How do you measure the size of a volcanic eruption?

Just as seismologists measure the size of an earthquake using the Richter scale, volcanologists use an eruption magnitude scale called the Volcanic Explosivity Index, or VEI to classify eruptions. This scale assigns a number to an eruption based on things that can be observed, such as the height of an eruptive plume and the volume of the materials erupted.

Ready to rate the eruption you're watching? Here's what to do:

First, check out the Volcanic Explosivity Index (VEI) chart.

Photos: Gary Rosenquist