SME
Physical Geology · Problem type
Volcano types from magma and shape
Use this for “A steep cone of andesite layers erupts explosively. What type of volcano is it, and why?”
Explore
Basalt with about 50 % silica is hot and runny, so its gas bubbles out and lava flows quietly for kilometers.
Thin flows stack into a broad dome with slopes under 10°, like Mauna Loa above the Hawaiian hotspot.
Assumptions
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More silica links more SiO₄ tetrahedra into chains in the melt, so the magma is stickier (more viscous).
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Sticky magma holds its dissolved gas until it bursts out; runny magma lets the gas escape quietly.
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Cooler magma is stickier too: basalt erupts near 1,150 °C, andesite near 900 °C.
Topic check
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