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Byline: Keay Davidson San Francisco Examiner

The ``riskiest volcano on the planet'' isn't just a threat to millions of Mexicans who live literally in its shadow.

It's also a traffic hazard.

Major roads snake near the snow-capped volcano, Popocatepetl, a short commute from Mexico City. So when it starts huffing and puffing, as it did recently, a local radio station's traffic helicopter broadcasts the news to drivers, who naturally seek a new route - one that won't soon vanish under red-hot ash and searing lava.

The next thing you know, the ``word spreads that it's about to explode,'' laments Mexican volcano expert Claus Siebe. And when that happens, ``you can imagine how many phone calls we get.''

Siebe and his fellow geophysicists at Universidad Nacional Autonoma de Mexico are gambling that Popocatepetl's latest grumblings are just restless sleep, nothing more. At worst, they hope, it's just a repeat of its last display of ill temper, in the 1920s.

Back then, in a Mexico emerging from the fires of political revolution, Popocatepetl's brief, smoky tantrum was an exciting diversion that didn't cost a single life.

But recent geological research shows that every thousand years or so, Popocatepetl turns mean - perhaps mean enough to dump a mountain of ash on Mexico City, about 25 miles away, or to flood closer communities beneath waves of gray debris, the scientists said at last week's meeting of the American Geophysical Union in San Francisco.

``This is a huge volcano surrounded by millions of people. That makes Popocatepetl the riskiest volcano on the planet,'' said one of their U.S. collaborators, Michael F. Sheridan, who chairs the geology department at the University of Buffalo.

When Europe was still a dark forest, 23,000 years ago, Popocatepetl underwent the volcanic equivalent of a total nervous breakdown: a ``sector collapse.''

A major part of the 17,991-foot mountain collapsed and sprawled across the countryside, crushing whatever living creatures happened to be in the way. A similar event today might kill millions.

Then, 14,000 years ago, Popocatepetl suffered a ``Plinian eruption,'' a massive blast that probably ejected a dust cloud a few miles high.

Geological evidence suggests the disaster resembled the famous eruption of the volcano Vesuvius, which destroyed the town of Pompeii in ancient Roman times. (That event was recorded by Pliny the Younger, the nephew of one of its celebrated victims, Pliny the Elder; hence the eruption's name.)

Popocatepetl's last severe fit was 1,700 years ago, when it underwent another Plinian eruption.

By analyzing the geological layers of past eruptions, the scientists have concluded that Popocatepetl either emits river-like floods of ash or undergoes a Plinian eruption every 1,650 years. If their data is valid, then Popocatepetl may be overdue for its next big paroxysm.

That's why Siebe and his associates grew nervous in 1993, when the volcano's steam vents started hissing ominously. Seismic activity increased, too.

Act II commenced in December 1994, when the volcano began spouting ash. The amount was ``relatively small but very noticeable (to) all the people living around the volcano,'' Siebe recalled. Thousands fled or were temporarily evacuated.

At the time, Sheridan said the worst might be ahead. ``The chamber is loaded,'' as he put it.

Then, early this year, as scientists hiked around the volcano's huge mouth - a half-mile wide - they looked down inside and saw that their worst nightmare had reached the Earth's surface: a pool of red-hot lava. Was it the prelude to a major eruption?

Well, no ... not yet, anyway. As it turns out, the lava has cooled and formed a black ``dome,'' like a scar on a wound. The dome still vents steam, but that's about it.
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Publication:Daily News (Los Angeles, CA)
Date:Dec 22, 1996

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