Miravalles Geothermal Field, Costa Rica 

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Udo Fehn, Professor of Geology

Post-Doctoral Researcher

Graduate Students

Former Students


U of R Earth and Environmental Sciences


Recent Publications:

  • Z. Lu, H. Tomaru, and U. Fehn: Iodine ages of pore waters at Hydrate Ridge (ODP Leg 204), Cascadia Margin: implications for sources of methane in gas hydrates: Earth and Planetary Science Letters (in press).
  • Z. Lu, C. Hensen, U. Fehn, and K. Wallmann (2007): Old iodine in fluids venting along the Central American convergent margin. Geophysical Research Letters, 34, L22604, doi:22610.21029/22007GL031864.
  • H. Tomaru, Z. Lu, U. Fehn, Y. Muramatsu and R. Matsumoto (2007): Age variation in pore water iodine from the eastern Nankai Trough, Japan: evidence for different source regions in a gas hydrate field. Geology, 35, 1015-1018.
  • U. Fehn, G.T.Snyder and Y.Muramatsu (2007): Iodine as a tracer of organic material: 129I results from gas hydrate systems and fore arc fluids. J. Geochem. Explor., 95, 66-80.
  • H. Tomaru, Z. Lu, G. T. Snyder, U. Fehn, A. Hiruta and R. Matsumoto (2007). Origin and flow of pore waters in an actively venting gas hydrate field near Sado Island, Japan Sea: interpretation of halogen and 129I distributions. Chem. Geol.,236, 350-366.
  • Y. Muramatsu, T. Doi, H. Tomaru, U. Fehn, R. Takeuchi, and R. Matsumoto (2007). Halogen concentrations in pore waters and sediments of the Nankai Trough, Japan: Implications for the origin of gas hydrates.  Appl. Geochem., 22, 534-556.
  • H. Tomaru, U.Fehn,  Z.Lu and R. Matsumoto (2007) Halogen systematics in the Mallik Gas Hydrate Well, Northwest Territories, Canada: Implications for the origin of gas hydrates under terrestrial permafrost conditions. Appl. Geochem., 22, 656-675.
  • H. Tomaru, S. Ohsawa, K. Amita, Z. Lu and U.Fehn (2007). Influence of subduction zone settings on the origin of fore arc fluids: Halogen and 129I systematics in Kyushu, Japan. Appl. Geochem., 22, 676-691.
  • Z. Lu, U. Fehn, H. Tomaru, D. Elmore and X. Ma (2007). Reliability of 129I/I ratios produced from small sample masses. Nuclear Instruments and Methods in Physics Research, B, 259, 359-364.
  • U. Fehn, J.E. Moran, G.T. Snyder and Y. Muramatsu (2007). The initial 129I/I ratio and the presence of ‘old’ iodine in continental margins. Nuclear Instruments and Methods in Physics Research, B, 259. 496-502.
  • U. Fehn, Z. Lu and H. Tomaru (2006). 129I/I ratios and halogen concentrations in pore waters of the Hydrate Ridge: Relevance for the origin of gas hydrates in ODP Leg 204.  Proc. ODP, Sci. Results 204, 1-25, MS 204SR-107. Full Text
  • S. Hurwitz, R.H.Mariner, U. Fehn and G.T.Snyder (2005). Systematics of halogen elements and their radioisotopes in thermal springs of the Cascade Range, Central Oregon, Western USA.  Earth Planet. Sci. Lett., 235, 700-714.
  • U. Fehn and G.T.Snyder (2005): Residence times and source ages of deep crustal fluids: Interpretation of 129I and 36Cl results from the KTB-VB drill site, Germany. Geofluids, 5, 42-51. Full Text
  • G.Snyder and U. Fehn (2004): Global distribution of 129I in rivers and lakes: Implications for iodine cycling in surface reservoirs. Nuclear Instruments and Methods in Physics Research, B 223/224, 579-586.
  • G. Snyder, R. Poreda, U. Fehn, and A. Hunt (2003): Sources of nitrogen and methane in Central American geothermal settings: Noble gas and 129I evidence for crustal and magmatic volatile components. Geochem. Geophys. Geosyst., 4(1), 9001: 10.1029/2002GC000363, 2003; 28p.
  • U. Fehn, G.T.Snyder, R.Matsumoto, Y.Muramatsu and H.Tomaru (2003): Iodine dating of pore waters associated with gas hydrates in the Nankai area, Japan. Geology, 31, 521-524. Full Text
  • U.Fehn and G.T.Snyder (2003): Origin of iodine and 129I in volcanic and geothermal fluids from the North Island of New Zealand: Implications for subduction zone processes. Econ. Geol., Spec. Publ.10, 159-170. Full Text
  • G.T. Snyder, W.C Riese, S. Franks, U. Fehn, W.L. Pelzmann, A.W. Gorody, and J.E. Moran (2003): Origin and history of waters associated with coal-bed methane: 129I, 36Cl, and stable isotope results from the Fruitland Formation, CO and NM. Geochim. Cosmochim. Acta, 67, 4529-4544
  • G.T.Snyder, U.Fehn and F.Goff (2002): Iodine isotope ratios and halide concentrations of the Satsuma-Iwojima volcano, Japan. Earth, Planets & Space, 54, 265-273. Full Text
  • U.Rao, U.Fehn, Y.Muramatsu, H.McNeil, P.Sharma and D.Elmore (2002): Tracing the history of nuclear releases: Determination of 129I in tree rings. Environmental Science & Technology, 36, 1271-1275. Full Text
  • U.Fehn, G.Snyder and J.Varekamp (2002): Detection of recycled marine sediment components in crater lake fluids using 129I. J. Volcanol. Geotherm. Res.,115, 451-460.
  • G.T.Snyder and U.Fehn (2002): The origin of iodine in volcanic fluids: 129I results from the Central American Volcanic Arc. Geochim. Cosmochim. Acta, 66, 3827-3838. Full Text
  • G. Snyder, R.Poreda, A.Hunt and U.Fehn (2001): Regional variations in volatile composition: isotopic evidence for carbonate recycling in the Central American Arc. Geochem. Geophys. Geosyst., 2, 10.129/ 2001GC000163. 25 p. Full Text
  • Y.Muramatsu, U.Fehn and S.Yoshida (2001): Recycling of iodine in fore-arc areas: evidence from the iodine brines in Chiba, Japan. Earth Planet. Sci. Lett.,192, 583-593.
  • U.Fehn, G.Snyder and P.K.Egeberg (2000): Dating of pore waters with 129I: Relevance for the origin of marine gas hydrates. Science, 289, 2332-2335. Abstract   Full Text