28. Modeling the dynamics of volcanic tephra plumes

The dispersal and fallout of tephra and ash (<2 mm) during volcanic eruptions represents a major hazard to aviation, infrastructure, life, and property. Volcanic Ash Advisory Centers throughout the world have the responsibility to model and forecast the trajectories of ash clouds to mitigate potential tephra hazards to aviation. Ash cloud dispersal models require information on the rate of ash loading in the atmosphere, its vertical distribution, and grain size as source parameters. Because the USGS is responsible for monitoring active U.S. volcanoes and for notifying others of eruptions and their potential hazards, it has begun a multi-year effort with the International Civil Aviation Organization (ICAO) to better constrain eruption source parameters to improve numerical modeling of ash cloud dispersal.

Currently, eruption source parameters are inferred from satellite images, seismic or other monitoring data, empirical relationships between plume height and eruption rate, and simple 1-D plume models that can adjust height-rate relations for specific atmospheric conditions. This approach can reasonably relate plume height and eruption rate in strong plumes which rise vertically into the atmosphere and feed a horizontal umbrella cloud, but is less certain for weak plumes that rise slowly and are bent over by wind. Weak plumes occur during smaller eruptions, which are the most frequent.

The USGS is also responsible for assessing and forecasting ground-based hazards associated with tephra fall. At present our forecasting capability is hampered by the limitations of our models and their lack of integration with monitoring, meteorological, and satellite data. The distribution of tephra fallout is currently modeled using simple advection-diffusion models, in which a constant diffusion coefficient controls the rate of widening of the resulting deposit with increasing distance from the vent. Meteorological models of 3-D wind patterns, topography, and particle size variations are not included, limiting the accuracy of such models in predicting the pattern of tephra deposition. Improved volcanic plume models are needed that better predict the distribution of tephra in the atmosphere and fallout distribution downwind.

We seek a postdoctoral candidate who can develop or modify models of plume dynamics and tephra fallout for the purpose of improved prediction of tephra hazards for routine hazard assessments as well as operational applications during volcanic unrest. The candidate should have a strong background in numerical modeling, fluid dynamics, and turbulent processes. They should also be able to integrate model results with visual observations, satellite data, tephra deposit studies, and new technologies such as a Doppler radar system soon to be deployed by the USGS to study properties of volcanic plumes. Tephra deposit studies, satellite data, and archived wind-field patterns from several well-studied eruptions in the past few decades are available for model input or comparison with model results.

The types of code and methods of solution are open to the candidate. For research, open-source, multi-phase codes such as Clawpack and ATHAM are available, as are collaborative arrangements with other institutions (Los Alamos, University of Washington or others) as can be arranged by the candidate and the USGS. Platforms and programming languages for construction of Web-based interfaces are also up to the candidate. Plume models may be integrated with meteorological models such as the Air Force Weather Agency MM5 or WRF model that can simulate local wind fields, or with larger-scale models of airborne ash dispersion and tephra dispersal such as PUFF or HYSPLIT.

The goal of this research is an improved model or models that can be used to forecast ash-cloud and tephra-fall distributions for eruptions of different sizes under varying atmospheric conditions. Results could be used for regional and national assessments and interactively as an operational tool during anticipated or ongoing eruptive activity. This research will contribute to the joint USGS/ICAO effort to better constrain eruption source parameters and improve forecasts of ash-cloud trajectories tens to thousands of kilometers downwind of an erupting volcano.

Proposed Duty Station: Anchorage, AK; Vancouver, WA

Areas of Ph.D.: Volcanology, physics, fluid mechanics, applied mathematics, geophysics, geology

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Geophysicist, Research Physicist

(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.)

Research Advisor(s): Larry Mastin, (360) 993-8925, lgmastin@usgs.gov; Chris Waythomas, (907) 786-7122, cwaythomas@usgs.gov

Human Resources Office contact: Erica Settlemyer, (916) 278-9383, esettlemyer@usgs.gov

Summary of Opportunities