Baxter and his colleagues plan to use the Montserrat data to develop a computer model of an eruption of Vesuvius. A new study of the effects of such flows on the Roman city of Pompeii, by Lucia Gurioli of Italy's National Institute of Geophysics and Volcanology in Pisa and coworkers2, might aid their efforts.

Gurioli's team estimated the temperatures in Pompeii from the amount of magnetism left unmelted in rocks and building fragments. By mapping the temperatures throughout the remains, the researchers could see how the shapes and arrangements of buildings and streets set up turbulence that could have cooled the flow in some places.

The findings paint a bleak picture. The town, nine kilometres southeast of Vesuvius, was smothered in about 2.5 m of ash even before the 300 °C pyroclastic flows struck, choking life and caving in roofs. And changes in the flow swirling over walls didn't seem to reduce the temperature below about 100 °C, so survivors of the ash would have burned to death.

Civil engineers are interested in the temperature measurements at Pompeii, says Gurioli's colleague Roberto Lanza of the University of Turin, because they offer clues about how soon emergency vehicles could drive into a town struck by pyroclastic flows without their tyres melting.