(left) Orienting a block sample of the Katmai tuff in the Valley of Ten Thousand Smokes, Alaska. (center) The Alvin submersible returns to the surface after collecting rock samples from the Galapagos Spreading Center. Photo by Rod Catanach, Woods Hole Oceanographic Institution. (right) Ash flows from the 1980 eruptions of Mount St. Helens, Washington, exposed in a stream cut.
By comparing records of the Earth’s field recorded in igneous rocks with known variations in in the field, we can place some age constraints on lava flows or estimate whether or not two flows were likely erupted at the same time. Additionally, by studying the orientation of magnetic minerals in some igneous rocks like ignimbrites, we can learn something about flow direction and source location. Identifying stratigraphic changes in the polarity of the Earth’s magnetic field (i.e., magnetostratigraphy) has long been used to date both sedimentary and volcanic sequences, and the resulting age constraints can be used to better understand many Earth processes like paleoclimate change. Previous and ongoing work in this area has involved estimating eruptive timing of young mid-ocean ridge lava flows; examining flow direction and post-emplacement rotations in pyroclastic flows; and magnetostratigraphic dating of sediments from the southeast Atlantic in conjunction with paleoclimate studies.
Bowles, J.A., †D. Gerzich, and M.J. Jackson (2018), Assessing New and Old Methods in Paleomagnetic Paleothermometry: A Test Case at Mt. St. Helens, USA, Geochemistry, Geophysics, Geosystems, 19, doi:10.1029/2018GC007435. Link to pdf.
Bowles, J.A., A. Coleman, J.T. McClinton, J. Sinton, S.M. White, K. Rubin, Eruptive timing and 200-year episodicity at 92°W on the hotspot-influenced Galapagos Spreading Center derived from geomagnetic paleointensity, Geochem. Geophys. Geosys, 15, doi:10.1002/2014GC005315, 2014. Link to pdf.
Westerhold, T., U. Röhl, I. Raffi, E. Fornaciari, S. Monechi, V. Reale. J. Bowles, H.F. Evans, Astronomical calibration of the Paleocene time scale, Palaeogeogr. Palaeoclimatol. Palaeoecol., 257, 377-403, 2008. Link to pdf.
Westerhold, T., U. Röhl, J. Laskar, I. Raffi, J. Bowles, L. Lourens, J.C. Zachos, On the duration of magnetochrons C24r and C25n and the timing of early Eocene global warming events: Implications from the Ocean Drilling Program Leg 208 Walvis Ridge depth transect, Paleoceanography, 22, PA2201, doi:10.1029/2006PA001322, 2007. Link to pdf.
Bowles, J. Data Report: Revised magnetostratigraphy and magnetic mineralogy of sediments from Walvis Ridge, Leg 208, In D.Kroon, J.C. Zachos, J.C., and C. Richter (Eds.), Proc. ODP, Sci. Results, 208: College Station, TX (Ocean Drilling Program), 1–24, doi:10.2973/odp.proc.sr.208.206.2006, 2006. Link to report.
Bowles, J., J.S. Gee, D.V. Kent, M. Perfit, A. Soule, D. Fornari, Paleointensity results from 9° – 10°N on the East Pacific Rise: implications for timing and extent of eruptive activity, Geochem. Geophys. Geosys., 7, Q06006, doi:10.1029/2005GC001141, 2006. Link to pdf.
Bowles, J., J. Gee, D. Kent, E. Bergmanis, J. Sinton, Cooling rate effects on paleointensity estimates in submarine basaltic glass and implications for dating young flows, Geochem. Geophys. Geosys., 6, Q07002, doi: 10.1029/2004GC000900, 2005. Link to pdf.
Lourens, L., A. Sluijs, D. Kroon, J. Zachos, E. Thomas, U. Röhl, J. Bowles, I. Raffi, An early Eocene transient warming (~53 Ma): Implications for astronomically paced early Eocene hyperthermal events, Nature, 435, 1083-1087, 2005. Link to pdf.