How Can You Tell if a Volcano Is Restless? It's Complicated

A steam plume from Nevado del Ruiz in Colombia, seen on April 23, 2014. Quantifying how intense is this unrest would the goal of the Volcanic Unrest Index. SGC 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 ...