Book 12, Question 18
How Do Geologists Measure How Big an Eruption Is?
Geologists rate eruptions with the Volcanic Explosivity Index. It is a scale from 0 to 8, mostly based on how much material was thrown out and how high the plume rose. Each step is about ten times bigger!
More fun facts
- The most common way to measure eruption size is the Volcanic Explosivity Index, or VEI.
- Unlike earthquakes, eruption size cannot be measured directly with instruments.
- The VEI is based on a mix of measurements and observations.
- A key part of the VEI is how much ash an eruption throws out.
- Like earthquake scales, each step up the VEI means about 10 times more ash.
- Some quiet eruptions, like Kilauea's long Puu Oo eruption, poured out huge amounts of lava without exploding.
Sources: U.S. Geological Survey, U.S. Geological Survey
Questions kids ask
Why can't scientists just use instruments?
There is no consistent instrument for eruption size, so they combine ash volume, plume height and observations.