In Paul W.S. Anderson’s Pompeii—in theaters now—Kit Harington and Emily Browning play a couple of star-crossed lovers in 79 A.D. whose forbidden relationship is the most minor of problems: The city they know and love is about to come crashing down, literally, as Mount Vesuvius starts spitting lava.

Like any good Hollywood disaster flick worth its ticket price, Pompeii’s filmmakers employed a fair amount of creative license. But Dr. Rosaly M. Lopes-Gautier, Senior Research Scientist and Manager of Planetary Science at NASA’s Jet Propulsion Laboratory and author of The Volcano Adventure Guide, says there’s a lot the movie gets right, scientifically-speaking. We pressed her for details. 

Among your many other achievements, you’re one of the world’s leading volcano experts. So—scientifically speaking—what parts of a volcanic eruption, and the eruption of Mount Vesuvius in particular, does Pompeii get right?
They got the sequence of events right: the fact that there were earthquakes before the main eruption, that a big explosion happened during the day but pyroclastic flows [rapidly-moving flows of rock and hot gasses] only reached Pompeii much later (in the movie, it’s during the night; in reality, it was early the next morning). The explosion cloud, the pyroclastic flows, [and] earthquakes, were all done very realistically.

Which aspects are most clearly a case of creative license?
There was pumice rock fall but no fiery bombs, which don’t happen in that type of very explosive eruption. However, the rock and pumice fall did destroy structures and caused fires (probably from overturned oil lamps). The lava lake in the crater was artistic license to convey the idea of magma coming up without the people realizing. The tsunami in the movie was larger than the one reported, and in reality the tsunami didn’t move ships in the city.

What’s the one thing you would have done differently?
I’d probably have made the tsunami less dramatic. However, this is a movie drama, not a documentary, so I think artistic license is perfectly fine.

Could the events of Aug. 24, 79 A.D. happen at Mount Vesuvius again?
Yes, though the eruptions of Vesuvius are not generally as large as the 79 A.D. one. Vesuvius tends to erupt in cycles, and the first eruption in the cycle is the largest. 79 A.D. was the opening of a new cycle, so was the large eruption of 1631.

What are the factors that could contribute to that being a reality?
It seems that the longer the volcano rests between cycles, the larger the initial eruption can be. The end of the last cycle was in 1944, with a not particularly violent eruption. Vesuvius could rest for many years before the next one.
What might the potential impact of that look like?
There are over one million people living near the volcano today. Potentially, the impact could be much larger than that of the 79 A.D. eruption. However, the volcano is very well monitored, so there would be warning. 

What are some of the other most potentially dangerous volcanoes around the world?
Many of the volcanoes in Indonesia, the Philippines, Japan, and other places around the “ring of fire” of the Pacific are potentially very dangerous, as they can have violent explosive eruptions such as Vesuvius did in 79 A.D., or even more violent. The most hazardous volcano in the U.S. is Mt. Rainier, although Yellowstone has the potential for catastrophic eruptions. When we consider volcanic hazard, we look at the probability of the volcano erupting in the near future, such as the next few decades, and the impact to human life and property. Even a not very large eruption from Mt. Rainier could cause ice in glaciers to melt, creating devastating mudflows.
What are three facts about volcanoes that most people don’t know?
1. Volcanoes don’t suddenly erupt without any warning. The movie correctly depicted that they had warning, because of the many earthquakes, but the people at the time did not connect the earthquakes to the volcano.

2. Pyroclastic flows and mudflows are much more dangerous than lava flows. Many lava flows travel slowly enough that you can get away from them, or even walk over them if the crust has cooled enough (cooled lava is a very good insulator, so the flow may still be molten underneath, but with a cool hard crust). Pyroclastic flows and mudflows travel much faster and often it is not possible to escape them using a car.

3. The most spectacular volcanoes to photograph and visit while in eruption are usually the least dangerous ones. For example, Stromboli in Italy, Yasur in Vanuatu, and Kilauea in Hawaii. They have either small explosions or no explosions at all, which makes them very tame as far as volcanoes go.