FIERY lava and billowing ash pouring from an erupting volcano are obvious hazards. But what of the more subtle danger of collapse of the volcanic mountain itself? This can produce overwhelming avalanches that race along as fast as 360 kilometers (224 miles) an hour for many tens of kilometers. Moreover, it can happen even in the absence of an eruption.
The danger is subtle because the majestic structures of volcanic mountains "have an air or permanence that belies their inherent instability," to quote Lee Siebert of the Smithsonian Institution in Washington, D.C. It's easy to overlook this possibility in assessing a volcano's potential hazard. Yet, as Dr. Siebert notes in a recent issue of the journal Nature, worldwide study of volcanic debris deposits shows that such structural collapse "once thought to be extremely rare is not all that uncommon."
Siebert was commenting on a study, published in the same issue of Nature, that drives this point home. Geophysicists James E. Beget and Juergen Kienle of the University of Alaska at Fairbanks report that the active volcano Mt. St. Augustine represents a structural failure waiting to happen.
The mountain rises 1,220 meters above Augustine Island near the mouth of the Cook Inlet in south-central Alaska. Drs. Beget and Kienle find it to be the most active volcanic land-slide generator known. It has repeatedly collapsed and regenerated over the past 2,000 years, averaging 150 to 200 years per cycle.
The scientists warn that the mountain is again at a stage where "There is a high likelihood of another debris avalanche occurring in the near future." They note that such an avalanche would generate a tsunami that could cause much damage throughout the Cook Inlet area. Some 250,000 people live in the region. There also are major oil-storage depots, oil tanker facilities, and offshore oil platforms. Cook Inlet inhabitants would likely have only about an hour's warning following a Mt. St. Augustine edifice
collapse, according to Siebert.
While Mt. St. Augustine may be the most spectacular example of repeated edifice collapse, it's not the only volcano that bears watching. This type of danger caught vulcanologists' attention when they documented the collapse and avalanche that accompanied Mt. St. Helens' eruption 12 years ago Monday. As Siebert notes, they now can do a fair job of predicting eruptions and collapses when volcanic mountains are well mapped geologically and instrumented for continuous surveillance. But many potentially dange rous volcanoes are not.
It seems ironic that the Bush administration should propose a major cut in the US Geological Survey's volcano hazards program just as vulcanologists are awakening to the need to add the lurking danger of structural collapse to their list of volcanic hazards. The Survey's $540.3 million requested fiscal 1993 budget is 7 percent less than its current budget. But the program for geological hazards surveys would be cut 15 percent.
It seems foolhardy to undercut the work of American vulcanologists by trying to save money in what really is a minor part of the federal government's research budget.