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Predicted Questions with Model Answers
Q1 (5 marks — 50 words): Describe the Circum-Pacific belt of volcanoes.
Model Answer:
The Circum-Pacific Belt ("Ring of Fire") encircles the Pacific Ocean for 40,000 km, accounting for ~80% of world earthquakes and ~75% of active volcanoes. It extends from New Zealand through Indonesia, Philippines, Japan, Kamchatka, Alaska, and down the Americas to Chile. Formed by Pacific Plate subducting under surrounding plates, creating island arcs and explosive composite volcanoes (Fuji, Pinatubo, Krakatoa, Andes chain).
Q2 (5 marks — 50 words): Explain the difference between earthquake focus and epicentre. Describe any two types of earthquakes based on depth of focus.
Model Answer:
Focus/Hypocenter is the underground point of energy release; Epicentre is the surface point directly above, receiving maximum seismic impact. By depth: Shallow-focus (0–70 km) — most destructive as energy reaches surface quickly (e.g., Bhuj 2001, Mw 7.7); Deep-focus (300–700 km) — felt over vast areas but less surface destruction; occur in subduction zones (Japan, South America).
Q3 (5 marks — 50 words): What is a tsunami? Briefly describe the 2004 Indian Ocean Tsunami.
Model Answer:
A tsunami is a series of long-wavelength (100–500 km) ocean waves triggered by seafloor disturbance — primarily submarine earthquakes. The 2004 Indian Ocean Tsunami (26 December, Mw 9.1–9.3) was triggered by the Sunda Megathrust fault off Sumatra. It killed 227,898 people in 14 countries; waves reached 30 m at Banda Aceh. Led to establishment of the Indian Ocean Tsunami Warning System (2006).
Q4 (10 marks — 150 words): Classify volcanoes on the basis of their eruption style and structure. Give examples of each type and discuss their global distribution.
Model Answer:
Volcanoes are classified by eruption style and structural form:
1. Shield Volcanoes — Broad, low-slope (2°–10°) cones of basaltic lava (low viscosity, flows freely). Eruption style: effusive — lava fountains, non-explosive. Form at hotspots and divergent boundaries. Examples: Mauna Loa, Kilauea (Hawaii — world's largest and most active); Etna (Italy); Icelandic shield volcanoes on Mid-Atlantic Ridge. Pose low direct danger but long-duration lava flows destroy property.
2. Composite/Strato Volcanoes — Steep-sided (30°–40°) alternating-layer cones of andesitic or rhyolitic lava. Eruption style: violently explosive — pyroclastic flows, ash clouds, VEI 5–7. Most dangerous type. Located at convergent/subduction boundaries (Ring of Fire). Examples: Mt. Fuji (Japan, 3,776 m — dormant since 1707); Mt. Vesuvius (Italy — buried Pompeii 79 CE); Krakatoa (Indonesia — 1883 eruption heard 5,000 km away; 36,000 deaths); Pinatubo (Philippines — 1991, cooled Earth by 0.5°C).
3. Cinder Cone Volcanoes — Small, steep, symmetrical; single vent; erupts cinders. Example: Paricutín (Mexico — emerged 1943 in a cornfield; grew 424 m in one year). Abundant along Ring of Fire.
Global Distribution: Volcanoes concentrate at three tectonic settings: (a) Subduction zones (Ring of Fire — 75% of active volcanoes: Indonesia with 273 volcanoes, most of any nation); (b) Divergent boundaries (Mid-Atlantic Ridge, East African Rift — Iceland, Kenya, Ethiopia); (c) Hotspots (Hawaii, Galápagos, Yellowstone — not at plate boundaries). India: Barren Island (Andaman — only active; on Indo-Australian-Burmese subduction).
Q5 (10 marks — 150 words): Discuss the positive and negative impacts of volcanoes on human society and the environment.
Model Answer:
Volcanoes are among Earth's most powerful forces — causing both catastrophic destruction and remarkable life-sustaining benefits.
Negative Impacts:
Immediate hazards: Pyroclastic flows — superheated (800°C) ash-gas-rock mixtures at 150–700 km/h — the deadliest hazard (Vesuvius 79 CE: Pompeii buried; 2,000 deaths). Lava flows destroy property but are slow enough for evacuation. Volcanic ash collapses roofs, contaminates water, disrupts aviation (Iceland's Eyjafjallajökull 2010 closed European airspace for 6 days; €1.3 billion loss). Lahars (volcanic mudflows) can bury entire towns — Nevado del Ruiz 1985 (Colombia): 23,000 deaths.
Global effects: Large eruptions inject sulphur dioxide into stratosphere, creating volcanic winter. Tambora (1815, Indonesia, VEI 7) caused 1816's "Year Without a Summer" — crop failures across Europe and North America, famine, 200,000+ starvation deaths. Pinatubo (1991, VEI 6) cooled Earth by 0.5°C for 2 years, disrupting agriculture.
Tsunami generation: Volcanic collapses trigger tsunamis (Krakatoa 1883: 36,000 deaths from tsunami).
Positive Impacts:
Fertile soils: Volcanic ash weathers into exceptionally mineral-rich soils. Java (Indonesia) — 40+ active volcanoes, yet supports 1,000 people/km² rural density with highest rice yields in Asia. Italy's Campania region (Mt. Vesuvius area) — world-renowned wines and agriculture.
Geothermal energy: Iceland generates 66% of electricity and 90% of home heating from geothermal. Kenya, Philippines, New Zealand similarly exploit volcanic heat. India has geothermal potential in Ladakh and Himalayan belt.
Mineral resources: Hydrothermal volcanic vents deposit gold, silver, copper, lead, zinc. Chile (world's largest copper producer) owes deposits to Andes volcanism.
New land: Hawaiian Islands created entirely by volcanism; ongoing Lō'ihi seamount building.
Scientific value: Hydrothermal vent ecosystems support unique life independent of sunlight — relevant for astrobiology.