03. Our Changing Earth Class 7 Geography Chapter 3 Notes for CBSE and UPSC
Welcome to Our Changing Earth Class 7 Geography Chapter 3 Notes for CBSE and UPSC.
Chapter 3: Our Changing Earth
Lithospheric Plates
Lithospheric plates: The Earth’s crust consists of several large and some small, rigid, irregularly-shaped plates (slabs) which carry continents and the ocean floor.
- These plates are like puzzle pieces that fit together on the Earth’s surface.
- They constantly move, albeit very slowly, reshaping the planet over millions of years.
Plate Movement
The movement of these lithospheric plates is driven by the circulation of molten magma beneath the Earth’s surface.
- Magma is molten rock material found beneath the Earth’s crust.
- The movement of magma creates currents that push the plates.
Earth Movements
Earth movements can be categorized into two types based on the forces causing them: Endogenic forces and Exogenic forces.
Endogenic Forces
Endogenic forces: These forces originate from within the Earth and can result in both sudden and slow movements.
- These forces are responsible for shaping the Earth’s internal structure.
- They can lead to significant geological events like earthquakes and volcanic eruptions.
Sudden Movements
Sudden movements caused by endogenic forces include earthquakes and volcanic eruptions.
- Earthquakes are sudden shaking of the Earth’s surface due to the release of energy.
- Volcanic eruptions involve the sudden release of molten rock, ash, and gases from a volcano.
Exogenic Forces
Exogenic forces: These forces act on the Earth’s surface and are responsible for shaping the landforms we see.
- These forces are responsible for sculpting the Earth’s surface features.
- They include processes like weathering, erosion, and deposition.
Earthquakes
Earthquakes: These are vibrations or tremors in the Earth’s surface caused by the movement of lithospheric plates. They occur when there is a release of energy due to plate movement.
- Earthquakes can range in intensity from mild tremors to catastrophic events.
- The energy released during an earthquake travels in waves through the Earth, causing the ground to shake.
Key Terms
Focus: The point within the Earth where the earthquake originates.
- The focus is usually located deep underground, and it’s where the stress on rocks is released.
- The type of rocks and the depth of the focus can affect the earthquake’s intensity.
Epicentre: The point on the Earth’s surface directly above the focus.
- The epicentre is the point where the earthquake’s effects are most strongly felt.
- It’s where damage and shaking are most severe during an earthquake.
These were related key terms to Our Changing Earth Class 7 Geography Chapter 3 Notes for CBSE and UPSC Earthquakes
Volcanoes
Volcanoes: These are openings or vents in the Earth’s crust through which molten material (magma) erupts.
- Volcanoes are often found at plate boundaries where the Earth’s crust is weak.
- When magma erupts, it can form new landforms like mountains and volcanic islands.
Understanding Earthquake Waves
Earthquake waves can be categorized into three types:
P waves (Primary waves)
- P waves are the fastest seismic waves.
- They compress and expand the ground in the direction they travel.
S waves (Secondary waves)
- S waves move more slowly than P waves.
- They shake the ground from side to side, creating a swaying motion.
L waves (Surface waves)
- L waves travel along the Earth’s surface.
- They cause the most damage and are responsible for the shaking felt during an earthquake.
Earthquake Preparedness
During an earthquake, taking shelter is crucial for safety. Safe spots include under a kitchen counter, table, or desk, or against an inside corner or wall.
- These safe spots provide protection from falling objects and debris.
- It’s essential to stay away from areas prone to shattering, like windows and mirrors.
Avoid areas near fireplaces, chimneys, and shatter-prone windows, mirrors, and picture frames.
- These areas are more likely to be hazardous during an earthquake.
- Falling objects and debris can cause injuries.
Promote earthquake preparedness among friends and family members to minimize the impact of disasters.
- Awareness and preparedness can save lives during an earthquake.
- Encourage education and planning for emergency situations.
Case Study: Earthquake in Bhuj
A massive earthquake measuring 6.9 on the Richter scale hit Bhuj Town on January 26, 2001, causing widespread damage and loss of life.
- The earthquake’s epicentre was near Bhuj, Gujarat, India.
- It resulted in extensive damage to buildings, infrastructure, and caused loss of lives.
The earthquake’s impact was severe, leading to fires, destruction of school buildings, and disruptions in communication and essential services.
- The scale of destruction required a significant relief and recovery effort.
- The disaster highlighted the importance of earthquake preparedness and response measures.
Major Landforms
As defined in Our Changing Earth Class 7 Geography Chapter 3.
The Earth’s surface is constantly evolving due to the processes of weathering and erosion. These processes, along with deposition, give rise to various landforms.
