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With Bogoslof volcano's continuing eruptions, island has tripled in size

Bogoslof volcano erupted once again early Saturday morning as a series of rumblings continue that have so far tripled the island's size.

Around 4:30 a.m. Saturday, an eruption lasting a few minutes shot an ash cloud at least 25,000 feet into the sky, the Alaska Volcano Observatory wrote in an activity notice.

Bogoslof volcano rises from the sea about 60 miles west of Dutch Harbor, in Alaska's Aleutian Islands.

"We're basically just seeing the tiptop of the volcano itself," Jeff Freymueller, coordinating scientist for the Alaska Volcano Observatory at University of Alaska Fairbanks' Geophysical Institute, said of the island.

Bogoslof isn't considered an especially active volcano. Scientists have recorded eight eruptive events since 1796. The last one was in 1992, for about three weeks in July, Freymueller said.

Since eruptions began on Dec. 12, rock fragments and ash — called tephra — have been erupting from Bogoslof, Freymueller said. The result is a landscape that has shifted and grown dramatically in the past few months.

Bogoslof eruptions began Dec. 12, 2016, and by Jan. 31, 2017, had roughly tripled the size of the island. (Chris Waythomas, Alaska Volcano Observatory / U.S. Geological Survey)

As of Jan. 31, the island was just over .38 square miles (1 square kilometer), about three times its size before the series of eruptions started in December. This new land, created from tephra, will be highly susceptible to wave erosion, and the island's shoreline will likely continue to change, Freymueller said.

Sometimes those changes are quick. A composite image shows how much the island morphed just between Jan. 16 and Jan. 18.

Bogoslof’s shifting shoreline. The base image is from Jan. 11. The green line is the shoreline on Jan. 16, and the orange dotted line shows the shoreline on Jan. 18. (Kim Angeli, Alaska Volcano Observatory / U.S. Geological Survey)

There's no telling how long this series of eruptions will last, Freymueller said. Eruptions in the early 20th century lasted more than a year, he said, but the 1992 eruption was brief.

Scientists monitor the volcano from a series of seismic networks in the Aleutians. "We can't always see low-level activity, but we actually have been able to see pretty clearly when it's erupting," Freymueller said. Beyond that, scientists use satellite data.

Ash samples were collected when ash fell on Dutch Harbor on Jan. 31.

Ash-fall from Bogoslof volcano covers the snow in Unalaska’s Pyramid Valley on Jan. 31. (Andy Dietrick)

No one will venture to Bogoslof island to collect more samples until the eruptions stop, Freymueller said.

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