How to Use This Page
Solve each Samacheer Kalvi exercise question on your own first, then compare your answer with the solutions below. Endogenic processes are Earth's internal forces — understand how plate tectonics, earthquakes, and volcanism shape the landscape.
Key Concepts (Quick Recap)
Endogenic vs Exogenic Forces
| Feature | Endogenic Forces | Exogenic Forces |
|---|---|---|
| Origin | Inside the Earth | Earth's surface (atmosphere, hydrosphere) |
| Effect | Build landforms (constructive) | Wear down landforms (destructive) |
| Examples | Earthquakes, volcanism, folding, faulting | Weathering, erosion, deposition |
| Energy source | Internal heat, radioactivity | Solar energy, gravity |
Plate Tectonics
- Lithosphere: Rigid outer shell (crust + upper mantle), divided into 7 major plates
- Asthenosphere: Semi-fluid layer below lithosphere on which plates move
- Convection currents in the mantle drive plate movement
Types of Plate Boundaries
| Boundary | Movement | Feature | Example |
|---|---|---|---|
| Divergent (Constructive) | Plates move apart | Mid-oceanic ridges, rift valleys | Mid-Atlantic Ridge, East African Rift |
| Convergent (Destructive) | Plates collide | Mountains, trenches, volcanoes | Himalayas (continent-continent), Andes (ocean-continent) |
| Transform (Conservative) | Plates slide past | Faults, earthquakes | San Andreas Fault |
Diastrophism (Mountain Building)
- Folding: Compressive forces bend rock layers → anticlines (upfolds) and synclines (downfolds)
- Faulting: Tensional or compressive forces fracture and displace rocks
- Types of faults: Normal fault (tension), Reverse/Thrust fault (compression), Transform fault (lateral)
Types of Mountains
| Type | Formation | Example |
|---|---|---|
| Fold mountains | Folding of rock layers by compressive forces | Himalayas, Alps, Andes, Rockies |
| Block mountains | Faulting — land between two faults rises | Vosges (France), Black Forest (Germany) |
| Volcanic mountains | Accumulation of volcanic material | Mt. Kilimanjaro, Mt. Fuji, Mt. St. Helens |
| Residual mountains | Erosion of surrounding land over millions of years | Aravalli Hills, Appalachian Mountains |
Volcanism
- Magma: Molten rock below the Earth's surface
- Lava: Magma that reaches the surface
- Active volcano: Has erupted recently and may erupt again (e.g., Mt. Etna, Mt. St. Helens)
- Dormant volcano: Has not erupted recently but may erupt in the future (e.g., Mt. Fuji)
- Extinct volcano: Has not erupted for thousands of years and is unlikely to erupt (e.g., Mt. Kilimanjaro)
Volcanic Landforms
| Landform | Description |
|---|---|
| Shield volcano | Broad, gently sloping; formed by fluid basaltic lava (e.g., Mauna Loa, Hawaii) |
| Composite volcano | Steep, conical; formed by alternating layers of lava and ash (e.g., Mt. Fuji) |
| Caldera | Large depression formed by collapse of volcano summit (e.g., Crater Lake, Oregon) |
| Flood basalt | Extensive flat lava flows covering large areas (e.g., Deccan Traps, India) |
Earthquakes
| Term | Definition |
|---|---|
| Focus (Hypocentre) | Point of origin of earthquake inside the Earth |
| Epicentre | Point on the surface directly above the focus |
| Seismic waves | Energy waves released during an earthquake |
| P-waves (Primary) | Fastest, travel through solids and liquids, push-pull motion |
| S-waves (Secondary) | Slower, travel through solids only, perpendicular motion |
| L-waves (Surface) | Slowest, cause maximum damage, travel along surface |
| Richter scale | Measures earthquake magnitude (1-10) |
| Mercalli scale | Measures earthquake intensity (I-XII) based on damage |
I. Choose the Best Answer (MCQs)
Q1. The theory of plate tectonics was proposed by (a) Alfred Wegener (b) Harry Hess (c) J. Tuzo Wilson (d) Arthur Holmes
