Todd C. Feeley

Associate Professor of Geology

It is with great sadness we share with you news of the passing of Dr. Todd Feeley.

Dr. Feeley was an internationally recognized volcanologist in the Department of Earth Sciences. His work took him around the world studying volcanoes in Bolivia, Chile, the Bering Sea, and Washington state’s Mount St. Helens.

Dr. Feeley had been with Montana State University since 1996. He will be remembered for his passion for geology and for promoting scientific thinking and evolution, as well as for leading volcanology field trips around the American West.

We extend sympathies to Dr. Feeley’s family, friends, students and colleagues in Bozeman and around the world.


B.A., University of California, Santa Barbara, 1985
M.S., Oregon State University, 1989
Ph.D., University of California, Los Angeles, 1993

Research Interests:

My research centers on the behavior of magma in and on the Earth's crust as deduced from field relationships and the chemical analysis of rocks and minerals. The broad goal is to further understanding of the origin and evolution of magmas in crustal reservoirs, their behavior during volcanic eruptions, and their implications for magmatic, volcanic, and tectonic processes. The methods I employ include major and trace element analyses by XRF and ICP-MS, radiogenic isotope analyses by TIMS, stable isotope analyses by conventional and laser techniques, and mineral analyses by electron microprobe. My previous and ongoing research projects include studies of large stratovolcanoes in the Andean and Cascades volcanic arcs, Cenozoic volcanic fields in the U.S. Cordillera, and basaltic lava fields in the back-arc of the Aleutian subduction system.

Mount St. Helens Self-Led Geologic Trail Guide (PDF)

Through support from the National Science Foundation (EAR-9983769), my students and I have also been working at Mount St. Helens, where among other things we have created a self-led geologic trail guide for the trail linking the Johnston Ridge Observatory to Windy Ridge. Our PDF trail guide is formatted to print double-sided on a single 11x17 sheet. Crease marks for folding are marked. This guide will continue to be updated as eruptive activity at the volcano continues.


Selected Publications:

Michelfelder G., Feeley, T., Wilder, A., in press. The Volcanic Evolution of Cerro Uturuncu: A High- K, Composite Volcano in the Back- Arc of the Central Andes of SW Bolivia.  International Journal of Geosciences Special Edition on Volcanic Eruption Research.

Michelfelder, G.S., Feeley, T.C., Wilder, A.D., Klemeti, E. W., 2013. Modification of the continental crust by subduction zone magmatism and vice-versa: across-strike geochemical variations of silicic lavas from individual eruptive centers in the Andean Central Volcanic Zone. Geosciences Special Issue on Continental Accretion and Evolution, Geosciences 20133(4), 633-667; doi:10.3390/geosciences3040633 (pdf:

Underwood, S.J., Feeley, T.C., Clynne, M.A., 2013, Hydrogen Isotope Investigation of Amphibole and Glass in Dacite Magmas Erupted in 1980–1986 and 2005 at Mount St. Helens, Washington. Journal of Petrology, 2013 doi: 10. 1093/petrology/egt005.

Underwood, S.J., Feeley, T.C., Clynne, M.A., 2012. Hydrogen isotope investigation of amphibole and biotite phenocrysts in silicic magmas erupted at Lassen Volcanic Center, California.  Journal of Volcanology and Geothermal Research, 227-228: 32-49; doi: 10.1016/j.jvolgeores.2012.019.

Chang, J.M., Feeley, T.C., and DeRaps, M.R., 2009. Petrogenesis of basaltic volcanic rocks from the Pribilof Islands, Alaska, by melting of metasomatically enriched depleted lithosphere, crystallization differentiation, and magma mixing. Journal of Petrology. 50:2249-2286; doi:10.1093/petrology/egp075

Feeley, T.C., Winer, G.S., 2009. Volcano hazards and potential risks on St. Paul Island, Pribilof Islands, Bering Sea, Alaska. Journal of Volcanology and Geothermal Research 182; 57-66.

Feeley, T.C., Clynne, M.A., Winer, G.S., Grice, W.A., 2008. Oxygen Isotope Geochemistry of the Lassen Volcanic Center, California: Resolving Crustal and Mantle Contributions to Continental Arc Magmatism. Journal of Petrology 49:971-997; doi:10.1093/petrology/egn013.

Grunder, A.L., Klemetti, E.W., Feeley, T.C., McKee, C.L. 2008. Eleven million years of arc volcanism at the Auganquilcha Volcanic Cluster, northern Chilean Andes: Impliacations for the lifespan and emplacement of plutons.  Plutons and Batholiths - Wallace Pitcher Memorial Issue, Transactions of the Royal Society of Edinburgh: Earth Sciences, 97:415-436.

