Magma Rising Beneath Edgecumbe
One crisp April day, Sitka residents were shocked to see Mount Edgecumbe, the volcano just 15 miles from town, erupting. “Smoke was pouring over the edge of the volcano,” recalls Alice Johnstone. “I never ever called my husband at work, but I was so excited I called to tell him about it. I even phoned FAA to get more information.”
Phones rang off the hook at the police station while the Coast Guard dispatched a helicopter to investigate. Spray painted in 50-foot letters at the summit they found the words “April Fools.” It was April 1, 1974. Local prankster Oliver “Porky” Bickar had flown 70 old tires to the summit crater and lit them on fire. The Edgecumbe hoax hit international news and went down as one of the best April Fools jokes of all time.
But it was no joke on April 11, 2022, when a Sitka resident noticed a magnitude 2.1 earthquake measured by the local seismometer. They asked the Alaska Volcano Observatory if the quake was related to Edgecumbe. Was the long-dormant volcano reawakening?
As hundreds of earthquakes rumbled around Edgecumbe, Ronni Grapenthin, associate professor of geodesy at University of Alaska Fairbanks, and his students Yitian Cheng and Mario Angarita, crunched data to understand what was happening. Four days later, they had an answer: Edgecumbe was steadily inflating as magma rose beneath the mountain.
“Edgecumbe is interesting because it’s in an unusual tectonic environment,” says Grapenthin. Most Alaskan volcanoes are formed by subduction as the Pacific plate dives beneath the North American plate, but Edgecumbe sits 10 miles east of the strike-slip Queen Charlotte-Fairweather Fault. Volcanoes along such transform faults are rare.
A picturesque 3,200-foot cone, Edgecumbe is the high point of a sprawling 100-square-mile volcanic field on southern Kruzof Island. The area is pocked by smaller cones and laced with pyroclastic and lava flows. The most recent large eruptions occurred 4,000 and 5,000 years ago as the ice sheets retreated. The volcano then returned to a state of quiescence until a Tlingit party witnessed the mountain emitting smoke and fire 800 years ago. Their oral history says the mountain was “blinking,” probably from fire-fountaining lava. “Blinking Mountain,” or L’úx Shaa, is the mountain’s Tlingit name. Centuries later, in 1778, Captain James Cook named it Mount Edgecumbe, possibly after the mountain at the entrance of England’s Plymouth Harbor.
The 2022 earthquake swarm presented a rare opportunity for Grapenthin to study a volcano reawakening from dormancy. Due to its many years of inactivity, however, Edgecumbe had no ground-based monitoring equipment. Grapenthin instead turned to remote sensing. Satellite radar observations taken since 2014 provide a detailed picture of the region’s surface. By comparing radar observations, Grapenthin’s team created interferograms, maps that show ground movement over time. “By using some physics and models, we can use the surface deformation to get at how much magma is moving to where under the volcano,” Grapenthin says.
Interferograms show the ground starting to inflate in August 2018 as magma rose from 12 to six miles beneath the mountain. As molten rock moved upward, it caused earthquakes and forced the surface to bulge like an inflating balloon. An area 11 miles in diameter has risen 11 inches since 2018, the fastest rate of volcanic deformation in the state.
To process this radar data in only a few short days, Grapenthin’s team used a new technique. Huge amounts of scientific data, including satellite radar data, are stored remotely on servers and accessible through the Cloud. Prior to the Edgecumbe quakes, Grapenthin downloaded data and processed it on local servers, but this time he used the Cloud.
“Using the Cloud meant that we could analyze eight years of data—hundreds of satellite radar images and thousands of interferograms—in a matter of hours to days rather than weeks to months,” Grapenthin says. “This was a major step forward to move away from the old model of doing everything on lab computers to just letting the Cloud take care of giving us the resources, especially since we had to do the analyses in many different ways to convince ourselves the signal was real in the absence of ground-based observations.” Today, Grapenthin and the Alaska Volcano Observatory are using the same approach to analyze radar data for all of Alaska’s volcanoes.
It could be years, centuries even, before Sitka residents again see smoke unfurling from Edgecumbe. There is also a very real possibility that no eruption will occur, and the mountain will settle back into dormancy. Though the future is not easy to predict, scientists have a better understanding of the volcano’s behavior. A seismometer and GPS sensor were installed in 2022. This year, the team will deploy additional instruments to measure previously undetectable small earthquakes, more precisely pinpoint quake locations, and measure ground deformation. This information is crucial to determine if an eruption is pending. “As of now we can say there’s no eruption that’s imminent,” Grapenthin states. “It seems fairly stable, but we cannot say whether it will erupt in the future or not. My job right now is to keep an open mind.”
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