushroom?

Winds erode the lower section of the rock more than the upper part. Therefore, such rocks have a narrower base and wider top which resemble a mushroom. These rocks are in the shape of a mushroom commonly called mushroom rocks.

Q.8. How are flood plains formed?

At times the river overflows its banks. This leads to the flooding of the neighboring areas. As it floods, it deposits layers of fine soil and other material called sediments along its banks. This leads to the formation of a flat fertile flood plain.

Q.9. Name some waterfalls.

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

Q.10. What are sand dunes?

When the wind blows, it lifts and transports sand from one place to another. When it stops blowing the sand falls and gets deposited in low hill–like structures. These are called sand dunes.

Q.11. What are some other methods used to predict an earthquake?

Some common earthquake prediction methods adopted locally by people include studying animal behavior; fish in the ponds get agitated, and snakes come to the surface.

Q.12. How earthquakes are measured?

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 a 7.0 is classified as a major earthquake.

Q.13. How a delta is formed?

As the river approaches the sea, the speed of the flowing water decreases, and the river begins to break up into a number of streams called distributaries. 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.

Q.14. Sea caves are turned into stacks. Give reason. 

Sea waves continuously strike at the rocks. Cracks develop. Over time they become larger and wider. Thus, hollow caves are formed on the rocks. They are called sea caves. As these cavities become bigger and bigger only the roof of the caves remain, thus forming sea arches. Further, erosion breaks the roof and only walls are left. These walls like features are called stacks.

Q.15. Explain the work of ice. 

Glaciers are “rivers” of ice that too erode the landscape by bulldozing soil and stones to expose the solid rock below. Glaciers carve out deep hollows. As the ice melts they get filled up with water and become beautiful lakes in the mountains. The material carried by the glacier such as rocks big and small, sand and silt gets deposited. These deposits form glacial moraines.