How do volcanologists know when a volcano may erupt soon?
Quick Answer
They watch for swarms of small earthquakes, ground swelling, changes in gas output, and rising heat. These signs can show magma is moving upward, though they do not guarantee an eruption.
The Full Story
Volcanologists monitor volcanoes using seismometers, GPS, satellite radar, gas sensors, and thermal cameras. A common warning sign is an earthquake swarm, which can mean magma is cracking rock as it rises. The ground may also inflate by centimeters or even more as magma pushes upward. Sulfur dioxide and other gases often increase when fresh magma approaches the surface. These signals help scientists issue alerts, but not every unrest episode ends in an eruption.
Key Facts
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