Class 7 Geography Chapter 3 Question Answers - Our Changing Earth

Short Answer Question

Q1. What do you mean by lithospheric plates?
Ans: The lithosphere is the solid outer layer of the Earth, consisting of the crust and the upper mantle. It is divided into several large and small pieces known as lithospheric plates.

• These plates float on the semi-fluid layer beneath them.
• They move very slowly, typically just a few millimetres each year.
• This movement is driven by the circulation of molten magma within the Earth.
• The movement of lithospheric plates can lead to geological events like earthquakes and volcanic eruptions.

Q2. Name the two types of tectonic movement.
Ans: Vertical and horizontal movements are the two types of tectonic movement.

• Vertical movement: This involves the up and down movement of the Earth's crust.
• Horizontal movement: This refers to the side-to-side movement of tectonic plates.

Q3. What are volcanoes?
Ans: A volcano is an opening in the earth's crust that allows hot molten rock, ash, and gases to escape from below the surface. Key points include:

• Volcanoes can erupt suddenly, releasing magma and gases.
• They are formed by the movement of tectonic plates.
• Volcanic eruptions can create new landforms and affect the surrounding environment.

Q4. Where are the volcanoes found?
Ans: Volcanoes are typically found in specific geological settings:

• Where tectonic plates are either pulled apart or pushed together.
• In regions where the Earth's crust is stretched and thinned, such as the African Rift Valley.

Q5. What is an earthquake?
Ans: When the lithospheric plates move, the surface of the Earth vibrates. These vibrations, known as earthquakes, can travel around the globe. Key points about earthquakes:

• The point where the movement starts is called the focus.
• The point directly above the focus on the surface is the epicentre.
• Vibrations radiate outwards from the epicentre.
• The most damage usually occurs near the epicentre, with strength decreasing further away.

Q6. Define weathering.
Ans: Weathering is the process that breaks down rocks on the Earth's surface. It occurs due to various factors, including:

• Atmospheric moisture
• Rain
• Frost
• Temperature changes
• Chemical reactions
• Groundwater

Over time, these factors cause rocks to crumble or decay.

Q7. How a water fall formed?
Ans: The running water in a river gradually erodes the landscape. When the river flows over hard rocks or down a steep slope, it creates a waterfall.

Q8. What are meanders?
Ans: As a river flows into the plains, it twists and turns, creating large bends known as meanders. This process involves:

• Erosion and deposition occurring along the sides of the meander.
• The ends of the meander loop gradually move closer together.
• Eventually, the meander loop can cut off from the river, forming a cut-off lake, also called an ox-bow lake.

When the river overflows its banks, it floods surrounding areas, depositing layers of fine soil and other materials, known as sediments, which create a flat, fertile floodplain. The raised banks formed during this process are referred to as levees.

Q9. What do you mean by mushroom rocks?
Ans: An active agent of erosion and deposition in deserts is the wind. In these regions, you can find rocks shaped like mushrooms, known as mushroom rocks. The wind erodes the lower part of the rock more than the upper part, resulting in a narrower base and a wider top.

Q10. Define Loess.
Ans: Loess is a type of soil formed from very fine, light grains of sand that are carried by the wind over long distances. When these grains settle in large areas, they create a significant deposit known as loess. Key points about loess:

• Composed of fine, wind-blown sand.
• Deposited in extensive areas.
• Commonly found in regions like China.

Q11. What is a delta?
Ans: The river slows down as it approaches the sea, leading to the deposition of its load. This process creates distributaries, each forming its own mouth. The accumulation of sediments from these mouths results in the formation of a delta.

Q12: How are beaches formed?
Ans: The erosion and deposition of the sea waves gives rise to coastal landforms. The sea wave deposit sediments along the shores forming beaches.

Long Answer Question

Q1. How man is also responsible for earth quake?
Ans: Humans can contribute to earthquakes through various activities. Geologists and seismologists have identified five main ways in which human actions can induce seismic events:

• Fluid injection into the earth
• Fluid extraction from the earth
• Mining activities
• Nuclear testing
• Construction of dams and reservoirs

There are documented cases of earthquakes caused by these human activities.