Okmok volcano in Alaska appears to erupt every decade or so, most recently in 1997 and again in 2008. Its activity has been monitored using modern methods, forming a rich observational data set. The investigators are developing a geophysical model that should explain the timing and location of most of the observed activity. The new information from this study will be directly relevant to understanding time-dependent volcanic hazard posed by Okmok and other, similar volcanoes lying beneath the heavily-used north Pacific air traffic corridors. The same type of model should be applicable to other volcanoes displaying cyclic activity, such as Westdahl in Alaska or Hekla in Iceland.
Okmok is an excellent natural laboratory for such an experiment because a complete cycle of deformation has been monitored using geodetic and seismic means. Using this rich observational data set and a formal protocol for numerical modeling, the investigators are studying Okmok volcano to address the following questions: (1) What is the distribution of material properties within Okmok? (2) How does anelastic rheology modify the temporal evolution of the deformation field? (3) How do material properties at depth influence the deformation observed at the surface? (4) What are the uncertainties of the model parameters that describe the magma chamber?
The impulse-response rheological experiment will improve understanding of the volcano deformation cycle. Specifically, the research project will test four hypotheses: (I) Deformation following the 1997 eruption did not reach a steady state before the eruption in 2008. (II) Viscoelastic stress relaxation contributes to the transient deformation observed during the co-and post-eruptive time intervals. (III) The effective viscosity is several orders of magnitude smaller in the rind of the magma chamber than in the surrounding crust. (IV) The lava flow extruded from Cone A during the 1997 eruption produces a stress field that favors dike propagation from the magma chamber to Cone D.
The results will be published in the international, peer-reviewed literature. A graduate student from a group under-represented in Science, Technology, Engineering and Mathematics (STEM) will be trained for a career in geophysical research at the intersection of three disciplines: seismology, geodesy and volcanology. The modeling protocol and approach will be disseminated among the scientific community at an operational level. Investigator Masterlark, a junior faculty member from an institution funded by the Office of Experimental Program to Stimulate Competitive Research (EPSCoR), will offer a short course on how to apply the Finite Element Method to volcanic deformation. Applicants from underrepresented groups will be especially encouraged to participate. The project will enhance collaboration between the investigators and scientists at the U.S. Geological Survey
The migration of magma within a volcano produces a deformation signature at the Earth’s surface. The internal structure, magmatic pressure characteristics, and stress conditions of a volcano contribute to the specific deformation that we observe with geodetic data, such as GPS or satellite radar data. Numerical models can simulate the behavior of these volcanic systems. Forward models allow us to predict surface deformation for a given scenario of magma intrusion at depth. Unfortunately, because we are residents of the Earth’s surface, we cannot directly observe such magma intrusion scenarios within an active volcano. Therefore, we are faced with the much more challenging problem of developing inverse models that use observed deformation (what we can directly observe at the Earth’s surface) to estimate a few parameters that describe the unknown characteristics of the magmatic intrusion, such as geometry, position, and strength (what we want to know). An accurate understanding of such magma intrusion characteristics is essential to understanding the magma supply budget of an active volcano, which in turn strongly controls the timing, style, and magnitude of eruption activity. Distortions of these estimated magmatic intrusion characteristics are tied to our ability to: (1) identify and resolve the internal structure of the volcano; (2) simulate the magmatic intrusion over a problem domain having this internal structure; and (3) estimate the specific parameters that characterize magmatic intrusion from observed deformation. Minimizing the combined distortion requires inverse models that estimate magmatic intrusion parameters, while simultaneously accounting for the geometry and internal structure of a volcano. Prior to this project, no such inverse models with these capabilities were available. The field of seismic tomography successfully addressed (1). From the standpoint of Intellectual Merit, the primary goal of this project was to develop inverse methods that satisfy the requirements for (2) and (3). This project successfully developed such methods and demonstrated the implications using the specific example of Okmok Volcano Alaska. Results indicate that inverse models of surface deformation, observed with satellite radar data, using numerical models that simulate the actual internal structure (as determined from existing seismic tomography) predict that the magma chamber is significantly deeper compared to results determined from standard models that ignore the complex internal structure. Furthermore, the inclusion of the more complex and realistic internal structure by the numerical models significantly improves the predictive capability of magma intrusion models. In summary, these more realistic numerical models provide more reliable predictions of the interior process of active volcanoes, compared to standard models that oversimplify the interior structure of a volcano. From the standpoint of Broader impacts, this project trained graduate students to conduct research at the important intersection of numerical methods and geodesy (the study of Earth’s deformation). This training included in-depth technical aspects associated with the goals of the Intellectual Merits for two graduate students. Additionally, the project trained several other graduate students from domestic universities via a workshop for designing and constructing numerical models of volcano deformation. This workshop was held at the UNAVCO facility in Boulder, CO., in May 2013.
