Most of the time, volcanoes are quiet. When they do become restless, the people living around them are, understandably, interested in what that unrest might mean. Sometimes that unrest leads to an eruption that can impact people, property and economies on a local to global scale. Most of the time, the unrest will lead to nothing beyond a period where the volcano shows signs that something is happening deep beneath our feet.

However, trying to tell people how severe the restlessness is and what level of concern you should have can be very difficult. Many volcano monitoring agencies try using volcanic alert statuses that get at how likely an eruption might be and in what timescales (months? days? hours?) Those alert statuses tend to be defined by volcanologists and seismologists for the monitoring agency who try to look at the data in hand of the unrest and project what they think the future might hold.

There is a problem with that model: it is mostly a qualitative assessment. We see signs of unrest like earthquakes, increasing gas emissions, deformation of the volcano’s surface, increased temperature at hot springs — all signs that things are heating up under the volcano. That heat likely means that new magma is making its way closer to the surface, but that magma may or may not erupt. Volcano monitoring scientists will look at past activity at the volcano (or volcano’s like it) and try to place a level of concern. Yet, no fixed international model exists to say that one country’s Level 2 (or yellow or moderate) alert means the same as another country’s (or another country’s).