Thursday, March 02, 2006
Augustine volcano is about to go back to sleep!
She said the 4,134-foot mountain may be a little taller when the dome-building phase is complete.Seismic tremors from the island now indicate rockfall from unstable parts of the new dome, not deep magma movement, said Stephanie Prejean, a U.S. Geological Survey seismologist with the observatory.
These signals have decreased over the last few days, she said.Also slowing down is the pace at which the island has been deflating since the last big explosions, Prejean said. Five global positioning satellite sensors on the island began detecting inflation of the island last summer as magma moved into the core. By January, Augustine had swollen by about one inch.Then, two days after a series of explosions ended Jan. 28, the tumescent mountain began to subside.
An inch may not seem like a lot, but it’s indicative of forces working deep underground, Bull said. In any event, it’s the change that’s significant, not the amount of shift in the earth’s surface, she said.Augustine, located 75 miles southwest of Homer, first exploded Jan. 11 after weeks of growing seismicity. The mountain let off 13 explosive eruptions during the month.
If the eruption is in fact tapering off, that would make this year’s event smaller and less vigorous than the three previous eruptions, in 1963-4, 1976 and 1986, Prejean said.The 1964 eruption’s explosive phase continued for 11 months. The 1976 eruption, which dumped measurable ash onto Kenai Peninsula communities, fell quiet for several months, then returned with a second explosive period. The 1986 eruption had just one initial explosive phase, but it too was larger than this year’s.Comparing the patterns of earlier eruptions is difficult because they produced nothing like the wealth of data scientists harvested this year, Prejean said.
But the seismic buildup detected in previous eruptions helped alert scientists to the approach of magma last summer, giving them time to prepare their instruments, she said.‘‘I think this data set rivals any data set in the world,’’ she said. ‘‘It’s an amazing data set.’’Among the new technology deployed for Augustine were cameras (remote, thermal and infra-red), satellites and more frequent overflights. A low-light camera mounted on the Homer bluff has detected a glow on the island’s summit lately, providing evidence that dome-building continues.
Looking ahead, Prejean said she hoped the recent deployment of ocean-bottom seismometers in lower Cook Inlet will allow scientists to measure the location of magma inside the mountain using a system called seismic tomography. Describing it as a kind of MRI of the mountain, Prejean said the technique looks for magma by measuring the velocity and flow of seismic waves through the volcano.Augustine remains at alert-code color orange while the eruptive dome-building continues, the observatory said Friday.
Meanwhile this week, the observatory downgraded Spurr Volcano west of Anchorage from code yellow to code green, the lowest level for a dormant volcano. Growing seismicity had prompted an increase to yellow in July 2004 on Spurr, which last erupted in 1992. But the seismicity started tapering off last June.Scientists had been paying special attention to a meltwater lake in the ice on the summit of Mount Spurr, which was the source of occasional roiling gas emissions.
A recent change in color of the lake water indicates reduced acidity and, along with a decline in gas emissions, helped prompt the color-code change, the observatory said.At the same time, the observatory upgraded Korovin Volcano in the remote Aleutians to code yellow. Sensors on the Atka Island mountain picked up four recent days of increased seismicity, the observatory said.