十万个为什么·科学启蒙30篇（2）

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为什么火山在沉寂多年后会突然喷发？

Molten rock called magma rises slowly from deep inside Earth’s mantle.
Pressure builds up beneath the surface when magma cannot escape through solid rock.
Gas bubbles trapped in the magma expand as it rises, increasing pressure further.
When pressure exceeds the strength of the overlying rock, an eruption occurs.
Some volcanoes stay quiet for centuries while magma slowly accumulates underground.
Scientists monitor earthquakes, ground swelling, and gas emissions to predict eruptions.
The type of eruption depends on magma thickness and gas content.
Explosive eruptions happen when thick, sticky magma traps gas until it bursts.
Quiet eruptions occur when thin, runny magma lets gas escape easily.
Volcanic ash can travel thousands of miles and affect global weather patterns.