Q2. The point of origin of an earthquake inside the Earth is called (a) Epicentre (b) Focus (c) Seismograph (d) Crater
Q3. Fold mountains are formed by (a) Tensional forces (b) Compressive forces (c) Shearing forces (d) Volcanic activity
Q4. The Himalayas were formed by the collision of (a) Pacific Plate and Eurasian Plate (b) Indian Plate and Eurasian Plate (c) African Plate and Eurasian Plate (d) Nazca Plate and South American Plate
Q5. The Mid-Atlantic Ridge is an example of (a) Convergent boundary (b) Divergent boundary (c) Transform boundary (d) None of the above
II. Fill in the Blanks
1. Endogenic forces originate from within the Earth. 2. Exogenic forces originate from the Earth's surface (atmosphere, hydrosphere). 3. The theory of continental drift was proposed by Alfred Wegener. 4. The Earth's lithosphere is divided into 7 major plates and several minor plates. 5. Plates move due to convection currents in the mantle. 6. When plates move apart, it is called a divergent boundary. 7. When plates collide, it is called a convergent boundary. 8. When plates slide past each other, it is a transform boundary. 9. The point of origin of an earthquake inside the Earth is the focus (hypocentre). 10. The point on the surface directly above the focus is the epicentre. 11. The Richter scale measures earthquake magnitude. 12. Fold mountains are formed by compressive forces. 13. Block mountains are formed by faulting. 14. The Deccan Traps in India are an example of flood basalts.
III. True or False (with corrections for false statements)
IV. Match the Following
| Column A | Column B | Answer |
|---|---|---|
| 1. Fold mountains | (a) Faulting | (b) Compressive forces |
| 2. Block mountains | (b) Compressive forces | (a) Faulting |
| 3. Divergent boundary | (c) Plates collide | (d) Plates move apart |
| 4. Convergent boundary | (d) Plates move apart | (c) Plates collide |
| 5. Focus | (e) Surface point above focus | (f) Point inside Earth where quake starts |
| 6. Epicentre | (f) Point inside Earth | (e) Surface point above focus |
V. Answer Briefly (2-mark questions)
VI. Answer in Detail (5-mark questions)
Common Mistakes to Avoid
- Confusing focus and epicentre: Focus is INSIDE the Earth (where the earthquake starts). Epicentre is ON the surface (directly above the focus).
- Confusing endogenic and exogenic forces: Endogenic = from WITHIN the Earth (constructive). Exogenic = from the surface (destructive).
- Saying S-waves travel through liquids: S-waves travel through SOLIDS only. P-waves travel through both solids and liquids. This is how we know the outer core is liquid (S-waves don't pass through it).
- Confusing fold mountains and block mountains: Fold mountains = compressive forces (folding). Block mountains = tensional forces (faulting).
- Mixing up divergent and convergent boundaries: Divergent = plates move APART (new crust forms). Convergent = plates COLLIDE (crust destroyed).
- Forgetting that dormant volcanoes can erupt again: Dormant = sleeping, may erupt. Extinct = dead, unlikely to erupt.
Exam Checklist
- [ ] Can you distinguish between endogenic and exogenic forces?
- [ ] Can you explain plate tectonics and name the three types of plate boundaries?
- [ ] Can you describe divergent, convergent, and transform boundaries with examples?
- [ ] Can you explain folding and faulting with examples?
- [ ] Can you distinguish between fold mountains, block mountains, volcanic mountains, and residual mountains?
- [ ] Can you explain the causes and types of volcanic eruptions?
- [ ] Can you distinguish between active, dormant, and extinct volcanoes?
- [ ] Can you explain earthquakes — causes, seismic waves, focus, epicentre?
- [ ] Can you distinguish between P-waves, S-waves, and L-waves?
- [ ] Can you describe the Richter and Mercalli scales?