22. Quaternary rates of magma production in the Aleutian arc

The Aleutian arc is one of the most spectacular examples of a volcanic arc in the world, and it is home to over 80 percent of the active volcanoes in the United States. It is also the site of numerous voluminous caldera-forming eruptions and massive volcanic edifice failures since the late Pleistocene. While we have made recent advances in determining the eruptive histories of individual volcanoes within the arc, an arc-wide synthesis of Quaternary volcanism does not exist. A comprehensive understanding of eruptive volumes and chrono-stratigraphic information is an essential step in fully assessing the hazards posed by Aleutian volcanoes, and understanding the underlying processes that create them.

New seismic and geochronologic data imply that the Aleutian arc has grown at an extremely high rate since its inception at 46 Ma. It still is unknown, however, whether these high magma flux rates have continued in the Quaternary. The Aleutian arc provides an unparalleled opportunity to study the effects of tectonic setting (continental versus oceanic crust), convergence rate, and amount of subducted sediment, among other factors, on the rates of magma production. In turn, it will also be possible to evaluate how magma flux rate affects the occurrence of major volcanic hazards such as caldera-forming eruptions and edifice failure. Accurate determinations of flux rates are also central to the global issue of continental growth. Recent advances in estimates of the volume of continental material returned to the deep mantle through subduction erosion permit the interpretation that continents are not growing, but that interpretation needs to be checked against accurate determinations of arc growth rate. Using existing data, coupled with strategically acquired new ages, the time is ripe for an arc-wide study of this nature.

We seek a postdoctoral fellow to investigate the relationships between changing tectonic setting, magma flux rates, and volcanic hazards for select Quaternary volcanoes of the Aleutian arc. Specifically, the investigator would use geologic map data, DEMs, satellite imagery, and bathymetric data to determine volumes for volcanic edifices, and ⁴⁰Ar/³⁹Ar geochronology to better constrain their ages. We suggest that the fellow focus on <10 volcanic centers that represent varying subduction parameters, and for which good geochemical datasets, base map data, and sample suites already exist.

A systematic study of magma flux rates for Quaternary Aleutian volcanoes will act as a springboard that will allow a host of other questions to be tackled, and the fellow would have substantial freedom in what avenues of research to pursue. A main query will be, how do magma flux rates correlate with large-scale hazards? Other possible areas of inquiry may be: (1) rates of erosion and the effect on flux estimates, (2) relationship between magma flux and along-arc geochemical signatures, (3) ratios of intrusive versus extrusive magmatism, and (4) correlation of magma flux at individual volcanoes with volcano spacing, and implications for sub-arc magma generation.

Proposed Duty Station: Anchorage, AK

Areas of Ph.D.: Volcanology, geochemistry, geology, geochronology

Qualifications: Applicants must meet one of the following qualifications: Research Geologist, 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.)

Research Advisor(s): Michelle Coombs, (907) 786-7403, mcoombs@usgs.gov; Andrew Calvert, (650) 329-5276, acalvert@usgs.gov; Chris Nye (Alaska Division of Geological and Geophysical Surveys), (907) 474-7430; David Scholl, (650) 329-3762, dscholl@usgs.gov

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

Summary of Opportunities