Feeley, T.C., Wilson, L.F., Underwood, S.J., 2008. Distribution and Compositions of Magmatic Inclusions in the Mount Helen Dome, Lassen Volcanic Center, California: Insights into Mama Chamber Processes. Lithos 106: 173-189.

Winer, G.S., Feeley, T.C., & Cosca, M.A., 2004. Basaltic volcanism in the Bering Sea: geochronology and volcanic evolution of St. Paul Island, Pribilof Islands, Alaska. Journal of Volcanology and Geothermal Research, 134: 277-301.

Feeley, T.C., 2003. Origin and tectonic implications of across-strike geochemical variations in the Eocene Absaroka volcanic province, United States. Journal of Geology, 111:329-346.

Feeley, T.C. & Cosca, M.A., 2003. Time vs. composition trends of magmatism at Sunlight volcano, Absaroka volcanic province, Wyoming. Geological Society of America Bulletin, 115:714-728.

Lindsay, C.R. & Feeley, T.C., 2003. Magmagenesis at the Eocene Electric Peak-Sepulcher Mountain complex, Absaroka Volcanic Province, USA. Lithos 67:53-76.

Feeley, T.C., Cosca, M.A., & Lindsay, C.R., 2002. Petrogenesis and implications of cryptic hybrid magmas from Washburn volcano, Yellowstone National Park, USA. Journal of Petrology, 43:663-703

Feeley, T.C. & Winer, G.S., 1999. Evidence for fractionation of Quaternary basalts on St. Paul Island, Alaska, with implications for the development of shallow magma chambers beneath Bering Sea volcanoes. Lithos, 46:661-676.

Feeley, T.C., Dungan, M.A. & Frey, F.A., 1998. Geochemical constraints on the origin of mafic and silicic magmas at Cordon El Guadal, Tatara San Pedro complex, Chile. Contributions to Mineralogy and Petrology, 131:393-411.

Singer, B.S., Wijbrans, J.R., Nelson, S.T., Pringle, M.S., Feeley, T.C., & Dungan, M.A., 1998. Inherited argon in a Pleistocene andesite lava: 40Ar/39Ar incremental-heating and laser-fusion analyses of plagioclase. Geology, 26:427-430.

Singer, B.S., Thompson, R.A., Dungan, M.A., Feeley, T.C., Pickens, J., Brown, L.L., Nelson, S.T., Wulff, A.W., Davidson, J.P., & Metzger, J., 1997. Volcanism and erosion during the past 930 K.Y. at the Tatara-San Pedro complex, Chilean Andes. Geological Society of America Bulletin, 109:127-142.

Feeley, T.C. & Dungan, M.A., 1996. Compositional and dynamic controls on mafic-silicic magma interactions at continental arc volcanoes: evidence from Cordon el Guadal, Tatara San Pedro Complex, Chile. Journal of Petrology, 37:1547-1577.

Feeley, T.C. & Sharp, Z.D., 1996. Geochemical and hydrogen isotopic evidence for in situ dehydrogenation of biotite in silicic magma chambers. Geology, 24:1021-1024.

Feeley, T.C. & Hacker, M.D., 1995. Intracrustal derivation of Na-rich andesitic and dacitic magmas: an example from Volcan Ollague, Andean Central Volcanic Zone. The Journal of Geology, 103:213-216.

Feeley, T.C. & Sharp, Z.D., 1995. 18O/16O isotope geochemistry of silicic lava flows erupted from Volcan Ollague, Andean Central Volcanic Zone. Earth and Planetary Science Letters, 133:239-254.

Feeley, T.C. & Davidson, J.P., 1994. Petrology of calc-alkaline lavas at Volcan Ollague and the origin of compositional diversity at central Andean stratovolcanoes. Journal of Petrology, 35:1295-1340.

Feeley, T.C., 1993. Crustal modification during subduction-zone magmatism: evidence from the southern Salar de Uyuni region (20o-22oS), central Andes. Geology, 21:1019-1022.

Feeley, T.C., Davidson, J.P., & Armendia, A., 1993. The volcanic and magmatic evolution of Volcan Ollague, a high-K, late Quaternary stratovolcano in the Andean Central Volcanic Zone. Journal of Volcanology and Geothermal Research, 54:221-245.

Feeley, T.C. & Grunder, A.L., 1991. Mantle contribution to the evolution of Middle Tertiary silicic magmatism during early stages of crustal extension: The Egan Range volcanic complex, east-central Nevada. Contributions to Mineralogy and Petrology, 106:154-169.