Thursday, December 15, 2005
Augustine volcano is showing some active behavior
People in Kachemak Bay communities reported "sewer" smells in the air, and the FAA restricted flights below 6,000 feet within five miles of the summit.
A gigantic plume stretched into the mouth of Cook Inlet. Ash dusted the snow. New vents emerged.
Welcome back, Augustine.
"Augustine is doing all the things that Augustine does prior to an eruption," said volcanologist Game McGimsey on Tuesday. "Now, that doesn't mean that Augustine is going to erupt -- we're still at color code 'yellow.' But we're at a little higher level of concern than we were yesterday."
The storybook cone, which rises 4,134 feet from an island in lower Cook Inlet about 75 miles west of Homer, has been listed as restless for the past two weeks by the Alaska Volcano Observatory.
One of Alaska's most active volcanoes, Augustine last blew its top in 1986, when it drove a column of ash almost seven miles high and dusted Anchorage with ash.
It's one of 30 volcanoes monitored around the clock by the observatory, stretching from Mount Spurr 80 miles due west of Anchorage on out the Aleutian Chain.
"What we've seen is a pretty slow but sustained increase in seismicity (at Augustine) that began about early summer," said volcano seismologist John Power. "We have not seen this level of seismic activity since the 1986 eruption, so this is fairly substantial."
The volcano swelled about one inch in size too, based on measurements taken by global positioning system sensors near the summit.
All that suggests that a dike of molten rock or magma has intruded beneath the volcano from deep within the earth, squeezing into cracks and fissures inside the cone near sea level, Power said.
A batch of tiny quakes shook the volcano Friday and Sunday, one lasting 45 minutes. These new temblors jostled Augustine's plumbing -- the scientists say "perturbed" -- and apparently triggered steam explosions at the summit.
On Sunday night, people in the Kachemak Bay villages of Nanwalek and Port Graham, about 50 miles downwind, whiffed nasty fumes and got worried.
"I had received a call from a community member, and they were fearful that the volcano had erupted," said Nanwalek village police officer Kevin Seville. "There was distinct smell of sulfur in the air."
The observatory reassured him that the smells were minuscule amounts of sulfur carried by steam, and the volcano wasn't going to erupt immediately. Seville passed the word.
"Depending on the direction of the wind and the amount of gas emitted at the volcano, sulfur odors may persist," the observatory reported. "These periods should be relatively brief and are not expected to be a significant health concern."
On Monday, a team of scientists that included McGimsey and Power flew over the volcano. They spied a nest of fumaroles -- columns of rising steam ---- south of the summit in an area undisturbed in 1986. Light ash had dusted the snow.
"It's a lot of steaming and from multiple vents, and no doubt it is putting out sulfur," McGimsey said.
A satellite image taken Monday clearly showed a steam plume stretching at least 50 miles over the Barren Islands, out the mouth of Cook Inlet. By Tuesday, the plume shifted north, triggering a few reports of sulfurous "rotten egg" odors in Homer.
Augustine eruptions typically begin with months of rumbling that climax in a big explosion that busts open its throat and blasts ash thousands of feet into the sky, Power and McGimsey said. After that, sticky viscous magma oozes up and clogs the summit with a giant dome. The magma can dribble down the steep slopes as it cools, or collapse in floes of hot ash and rock.
"Prior to both the 1976 and 1986 eruptions, there were very marked increases in earthquake activity, and we have not seen levels that compare yet to those," said Power, who has studied Augustine for decades.
"If this activity is going to lead to an eruption, we believe we're still early in the game here."
Nonetheless, something inside the volcano has been heating up the summit, though it's not clear whether it's rising magma or hot liquids.
"Basically what the volcano is doing right now is drying itself out," McGimsey said.
Scientists in airplanes will sample the gases emerging from the volcano and use an infrared sensor to detect hot spots. Depending on the weather, scientists also hope to travel by helicopter to Augustine next week to install extra seismic instruments on its flanks, Power said.
McGimsey, the volcanologist, wants to snatch a sample of the ash to figure out whether it came from new magma or just old shattered rock.
Ash blasted from Cook Inlet or Aleutian volcanoes like Augustine can damage or destroy aircraft, and the observatory has the mission to warn people of possible dangers.
The prospect of an eruption has got the scientists on edge.
"Extremely," McGimsey said.