Listening to the Heartbeat of Alaska's Volcanoes

Volcanoes are a lot like people, according to John Power of the Alaska Volcano Observatory---no two are alike, and each one gives different signs of a pending eruption.

Because of their unpredictability, forecasting volcanic eruptions is an inexact science for those at the Alaska Volcano Observatory, an organization made up of a team of researchers from the U.S. Geological Survey, the UAF Geophysical Institute and the Alaska Division of Geological and Geophysical Surveys, with centers in Fairbanks and Anchorage.

Forty-two Alaska volcanoes have spit up magma, or molten rock, since people started writing down eruption observations in 1767, according to Volcano Seismologist Steve McNutt, who works at AVO in Fairbanks. Because most of Alaska's volcanoes are far removed from cities and towns, the abrasive ash they belch during an eruption presents the greatest danger to humans---not, as in other parts of the world, lava flows or mud slides.

When Mount Redoubt erupted in December 1989, for example, a Boeing 747 descending toward an airport in Anchorage flew through an ash plume, which caused all four engines to quit. The pilots were able to restore power and land, even though investigators later discovered that the engines contained glassy deposits created after the ash had melted and then resolidified.

At AVO in Fairbanks, located in the Geophysical Institute, scientists keep their fingers on the pulse of six volcanoes in the Cook Inlet region and two on the Alaska Peninsula through a system of more than 40 seismometers cemented into mountainsides.

Seismometers, instruments about the size of a coffee can, detect movement in the ground, then transfer it by radio signal to a sophisticated computer system and to pens that scribble the story of the volcano's activity on rotating paper drums in an AVO lab.

Monitoring the Earth's movement with seismometers is the researchers' number one tool for eruption forecasting, but volcanologists improve their accuracy by combining seismic results with other clues.

For example, measurable bulges in the surface of a volcano can hint that magma under the surface is building up. Another visual clue signaling a potential eruption occurred shortly before the 1992 eruption of Mount Spurr. Just before Mount Spurr blew, a lake on its summit began steaming and changed color from pale blue to dark gray. Scientists now suspect the color changed due to chemical reactions in the water created by gases in the moving magma.

Volcanoes commonly release small amounts of gas, but a volcano that's about to erupt will sometimes exhale a larger amount of gases into the air. The easiest gas for volcanologists to measure is sulfur dioxide, which can be gauged by a device carried in an aircraft that circles the volcano.

Researchers also study the eruptive history of a volcano in the geologic record to see if any patterns can be determined. Alone or combined, no method is foolproof, as is evident by looking at the different pre-eruption actions of Mount Redoubt and Mount Spurr.

Before its 1989 eruption, Mount Redoubt rumbled its intentions with a 23-hour-long swarm of low-frequency earthquakes probably caused by magma moving within the mountain or by gas released by the magma, which acts like a shaken soda. Volcanologists issued warnings when the number of earthquakes jumped from a couple each day to 4,000 in one day.

By contrast, Mount Spurr shook for about 10 months with high-frequency earthquakes (during which the ground shakes faster than it does during low-frequency earthquakes) until the eruption finally occurred.

When a volcano shows signs that it might erupt, AVO scientists literally sit near the seismic monitors around the clock, listening for the scratch of pen on drum paper that indicates an earthquake.

Warnings are issued to state and federal agencies when a volcano becomes increasingly restless, but if volcano activity remains interesting but constant, the waiting continues.

The AVO monitors were quiet as this column was being written, but who knows what tomorrow will bring.