Concerns that the Campi Flegrei volcano in southern Italy, which has been dormant for over five centuries, could shortly erupt have been fueled by over a thousand little earthquakes in the region in recent months.
Small earthquakes and ground deformation have been observed for decades in the Long Valley Caldera, a volcano in eastern California that is next to Mammoth Mountain, some 6,000 miles distant.
Does the recent seismic activity actually indicate that a volcanic eruption is imminent? Depending on who you ask, maybe.
It is more difficult to predict the behaviour of these two volcanoes because they are calderas, which are vast depressions formed by ancient explosive "super-eruptions" that effectively collapsed in on themselves.
Seismic activity may indicate a volcano is reawakening, but there is usually more to the tale than meets the eye.
Supervolcanoes, like Campi Flegrei and the Long Valley Caldera, are defined as having produced more than 240 cubic miles of material during a single eruption.
Although both Campi Flegrei and Long Valley are potential of producing massive explosions, the term "supervolcano" may be deceptive, according to Michael Poland.