LATIN AMERICA : Fears in Mexico Heating Up as Volcano Stirs

A plume of steam and gases can frequently be seen rising hundreds of feet above Popocatepetl volcano near Mexico City this summer, providing a visible focus for scientists’ concern that the volcano’s first eruption in 50 years may not be far away.

Two Arizona State University geologists, flying over the crater this month at the invitation of Mexican volcanologists, measured sulfur dioxide emissions at an ominous 3,000 metric tons (about 6.6 million pounds) a day, double the rate earlier this year.

Fumaroles--vents often surrounded by intensely glowing red sulfur deposits--have grown substantially in number since 1986, and a crater lake has changed color from clear green to milky green and heated up from 84 degrees Fahrenheit to 149 degrees.

These are among the signs that the famous volcano, at 17,887 feet one of the highest in the world, is stirring. But so far the number of earthquakes, often the most imminent sign of an eruption, has remained low.

A leading Mexican volcanologist, Servando de la Cruz Reyna, messaged Robert I. Tilling, a volcano expert with the U.S. Geological Survey, this week that the Mexican government has now approved funding for a network of seismic recording stations on the mountain to try to more precisely gauge the seismicity, measuring even the tiniest quakes.

Cruz Reyna, meanwhile, was reported by an associate, Manuel Mena, to be high on Popocatepetl to monitor the fumaroles and check for ground deformation, a significant precursor of an eruption.

Popocatepetl is of special concern because of its location, just 45 miles southeast of Mexico City and even closer to the city of Puebla. More than 20 million people live within 62 miles of the crater, and while most of the 25 to 30 eruptions of the past 600 years of recorded history have been relatively weak, there is evidence on the ground of great, disastrous eruptions in prehistoric times.

It is the potential that has scientists on edge.

Stanley N. Williams, one of the Arizona State geologists who measured the sulfur dioxide emissions, says that “absolutely the next thing that has to happen now” is for the Mexican government to initiate hazard mitigation steps in Mexico City and Puebla.

The most important of these would be to educate the population about what would happen during a heavy ash fall from an eruption, particularly the importance of sweeping or hosing ash off roofs, Williams said.

“The single greatest cause of death in 1991 in the Pinatubo eruption in the Philippines was the collapse of roofs in nearby towns covered by large amounts of ash,” he said.

French experts have prepared hazard maps indicating that mud and lava flows, as well as the superheated mixture of rock and gases known as pyroclastic flows, from a major Popocatepetl eruption could cut road and rail communications between Mexico City and Puebla, and affect small cities near the volcano’s base.

Such flows, which can occur rapidly, unexpectedly and even explosively, could cause a significant loss of human life, because the Mexico City-Puebla road and rail lines are both vital and busy.

But the most direct impact on Mexico City and Puebla would probably be the ash. Not the least of the ash impact could be on civil aviation. With Mexico City’s airport lying on the capital’s eastern side, toward Popocatepetl, all air travel would have to be suspended during an ash fall at the airport. During the past 20 years, according to a U.S. Geological Survey report, more than 60 airplanes worldwide, mostly commercial jetliners, have been damaged by encounters with ash clouds.

Still, Williams noted, depending on wind direction, Mexico City could be spared most of any Popocatepetl ash, just as Portland, Ore., was spared during the 1980 eruptions of nearby Mt. St. Helens.

The leading Mexican volcanologists, Cruz Reyna, Hugo Delgado Granados and Gerardo Suarez, have been seeking government money for not just seismic stations but many other types of monitoring at Popocatepetl during the present uncertainty.

Despite monitoring, the exact time of an explosive eruption can be a surprise, as it was at Mt. St. Helens. But the more extensive the monitoring, the greater the chance that a combination of signs may allow timely evacuations to save lives.

Popocatepetl’s last eruptive period was between 1943 and 1947, but the last really major eruptions are believed to have occurred in the century before the Spaniards under Hernando Cortes arrived in 1519.

Monitoring a Giant

The 17,887-foot-high Popocatepetl volcano, which is showing signs of impending activity, is located 45 miles southeast of Mexico City. More than 20 million people live within 60 miles of the crater, which has lately been emitting about 3,000 metric tons of sulphur dioxide a day.

Source: “Volcanic Hazards,” J.H. Latter, editor; Researched by KENNETH REICH / Los Angeles Times