Stark Picture Painted of Volcano Threat

Displaying a series of striking pictures and graphic images, scientists demonstrated here Tuesday how quickly a nonthreatening volcano can turn into an extremely hazardous blowup.

The primary volcanoes discussed at the annual meeting of the American Geophysical Union were Popocatepetl near Mexico City, Kilauea on the island of Hawaii, Mammoth Mountain in California and Newberry Crater in Oregon.

Popocatepetl, the 17,887-foot peak just 40 miles from Mexico City, has been occasionally spewing ash and building a dome in its crater since 1994. But 23,000 years ago, one whole side of the mountain blew off, and as little as 1,100 years ago, an eruption occurred that sent mudslides into areas where millions of people now live.

Claus Siebe of the Geophysics Institute in Mexico City showed pictures of various kinds of deposits from big eruptions at one session here Tuesday. Mixed in the deposits were pieces of pottery and adobe bricks from early human settlements that were caught up in what happened.

In modern Mexico, Siebe noted, 30 million people live in areas where a catastrophic eruption, which could occur unexpectedly, could have such direct impact again.

“Popo [its nickname] is a special volcano, not so much because of its size as its populated surroundings,” said Siebe.

Hawaii’s Kilauea has been in nearly continuous eruption for 14 years, but aside from some houses burned by slow-moving lava and a highway destroyed in various spots, it is mostly a tourist attraction and an area of scientific study.

But at 8:09 a.m. last Feb. 1, Paul Okubo of the Hawaiian Volcano Observatory on the Kilauea summit rim related Tuesday, there was a sudden spate of earthquakes, and a colleague told him, “The summit is about to burst!”

Instruments showed a dramatic inflation of the Kilauea caldera on the summit, which had not erupted since 1952, within 15 minutes. But four hours later, the crisis had passed. Great quantities of lava had drained away from under the summit through the nearby Pu’u O’o cone. The summit began to deflate.

What saved the human habitations just outside the caldera from a possible catastrophic event? Okubo explained, “This time the underground plumbing wasn’t blocked, and the lava had an escape.”

Mammoth Mountain and the nearby Long Valley area at the resort town of Mammoth Lakes in the Eastern Sierra have had very few earthquakes in the last six months, after occasional high seismicity that scientists believe is volcanically related.

But in academic posters displayed here Tuesday, two scientists from the Cascade Volcano Observatory in Vancouver, Wash., revealed that on Aug. 30-31, there was a seven-hour surge of carbon dioxide gas emission levels--four times the normal level--at Horseshoe Lake, three miles from Mammoth Lakes.

Soon afterward, Kenneth McGee and Terrence Gerlach reported, they observed that a small fault had opened up at Horseshoe Lake along with a series of 2-foot-deep pits. They surmise that seismic activity released very suddenly a large volume of carbon dioxide that is believed to be welling up from underlying lava.

Finally, Oregon’s Newberry Crater, southeast of the town of Bend, last erupted 1,300 years ago.

Now, geologist Larry Chitwood reported on another poster Tuesday, measurements show that over a long period the floor of the crater has been rising--about 14 feet in the last 1,300 years. This may show inflation caused by lava underneath.

The scientist in charge of the Cascade Volcano Observatory, Dan Dzurisin, has said Newberry is one of the volcanoes in the West most likely to erupt fairly soon.