Our Changing Earth — AP Class 7 Geography
1. About the Chapter
'The Earth is NOT static — it is CHANGING every moment.' Some changes are FAST (earthquakes, volcanoes) and some are SLOW (river erosion, weathering). This chapter explores both types of changes.
Key Themes
- Endogenic forces (inside the Earth)
- Exogenic forces (outside the Earth)
- Earthquakes and volcanoes
- Work of rivers: erosion, transportation, deposition
- Work of sea waves, ice, wind
- AP: Godavari and Krishna delta formation, Penna river
2. Endogenic and Exogenic Forces
Endogenic Forces (From INSIDE)
'These forces ORIGINATE inside the Earth — from the heat and movement of the mantle.'
| Type | Speed | Example | Result |
|---|---|---|---|
| Sudden | Fast | Earthquake, volcano | IMMEDIATE change |
| Diastrophic | Slow | Plate movement | GRADUAL change (mountain building) |
Exogenic Forces (From OUTSIDE)
'These forces ORIGINATE on the Earth's surface — from air, water, and temperature changes.'
| Process | What Happens |
|---|---|
| Weathering | Rocks BREAK DOWN in place (no movement) |
| Erosion | Rocks are CARRIED away |
| Deposition | Sediments are DROPPED (laid down) |
3. Earthquakes
What Causes Earthquakes?
'When the Earth's CRUST SUDDENLY moves — that is an EARTHQUAKE.'
Cause: Movement of TECTONIC PLATES. Plates GRIND against each other → STRESS builds → sudden RELEASE → seismic waves.
Key Terms
| Term | Meaning |
|---|---|
| Focus (Hypocentre) | Point INSIDE Earth where earthquake starts |
| Epicentre | Point on SURFACE directly above focus |
| Seismic waves | Energy waves that travel through Earth |
| Seismograph | Instrument that MEASURES earthquakes |
| Richter scale | Measures MAGNITUDE (1 to 10) |
Earthquake Effects
- Ground shaking
- Building collapse
- Landslides
- Tsunamis (if under the ocean)
- 'Earthquakes DON'T kill people — BUILDINGS do'
Earthquake Preparedness
- Stay CALM
- Drop, Cover, Hold On
- Stay away from windows
- Do NOT use lifts
- After shaking stops — move to OPEN ground
AP and Earthquakes
AP is in Seismic Zone II (LOW risk) and Zone III (MODERATE risk in some areas). 'AP is NOT a high-risk earthquake zone — but mild tremors have been felt in Visakhapatnam and Hyderabad areas.'
4. Volcanoes
What is a Volcano?
'A volcano is an OPENING in the Earth's crust through which MOLTEN ROCK (magma/lava), gases, and ASH escape.'
Types of Volcanoes
| Type | Characteristic | Example |
|---|---|---|
| Active | Erupts REGULARLY | Mt. Etna (Italy), Barren Island (Andaman) |
| Dormant | Has NOT erupted in a long time — but CAN | Mt. Fuji (Japan) |
| Extinct | Will NEVER erupt again | — |
Famous Volcanic Events
- 79 CE: Mount Vesuvius buried Pompeii
- 1883: Krakatoa explosion (heard 3,000 km away)
- 1991: Mount Pinatubo (Philippines) — affected global climate
AP Context
There are NO active volcanoes in AP. However, the Deccan Traps (volcanic rock covering parts of Rayalaseema) were formed by MASSIVE volcanic eruptions 65 MILLION years ago. 'These eruptions may have contributed to the extinction of the DINOSAURS.'
5. Work of Rivers
The Three-Stage River
| Stage | Region | Gradient | Work | Landforms |
|---|---|---|---|---|
| Upper | Mountains | Steep | Erosion (downcutting) | V-shaped valley, waterfall |
| Middle | Plains | Moderate | Transportation | Meanders, oxbow lakes |
| Lower | Delta/Coast | Gentle | Deposition | Delta, floodplain, levees |
Erosional Landforms (Upper Course)
- V-shaped valley: River cuts DEEP into rock
- Waterfall: River falls over a HARD rock ledge
- Example: Bogatha Waterfall (Khammam, Telangana — near AP border)
Depositional Landforms (Lower Course)
- Floodplain: Flat land on either side of river — formed by flooding
- Delta: Triangular land at river mouth — formed by sediment deposition
- Levees: Natural embankments along river banks
AP Focus: Godavari and Krishna Deltas
| River | Origin | Length | Delta Area (AP) | Significance |
|---|---|---|---|---|
| Godavari | Nasik (Maharashtra) | 1,465 km | East Godavari district | 'The DAKSHINA GANGA — largest river of South India' |
| Krishna | Mahabaleshwar (Maharashtra) | 1,400 km | Krishna, Guntur districts | FERTILE delta — 'Rice bowl of AP' |
| Penna | Nandidurg (Karnataka) | 597 km | Nellore district | Ephemeral river — flows only during rains |
Delta Formation
'When a river meets the sea, it DROPS its sediment load — forming a TRIANGULAR DELTA.'
The Godavari and Krishna deltas are among the MOST fertile regions of India. 'This is where AP's RICE is GROWN — in the rich alluvial soil of the deltas.'
