CAPF AC 2025 Q74: Geography – Physical Geography & Geomorphology
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (c) Both 1 and 2
Explanation
Stratovolcanoes
How to think: a stratovolcano (composite volcano) is a tall, steep cone built from alternating layers of lava and ash.
The lava is thick and sticky, so it traps gas under pressure and the eruption is explosive.
| Statement | Fact | Verdict |
|---|---|---|
| 1. Tall, steep cones built of layers of felsic lava and volcanic ash | Layers of viscous lava (andesite to rhyolite) and ash | Correct |
| 2. Explosive eruptions because the lavas hold large amounts of gas under pressure | Viscous lava traps gas until it bursts out | Correct |
Examples: Mount Fuji, Mount St Helens, Mount Vesuvius, Mayon.
Answer: (c) Both 1 and 2.
Why each option is right or wrong
- (a) Incorrect. Statement 2 is also correct.
- (b) Incorrect. Statement 1 is also correct.
- (c) CORRECT. Both statements describe a stratovolcano.
- (d) Incorrect. Both statements are true.
Key point
Composite (stratovolcano): alternating lava and pyroclastic layers, steep cone, viscous felsic to intermediate lava, explosive eruptions. Shield volcano: runny basaltic lava, gentle slopes, quiet eruptions.
Remember
Stratovolcano: layered, steep, sticky lava, explosive.
Common mistakes
- Confusing stratovolcanoes with shield volcanoes, which are broad and gentle.
- Thinking runny lava makes explosive eruptions.
- Rejecting 'felsic' because many books say 'andesitic'.
Exam tip
Educated guess: both statements are standard descriptions: steep layered cones and explosive eruptions. When both read like a textbook definition, choose 'both'.
Sources
- NCERT Class XI Fundamentals of Physical Geography, Chapter 3 (Interior of the Earth: volcanoes, composite volcanoes)
- United States Geological Survey, Volcano Hazards Program: Volcano types (composite volcanoes)