An earthquake swarm indicates unrest at a volcano in the western Aleutian Islands, Alaska

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Tanaga volcano near Adak, Alaska, on May 23, 2021. A swarm of earthquakes that have occurred over the past few weeks have intensified at a remote Alaskan volcano that has been dormant for more than a century, a possible sign of an imminent eruption. (Matt Lewin/Alaska Volcano Observatory/USGS via AP)

A swarm of earthquakes over the past few weeks has intensified at a remote volcano in Alaska that has been dormant for more than a century, a possible sign of an imminent eruption.

The Alaska Volcano Observatory raised the alert level to advisory status for Tanaga volcano late Tuesday after the earthquakes became very strong.

“We’re starting to see a huge number of earthquakes happening, one after another, many times a minute,” said John Bauer, a research geophysicist with the USGS stationed in Anchorage at the Alaska Volcano Observatory.

He said there were hundreds of small quakes, no larger than 2.75 magnitude, but they were concentrated under the volcano’s summit.

“This indicates that we are seeing significant disturbances at the volcano,” Bauer said.

“Whether or not this will lead to an eruption is something we cannot say at this time,” he said. “But we’re concerned enough about it that we’ve gone and raised the alert level.”

While the increase is concerning, he said seismic activity would decrease many times without an eruption.

“It is anyone’s guess where this particular round of seismic activity might end,” he said.

The volcano is located on an uninhabited island in the western Aleutian. There are no communities or buildings there, but Adak, a town of about 170 residents located on another island, is about 65 miles away and you can see Ashfall.

[Previously: Multiple Aleutian volcanoes are showing signs of unrest]

If the volcano erupts, the biggest threat will be planes. The Aleutians are fewer than the routes that planes fly between North America and Asia. Volcanic ash is angular and sharp and can cause aircraft engines to shut down. Previous eruptions have had clouds of viscous ash and lava moving very slowly away from the mountain, just like what happened at Mount St. Helens in Washington state in 1980.

“It’s very different from what you might see in, say, Hawaii or Kilauea or Mauna Loa, where you see these beautiful red rivers of lava flowing down the side of the volcano,” Bauer said.

Tanaga is actually part of a tri-volcanic complex on the island. It is the tallest of the three at 5,925 feet. It lies in the center, with Sajaca, a 4,443-foot volcano to the west. Sajaka had an old cone that collapsed into the North Pacific Ocean as a new cone emerged.

Located east of Tanaga, Takawangha is a 4,754-foot-tall volcano that is mostly covered in ice except for four craters, according to the Alaska Volcano Observatory.

The last known eruption of Tanaga was in 1914. It erupted twice in the late 18th century and again in 1829.

The observatory said in a statement that there are no known volcanic eruptions for Takawanga or Sagaca. However, field work has indicated that volcanic eruptions may have occurred from those volcanoes and were attributed to Tanaga.

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