Class – 7

Our Changing Earth Notes

The Earth is Changing

Earth’s surface is not static – it keeps changing due to natural forces.

• These forces can be:

  • Endogenic forces – from inside the Earth

  • Exogenic forces – from outside the Earth

Major Natural Forces

A. Endogenic Forces

• Originate inside the Earth.

• Often sudden and powerful.

• Examples:

  • Earthquakes

  • Volcanic eruptions

  • Formation of mountains
    

Types of Endogenic Forces

1. Tectonic Forces: These forces cause the movement of tectonic plates, resulting in earthquakes, volcanic activity, and mountain formation.

2. Volcanic Forces: Volcanic eruptions occur when magma from the Earth’s interior is released through the surface, creating new landforms.

3. Diastrophic Forces: These forces cause the deformation of the Earth’s crust, resulting in folding, faulting, and the creation of mountains.

Effects of Endogenic Forces

1. Mountain Building: Endogenic forces can lead to the formation of mountains through the process of plate tectonics and volcanic activity.

2. Earthquakes: The movement of tectonic plates can cause earthquakes, which can have devastating effects on the environment and human populations.

3. Volcanic Landforms: Volcanic eruptions can create new landforms, such as volcanic cones, lava flows, and volcanic fields.

Importance of Endogenic Forces

1. Shaping the Earth’s Surface: Endogenic forces play a crucial role in shaping the Earth’s surface and creating various geological features.

2. Understanding Earth’s History: Studying endogenic forces helps us understand the Earth’s history, including the formation of mountains, oceans, and continents.

3. Natural Hazard Mitigation: Understanding endogenic forces can help us mitigate the effects of natural hazards, such as earthquakes and volcanic eruptions.

B. Exogenic Forces

• Originate on the surface of the Earth.

• Mainly due to natural agents like wind, water, glaciers, sea waves.

• Cause erosion, weathering, and deposition.

Types of Exogenic Forces

1. Weathering: The breakdown of rocks into smaller fragments due to exposure to wind, water, ice, and temperature fluctuations.
2. Erosion: The removal and transportation of weathered rock particles by agents like water, wind, and glaciers.
3. Deposition: The accumulation of eroded sediments in a new location, such as at the bottom of a river or ocean.

Agents of Exogenic Forces

1. Water: Rivers, oceans, and glaciers play a significant role in shaping the Earth’s surface through erosion and deposition.
2. Wind: Wind can cause erosion and deposition, particularly in arid and semi-arid regions.
3. Ice: Glaciers can carve out valleys and create unique landforms through the process of glaciation.

Effects of Exogenic Forces

1. Landform Changes: Exogenic forces can lead to the formation of new landforms, such as deltas, canyons, and sand dunes.
2. Soil Formation: The breakdown of rocks through weathering can lead to the formation of soil.
3. Sedimentary Rock Formation: The accumulation of sediments through deposition can lead to the formation of sedimentary rocks.

Importance of Exogenic Forces

1. Shaping the Earth’s Surface: Exogenic forces play a crucial role in shaping the Earth’s surface and creating various geological features.
2. Understanding Earth’s History: Studying exogenic forces helps us understand the Earth’s history, including the formation of landscapes and geological features.
3. Environmental Management: Understanding exogenic forces can help us manage environmental issues, such as soil erosion and sedimentation.

3. Earthquakes

• Sudden shaking of Earth’s surface.

• Occurs due to movement of tectonic plates.

Key Terms:

• Focus: The place inside the Earth where the earthquake starts.

• Epicentre: The point on Earth’s surface directly above the focus.

• Seismograph: Instrument that measures earthquakes.

• Richter Scale: Measures the magnitude of earthquakes (1–10 scale).

Effects:

• Ground cracks

• Buildings collapse

• Tsunamis (if underwater)

Fun Fact:
The highest magnitude ever recorded was 9.5 in Chile in 1960.

4. Volcanoes

• Opening in Earth’s crust through which magma, gases, and ash escape.

• When magma comes out, it’s called lava.

Types of materials:

• Lava (molten rock)

• Ash

• Gases

Fun Fact:

Mauna Loa in Hawaii is the largest active volcano in the world.

5. Types of Forces Based on Results

6. Major Landforms Created

A. Work of Rivers:

• Erosion in upper course → forms V-shaped valleys, waterfalls, gorges.

• Meanders: Loops formed in middle course.

• Ox-bow lake: A cutoff loop.

• Deposition in lower course → forms floodplains and deltas.

B. Work of Wind:

• Common in deserts.

• Erosion forms mushroom rocks.

• Deposition forms sand dunes and loess (fine dust).

C. Work of Glaciers:

• Erode land as they move → U-shaped valleys.

• Deposition → moraines (rocks & debris).

D. Work of Sea Waves:

• Erosion → forms cliffs, sea caves, arches, stacks.

• Deposition → beaches.

7. Important Terms & Definitions

• Class 7 SST notes

• Our Changing Earth Class 7

• Our Changing Earth notes

• Class 7 Geography chapter summary

• Class 7 Our Changing Earth notes