Popocatepetl is close enough to Mexico City to cover its population of 22 million people with a blanket of ash. Mount Rainier, considered the most dangerous volcano in the Cascade Range, dominates the landscape over the Seattle/Tacoma area. Catastrophic volcano eruptions such as the one that buried Pompeii during ancient times have the potential to wreak havoc on modern humans as well, said the speakers in a program, “Explosive Volcanism in Human History,” held at the University of Pennsylvania Museum on the evening of Jan. 17.

In spite of our experience with Mount St. Helens, the public remains unalarmed. “Pacific volcanoes are seen now as places for recreation and skiing,” said Katharine Cashman, professor of geological sciences at the University of Oregon. Although 15 to 20 volcanoes are still considered active in the Pacific Northwest, she said, people seem inured to the constant threat.

Professor of Environmental Studies Robert Giegengack, who moderated the discussion, stressed the need to understand the past in order to avert disaster in the future.

Speakers offered examples from the past. Cavities left by ancient bedframes reveal that residents of the Greek island of Santorini were sleeping outdoors before the final eruption, said Temple University’s Philip Betancourt, who is also a consulting scholar for the Mediterannean Section of the Museum. About 300 years prior to the time of Moses, a volcano vaporized a huge chunk of the ancient island.

Brown University Professor of Archaeology Rudolph Winkes described evidence that many residents of the city of Herculaneum were able to relocate to Naples before the eruption of Mount Vesuvius, though archaeologists did discover hundreds of corpses along the shoreline — those who waited too long to leave.

Thanks to modern understanding of volcanic activity, the U.S. military base located near Mount Pinatubo in the Phillipines was evacuated — only two days before the volcano erupted in June 1991.

Averting disaster was what dominated the question and answer session at the end of the program. “Popocatepetl is putting out enormous amounts of sulphur dioxide, which suggests enormous amounts of magma but also means that the system is fairly open,” Cashman explained. Scientists have found that when the level of gas released goes down, the likelihood of an explosion goes up. However, even if pressure begins to build inside Popocatepetl, an evacuation of 22 million people seems impossible.

Cashman said that study of the past can do only so much. “We know how volcanoes wake up. We know their past. We don’t know their future.”