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Mexico sees rapid evacuation

BY SUSAN KIM | Baltimore, MD | December 19, 2000

Popocatepetl erupted last night. No one was surprised when sparks flew hundreds of feet into the air and lava flowed down the slopes around the three-mile high volcano that towers southeast of Mexico City.

Yet many people in the path of the lava had ignored earlier evacuation orders. And army troops had to rush to rescue them from the path of the hot molten material, flaming ash and flying rocky debris.

"In my opinion this is the world's most dangerous volcano, potentially," said Michael Sheridan, a geologist at the University of Buffalo. Sheridan has contributed computer models to volcano-response disaster plans for communities near Popocatepetl and Mexico City.

Evacuation near the cone is made very complex by many factors, according to Sheridan. Among them are the memory indigenous people who were evacuated in Dec. 1994 have of leaving, spending two weeks in refugee centers, and missing holidays with friends and family who chose to stay. In that year, Popocatepetl erupted, but it did not do significant harm.

Popocatepetl began puffing out ash and gas eight days ago, signaling a possible eruption. Late last week, CENAPRED (Centro Nacional de Prevencion de Desastres), the governmental body charged with disaster preparedness in Mexico advised evacuations from 22 communities very close to the volcano, putting the safe distance from the base at more four miles.

CENAPRED posts information about the activity of the volcano, including seismic activity and gas emissions, at its Web site. Popocatepetl grew more agitated early yesterday, and CENAPRED issued a Yellow III alert, indicating no one should be closer than six miles (10 kilometers) to the volcano.

The volcano should be taken seriously, according to volcanologists. "Popo has had several catastrophic eruptions in the last few thousand years, most recently in 822 AD," said Michael Abrams, a research scientist and a volcanologist at NASA's Jet Propulsion Laboratory in Pasadena, CA.

"Popo has the capacity to produce a very large eruption, far larger than its current (activities of the last six years)," said Abrams. "There are tens of thousands of inhabitants living directly on its flanks. They could be affected by eruptive products from a large eruption, such as ash flows, mud flows and ash deposits."

Millions more inhabitants live in Mexico City. They could be affected by ash deposits. Indeed, the volcano towers at 17,887 feet, so high its cone is snowcapped. But the vicinity of Popocatepetl, which was named "smoking mountain" by the Aztecs, is no wilderness area. In its shadow to the northwest live the 20 million residents of Mexico City, which is about 40 miles away.

"Popo is big and complicated," said Barry Voight, a volcanologist at Pennsylvania State University, State College, PA, who has garnered research support from the National Science Foundation's Division of Natural and Manmade Hazard Mitigation. Voight has earned recognition for many scientific predictions, including the one he made one month before the May 1980 eruption of Mount St. Helens.

He said the blast from that volcano would be sideways and it was. Like Abrams, Voight points to the "potential size of the eruption and explosive style" of Popocatepetl and people living "on and near the flanks."

"Mexico City is basically out of reach," said Voight. "But hundreds of thousands live within say 25-35 kilometers (15-22 miles) of the summit. "The worst hazards are pyroclastic flows-scorching hot bouldery pumice and ash floods, and hot ashy hurricanes. These are devastating and few would survive them.

"The dangerous outcomes not end there. "Other hazards include ballistic blocks and bombs to distances of say 5 kilometers [3 miles], and heavy ash accumulations to tens of kilometers." The ash is so heavy it can cause breakdowns in structures. The "bombs" can cause fires. Rainstorms and snowstorms compound the effects of ash fallout, creating boulderly mudfloods into valleys.

Just before the eruption last night, Voight characterized the seismic readings CENAPRED reported as "very strong" and "a good indication for an eruption that is bigger than average.

"But "over the past six years or so," explained Voight, Popocatepetl has had several "relatively small explosions." Distinguishing which "symptoms" indicate a big eruption is not entirely clear-cut. "A question always is, at volcanoes like this, whether the bigger and more dangerous event will be recognized in advance," said Voight. Still, he notes he took the warnings from CENAPRED quite seriously because of the "state-of the art equipment" and "skilled personnel" that are doing the monitoring.

So why were people so reluctant to leave their homes before the volcano erupted, many simply ignoring warnings from CENAPRED? "Volcano action history plays an important roles," said Voight. "In an eruption that lasts for five or six years, the longevity makes the population somewhat bored with hazard warnings. And if nothing very serous has happened the last time they were warned, it's difficult to get them to respond."

Culture, economic and political style also determine how residents will meet an evacuation response, according to Voight. And University of Buffalo's Sheridan points out three different states have jurisdiction for planning because of their intersection at the volcano. Moreover, en masse evacuation is costly, and if nothing untoward happens, residents become even more inured to warnings.

"There have been three big pyroclastic flow events [at Popocatepetl] in the last 5000 years," said Voight, "devastating areas to around 30 kilometers [20 miles] from the top. ...and lots of smaller [events], going less far. That may seem like a long time, but these events tend to occur and volcanologists take them seriously."

So what can change the too common public response of habituation to "symptoms"? Prediction that is extremely precise. And it is what Voight, Sheridan, Abrams and geologists and volcanologists around the world continue to pursue.

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