Thursday, January 12, 2006

Augustine volcano displays small eruptions

A pair of small eruptions that blew ash six miles high above Augustine Island Wednesday were probably just the warm up for bigger explosions to come, scientists say.

The pre-dawn eruptions, following weeks of growing anticipation, sent nervous Alaskans scrambling to stores for face masks and auto air filters. Local airlines played it safe, waiting for daylight and a view of any ash cloud before dispatching some flights. In the end, no ash fell on settled areas around Cook Inlet.

After a morning of quiet, however, tremors began building again on the island Wednesday afternoon, suggesting more activity on the way.

Scientists with the Alaska Volcano Observatory expect the climax of the eruption cycle is still ahead. They say Augustine Volcano is behaving similarly to its eruptions in 1976 and 1986, which peaked with explosions that belched ash steadily for hours.

By contrast, Wednesday's two initial bursts, at 4:44 a.m. and 5:13 a.m., lasted only a few minutes each.

Such explosions are usually triggered by a build-up of gas that accompanies rising magma inside the volcano, said Tina Neal, a U.S. Geological Survey geologist with the Alaska Volcano Observatory. The pattern of seismic swarms in recent weeks suggests a large magma body that would probably not be finished with its work after those two small bursts, she said.

"We still could see something bigger. I think most of us expect it at this point," Neal said.
The ash plume drifted away from the volcano like a smoke signal, and headed north over the unsettled western side of Cook Inlet, according to the National Weather Service. At high elevations, the dispersing cloud drifted east toward the Kenai Peninsula.

Overcast weather limited reports. The volcano observatory said it had received reports of a brown haze over the middle of Cook Inlet Wednesday afternoon. An ash cloud was also reported moving slowly west from the island.

Scientists who flew over the island in the afternoon saw a pure white steam cloud rising from the summit. They also reported seeing new mudflows streaking the snow on the mountain's lower flanks. The mudflows – made up of melted snow and ash – did not descend below 500 feet elevation and posed no risk of triggering waves, scientists said. A webcam mounted on the island provided daytime photos of those mudslides over the Internet.

"It's very exciting," said Michele Coombs, a research geologist with the USGS as she prepared to leave for the flight. She said scientists at the observatory were trying to contain their enthusiasm and pace themselves because the eruption could go on for weeks or months.

The 4,134-foot volcano is 75 miles southwest from Homer and about 180 miles from Anchorage. Augustine is one of the most heavily instrumented volcanoes in Alaska, with 14 seismometers now on the island thanks to recent visits by scientists.

A buildup of seismic signals from the island started around 4 p.m. Tuesday, and by 9 p.m. the alert code was upgraded by the observatory from yellow to orange. It hit code red Wednesday morning with the first explosion, which registered as magnitude 2.6.

The overnight buildup was "beautifully displayed" on a digital graph picking up the island's seismometers, said Neal. "I think this will be showing up in textbooks," she said Wednesday.
That digital graph was also showing up on computer screens hooked to the Internet, including some in Nanwalek, a small village on the lower Kenai Peninsula that was hit by a tsunami after an 1883 eruption of Augustine. That tsunami was triggered by a major landslide, something that occurs only rarely during Augustine eruptions. But it keeps villagers' attention on the island that looms across the water.

Nanwalek residents noticed the uptick in tremors Tuesday afternoon and were watching closely when the alert code was increased to orange, said village second chief James Kvasnikoff.
"The rest of the community got pretty nervous about that," he said. Nanwalek has held several emergency preparedness meetings in recent weeks, he said.

In Homer, shoppers were grabbing items to protect their lungs and their cars. "Particle masks and panty hose, those are the items of the day," said Scott Ulmer, owner of Ulmer's Drug and Hardware, who had stocked up on those items in response to early warnings.

After the mountain blew, officials said some light ash might reach the Kenai Peninsula. There were no confirmed reports, however. An early-morning report of ash falling in Clam Gulch proved untrue, said Scott Walden, emergency management coordinator for the Kenai Peninsula Borough. State troopers dispatched to Clam Gulch traced the reports to ice fog and someone who smelled sulfur in the air, he said.

There was also some early confusion over media reports that ash was headed south for Kodiak. The reports were apparently the result of a National Weather Service ash fall advisory issued for the Kodiak area, a district that includes Augustine Island to the north.

Augustine's past eruptions have gone on several months. The 1976 event included clusters of eruptions lasting several days each over a three-month period. Heavy ash fall and early darkness shut down traffic in Homer during one eruption. Two F-4E Phantom jets that flew through ash clouds ended up with sandblasted canopies and exteriors, according to observatory records.
The 1986 eruption started in late March and continued until August. At one point it sent a column of ash seven miles high, which drifted over Anchorage and kept flights out of the skies over Cook Inlet. Ash fall in Anchorage shut down many businesses one day, while power companies called for reduced consumption to protect turbines from the ash.

Ash fall also hit Anchorage during recent eruptions from two other Cook Inlet volcanoes, Redoubt in 1989-90 and Spurr in 1992. The explosive phases of Spurr's 1992 eruption lasted three to four hours each, at one point shutting down Anchorage International Airport.

Comments: Post a Comment

<< Home

This page is powered by Blogger. Isn't yours?