Sunday, May 01, 2005
US volcanoes not as quiet as people believe
At present, two of the three most dangerous California volcanoes are not only in the northern part of the state, several hours' drive from San Francisco, but those two -- Mount Shasta and Lassen Peak -- are like bomb factories without burglar alarms: They're inadequately monitored with seismic and other scientific instruments that could provide "24-hour, seven-day-a-week" monitoring and early warnings of disasters, the report said.
All three volcanoes -- the third is the Long Valley Caldera, on the eastern side of the Sierra Nevada -- are frequent tourist destinations.
"We cannot afford to wait until a hazardous volcano begins to erupt before deploying a modern monitoring effort," USGS director Chip Groat said in a statement that accompanied the report. "The consequences put property and people at risk, including volcano scientists on site and pilots and passengers in the air. It forces citizens, scientists, civil and aviation authorities, and businesses into playing catch-up with a dangerous volcano, a risky game indeed."
Geologically speaking, Northern California is part of the Cascade Range of volcanoes, which stretches from Washington through California. The most infamous Cascade volcano is Mount St. Helens in Washington, which blew its stack in 1980, killing 57 people and gouging out a 20-mile blast zone.
Shasta and Lassen lie on the southern tail end of the range, which formed over millions of years as a crustal "plate" dove under the western edge of prehistoric California. As the plate subducted, crust heated and rose to the surface in the form of molten bubbles of lava, which intermittently burst to the surface.
The report identified other dangerous volcanoes of the Cascades Range that are "significantly under-monitored" for eruptive activity: Rainier, Hood, South Sister, Crater Lake, Baker, Glacier Peak and Newberry.
Since 1980, "45 eruptions and 15 cases of notable volcanic unrest have occurred at 33 U.S. volcanoes," the report said. Only "a few" of the volcanoes are "well monitored with a suite of modern instruments," while about half the volcanoes "are monitored at a basic level."
The report is basically a wish list for volcano experts, in which they describe the kind of equipment they'd love to install around volcanoes -- seismic stations, "tiltmeters" and other gizmos that can detect subtle, ominous alterations of the ground surface, and so on -- if they only had the money.
California's troublemaking trio has plenty of wanna-be lava-spewers for company. Sixteen other California-canoes pose dangers that range from "very low" to "high," said the report issued from USGS' national headquarters in Reston, Va. The latest to undergo a major eruption was Lassen Peak, which fumed and smoked in the 1910s.
The state's "high threat" volcanoes are Clear Lake, Inyo Craters, Medicine Lake and Mono Craters, the report said. The "moderate threat" volcanoes in California are the Coso Volcanic Field, Mono Lake Volcanic Field, Red Cones and Ubehebe Craters.
California has no volcanoes listed in the USGS' "low threat" category. But many fall into the "very low threat" classification, including: Amboy, Big Cave, Brushy Butte, Eagle Lake Field, Golden Trout Creek, Lavic Lake, Tumble Buttes and Twin Buttes.
The report offers no hint of when future eruptions might occur. The fact that so many California volcanoes are not officially extinct, though, is a reminder that they might blow in the foreseeable future.
Indeed, since 1980, "volcanic unrest" has occurred at two California volcanoes, the report notes. The Long Valley volcano has experienced "recurrent earthquake swarms and (ground) uplift since 1980," and emissions of carbon dioxide since 1989. And the Medicine Lake volcano, about 30 miles northeast of Mount Shasta, experienced a "swarm" of earthquakes in 1988-89.Few Californians would rank volcanoes high on the list of potential disasters in the Golden State. When they think of volcanoes, they're likeliest to think of the searing, red-hot lava flows of Hawaii or the explosive, self-decapitating, sky-blackening vulcanism of Mount St. Helens.
Yet California is part of the same geological war zone -- the stretch of the Pacific "ring of fire" that formed in some places because of incessant plate activity along the western edge of North America and, in other places, because of what many scientists regard as the rise of hot "plumes" from deep beneath the Pacific Ocean.
The report cites a total of 18 "very high" threat volcanoes.
"All the volcanoes in the very high and high threat groups are found in Alaska, California, Washington, Oregon, Hawaii, the CNMI (Commonwealth of the Northern Mariana Islands), and Wyoming," the report said.