Quake swarms at neighboring Alaska volcanoes raise concerns

[20000 years ago...]

ANCHORAGE, Alaska (AP) — Not one but two volcanoes on the same island in
Alaska’s Aleutian chain were rocked by earthquakes on Friday, prompting
concerns about a possible eruption.

Elevated earthquake activity was reported at both 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 if it would
come from Takawangha or Tanaga,” officials at the Alaska Volcano
Observatory said in a statement that raised the alert level for the two
volcanoes.

WHAT'S THE LATEST?

Even though the frequency of tremors slightly diminished Friday,
earthquake activity at the volcanoes was still occurring about every
minute or two.

“We’re still getting earthquakes up above magnitude 3 going on quite
regularly,” said John Power, a research geophysicist with the U.S.
Geological Survey stationed at the Alaska Volcano Observatory in
Anchorage.

Seismic activity ramped up 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 major population area.

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

“We’ve seen actually earthquake activity building beneath both epicenters
and in between them, which is causing 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) to the
west of Tanaga, is not showing any sign of activity.

WHAT’S THE BIGGEST THREAT?

Since the island is uninhabited, the thick, viscous lava that could flow
in an eruption would not cause harm. The nearest community, Adak, is about
65 miles (104 kilometers) 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 farther away. Volcanic ash is angular and sharp and has
been used as an industrial abrasive. The powdered 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 region that can cast ash throughout the area. It calls for the Alaska
Volcano Observatory to take the lead in confirming an eruption and notify
other agencies, which would then alert pilots, mariners and local
communities.

Where and how far any ash would go would depend on numerous factors. Fine
ash drifting to cities can cause respiratory problems for people and
animals, interfere with electrical equipment and damage air filters and
gasoline engines.

DOES QUAKE ACTIVITY MEAN AN IMPENDING ERUPTION?

The short answer is no.

Both Takawangha and Tanaga volcanoes in 2005 had smaller earthquake swarms
that eventually just dissipated without an eruption — at least none that
officials know about.

“We did see some signals that might have been very minor eruptive
activity, but we were never able to confirm that,” Power said.

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

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

Having two volcanoes this close and both in a state of unrest is very
unusual in Alaska, Power said, even though there are such occurrences
elsewhere in the world.

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

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

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