📑 Topics on this page (Jump to Topic):
📌 1. Continental Drift & Plate Tectonics
- Continental Drift — Alfred Wegener (1912): all continents formed one landmass Pangaea surrounded by the ocean Panthalassa; it split into Laurasia (north) and Gondwanaland (south) with the Tethys Sea between.
- Sea-floor spreading — Harry Hess (1960s). Plate tectonics (1960s): the lithosphere is broken into 7 major and many minor plates moving over the asthenosphere.
| Boundary | Motion | Result / Example |
|---|---|---|
| Divergent (constructive) | Move apart | Mid-Atlantic Ridge, East African Rift |
| Convergent (destructive) | Collide | Himalayas (Indian-Eurasian), Andes, Japan Trench |
| Transform (conservative) | Slide past | San Andreas Fault (USA) |
📌 2. Earthquakes & Volcanoes
- The point of origin inside = focus (hypocentre); the surface point above it = epicentre — maximum damage there.
- Measurement: Richter scale (magnitude, logarithmic — one unit = 10× amplitude), Mercalli scale (intensity/damage). Instrument: seismograph.
- Pacific "Ring of Fire": ≈ 75% of active volcanoes and ≈ 90% of earthquakes.
- Volcano types: active (Etna, Stromboli — "Lighthouse of the Mediterranean"), dormant (Vesuvius, Fujiyama), extinct (Kilimanjaro, Popa). India's only active volcano — Barren Island (Andaman).
- Highest active volcano — Ojos del Salado (Chile-Argentina); largest active by volume — Mauna Loa (Hawaii).
- Tsunami (Japanese = "harbour wave") is caused by undersea earthquakes; e.g. the Indian Ocean tsunami of 26 Dec 2004.
📌 3. Mountains, Plateaus & Plains
| Type | Formation | Examples |
|---|---|---|
| Fold mountains | Folding of layers by compression — young and highest | Himalayas, Alps, Andes, Rockies; old — Aravalli, Appalachians, Urals |
| Block mountains | Uplifted block by faulting (horst); sunken part = graben/rift valley | Black Forest (Germany), Vosges; Satpura |
| Volcanic mountains | Accumulation of lava | Kilimanjaro, Fuji, Cotopaxi |
| Residual mountains | Remnants left after erosion | Aravalli, Nilgiris, Parasnath |
- Plateaus: highest and largest — Tibetan Plateau ("Roof of the World"); in India the Deccan and Chota Nagpur (mineral storehouse, "Ruhr of India").
- Plains: alluvial plains built by river deposits are the most fertile and densely populated — e.g. the Indus-Ganga-Brahmaputra plain.
📌 4. Agents of Erosion & Landforms
| Agent | Erosional | Depositional |
|---|---|---|
| River | V-shaped valley, gorge/canyon, waterfall, pothole | Meander, ox-bow lake, floodplain, levee, delta |
| Glacier | U-shaped valley, cirque, arête, horn, fjord | Moraine, drumlin, esker |
| Wind | Mushroom rock, inselberg, yardang | Sand dunes — barchan (crescent), loess |
| Sea waves | Sea cliff, cave, arch, stack | Beach, bar, spit, lagoon |
| Groundwater | Sinkholes, caves in limestone (karst) | Stalactites (hang from roof), stalagmites (rise from floor) |
- World's largest delta — Sundarbans (Ganga-Brahmaputra); famous canyon — Grand Canyon (Colorado River, USA).
⚠️ Exam Traps:
- The epicentre is on the surface; the focus is underground.
- U-shaped valley = glacier; V-shaped valley = river.
- One unit rise on the Richter scale = 10× amplitude (≈ 32× energy), not double.
- Stalactite hangs from the ceiling ("c"); stalagmite rises from the ground ("g").
📌 5. Practice MCQs
📝 Practice MCQs (prepared by SF Prep — not PYQs)
Q1. Who proposed the Continental Drift theory? Practice
Correct answer: (B)
Wegener proposed Pangaea in 1912.
Wegener proposed Pangaea in 1912.
