April 30, 2013
Researchers Work To Improve Volcanic Eruption Forecasting
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April Flowers for redOrbit.com - Your Universe OnlineRecognizing well-established patterns of pre-eruption unrest in monitoring data is vital in volcanic eruption forecasting. To develop better monitoring procedures, however, understanding volcanic eruptions that deviate from these patterns is crucial as well.
Diana Roman from the Carnegie Institution for Science led a research team that retrospectively documented and analyzed the period immediately preceding the 2009 eruption of the Redoubt volcano in Alaska. This eruption was characterized by an abnormally long period of pre-eruption seismic activity that´s usually found with short-term warnings of eruption.
A gradual increase in the rate of seismic activity is part of well-established pre-eruption patterns, as well as a progressive alteration in the type of seismic activity, or a change in ratios of gas released.
"But there are numerous cases of volcanic activity that in some way violated these common patterns of precursory unrest," Roman said. "That's why examining the unusual precursor behavior of the Redoubt eruption is so enlightening."
Approximately six to seven months before the 2009 eruption, Redoubt began experiencing long-period seismic events. Shallow volcanic tremors, which intensified into a sustained tremor over the next few months, also began. Immediately after the sustained tremor developed, shallow, short-period earthquakes occurred at an increased rate below the summit. Both deep and shallow earthquakes were recorded in the 48 hours prior to eruption.
Precursor observations usually involve a transition from short-period to long-period seismic activity, making Redoubt unusual. Additionally, seismic tremors are normally seen as a short-term warning, not something that happens months in advance of the eruption. During the 1989-90 Redoubt eruption, however, this same behavior was observed. This indicates that the unusual seismic pattern is reflective of a unique aspect of Redoubt´s magma system.
Roman and her team performed advanced analysis of the seismic activity taking place under the volcano, allowing them to understand the changes taking place before, during and after eruption. The results of this study, published in the journal Earth and Planetary Science Letters, reveals that the eruption was likely preceded by a protracted period of slow magma ascent, followed by a short period of rapidly increasing pressure beneath the volcano.
By elucidating the underlying magma processes that cause these unusual precursor events, the team´s findings will help scientists to hone their seismic forecasting, rather than relying on the current tools that are unable to detect anomalies.
Current techniques, for example, wavered on predictions for Redoubt´s 2009 eruption over a period of five months. They placed the eruption as being likely within a few weeks to within a few days during the whole time period. If the new analytical techniques had been taken into consideration, the early risk escalation might not have been issued.
"Our work shows the importance of clarifying the underlying processes driving anomalous volcanic activity. This will allow us to respond to subtle signals and increase confidence in making our forecasts." Roman said.