Why are some volcanoes eruptive while others mostly ooze lava?
Quick Answer
Volcanoes erupt explosively when gas-rich, viscous magma traps pressure; runny basaltic magma lets gas escape more easily and tends to flow instead. The key differences are magma composition, temperature, and dissolved gas content.
The Full Story
Explosive eruptions usually happen when magma is silica-rich and thick, because high viscosity slows the rise of gas bubbles and lets pressure build up. Basaltic magma, which is hotter and lower in silica, is more fluid, so gas can escape more readily and eruptions are often gentler. This is why shield volcanoes such as those in Hawaii commonly produce long lava flows, while many subduction-zone volcanoes can produce ash-rich blasts. The 1980 Mount St. Helens eruption is a classic example of a volatile-rich, viscous magma system producing a major explosive event.
Key Facts
YouTube Angle
Suggested video title for this topic:
"Same planet, totally different eruptions — here’s why some volcanoes explode and others flow."
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