How can scientists tell how powerful a volcanic eruption was from its ash layers?
Quick Answer
They measure the thickness, spread, grain size, and chemistry of the ash, then compare it with known eruption deposits. The amount of erupted material is often expressed as VEI, the Volcanic Explosivity Index.
The Full Story
Volcanologists study ash layers in the field and in lab samples to estimate how much material a volcano erupted. Thick deposits near the volcano, very fine ash spread over large distances, and certain chemical fingerprints can all point to a major explosive event. They then compare the deposit with historical and geologic records and classify the eruption using the Volcanic Explosivity Index, which ranges from 0 to 8. For example, the 1991 Pinatubo eruption was VEI 6, while the 1815 Tambora eruption was VEI 7 and caused global climate effects. This work helps scientists reconstruct eruptions long before written history.
Key Facts
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"What ash layers can tell us about a volcano’s hidden power"
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