Redoubt is one of three active volcanoes in Cook Inlet. Like Spurr, the northernmost, Redoubt is ice covered. Augustine is an island volcano. The trio have erupted eight times in the last 50 years. 

The most powerful eruption on Earth during the 20th century wracked the Alaska Peninsula in 1912, when Novarupta Volcano, in what is now Katmai National Park, spewed three cubic miles of magma, collapsing Mount Katmai’s summit into a steaming crater and birthing the Valley of Ten Thousand Smokes. Airborne ash encircled the globe, coloring sunsets for more than a year. Similarly staggering explosions shook Alaska in the distant past, but the 1912 blast remains the greatest in recorded Alaska history.

Today, technology unimaginable a century ago makes it nearly impossible for another Novarupta to explode unannounced.  The Alaska Volcano Observatory (AVO) has some 180 instrument stations ringing scores of volcanoes. Seismometers detect shaking and tremor from molten rock flowing underground, while GPS units note ground rising or falling as magma chambers fill or drain. Microphones listen for low-frequency sounds from explosions while lightning detectors watch for rebolts from ash clouds charged with static electricity. Above these, satellites look down for telltale hot spots or track erupted ash through the sky.

All this ceaseless vigilance paid off in 2008 when a remote Aleutian island called Kasatochi awoke. Like virtually all Aleutian islands, Kasatochi is volcanic, but there were no AVO instruments there since it hadn’t erupted in centuries.  The verdant island supported Steller sea lions and a quarter-million nesting seabirds plus the raptors they attracted. The U.S. Fish and Wildlife Service had a cabin on the island and had done studies there for years. In the summer of 2008, AVO had already responded to two Aleutian eruptions when the Fish and Wildlife Service called on August 4 to report shaking on Kasatochi. With the nearest seismometers 25 miles away, on Great Sitkin, little showed up on the AVO instruments at first.

“It wasn’t until August 6 when it was clear something big was going on,” seismologist Stephanie Prejean recalls. “Lots and lots of earthquakes, a stunning seismicity rate . . . more seismic energy than we often see in erupting volcanoes.”

By then, biologists on the island “could hear rockfalls in the crater,” volcanologist Game McGimsey says. “Then we did something that we almost never do. We don’t tell other people, other agencies what to do, we provide information. But on this occasion, we called up Fish and Wildlife and said, ‘You need to get those people off of Kasatochi ASAP. Right now!’”

More than a year after Novarupta erupted in June 1912, ash drifts cover the sod houses of Katmai village. (Courtesy of G. C. Martin, U.S. Geological Survey)

On August 7, with the nearest Coast Guard ship “many, many hours away” and its helicopter down for repairs, a fishing boat rescued the stranded biologists. About 20 minutes later, Kasatochi astern, “It just erupted,” McGimsey says. “You look at photographs, the whole island is tens of meters deep in pyroclastic [hot volcanic] deposits. I mean nobody would have survived.  The camp has never been seen again.  The whole island is different.”

McGimsey falls silent, a scientist awed by the power of the planet he studies. “On that day,” he quietly resumes, “we felt like—well, we saved lives! That was pretty neat.”

Richard Emanuel is a freelance science and nature writer who came to Alaska as a geologist. He lives in Anchorage with his wife and daughter

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