Q2. According to Wegener, the ocean surrounding Pangaea was — Practice
Correct answer: (C)
Panthalassa surrounded Pangaea; Tethys lay between Laurasia and Gondwana.
Panthalassa surrounded Pangaea; Tethys lay between Laurasia and Gondwana.
Q3. The Himalayas were formed by convergence of — Practice
Correct answer: (D)
The northward-moving Indian plate collided with the Eurasian plate, folding Tethys sediments into the Himalayas.
The northward-moving Indian plate collided with the Eurasian plate, folding Tethys sediments into the Himalayas.
Q4. The surface point directly above an earthquake's focus is the — Practice
Correct answer: (A)
Shaking is felt first and strongest at the epicentre.
Shaking is felt first and strongest at the epicentre.
Q5. Which scale measures the intensity (damage) of an earthquake? Practice
Correct answer: (B)
Richter measures magnitude; Mercalli measures observed intensity/damage.
Richter measures magnitude; Mercalli measures observed intensity/damage.
Q6. India's only active volcano is — Practice
Correct answer: (C)
Barren Island (Andaman Sea) is active; Narcondam is considered dormant.
Barren Island (Andaman Sea) is active; Narcondam is considered dormant.
Q7. Which volcano is called the "Lighthouse of the Mediterranean"? Practice
Correct answer: (D)
Stromboli (Italy) erupts constantly, glowing at night.
Stromboli (Italy) erupts constantly, glowing at night.
Q8. Most active volcanoes and earthquakes occur in the — Practice
Correct answer: (A)
The Pacific margins have destructive plate boundaries.
The Pacific margins have destructive plate boundaries.
Q9. Which of these is NOT a fold mountain? Practice
Correct answer: (B)
The Black Forest (Germany) is a block mountain.
The Black Forest (Germany) is a block mountain.
Q10. The Aravalli range is an example of a — Practice
Correct answer: (C)
The Aravalli is among the oldest fold mountains, now residual after erosion.
The Aravalli is among the oldest fold mountains, now residual after erosion.
Q11. What is called the "Roof of the World"? Practice
Correct answer: (D)
The Tibetan Plateau averages 4,500 m; the Pamir also gets this name.
The Tibetan Plateau averages 4,500 m; the Pamir also gets this name.
Q12. A U-shaped valley is formed by — Practice
Correct answer: (A)
A glacier erodes the floor and sides evenly.
A glacier erodes the floor and sides evenly.
Q13. An ox-bow lake is formed by — Practice
Correct answer: (B)
In the plains a river meander gets cut off.
In the plains a river meander gets cut off.
Q14. A crescent-shaped sand dune is called — Practice
Correct answer: (C)
Barchans are crescents with horns pointing downwind.
Barchans are crescents with horns pointing downwind.
Q15. The formation hanging from the roof of a limestone cave is a — Practice
Correct answer: (D)
A stalactite hangs from the roof; a stalagmite rises from the floor.
A stalactite hangs from the roof; a stalagmite rises from the floor.
Q16. The San Andreas Fault is an example of which plate boundary? Practice
Correct answer: (A)
Here the Pacific and North American plates slide past each other.
Here the Pacific and North American plates slide past each other.
Q17. The Mid-Atlantic Ridge lies on which type of boundary? Practice
Correct answer: (B)
Plates move apart here and new sea floor forms.
Plates move apart here and new sea floor forms.
Q18. A magnitude 6 earthquake has how many times the wave amplitude of a magnitude 5? Practice
Correct answer: (C)
The Richter scale is logarithmic: 1 unit = 10× amplitude.
The Richter scale is logarithmic: 1 unit = 10× amplitude.
Q19. Which is the largest delta in the world? Practice
Correct answer: (D)
The Ganga-Brahmaputra delta covers ≈ 100,000 km² in India-Bangladesh.
The Ganga-Brahmaputra delta covers ≈ 100,000 km² in India-Bangladesh.
Q20. Debris deposited by a glacier is called — Practice
Correct answer: (A)
Moraine is rock debris carried and dropped by a glacier; cirque and arête are erosional.
Moraine is rock debris carried and dropped by a glacier; cirque and arête are erosional.