Vesuvius has erupted dozens of times since the destruction of the ancient city of Pompeii. It most recently spewed an enormous mushroom cloud from its crater in 1944. “The eruption that destroyed Pompeii was about 100 times larger than the 1944 eruption,” says Kilburn, the volcanologist. But the latter still caused damage and the deaths of 26 people.
“The fascinating thing about Vesuvius is that the type of eruption it produces varies from time to time,” says Kilburn. By examining layers of volcanic material deposited in the area around Vesuvius, scientists discovered a pattern: After a period of lava flows, the volcano slumbers. This allows a rock plug to form, trapping gases inside. The gases build up, and so does the pressure inside the volcano. Eventually, like opening a shaken bottle of soda, the volcano goes KABOOM! This type of volcano, which alternately erupts flowing lava then clouds of ash is classified as a stratovolcano (see How Vesuvius Formed).
It’s only a matter of time until Vesuvius erupts again. And if it turns out to be one of the volcano’s more explosive eruptions, it could mean big trouble for the nearby city of Naples. It lies just 12 km (7.5 mi) away from the foot of the volcano.