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Unalaska Sees No Ash Fall In Bogoslof's Biggest Eruption Yet

Mar 8, 2017

A thermal infrared satellite image shows Bogoslof Volcano (dark grey and red) during Tuesday's eruption.
Credit Dave Schneider/USGS/AVO

Bogoslof Volcano exploded Tuesday night in its most powerful eruption since activity began three months ago.

Given the intensity of the three-hour blast, scientists expected Unalaskans to wake up and find the island dusted with ash.

Kristi Wallace of the Alaska Volcano Observatory (AVO) said she was puzzled when that didn’t happen.

“It was definitely the strongest seismicity we’ve seen in this eruption," said Wallace. "There were more than 200 lightning strokes, so it was very significant. I’m quite surprised there wasn’t fallout on Unalaska.”

Bogoslof blew around 10:30 p.m., spewing a strong cloud of ash 35,000 feet into the air, but Wallace said light winds may have only carried emissions far enough to reach water and remote areas of the island.

While scientists won’t have samples from this eruption, the AVO is studying ash from an earlier explosion to learn more about the composition and behavior of the submarine volcano.

“We’re still trying to understand the deposit from Jan. 31," said Wallace. "It’s still a puzzle to us, so I think having another sample -- to see if there's more glass, magma, or primary material -- would be really interesting."

In this long eruptive period, there’s a chance Bogoslof could drop more ash Unalaska, but Wallace said it may take a while.

“This eruption was funny. It was go, go, go for three solid hours and then it just shut down," she said. "It was big enough to drain the system for a little while, and now maybe it’ll build up again. It’s hard to say what will happen, but it looks pretty quiet right now."

Seismicity has declined since Tuesday, but the AVO has left Bogoslof’s alert level at red. That mean another hazardous eruption could occur with little warning.