St. Helens Blast Said Possible Within Days

29 September 2004 | 12:59 Code : 4322 Geoscience events
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A small explosion of rocks, ash and steam could occur within the next few days within the crater of Mount St. Helens, where earthquake activity has been steadily building for nearly a week, scientists said Tuesday.
A small explosion of rocks, ash and steam could occur within the next few days within the crater of Mount St. Helens, where earthquake activity has been steadily building for nearly a week, scientists said Tuesday.  "It could certainly happen today; it might not happen for weeks or months," said seismologist Seth Moran of the U.S. Geological Survey (news - web sites)'s Cascade Volcano Observatory. He added that the likelihood of a significant eruption "is fairly small." Scientists have watched the 925-foot-tall dome of hardened lava that has grown inside the crater since the May 18, 1980, eruption that blew the top off the mountain. Swarms of tiny earthquakes — more than 1,000 since the mountain began stirring on Thursday — have gradually increased, cranking up to a level not seen since 1986, when the volcano's last dome-building eruption occurred. Tuesday, the quakes were occurring at a rate of two or three a minute. The volcano was releasing three to four times the energy it was releasing Monday, said Jeff Wynn, chief scientist at the volcano observatory in Vancouver, Wash., about 50 miles south of the 8,364-foot mountain. Moran said that in an eruption, rocks 2 or 3 feet in diameter could break off from the lava dome and possibly be tossed as far as the rim. But, he and other scientists emphasized, that is not unusual at Mount St. Helens. Volcanologist Carl Thornber said scientists are baffled by the activity, unusual because the earthquakes are so shallow. "Where's the energy to keep driving this system?" he asked. Largely unheralded steam explosions in 1989, 1990 and 1991 all broke pieces of lava off the dome, Moran said. Seismologist George Thomas at the University of Washington said that on a scale of zero to 10, with 10 being the explosion at the mountain in 1980, the current activity would rate a one. Thomas said any rocks, ash or steam coming out of the volcano would most likely be contained within the crater itself. "The alerts we're sending out are just to protect hikers and scientists doing research within the crater," he said. The USGS (news - web sites) issued a notice of volcanic unrest on Sunday, citing "increased likelihood of a hazardous event." U.S. Forest Service officials closed hiking trails above the tree line at 4,800 feet. Mount St. Helens last roared to life in 1980, killing 57 people and leveling hundreds of square miles of forests.

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