POMPEII, ITALY — Any eruption at Mount Vesuvius comparable to the one that destroyed Pompeii in 79 A.D. is unlikely in the next few decades. However, magma is building up in a chamber below the volcano and smaller but still very dangerous eruptions like the ones in 1944 or 1631 are harder to predict, according to scientists behind a new Science Advances study.


The scientists used garnet crystals from the four largest eruptions of the last 10,000 years to calculate how long magma resided in a chamber below the volcano before being spewed out, and thus when equivalent eruptions are likely in future.


The crystals helped show that rather than magma coming directly up from deep below the volcano, larger eruptions all involve a top chamber filling with magma that subsequently cools and crystallizes over hundreds and even thousands of years.


When hotter magma later flows into the top chamber from below, it causes pressure rises which can force the cooler, more explosive magma upwards.


With these findings in mind, seismic surveys now show a magma reservoir building between six and eight kilometers below Vesuvius, but scientists believe it is unlikely to provide the basis for a 79 A.D. style eruption because the last major eruption at the site was only around eighty years ago, which means there has not been enough time for the cooler, more explosive magma to substantially accumulate yet. However, smaller yet still dangerous eruptions like the ones in 1944 or 1631 can occur after shorter periods of accumulation, according to the study, and thus close monitoring remains necessary.