Work of a River
Rivers play a significant role in shaping the landscape. They erode, transport, and deposit sediments, leading to landform formation.
Waterfalls
Waterfalls are formed when rivers flow over steep angles or hard rocks, creating dramatic cascades.
- Some of the world’s famous waterfalls include Niagara Falls, Angel Falls, and Victoria Falls.
- Waterfalls are created by the erosional force of flowing water.
Meanders and Oxbow Lakes
Meanders are large bends in rivers formed due to erosion and deposition along their sides. Over time, meander loops can cut off from the main river, forming oxbow lakes.
- Oxbow lakes are crescent-shaped lakes that were once part of a meandering river.
- They are formed when the meander loop is cut off from the river’s main flow.
Flood Plains and Levees
Flooding of riverbanks leads to the deposition of fine soil and sediments, forming fertile flood plains. Raised banks along rivers are called levees.
- Flood plains are flat, fertile areas adjacent to rivers.
- Levees act as natural barriers, preventing rivers from overflowing their banks.
Deltas
As rivers approach the sea, they slow down and deposit their sediments, creating deltas.
- Deltas are formed at the mouths of rivers.
- They are characterized by their triangular shape and rich soil.
Work of Sea Waves
- Sea waves continuously shape coastal landforms through erosion and deposition.
Sea Caves, Arches, and Stacks
- Erosion by sea waves leads to the formation of sea caves, which can evolve into sea arches and stacks.
- These coastal features are sculpted by the relentless force of waves.
- They create stunning geological formations along coastlines.
Sea Cliffs and Beaches
- Steep coastal cliffs and sandy beaches are formed through the actions of sea waves.
- Sea cliffs are towering rock formations along coastlines.
- Beaches are sandy shorelines where waves deposit sediments.
Work of Ice
- Glaciers are powerful agents of erosion and deposition in mountainous regions.
Glacial Moraines
- Glaciers bulldoze soil and rocks, exposing solid rock beneath. They also create moraines, which are deposits of material carried by the glacier.
- Glacial moraines are mounds of rocks, sand, and sediment left behind by retreating glaciers.
- They provide valuable clues about the movement of glaciers and their effects on the landscape.
Work of Wind
- Wind can erode and deposit sand, creating unique landforms in deserts.
Sand Dunes
- Wind-driven sand forms dunes in desert landscapes.
- Sand dunes come in various shapes and sizes, depending on wind patterns and sand availability.
- They are dynamic features that shift and change over time.
Loess
- Fine, wind-blown sand and silt deposits are called loess.
- Loess deposits are fertile and can support agriculture.
- They are valuable resources in regions where they occur.
Conclusion
The conclusion for Our Changing Earth Class 7 Geography Chapter 3 Notes for CBSE and UPSC.
In this chapter, we delved into the dynamic processes that shape our ever-changing Earth’s surface. From the movement of lithospheric plates to the forces responsible for earthquakes and volcanic eruptions, we explored the powerful geological events that shape our world. Additionally, we examined the role of rivers, sea waves, glaciers, and wind in creating various landforms, from waterfalls to sand dunes. Understanding these processes and landforms is essential for appreciating the complexity and beauty of our planet’s geology.
Keywords and Definitions:
Important Keywords for Our Changing Earth Class 7 Geography Chapter 3 Notes for CBSE and UPSC.
- Lithospheric Plates: These are large and rigid slabs of the Earth’s crust that carry continents and the ocean floor. They move due to the circulation of molten magma beneath them.
- Endogenic Forces: Forces originating from within the Earth, such as tectonic plate movements, volcanic activity, and earthquakes.
- Exogenic Forces: Forces acting on the Earth’s surface, including processes like weathering, erosion, and deposition.
- Earthquake: A sudden and violent shaking of the Earth’s surface caused by the release of energy from plate movements. It results in seismic waves.
- Focus: The point within the Earth where an earthquake originates due to the rupture of rocks.
- Epicentre: The point on the Earth’s surface directly above the focus of an earthquake, where the effects are most strongly felt.
- Volcano: An opening or vent in the Earth’s crust through which molten material (magma), gases, and ash can erupt onto the surface.
- P Waves (Primary Waves): The fastest seismic waves that compress and expand the ground in the direction they travel.
- S Waves (Secondary Waves): Slower seismic waves that shake the ground from side to side.
- L Waves (Surface Waves): Seismic waves that travel along the Earth’s surface and cause the most damage during an earthquake.
- Oxbow Lake: A crescent-shaped lake formed when a meander loop of a river is cut off from the main flow.
- Levee: A raised embankment along a river that helps prevent flooding by confining the river to its channel.
- Delta: A landform created at the mouth of a river where it deposits sediments into a body of water, typically forming a triangular shape.
