Earthquake in neighboring Alaska volcanoes raises concerns

Not one but two volcanoes on the same island in Alaska’s sand chain were rocked by earthquakes on Friday, sparking fears of a possible eruption.

Increased seismic activity was also reported at the Tanaga and Takawangha volcanoes on uninhabited Tanaga Island, hundreds of miles (kilometers) from Anchorage.

“If an eruption were to occur, it is uncertain at this stage whether it would come from Takawanga or Tanaga,” Alaska Volcano Observatory officials said in a statement raising the alert level for the two volcanoes.

WHAT’S THE LATEST?

Although the frequency of tremors decreased slightly on Friday, earthquake activity at the volcanoes still occurred about every minute or two.

“We still have magnitude 3 earthquakes happening fairly regularly,” said John Power, a research geophysicist at the US Geological Survey based at the Alaska Volcano Observatory in Anchorage.

Seismic activity intensified earlier this week at Tanaga Volcano, the middle of three volcanoes on Tanaga Island, located about 1,250 miles (2,012 kilometers) southwest of Anchorage, the state’s main population area.

Then, in the middle of the week, earthquake activity began to intensify at Takawangha, a volcano about 5 miles (8 kilometers) east of Tanaga.

“We’ve actually seen earthquakes building under the epicenters and between them, which gives us quite a bit of concern about what’s going on,” Power said. “It’s a very energetic sequence.”

A third volcano on the island, Sajaka, about 2 miles (3 kilometers) west of Tanaga, shows no sign of activity.

WHAT IS THE BIGGEST THREAT?

Since the island is uninhabited, the thick, viscous lava that could flow in an eruption would do no harm. The nearest community, Adak, is about 65 miles (104 km) to the east, on a separate island.

However, an ash cloud could pose threats to aircraft, potentially disrupting air travel between North America and Asia and health problems for communities further afield. Volcanic ash is angular and sharp and has been used as an industrial abrasive. Pulverized rock can cause a jet engine to shut down.

An interagency volcanic ash response plan, developed in 2011, details how state, federal and local agencies should respond to a volcanic eruption in the area that could spew ash across the region. It calls for the Alaska Volcano Observatory to take the lead in confirming an eruption and alerting other agencies, who will then alert pilots, mariners and local communities.

Where and how far the ash would travel would depend on many factors. The flow of fine ash into cities can cause respiratory problems for people and animals, affect electrical equipment and damage air filters and gasoline engines.

DOES EARTHQUAKE ACTIVITY MEAN AN IMMINENT Eruption?

The short answer is no.

Both the Takawangha and Tanaga volcanoes in 2005 had smaller clusters of earthquakes that eventually simply dissipated without an eruption — at least none that officials are aware of.

“We saw some signals that may have been very minor explosive activity, but we were never able to confirm that,” Power said.

Some of the areas that were active in 2005 are where scientists are seeing a lot of seismic activity now. “Where and how this activity will end, whether or not it will lead to an explosion is an open question,” Power said.

HOW UNUSUAL IS IT TO HAVE TWO ACTIVE VOLCANOES SO CLOSE TOGETHER?

Having two volcanoes so close together and both in a state of unrest is very unusual in Alaska, Power said, although such incidents do occur elsewhere in the world.

For example, Mauna Loa and Kilauea both erupted at the same time last year on Hawaii’s Big Island.

“It’s unusual that … we’re seeing earthquakes under the two centers at the same time and actually between the centers, which suggests to us that there’s probably something bigger here in the subsurface, the magma and so on under the volcanoes,” Power said.

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