Typically, the reawakening of a volcano can be seen by the increased rate of earthquakes (1 in figure) over a period of months or weeks as new magma works its way upward beneath the volcano. Volcano seismologist also look for a uniquely volcanic signal, long period earthquakes (2), that may indicate a change in the magma as it is rising. The Alaska Volcano Observatory maintains networks of seismometers on a subset of Alaska volcanoes.

Scientists can also see volcanic explosions (3) in earthquake data. This helps scientists know what is happening at far distances or when it is dark or bad weather.