Our Changing Earth Class 7 Worksheet Geography Chapter 3

Q.1. How do glacial moraines form? 

The material carried by a glacier, including rocks, sand, and silt, is deposited as the glacier melts. This accumulation of debris forms what are known as glacial moraines.

Q.2. What is a volcano? 

A volcano is an opening in the earth's crust that allows molten material to escape. Key points include:

• It acts as a vent for magma.
• Molten material erupts suddenly, often with gases and ash.
• Volcanoes can cause significant geological changes.

Q.3. What are Lithospheric plates? 

The lithosphere is divided into several large and small, rigid plates known as Lithospheric plates. These plates:

• Float on the semi-fluid layer beneath them.
• Move very slowly, typically a few millimetres each year.
• Are driven by the movement of molten magma inside the Earth.

This movement leads to significant changes on the Earth's surface, including:

• Earthquakes
• Volcanic eruptions
• Formation of mountains

Q.4. What is erosion? 

Erosion is the process where the landscape is gradually worn away by various natural forces.

• Water - Rivers and rainfall can erode rocks and soil.
• Wind - In deserts, wind shapes the land by moving sand and dust.
• Ice - Glaciers carve out valleys and transport materials.

The eroded materials are then carried away and deposited elsewhere, creating new landforms.

Q.5. Why do the plates move? 

Plates move due to the activity of molten magma beneath the Earth's surface. This movement occurs in the following ways:

• The molten magma circulates in a circular motion.
• This circulation causes the lithospheric plates to shift slowly, at a rate of just a few millimetres each year.
• As the plates move, they can lead to significant changes on the Earth's surface.

These movements can result in events such as earthquakes and volcanoes, which can cause destruction.

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

The magnitude of an earthquake is measured using the Richter scale.

• An earthquake of 2.0 or less is barely felt.
• Magnitude over 5.0 can cause damage from falling objects.
• A magnitude of 6.0 or higher is considered very strong.
• A magnitude of 7.0 is classified as a major earthquake.

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

Mushroom rocks are formed due to the process of erosion by wind. Here’s how it works:

• The lower section of the rock is eroded more than the upper part.
• This results in a narrower base and a wider top, resembling a mushroom.
• These uniquely shaped rocks are commonly referred to as mushroom rocks.

Q.8. How are flood plains formed? 

Flood plains are formed when a river overflows its banks, causing nearby areas to flood. During this flooding:

• The river deposits layers of fine soil and other materials called sediments along its banks.
• This accumulation creates a flat, fertile flood plain.
• The raised banks formed by these deposits are known as levees.

Q.9. Name some waterfalls. 

The highest waterfall in the world is Angel Falls, located in Venezuela, South America. Other notable waterfalls include:

• Niagara Falls - Situated on the border between Canada and the USA, North America.
• Victoria Falls - Found on the borders of Zambia and Zimbabwe, Africa.

Q.10. What are sand dunes? 

When the wind blows, it lifts and moves sand from one location to another. When the wind stops, the sand falls and is deposited in low, hill-like structures. These formations are known as sand dunes.

Q.11. How are sea caves formed, and what are they called?

Sea caves are formed when seawaves repeatedly hit the rocks, leading to the development of cracks. Over time, these cracks grow larger and wider, creating hollow spaces known as sea caves.

Q.12. How are earthquakes measured? 

An earthquake is measured using a device called a seismograph. The strength of the earthquake is indicated on the Richter scale, which categorises earthquakes as follows:

• An earthquake of 2.0 or less is barely felt.
• A magnitude over 5.0 can cause damage from falling objects.
• A magnitude of 6.0 or higher is very strong.
• A magnitude of 7.0 is classified as a major earthquake.

Q.13. How is a delta 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 caves are formed when sea waves continuously strike the rocks, leading to:

• Development of cracks in the rocks.
• Gradual enlargement of these cracks into hollow caves, known as sea caves.
• As the caves grow larger, only the roofs remain, creating sea arches.
• Eventually, erosion causes the roofs to collapse, leaving behind vertical walls called stacks.

Q.15. How do glaciers shape the landscape, and what do they form as a result of their erosion and deposition?

Glaciers, often referred to as 'rivers of ice', significantly shape the landscape through their processes of erosion and deposition. Here’s how they do it:

• Glaciers erode the land by bulldozing soil and rocks, exposing solid rock beneath.
• They carve out deep hollows that fill with water as the ice melts, creating beautiful lakes in mountainous areas.
• The materials carried by glaciers, including rocks, sand, and silt, are deposited as glacial moraines.