Modeling deformation and seismicity prior to the 2006 eruption of Augustine Volcano, Alaska
Abstract
Understanding unrest prior to volcanic eruptions requires both observations and physical models. About nine months prior to the 2006/1/11 eruption of Augustine Volcano, Alaska, an increasing number of volcano-tectonic (VT) earthquakes were recorded above sea level, within the volcano's edifice. In November 2005, the seismicity was accompanied by an acceleration in surface uplift observed by continuous GPS. We investigate the pre-eruption evolution of the Augustine magma system by assimilating GPS data into 3D finite element models using the Ensemble Kalman Filter. The resulting pressure source, which reproduces the surface deformation signal, is an oblate spheroid whose long axis orients almost vertically. In the months preceding the eruption (2005/11 to 2006/1), the pressure source migrated upwards from 6 km b.s.l to 0.5 km a.s.l indicating magma migration via dikes as suggested by previous investigations. Before 2005/11, the pressure source was located 5-7 km b.s.l with a maximum overpressure of 10 MPa. At above the sea level beneath the summit, the stress change is less than 0.1 MPa generated by this depth-overpressurized magma reservoir, which is hard to reconcile with the VT earthquakes during this timeframe. Considering topography, gravity, and crustal heterogeneity, our models show that both gravitational loading of the edifice and a strong conduit with a higher Young's modulus (as revealed through seismic tomography) likely promoted failure within the volcano edifice. The pressurized magma or its differentiated gas may have provided a critical supplementary stress to trigger additional earthquakes. Once the magma started to ascend, the frequency and total moment of the VT earthquakes increased, weakening the summit caprock prior to eruption. The study shows that the restless behavior of a volcano can be greatly impacted by its pre-existing characteristics, including topography and material heterogeneity.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMV026...07Z
- Keywords:
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- 8414 Eruption mechanisms and flow emplacement;
- VOLCANOLOGY;
- 8419 Volcano monitoring;
- VOLCANOLOGY;
- 8434 Magma migration and fragmentation;
- VOLCANOLOGY;
- 8439 Physics and chemistry of magma bodies;
- VOLCANOLOGY