Dust plumes off Argentina. Lago Colhue-Huapi at center left. Aqua MODIS image, 2013. NASA.

Soil and Loess Magnetism

Magnetic minerals, because of their iron content, are sensitive indicators of chemical weathering. The magnetic properties of soils and loess (windblown silt deposits, somewhat modified by soil formation) can therefore help us understand the moisture and temperature conditions in which soil and loess landscapes formed. Other processes besides climate affect soil magnetism, however: human-made dusts, incorporated into soils, can be highly magnetic, as can the original “parent material” on which a soil formed. Fire can drastically affect magnetic properties as well. In short, the magnetic properties of soil and loess can give a tremendous amount of environmental information about a landscape, but can be challenging to tease apart.

I have several projects going that focus on analyzing magnetic properties of soil and loess, mainly in the Tacoma, Washington area and in the Patagonia region of Argentina.
My work in Tacoma will continue for the foreseeable future. One component of the work is being done in conjunction with an EPA-led soil hydrology mapping project. Another component investigates the magnetic properties of pollution from the ASARCO smelter that operated in Ruston until 1985. Because of their local nature, these studies lend themselves to student-directed projects, and may be combined with class projects in Earth materials (TESC 347) or environmental field geophysics (TESC 419). Students working on these projects have presented at regional undergraduate research conferences. Some high-quality student work has led to undergraduate co-authors on posters presented at the Geological Society of America conference. There is also work to be done on the Argentine loess deposits, and on other loess deposits in the Pacific Northwest.

For Students
Timeline: Ongoing for the foreseeable future
Courses Required: Physical Geology w/Lab (TESC 117); Intro Stats (TMATH 110); Earth Materials, Sedimentology, and/or Physics 2 (Electricity and Magnetism) are helpful
Fieldwork: Yes
Laboratory Analyses: Bulk magnetic properties, size-fraction magnetic properties, magnetic hysteresis and components, magnetic anisotropy, reflected light microscopy, electron microscopy, UV-vis spectroscopy, particle size analysis
Data Analysis: Factor analysis and related techniques, least squares fitting
Software: Excel, Mathematica, R, Python
Conference Opportunity: Local undergraduate conferences, will need to seek additional funding for other presentations
Required Reading
Egli R. 2004. Characterization of Individual Rock Magnetic Components by Analysis of Remanence Curves, 1. Unmixing Natural Sediments. Studia Geophysica et Geodaetica 48:391–446.

Geiss CE, Egli R, Zanner CW. 2008. Direct estimates of pedogenic magnetite as a tool to reconstruct past climates from buried soils. Journal of Geophysical Research 113. doi:10.1029/2008JB005669 http://www.agu.org/pubs/crossref/2008/2008JB005669.shtml

Glass GL. 2003. Credible Evidence Report, the ASARCO Tacoma Smelter and Regional Soil Contamination in Puget Sound. Seattle, WA: Tacoma Pierce County Health Department and Washington Department of Ecology.

Roman SA, Johnson WC, Geiss CE. 2013. Grass fires–an unlikely process to explain the magnetic properties of prairie soils. Geophysical Journal International 195:1566–1575.

Selkin PA, Strömberg CAE, Dunn RE, Kohn MJ, Carlini AA, Davies-Vollum KS, Madden RH. 2015. Climate, Dust, and Fire Across the Eocene-Oligocene Transition, Patagonia. Geology In Press.

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