As Popocatepetl Activity Heats Up, Nerves Stay Cool

Immense plumes of ash and smoke billow from the Popocatepetl volcano within view of millions of people. It rumbles often and occasionally hurls showers of glowing rock.

But more than four years after the volcano began a new cycle of eruptions, scientists and officials are ever so cautiously growing less nervous--not that anyone takes an explosive, 17,925-foot mountain for granted.

Seismologists map its every quiver. Chemists study the gases and debris it burps out. Television cameras and radar keep constant watch on the crater, and a video image of the mountain is updated every minute on the Internet.

Trying to determine what occurs miles underground, geologists from Mexico and the University of Miami are turning to the skies, expanding a satellite monitoring system for the volcano.

All of that effort “has been able to give, little by little, a more complete and realistic vision of the risks for those in civil defense,” said Roberto Meli, head of the national Center for the Prevention of Disasters, which is in charge of monitoring Popocatepetl.

Some 20 million people live within 50 miles of the volcano. That has attracted attention to Popocatepetl’s threat, but Meli says it also blurs the fact that a far smaller number of people living much closer to the volcano are at greatest risk.

Popocatepetl is capable of immense eruptions--the last occurred about 800 years ago. It covers the ruins of two earlier volcanoes on the same site. Far more common, however, have been bursts of smoke, steam and ash recorded periodically since the 14th century.

Keeping watch on the volcano can be costly and tiresome. Gasping for breath in the thin air, scientists struggle up steep, sand-like slopes to build and maintain small monitoring stations near the fuming crater. Helicopters are sometimes pressed into duty to ferry equipment. Airplanes are used to check gas emissions.

“Nothing is enough,” said Roberto Quaas, the volcanologist in charge of monitoring Popocatepetl.

He said there are plans to install pressure meters to record the force of Popocatepetl’s outbursts and new monitors to measure expansion or contraction of the volcano’s surface.

At a recent conference of volcano experts in Mexico City, investigators showed photos of solar cells on recording stations peppered by volcanic debris--and a yards-wide hole blasted by a piece of rock hurled from the crater.

In 1995, five hikers were found dead near Popocatepetl’s crater, possibly due to volcanic gases. Officials now warn people to stay at least 4 miles from the crater.

Most scientists believe that somewhere below the volcano is a chamber of magma, fed by flows from deeper within the earth and vented to the surface at the volcano’s crater.

Earthquake studies indicate the chamber is deep below the surface --perhaps 6 miles beneath the crater, much deeper than the chambers of volcanoes like Mt. St. Helens.

If a chamber is shallow, a relatively small increase in pressure “could really weaken the walls and cause an immense explosion, such as occurred at Mt. St. Helens,” said seismologist Carlos Valdes of Mexico’s National Autonomous University.

The chamber beneath Popocatepetl “gives us security. If it is found further below, the pressure of the weight of the rock keeps it stable,” he said.

Valdes’ monitors also show a remarkably small number of earthquakes deep within the volcano--indicating that when magma flows, it seems to do so without meeting much blockage, so there may be less buildup of pressure.

Three Mexican states and Mexico City have mapped out plans to rapidly evacuate hundreds of thousands of people if the volcano some 40 miles southeast of Mexico City shows signs of a more dangerous eruption.

Residents of nearby villages have refused suggestions to relocate. Some of the Indian residents worship the volcano, yearly hiking up its slopes to a dark outcrop known as “the bellybutton” to leave offerings to “Don Goyo,” an affectionate and respectful nickname.

A large eruption could lead to fast-moving mudslides of volcanic ash that could swamp parts of some towns. Much of the sloping terrain to the east of the volcano is formed from such debris.

A huge, explosive eruption of the sort the volcano experiences every millennium or so could cause a blast of volcanic material that would destroy almost everything in its path.

Some villages were briefly evacuated in 1994 shortly after the volcano began its latest eruption cycle.

Mexican volcanologist Servando de la Cruz said that with what scientists know now, that evacuation might have been avoided. Officials fear people will lose confidence in emergency measures if evacuations seem unwarranted.

“Thanks to that understanding, the management of the situation has been a little different,” he said.

What would alarm him? “An activity completely different from what we have seen until now,” something that might leave investigators baffled about what the volcano is doing and what dangers it might pose.