Volcanic eruptions in high resolution

Volcano seismology has focused on the times before and after eruptions. Although the most important part of a volcano’s lifecycle is the eruption itself, few earthquakes have been measured during the large, explosive phase of an eruption. This lack is because of the technical difficulties of measuring earthquakes while the eruption is producing a wide range of seismic noise.

Here the researchers address this problem by using modern techniques of earthquake detection to chronicle the seismicity during a large-scale, explosive eruption. They illustrate the new approach with a preliminary analysis of the 2008 eruption of Mount Okmok; the volcano caldera, which exploded without warning, is located in the eastern Aleutian Islands of Alaska.

Multiple techniques increase the number of detected events by factor of 4. Event rate varies in a non-trivial way during the eruption which cause is still unclear. Earthquakes appear to be recording a history of stress and failure that is related to, but distinct from the history of explosions.

To better constrain earthquake rate during the eruption, the team re-analyzes recorded data using cutting-edge software. The trained algorithm is capable of identifying new seismic events among the noise. The new event catalog is used to better understand the volcano subterranean plumbing system.

The same approach is applied to other volcanos in the Aleutians, Iceland, and Russia, which exhibit similar large eruptions. The comparative study allows evaluating whether volcano seismicity can be used to constrain subterranean magma cycle during large eruptions. The project provides support and training for one graduate student and undergraduate students, notably from underrepresented groups in science.

Its outcomes improve volcanic hazard assessment, helping mitigating risks for local population and air traffic.

The researchers propose to improve the co-eruptive seismic record of Okmok by utilizing an unsupervised, globally trained detection algorithm. The relationship between earthquake rate and the eruption cycle is still unclear. Not only is there an obvious increase in the earthquake rate at the eruption initiation, but there also appears to be a seismicity burst at the end of the eruption.

Seismicity increases in the middle of the eruption may be associated with eruption reorganization but is not clearly associated with major plume-forming events. This may be a result of earthquakes’ sensitivity to the stresses in the solid crust rather than the eruptive processes in the conduit. Using the new record, the researchers identify and determine consistent magnitudes for the earthquakes.

The new earthquakes at known magnitudes allow a self-consistent measure of earthquake rate throughout the eruption. It can be used to evaluate whether the earthquakes are marking the least open, most pressurized times and places. In the project second phase, the same methods are applied to other similarly large eruptions that have sufficient, publicly available seismic data.

Those eruptions are: Grimsvotn, Kasatochi and Sheveluch. The team intends to explore the dataset of Nabro with an undergraduate, although it is not quite comparable. These comparative studies improve assessing the utility of earthquakes as an indicator of opened or closed volcano state.

The expected outcomes will help understanding whether rapid fluctuations between pressurization and opening are common in major explosive eruptions.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.