6. Work of Sea Waves
Erosional Landforms
| Landform | How Formed |
|---|---|
| Sea cliff | Waves cut into rock at base |
| Sea cave | Waves hollow out a cliff |
| Sea arch | Cave erodes THROUGH headland |
| Stack | Arch collapses — ISOLATED pillar of rock |
Depositional Landforms
| Landform | How Formed |
|---|---|
| Beach | Sand deposited by waves |
| Sandbar | Sand deposited ACROSS a bay |
AP Coastline
AP has a 974 km coastline. Important features:
- Visakhapatnam: Natural harbour — 'the JEWEL of the East Coast'
- Nellore coast: Sandy beaches
- Krishna-Godavari basin: Mangrove-lined delta coast
- 'The Bay of Bengal gives AP its RICH fisheries and port economy'
7. Work of Ice (Glaciers)
Glacial Erosional Landforms
| Landform | Description |
|---|---|
| U-shaped valley | Wide, flat-bottomed valley |
| Cirque | Bowl-shaped hollow at glacier's start |
| Arete | Sharp ridge between two glaciers |
Glacial Depositional Landforms
| Landform | Description |
|---|---|
| Moraine | Piles of rock debris carried by glacier |
| Drumlin | Teardrop-shaped hill of glacial debris |
AP Context: There are NO glaciers in AP (not in the Himalayas). 'But the Godavari and Krishna rivers originate in glaciers of the Western Ghats.'
8. Work of Wind
Erosional Landforms (Deserts)
| Landform | Description |
|---|---|
| Mushroom rock | Wind erodes LOWER part more (wider top) |
| Sand dunes | Wind DEPOSITS sand in mounds |
Depositional Landforms
| Landform | Description |
|---|---|
| Loess | Fine dust DEPOSITED by wind — very FERTILE soil |
| Sand dunes | Various shapes (barchan, crescent-shaped) |
9. Key Facts and Dates
- AP coastline: 974 km
- Godavari: 1,465 km (largest South Indian river)
- 2004: Indian Ocean tsunami affected AP coast
- 65 million years ago: Deccan Trap volcanic eruptions
- Seismic zones in India: 5 zones (Zone V = highest risk)
10. Common Mistakes
- Confusing weathering with erosion — Weathering BREAKS rocks in place; Erosion MOVES them.
- Thinking all rivers reach the sea — Penna and many Deccan rivers are EPHEMERAL (dry in summer).
- Believing earthquakes kill people — Building COLLAPSE kills people, not the earthquake itself.
- Forgetting that AP has a long coastline — 974 km — vital for economy and vulnerability to cyclones.
- Confusing delta with estuary — Delta = triangular (river deposits). Estuary = funnel-shaped (tide erodes).
11. Exam Focus
2 Marks
Q: What is the difference between endogenic and exogenic forces? A: Endogenic forces come from INSIDE Earth (earthquakes, volcanoes). Exogenic forces come from OUTSIDE (rivers, wind, sea, ice).
Q: Name the two major rivers that form deltas in AP. A: Godavari and Krishna.
4 Marks
Q: Explain how river deltas are formed, with reference to AP. A: When a river enters the sea, its speed DECREASES. The sediment it carries is DEPOSITED at the river mouth. Over time, this sediment builds up to form a TRIANGULAR delta. In AP, the Godavari and Krishna rivers form FERTILE deltas where rice is extensively cultivated. 'The delta is the GIFT of the river to the land.'
6 Marks
Q: Describe the work of rivers in the three stages of their course, with AP examples. A: In the UPPER course (mountains), rivers ERODE vertically — forming V-shaped valleys and waterfalls. The Godavari originates in the Western Ghats. In the MIDDLE course (plains), rivers TRANSPORT sediment and form meanders. In the LOWER course (delta), rivers DEPOSIT sediment — the Godavari and Krishna form the RICH deltas of AP. The Penna river is a different case — it is EPHEMERAL, flowing only during the monsoon season.
12. Quick Self-Test
-
What instrument measures earthquakes? Answer: Seismograph
-
Name the origin point of an earthquake inside the Earth. Answer: Focus (hypocentre)
-
Which AP river is called the 'Dakshina Ganga'? Answer: Godavari
-
How long is AP's coastline? Answer: 974 km
-
What is the difference between weathering and erosion? Answer: Weathering breaks rocks in place; erosion carries them away.
-
What is a delta? Answer: A triangular landform at a river's mouth formed by sediment deposition.
-
Name two depositional landforms created by rivers. Answer: Floodplain and delta (also levees, oxbow lakes)
-
Which landform is created by wind in deserts? Answer: Sand dunes / mushroom rock
13. Conclusion
'The Earth is ALIVE — changing, moving, and reshaping itself EVERY DAY.' From the FAST destruction of an earthquake to the SLOW carving of a river valley, the forces that shape our Earth are POWERFUL and CONSTANT. AP's rivers — the Godavari, Krishna, and Penna — are living examples of how Earth's changing forces create fertile lands and support millions of people.
Key takeaways:
- Endogenic forces (inside) cause earthquakes and volcanoes
- Exogenic forces (outside) cause weathering, erosion, deposition
- Rivers ERODE in upper course, TRANSPORT in middle, DEPOSIT in lower
- Godavari and Krishna deltas are AP's agricultural heartland
- AP's 974 km coastline faces both opportunities (ports) and hazards (cyclones)
- Understanding Earth's changes helps us PREPARE for natural disasters