- Moraines: Deposits of rocks, sand, and sediment left behind by a glacier as it moves and melts.
- Sand Dunes: Hill-like structures formed by wind-blown sand in deserts and coastal areas.
- Loess: Fine, wind-blown sand and silt deposits that are highly fertile and support agriculture.
Recap and Questions:
Frequently Asked Questions (FAQs):
Important Questions for Our Changing Earth Class 7 Geography Chapter 3 Notes for CBSE and UPSC.
1. What causes the movement of lithospheric plates?
- The movement of lithospheric plates is primarily caused by the circulation of molten magma beneath the Earth’s surface.
2. What are endogenic forces, and how do they shape the Earth’s surface?
- Endogenic forces originate from within the Earth and can result in both sudden (earthquakes, volcanic eruptions) and slow (tectonic plate movements) changes to the Earth’s surface.
3. How do earthquakes occur, and what are their effects?
- Earthquakes occur due to the sudden release of energy along fault lines, resulting in seismic waves that cause the ground to shake. They can lead to widespread damage, destruction, and loss of life.
4. What is the difference between P waves and S waves in an earthquake?
- P waves are primary waves that compress and expand the ground, while S waves are secondary waves that shake the ground from side to side. P waves travel faster than S waves.
5. How are volcanoes formed, and what do they release during eruptions?
- Volcanoes are formed by the eruption of molten material (magma) onto the Earth’s surface. They release lava, gases, and ash during eruptions.
6. What are meanders, and how do they lead to the formation of oxbow lakes?
- Meanders are large bends in rivers. Over time, erosion and deposition along the sides of meanders can lead to the formation of oxbow lakes when the meander loop is cut off from the main river.
7. What are levees, and how do they relate to river flooding?
- Levees are raised embankments along rivers. They help prevent river flooding by confining the river to its channel.
8. How are deltas formed, and what is their significance?
- Deltas are formed at the mouths of rivers where they deposit sediments into a body of water. They are significant as fertile areas and provide habitat for diverse ecosystems.
9. What geological features are created by sea waves?
- Sea waves can create sea caves, arches, stacks, cliffs, and beaches through erosion and deposition processes.
10. How do glaciers shape the landscape, and what are glacial moraines?
- Glaciers shape the landscape by eroding and depositing materials as they move. Glacial moraines are deposits of rocks, sand, and sediment left behind by retreating glaciers.
Multiple-Choice Questions (MCQs) with Answers:
Important MCQs for Our Changing Earth Class 7 Geography Chapter 3 Notes for CBSE and UPSC.
1. What is the primary cause of plate movement?
a) Gravitational pull
b) Solar radiation
c) Circulation of molten magma
d) Wind patterns
Answer: c) Circulation of molten magma
2. Which type of seismic wave is the fastest?
a) P waves
b) S waves
c) L waves
d) Tidal waves
Answer: a) P waves
3. What is the point on the Earth’s surface directly above the focus of an earthquake called?
a) Seismic center
b) Focus point
c) Epicentre
d) Hypocenter
Answer: c) Epicentre
4. How are oxbow lakes formed?
a) Volcanic activity
b) Erosion by sea waves
c) Cutting off a meander loop from a river
d) Glacial movement
Answer: c) Cutting off a meander loop from a river
5. What do levees along rivers help prevent?
a) Desertification
b) Tsunamis
c) Flooding
d) Glacial erosion
Answer: c) Flooding
6. What is the significance of deltas?
a) They are sources of drinking water
b) They are prime locations for mining
c) They are fertile areas and provide habitat for diverse ecosystems
d) They are ideal for building cities
Answer: c) They are fertile areas and provide habitat for diverse ecosystems
7. What is the primary agent of coastal landform creation?
a) Wind b) Rivers
c) Volcanic activity
d) Sea waves
Answer: d) Sea waves
8. What is the primary agent of sand dune formation in deserts?
a) Glacial movement
b) Rainfall
c) Volcanic eruptions
d) Wind
Answer: d) Wind
9. What is loess, and where is it commonly found?
a) A type of volcanic rock
b) A fine wind-blown deposit of sand and silt
c) A type of river sediment
d) A glacial feature
Answer: b) A fine wind-blown deposit of sand and silt
10. What are glacial moraines composed of?
a) Sedimentary rocks
b) Volcanic ash
c) Rocks, sand, and sediment deposited by glaciers
d) Coral reefs
Answer: c) Rocks, sand, and sediment deposited by glaciers
These FAQs and MCQs provide a comprehensive review of the chapter’s content and allow for self-assessment of knowledge.
This was the end of Our Changing Earth Class 7 Geography Chapter 3 Notes for CBSE and UPSC.
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