Closing the window keeps volcanoes at bay
Studies of Pompeii and Montserrat enlighten emergency plans for Naples.
An eruption of Mount Vesuvius, near Naples in Italy, could kill as many as the Indonesian tsunami, says a British researcher. But lessons learned from the 1997 eruption on the Caribbean island of Montserrat could reduce the damage, he says.
"Vesuvius is one of the most serious problems facing Europe," says Peter Baxter of Cambridge University's Department of Medicine, who collaborated with volcanologists and civil engineers on the Montserrat study.
Baxter and his colleagues are members of a European project called Exploris, which is studying the human risks of eruptions and how to mitigate them. As well as Vesuvius and Montserrat, Exploris is looking at hazards posed by Mount Teide in the Canary Islands, Sete Cidades in the Azores, and others.
The activity at the Soufrière Hills Volcano in Montserrat began in 1995, but the worst damage happened in 1997, when fast-flowing streams of hot gas and ash, called pyroclastic flows, struck several villages. The same kind of eruption devastated Pompeii in 79 AD.
Baxter's team looked at the effects of a pyroclastic flow on 26 December 1997. They found that the flow, already hot enough to ignite furniture and other materials, became even more damaging as it picked up debris and hurled it at buildings1.
Running hot and cold
This volcanic flow was not the "turbulent mess" that has often been assumed, says Baxter. The pressure of the hot gas was surprisingly low, and it caused much of its damage by entering buildings through open windows and doors.
These streams became highly focused. Like gusts of wind, they come in one window and go out another. A person cowering in a corner might escape the scorching material untouched.
Baxter says that people have assumed that pyroclastic flows would batter buildings down. But the Montserrat study shows that heat-resistant coverings on windows and doors could greatly reduce damage to buildings, he says.
The Neapolitan authorities plan a mass evacuation if Vesuvius threatens to blow, as one day it surely will. But they estimate that it could take at least five days to clear the area, and pyroclastic flows might strike sooner than that. "We just don't know how much time we'd have," says Baxter. Protective barriers for windows might save lives.
Choke and burn
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.
- Baxter P. J., et al. Bull. Volcanol., 67. 292 - 313 (2005).
- Gurioli L., et al. Geology, 33. 441 - 444 (2005).
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