Bogoslof volcano sends ash over Unalaska in 3-hour eruption

An intense, sustained eruption of Bogoslof volcano in the Aleutian Islands sent up a cloud that caused minor ashfall in Unalaska but didn't significantly affect aviation over the Gulf of Alaska on Wednesday.

According to the Alaska Volcano Observatory, Bogoslof began erupting at about 10:30 p.m. Tuesday and continued for roughly three hours. The eruption is the latest from the volcano about 60 miles west of Unalaska, in an active period that began in mid-December.

"A large volcanic ash cloud is visible in satellite data and is moving towards the east at an altitude of 35,000 feet above sea level," AVO forecasters wrote early Wednesday.

John Lyons, a geophysicist at the observatory, said observers in Unalaska reported trace amounts of ashfall, less than a millimeter.

"(It was) nothing significant, although it sounds like some locations got a light dusting," Lyons said.

Mitch Sego, a forecaster with the office's Alaska Aviation Weather Unit, said the cloud passed over Unalaska at about 1 a.m. Wednesday, then moved over the Gulf.

The weather unit had issued a meteorological advisory for pilots according to Alberta Vieira, the unit's lead forecaster, but the cloud dissipated relatively quickly and the advisory regarding it was set to be canceled by noon Wednesday.

Vieira hadn't heard of any aircraft being diverted Wednesday.

"We're not seeing very much ash on satellite pictures anymore," Vieira said.

Unalaska received some ash from Bogoslof in late January, but AVO reports said the volcano last erupted on Feb. 19. Sego said that spell of inactivity was definitively broken by Tuesday night's blast.

"There were over a thousand lightning strikes associated with it, so it was clear this was a pretty significant eruption," Sego said.

Because AVO doesn't have instrumentation on Bogoslof Island to assess the volcano's activity in detail, Lyons said, it was difficult to draw conclusions from the roughly two-week delay between eruptions.

"That was the 36th event since the eruption (cycle) began; it was one of the most energetic, if not the most energetic," Lyons said. "Before this eruption it was the longest repose period we've seen between explosive events, so maybe it built up some energy."