An advisory alert has been issued for a remote volcano in the western Aleutian Islands after dozens of earthquakes were reported in the area, an early sign of volcanic unrest.
The change means that five volcanoes being monitored in Alaska are now simultaneously active, the most in recent memory, said Matt Haney, a research geophysicist at the Alaska Volcano Observatory.
"We might have had four before, but we haven't had five," Haney said.
A total of 52 volcanoes in Alaska are considered by the observatory to be "historically active." All are monitored daily through satellites, and about 30 are monitored with ground-based seismometers that measure earthquake activity. On Friday, the observatory raised the color code alert level for the Semisopochnoi (pronounced Semi-so-poch-noi) volcano to "yellow," a reflection of heightened unrest.
Haney said there doesn't appear to be a connection between the five, just random chance. The other four volcanoes --Cleveland and Veniaminof volcanoes in the "yellow" alert level, and the Pavlof and Shishaldin volcanoes are classified as "orange"-- are among the most active in the state.
But Semisopochnoi is "kind of the oddball," Haney said. It's only erupted twice in recorded history, first in 1873 and then in 1987.
"There hasn't been any activity here for a long time," Haney said. The volcano is about 40 miles northeast of Amchitka Island and 130 miles west of Adak.
A better monitoring system also played a role in raising the alert level. Scientists have been receiving much more consistent seismic data about the volcano after a telemetry system on Amchitka Island was repaired in late May, said Game McGimsey, a volcanologist with the observatory. The seismic network for Semisopochnoi was installed in 2005, but the data were previously too spotty to assign a color code, McGimsey said.
On Thursday, the Semisopochnoi monitors recorded a total of 65 earthquakes on Thursday alone, an episode known as an "earthquake swarm." All of the quakes were listed at a magnitude of 2.0 or lower.
A day earlier, 22 earthquakes occurred, and 15 the day before that, showing a clear escalation pattern, Haney said. The quakes occur as a result of magma rising up beneath the earth.
In 2012, earthquake swarms occurred at the volcanic Little Sitkin Island and at Mount Iliamna, but there was no surface eruptive activity in either case.
In 2009, however, an earthquake swarm preceded the eruption at Mount Redoubt, Haney said.
"The jury's still out" on what will happen next at Semisopochnoi, Haney said. "We're going to keep a close eye and see if things progress."
All volcanoes on the Aleutian arc are considered a potential hazard to the North Pacific air routes.
Reach Devin Kelly at firstname.lastname@example.org or 257-4314.
By DEVIN KELLY