Redoubt history points to likely eruption

January 31, 2009 

Five days ago, when the ground around Mount Redoubt began to rumble, federal and state geologists in Anchorage quickly looked at the Cook Inlet volcano's past to venture a prediction about its future.

The past was clear. There wasn't a minute to lose.

Two decades earlier, when Redoubt last erupted on Dec. 14, 1989, its labor pains were fast and furious, recalls John Power, a veteran geophysicist at the Alaska Volcano Observatory in Anchorage.

One day prior to the eruption, the five seismographs positioned around Redoubt's flanks were still quiet -- then, in a matter of minutes, they were sounding the alarm. Which came not a moment too soon. Redoubt quickly erupted.

"It went basically from what we would describe as 'background activity' to full eruption over a 23-hour period. ... which is very rapid for a volcano," Power said.

With that as the only detailed account of a Redoubt eruption in the scientific record, observatory geologists on the night shift last Sunday reacted swiftly when -- at 1 a.m. -- the volcano's seismographs suddenly began to red-line all over again.

After a quick conference, AVO officials upgraded the aviation color code for Redoubt from yellow to orange and sent out an all-points advisory noting that an eruption was possibly imminent, "perhaps within hours to days."

Since then, earthquakes and seismic readings at Redoubt have waxed and waned -- but generally remained at a level not seen since 1989, Power said Thursday.

"This particular sequence seems to be playing out a little bit slower. It hasn't resulted in an eruption yet, but we are still seeing these very elevated levels of earthquake activity. ... We still feel the most likely outcome is going to be an eruption."

The stakes for getting that information out as fast as possible could hardly be higher, considering the special danger a volcanic ash plume poses to large passenger jets. But sometimes even a warning isn't enough, as the 1989 Redoubt eruption dramatically illustrated.

DUTCH JET PLUMMETS

The Alaska Volcano Observatory back then was barely a year old. Still, the multigovernment initiative -- consisting of federal, state and University of Alaska Fairbanks scientists -- managed to alert local aviators the night before the eruption. The warning also appeared in the morning newspaper.

No matter.

A day after the '89 eruption, a KLM Royal Dutch Airlines 747 bound for Anchorage with 231 passengers on board flew straight into the Redoubt ash cloud -- which by then had drifted nearly 200 miles north -- over the Talkeetna Mountains.

Suddenly the statically charged particles of glass and rock outside the cockpit began to flash off and on like fireflies. As the plane's four engines swallowed the particles, the silicon in the ash began to melt, coating the jet's turbines, choking the airflow.

The pilot applied full power, trying to fly above the cloud, and at first the jet responded, angling upward. But then the engines fell to half power and the "stall" warning buzzed. Then all four engines turned off.

Without the turbines to generate electricity, half of the instrument panel went dark. The other half functioned intermittently on battery power. Smoke filled the cockpit and a fire alarm sounded. The plane began to dive.

After informing his passengers that the jet had lost power, the captain and his pilots raced through the elaborate process of trying to restart the engines "seven or eight times" without success -- as the plane fell almost three vertical miles. The passenger cabin was frantic.

"People were screaming, throwing up, pretty near panic," David Farrell, a then-20-year-old West High School graduate, told a reporter afterward.

At literally the last minute, the frigid air outside began to crack the silicon off the turbines, and two of the engines kicked back on. The pilot pulled out of the dive, and the jet leveled off at about 13,000 feet -- a mere mile above the mountain tops. Eventually the crew was able to restore power to all four engines, and the jet landed safely in Anchorage.

But it wasn't a clean escape. Repairs to the plane cost more than $80 million. The whole episode prompted several initiatives to better monitor volcanoes and ash clouds.

NO STRANGER

With 44 historically active volcanoes -- about 10 percent of all the active volcanoes in the world -- Alaska is no stranger to eruptions. On average two volcanoes erupt here each year.

Last summer, three of them -- Cleveland, Okmok and Kasitochi volcanoes -- erupted nearly at the same time and place in the Aleutians.

Over the past half century, however, the three most active Cook Inlet volcanoes have made the most headlines.

The last to go was Augustine Volcano, located 170 miles southwest of Anchorage, which erupted in 2006. The last to smother Anchorage with a significant layer of ash was Mount Spurr, 75 miles to the west, which erupted in 1992.

But it was the '89 eruption of Mount Redoubt -- which remained active for five months -- that actually threatened a lot of lives. Besides frightening the KLM passengers with its ash cloud, Redoubt also shot millions of tons of rocks and gravel into the sky.

As the heavier volcanic material fell back to earth, it cascaded down the mountain, creating what volcanologists call a "pyroclastic flow," an extremely hot mixture of rock and gas.

"Think of rock debris that is about 600 degrees centigrade avalanching down the side of the mountain," Power said. "It's very fast and very deadly."

No one lives at the base of Redoubt to be incinerated. But the hot, falling rocks quickly melted the surrounding ice and snow, generating super-heated mud slides, called lahars.

The lahars, in turn, led to a massive flood surge down the Drift River basin -- which forced workers at the Drift River Oil Terminal on the west shore of Cook Inlet to evacuate with little time to spare.

That may well happen again, officials at the volcano observatory reported Wednesday: "An eruption consisting of multiple explosive events, episodic lava-dome growth and collapse, and lahars may last weeks to months."


Find George Bryson online at adn.com/contact/gbryson or call 257-4318.

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