Volcanic activity at Semisopochnoi prompts ashfall warning for fishing boats

Dave Schneider, a geophysicist with the AVO, said Semisopochnoi is still emitting some ash, but at a much lower rate than it was last week. (Courtesy of the Alaska Volcano Observatory)

Scientists have downgraded the alert level for an Aleutian volcano that began showing an increase in signs of eruption and emitting harmful ash late last week.

According to Dave Schneider, a geophysicist with the Alaska Volcano Observatory, satellites and pressure sensor data showed ramped up activity at Semisopochnoi last week. The volcano is on an uninhabited island in the Rat Islands, about 600 miles southwest of Unalaska.

Scientists detected steady ash emissions coming from the volcano Thursday, prompting them to upgrade the aviation color code to “red” and the alert level to “warning.”

“Ash started coming out on a more routine basis,” Schneider said. “And it was forming a plume that was going several hundred miles downwind, not at very high altitude.”

The ash wasn’t high enough to impact high-flying aircraft, but Schneider said it was persistent, and boats had been notified of possible ashfall.

He said the volcano is still emitting some ash, but at a much lower rate than it was last week. Even when emissions were more frequent, Schneider said the ashfall would likely be a minor issue for nearby fishermen, who often face more hazardous conditions.

If they were near the island, they could end up with an accumulation of ash on the deck,” he said. “If there’s any fish that are on deck, there could be an issue, perhaps just with some contamination, but this is not a huge eruption.”

Some small explosions are still occuring, and scientists observed sulfur dioxide gas emissions yesterday via satellite data, which indicates continued unrest at the volcano. But satellites also show that there is no longer a significant ash plume, and the AVO has returned the aviation alert level to “watch” and the color code to “orange.”

Schneider said the recent 5.3 earthquake reported Thursday evening near Attu was likely unrelated to the heightened activity at Semisopochnoi.

Activity at the volcano has been infrequent over the past few years, he said. Prior to 2018, the most recent eruptive activity at Semisopochnoi was in 1987.

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