Recurring episodes of growth and destruction of El Misti's domes in the past have triggered avalanches and pyroclastic flows. Alternating explosive events have catalysed pyroclastic flows, surges, and tephra falls. On average, pumice falls occurred every 2000 to 4000 years, and ashfall occurred every 500 to 1500 years. The extent and volume of the small event during the 1400s and of the eruption about 2050 years ago indicate that future Misti's eruptions, even moderate in magnitude, will entail considerable hazards to the densely populated area of Arequipa.
"The possible impact of Misti on Arequipa is as worrisome as that of Vesuvius near Napoli," said Thouret, a professor at the Université Blaise-Pascal in Clermont-Ferrand. "I have sent several reports to the civil authorities in Arequipa - City Hall, Government of the Region of Arequipa, and National Civil Defense. The Civil Defense regional office in Arequipa thus became aware of the problem, but damage induced by earthquakes and landslides in the region has exceeded the potential effects of any eruption, yet to happen, at El Misti. Therefore, they do not pay too much attention to the potential volcanic threat."
Arequipa suffered an earthquake on June 23, 2001. El Misti basically stayed stable - fumarolic activity increased at its summit right after the earthquake, but went back to "normal."
Thouret's work has focused on active volcanoes in Peru including Nevado Sabancaya, Ubinas, El Misti, and Huaynaputina. (In 1999, he published a paper on the large 1600 AD eruption of Huaynaputina, 70km east of Arequipa, in Geology.) He became painfully aware of the damage imposed by volcanoes when he was working on Nevado del Ruiz for his Ph.D. thesis in Columbia. It erupted on November 13, 1985 and its mudflows alone killed 23,000 people.
"El Misti's eruption is probable but we cannot forecast the magnitude of the future eruption unless we detect changes in the volcano's behaviour a few weeks or a few months in advance," Thouret said. "We are carrying out more work in Peru on active volcanoes and hazards, as well as on old volcanic deposits such as the widespread Tertiary ignimbrites. When I say 'we', I mean a group of French and German geologists-volcanologists from the Université Blaise Pascal (Clermont-Ferrand, France), the French Institute for Research and Development (IRD), and from the University of Göttingen (Germany). Of course, we also work in Peru with Peruvian colleagues of the Geophysical Institute of Peru and from two Universities in Lima, in the framework of an international agreement for research and cooperation."
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