18-20. Magma-physics based models of unrest at California’s volcanoes

Three volcanoes ranked as high-threat in California because of their eruptive history and observed unrest are actively deforming and can provide ample opportunities to apply modeling capabilities based on realistic physics. Long Valley Caldera has experienced several inflationary episodes of unrest observed by multiple methods due in part to the extensive USGS monitoring networks covering seismicity, deformation and gravity changes, geochemistry, structural geology, and more.  Lassen Peak, in contrast, has been subsiding for several decades, likely since the 1914-1917 eruptions, while Medicine Lake Volcano also continues to subside, as it has for several decades. Several physical mechanisms have been proposed to explain unrest at these volcanoes including subsurface magma or hydrothermal fluid flow (Long Valley caldera); cooling magma, gas escape, or hydrothermal alteration causing volume change (Lassen Peak and Medicine Lake) but there has not been conclusive support for any of these models yet.  In addition to volcanic deformation, California’s volcanoes are also subject to regional deformation due to their close proximity to the Pacific plate boundary and the Walker Lane that accommodates a sizeable fraction of the Pacific-North America plate motion.

Previous modeling methods have employed simplified rheology and reservoir geometries largely due to insufficient knowledge of the subsurface structural geology (e.g, the last regional gravity model of Long Valley caldera dates to 1985), incomplete physics-based models and computational limits. The recent acquisition of two gravimeters from the Volcano Science Center, the development of magma-physics based models and improved computational facilities will enable development of up-to-date structural models of these volcanoes.  The application of computationally intensive methods, for example finite element models, to incorporate realistic geometries and heterogeneous material properties. Other improvements will come from the employment of Bayesian methods to explore confidence ranges and the ability to incorporate more realistic magma physics in volcano models. 

We seek a Mendenhall Fellow to investigate deformation at California’s volcanoes with novel modeling methods, and incorporate a wealth of additional data which may include seismic, geochemical, hydrological or geological data.  These models will help inform future hazard assessments. Available geodetic data include campaign and continuous GPS/GNSS data both from USGS and other regional networks (e.g. Unavco’s PBO), InSAR time-series, and in some cases gravity, strainmeter and tiltmeter data.  It would be desirable that the Fellow is familiar with geodetic field techniques (gravity, GPS, InSAR) and has experience with analytical and/or numerical modeling.

Potential Fellows could apply novel modeling techniques to a variety of problems in California (see examples below) but need not be limited to these examples.

Ongoing deflation of Lassen Peak (or Medicine Lake).  Lassen Peak last erupted from 1914-1917, and has been subsiding at a relatively constant rate for the duration of its observational record.  There have been a number of proposed processes to explain the subsidence including cooling magma, gas escape, or hydrothermal alteration causing volume change.  Currently published deformation models can replicate the subsidence at Lassen, but with an over-simplified reservoir-type model that is not realistic. By incorporating additional data and novel modeling methods, it could be possible to substantially improve the interpretation to be consistent with additional geologic and geochemical data.  Existing geodetic data include campaign and continuous GNSS time-series, InSAR data, and recently updated campaign gravity measurements, while detailed geological and geochemical studies could provide additional input. 

Episodic inflation at Long Valley Caldera. Episodes of inflation at Long Valley Caldera have been observed since the permanent instrumentation was installed in the early 1980’s, and a very long-duration record of multidisciplinary data exists for the caldera.  There is still ongoing debate to differentiate between substantially different models of the inflation episodes including magma or gas/fluid accumulation, regional tectonics, and the effects of hydrologic processes. Recently acquired gravity campaign data, and two new CVO-based gravimeters that will allow for more frequent measurements, provide the opportunity to achieve more accurate model addressing the density change. 

Deformation of geothermal areas. Multiple geothermal areas in California’s volcanic regions are subsiding due to geothermal extraction.  These regions provide an important contribution to the energy production budget of the state. Stresses and strains induced by geothermal power production contributes to ground subsidence and can induce and/or trigger seismicity, and can inform interpretations of the mechanical and rheological properties of their volcanic regions. 

Magmatic-tectonic interaction at the Mono Domes - Inyo Craters chain. Recent magneto-telluric and tomographic studies have identified possible magma sources underneath the Mono-Inyo Volcanoes.  While these volcanoes are not actively deforming, there are larger regional-scale tectonic interactions that could influence where that magma preferentially accumulates.

Understanding the limitations of deformation models.  Volcano models are often over-simplified by nature, and in time-sensitive situations often the more simplified models are favored over more realistic ones that can take hours or days to produce.  What are the performance and trade-offs between simple models and more complex physical models? When are they important? In a time-constrained eruption scenario, how useful are simple models, and what are the impacts of the model biases on the interpretations and eruption forecast?  When do we have enough information to justify a more complex model?

Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.

Proposed Duty Station: Moffett Field, CA

Areas of PhD: Geophysics or applied mathematics with a focus on geodesy, seismology or physics based modeling of natural systems or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).  

Qualifications: Applicants must meet the qualifications for:  Research Geophysicist

(This type of research is performed by those who have backgrounds for the occupations stated above.  However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Human Resources Office Contact: Audrey Tsujita, 916-278-9395, atsujita@usgs.gov