Question: When you predict a volcanic eruption, how long do you normally have before the volcano erupts?

James Verdon answered on 25 Jun 2012:

Hi babbyhoff, really good question.

There are two main ways we can predict an eruption. Often, eruptions are preceded by lots of small earthquakes (called swarms) as the magma rises through the volcano. We can put out seismometers to detect these swarms as they happen. Also, the volcanoes often expand by a few centimeters as the magma chambers get filled up. We can measure the expansion using GPS stations or with radar techniques.

Sometimes, these things happen gradually over a few weeks or so, and we can see the volcano moving towards eruption fairly easily. However, sometimes volcanoes erupt with no prior warning – no seismicity, no expansion – and then it’s impossible to predict an eruption. Similarly, sometimes you might get all the signs that an eruption is about to happen, lots of seismicity and inflation, but then nothing happens and the volcano just goes quiet again. So making predictions about volcanic eruptions is really difficult.