Earthquake Swarms may Indicate Imminent Volcanic Eruption

Earthquake swarms, seismic events marked by sequences of many earthquakes in a short period of time, may signal imminent volcanic eruptions because they are triggered by blocked lava flow, according to a new study, and scientists suggest these types of earthquakes can be used to give the public warning of an impending eruption.

Writing in the journal Geophysical Research Letters, a team of scientists detail their study of the 2006 eruption of Augustine Volcano in Alaska. They contend that a swarm of 54 earthquakes in the three days prior to the eruption were triggered from sources within the volcano's magma conduit.

Helena Buurman, lead study author the University of Alaska, Fairbanks, said the research on earthquake swarms preceding volcanic eruption led her to believe that they were caused by subterranean lava behaving abnormally.

"Our article talks about a special type of volcanic earthquake that we think is caused by lava breaking, something that usually can't happen because lava is supposed to flow more like a liquid, rather than crack like a piece of rock," Burrman said.

"Much like breaking a piece of chewing gum by stretching it really fast, lab tests show that hot lava can break when stretched quickly enough under certain pressures like those that you might find in the conduit of a volcano."

In one 2 hour period of the earthquake swarm, the researchers observed the earthquake's "focus" moving 35 meters deeper down into the magma conduit, or the channel outside a volcano created by molten magma.

The researchers contend that because the focus of the earthquake swarm moved deeper into the earth, it indicates the magma conduit was getting clogged. As pressure built inside the clogged conduit, it may have triggered the eruption of Augustine Volcano the following day.

"We think that these earthquakes happened within the lava that was just beginning to erupt at the top of Augustine. The earthquakes show that the lava flow was grinding to a halt and plugging up the system. This caused pressure to build up from below, and resulted in a series of large explosions 36 hours later," Buurman said in a statement.

"We believe that these types of earthquakes can be used to signal that a volcano is becoming pressurized and getting ready to explode, giving scientists time to alert the public of an imminent eruption," she said.