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Volcanoes
Partial melting generally produces magma that is:
A. Compositionally different from its source
B. Always identical to its source
C. Always pure iron
D. Always water
Correct Answer: A
Minerals melt at different temperatures, fractionating melt from residue.
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Volcanoes
Flux melting in subduction zones is promoted by addition of:
A. Water and other volatiles
B. Sand
C. Oxygen from atmosphere only
D. Glacial ice at surface only
Correct Answer: A
Water released from the slab lowers the melting temperature of mantle rocks.
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Volcanoes
Decompression melting occurs when:
A. Hot mantle rises and pressure decreases
B. Pressure increases without heating
C. Lava freezes
D. Sediment compacts
Correct Answer: A
Rising mantle can cross its solidus as pressure falls.
CSS - PMS - CCE - PCS - Geography
Volcanoes
Iceland lies astride the:
A. Mid-Atlantic Ridge
B. Himalayan collision zone
C. San Andreas Fault only
D. Peru-Chile Trench
Correct Answer: A
Iceland combines divergent-ridge volcanism with a mantle hotspot.
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Volcanoes
Hawaii is a classic example of:
A. Hotspot volcanism
B. Continental collision volcanism
C. No volcanism
D. Glacial volcanism only
Correct Answer: A
The Hawaiian chain formed as the Pacific Plate moved over a hotspot.
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Volcanoes
Hotspot volcanism can occur:
A. Within tectonic plates
B. Only at subduction trenches
C. Only at collision zones
D. Only at river mouths
Correct Answer: A
Mantle upwelling can produce intraplate volcano chains.
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Volcanoes
Mid-ocean ridge volcanism is dominated by:
A. Basaltic magma
B. Rhyolitic magma only
C. Granite blocks
D. Limestone
Correct Answer: A
Decompression melting of upper mantle produces basaltic oceanic crust.
CSS - PMS - CCE - PCS - Geography
Volcanoes
Volcanic arcs commonly form:
A. Above subduction zones
B. At passive margins only
C. In stable shield interiors only
D. Along every transform fault
Correct Answer: A
Flux melting above descending slabs feeds chains of volcanoes.
CSS - PMS - CCE - PCS - Geography
Volcanoes
The Pacific Ring of Fire has many volcanoes because of widespread:
A. Subduction
B. Passive margins
C. Stable cratons
D. River deltas
Correct Answer: A
Subduction introduces water into mantle wedges and promotes magma generation.
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Volcanoes
Columnar jointing commonly develops in:
A. Cooling lava or shallow igneous bodies
B. Loose sand only
C. River water
D. Glacial ice
Correct Answer: A
Thermal contraction during cooling can form polygonal columns.
CSS - PMS - CCE - PCS - Geography
Volcanoes
Pillow lavas typically form:
A. Under water
B. Only in deserts
C. Only in continental glaciers
D. In coal mines
Correct Answer: A
Rapid quenching of basalt under water produces rounded pillow structures.
CSS - PMS - CCE - PCS - Geography
Volcanoes
Fumaroles are:
A. Openings emitting volcanic gases and steam
B. River mouths
C. Glacial cracks
D. Mineral grains
Correct Answer: A
Fumarolic activity vents hot gases from volcanic/geothermal systems.
CSS - PMS - CCE - PCS - Geography
Volcanoes
Volcanic gases commonly include abundant:
A. Water vapor, carbon dioxide and sulfur dioxide
B. Only oxygen
C. Only nitrogen
D. Only hydrogen
Correct Answer: A
H2O, CO2 and SO2 are major volcanic gases.
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Volcanoes
A lahar is:
A. A volcanic mud/debris flow
B. A lava fountain
C. A seismic wave
D. A mineral
Correct Answer: A
Water mixed with volcanic debris can rush down valleys as a lahar.
CSS - PMS - CCE - PCS - Geography
Volcanoes
Volcanic bombs are ejected:
A. While molten or semi-molten
B. Only as dissolved gas
C. Only as sediment
D. Only from rivers
Correct Answer: A
Bombs acquire aerodynamic shapes while still plastic during flight.
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Volcanoes
Lapilli are pyroclasts approximately:
A. 2–64 mm
B. Less than 0.002 mm
C. 64 cm–2 m only
D. Over 10 m
Correct Answer: A
Lapilli are intermediate-size tephra between ash and blocks/bombs.
CSS - PMS - CCE - PCS - Geography
Volcanoes
Volcanic ash consists of particles generally smaller than:
A. 2 mm
B. 2 cm
C. 20 cm
D. 2 m
Correct Answer: A
Tephra particles under 2 mm are classified as ash.
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Volcanoes
A pyroclastic flow is:
A. A hot, fast-moving mixture of gas and volcanic particles
B. A slow river
C. A cold glacier
D. A groundwater spring
Correct Answer: A
Pyroclastic density currents are among the most dangerous volcanic hazards.
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Volcanoes
Higher magma viscosity tends to:
A. Trap gases and favor explosive behavior
B. Always prevent eruptions
C. Eliminate pressure
D. Produce only shield volcanoes
Correct Answer: A
Gas escape is inhibited in viscous magma, increasing explosive potential.
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Volcanoes
Rhyolitic magma generally has:
A. High silica and high viscosity
B. Low silica and low viscosity
C. No dissolved gases
D. Only mantle olivine
Correct Answer: A
Silica-rich melts are highly polymerized and viscous.