Forecasting Volcanic Eruptions: Unusual Seismic Activity Discovered in Redoubt

We may be able to forecast volcanic eruptions a bit more easily. A new study has examined the sequence of events that led up to an eruption and has discovered a little bit more about these explosive events.

On March 22, 2009, the Redoubt volcano in Alaska erupted, spewing volcanic ash to an estimated 50,000 feet above sea level. These plumes of ash drifted through the skies before falling out of the air near Skwentna and the Chuitna area. Yet before this eruption took place, a series of seismic events occurred. It's these events that researchers are interested in and which could potentially help scientists predict volcanic eruptions.

Well-established pre-eruption patterns can often include a gradual increase in the rate of seismic activity, a progressive alteration in the type of seismic activity or a change in ratios of gas release. In order to better understand these pre-eruption events, researchers examined the activity leading up to the 2009 eruption.

About six to seven months before the eruption, Redoubt began to experience long-period seismic events, as well as shallow volcanic tremors. These tremors intensified into a sustained tremor over the next several months. After this sustained tremor occurred, shallow, short-period earthquakes happened at an increased rate below the summit. About 48 hours before the actual eruption, researchers noted that both deep and shallow earthquakes rocked the land.

Yet this behavior was unusual for pre-eruption events. Precursor observations usually involve a transition from short-period to long-period seismic activity rather than the other way around. In addition, seismic tremor is usually seen as a short-term warning rather than occurring months in advance.

The researchers examined the seismic activity taking place under the volcano and found that the eruption was likely preceded by a protracted period of slow magma ascent. This would have helped caused the seismic activity. It was then followed by a short period of rapidly increasing pressure beneath Redoubt.

The unusual seismic activity of the volcano shows how crucial it is to understand what is happening beneath the surface in order to predict future eruptions. Learning a bit more about these processes could help forecasts in the future.

"Our work shows the importance of clarifying the underlying processes driving anomalous volcanic activity," said Diana Roman, one of the researchers, in a press release. "This will allow us to respond to subtle signals and increase confidence in making our forecasts."

The study was published in the journal Earth and Planetary Science Letters.