Which statement describes volcanic domes?

Which statement describes volcanic domes?

• A. They are built from low-viscosity basaltic lava
• B. They are viscous lava that piles up near the vent
• C. They are formed by violent pyroclastic flows
• D. They are characteristic of calderas

Answer: (B)

Volcanic domes form when magma with high viscosity—typically rhyolitic or andesitic—erupts slowly and piles up around the vent. The thick lava doesn’t flow far, so it extrudes in place and builds a bulbous, steep-sided mound rather than spreading out into wide lava flows. This contrasts with low-viscosity basaltic lava, which flows easily and creates broad, shield-like shapes instead of a dome. While explosive activity can occur with domes, the dome itself is produced by viscous lava stacking up near the vent, not by violent pyroclastic flows. Calderas are large collapsed depressions and not the feature that defines domes, though a dome can sit within one. So, the statement about viscous lava piling up near the vent best describes volcanic domes.

Volcanic domes form when magma with high viscosity—typically rhyolitic or andesitic—erupts slowly and piles up around the vent. The thick lava doesn’t flow far, so it extrudes in place and builds a bulbous, steep-sided mound rather than spreading out into wide lava flows. This contrasts with low-viscosity basaltic lava, which flows easily and creates broad, shield-like shapes instead of a dome. While explosive activity can occur with domes, the dome itself is produced by viscous lava stacking up near the vent, not by violent pyroclastic flows. Calderas are large collapsed depressions and not the feature that defines domes, though a dome can sit within one. So, the statement about viscous lava piling up near the vent best describes volcanic domes.