Volcanoes and Earthquakes
ICSE · Class 11 · Geography
Complete topic list for Volcanoes and Earthquakes in ICSE Class 11 Geography. Key concepts, sub-topics, and what to focus on for board exams.
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Topics in Volcanoes and Earthquakes
1. Vulcanicity and Volcanoes - Fundamental Concepts
- Vulcanicity refers to all processes by which molten rock materials (magma) are forced into or escape from the Earth's crust
- Magma is molten rock material beneath the Earth's crust; lava is the same material after reaching the surface
- Intrusive rocks form when magma cools inside the crust; extrusive rocks form when lava cools on the surface
2. Causes of Volcanic Eruptions
- High temperature in Earth's interior: Temperature increases with depth; at sufficient depth, rock melts despite overlying pressure
- Weak points in Earth's crust: Volcanoes concentrate in tectonically active zones; Pacific Ring of Fire has 83% of world's active volcanoes
- Gases in the interior: Water vapor is the most significant (60-90% of gases); rainwater percolates through crust, converts to steam under heat and pressure
3. Materials Ejected by Volcanoes
- Gaseous materials: Steam (60-90%), hydrochloric acid, ammonium chloride, SO₂, H₂S, hydrogen, CO₂
- Water vapor dominates and causes heavy post-eruption rainfall; other gases create environmental pollution
- Liquid materials: Lava at 600-1200°C; viscosity determines flow rate (usually slow, rarely >15 km/h, occasionally 80 km/h)
4. Types of Volcanoes - Based on Eruption Nature
- Hawaiian type: Low-viscosity lava, quiet eruption, lava flows form 'Pele's hair' threads, examples: Mauna Loa (4168 m), Kilauea (1232 m)
- Strombolian type: Moderate eruption intensity, named after Stromboli (Mediterranean), rhythmic eruptions, 'lighthouse of Mediterranean'
- Vulcanian type: Highly viscous lava, rapid solidification blocks vent, builds pressure, violent secondary eruption with cauliflower-shaped ash cloud, Vulcano (Lipari) erupted 12+ times (5th century-18
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