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Bulletin of Volcanology

, Volume 62, Issue 1, pp 34–52 | Cite as

Contrasting hydrothermal activity at Sierra Negra and Alcedo volcanoes, Galapagos Archipelago, Ecuador

  • Fraser Goff
  • Gary M. McMurtry
  • Dale Counce
  • James A. Simac
  • Alfredo R. Roldán-Manzo
  • David R. Hilton
RESEARCH ARTICLE

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and approximately 85% SO2 of the total sulfur gas. Relative amounts of He, Ar, and N2 show a distinct hot-spot signature ( \(\)). The δ13C–CO2 is approximately −3.6‰ and δ34ST is approximately +3.3‰. The δD/δ18O of fumarole H2O indicates steam separation from local meteoric waters whose estimated minimum mean residence time from 3H analyses is ≤40 years. Fumarolic activity at Alcedo is controlled by a caldera-margin fault containing at least seven hydrothermal explosion craters, and by an intracaldera rhyolite vent. Two explosion craters which formed in 1993–1994 produce approximately 15 m3/s of steam, yet discharge temperatures are ≤97°C. Water content of the total gas is 95–97 mol.%, noncondensible gas is 92–98 mol.% CO2, and sulfur gas is dominated by H2S. Relative amounts of He, Ar, and N2 show extensive mixing between hot spot and air or air-saturated meteoric water components but the average \(\). The δ13C–CO2 is approximately −3.5‰ and δ34ST is approximately −0.8‰. The δD/δ18O of fumarole steam indicates separation from a homogeneous reservoir that is enriched 3–5‰ in 18O compared with local meteoric water. 3H indicates that this reservoir water has a maximum mean residence time of approximately 400 years and empirical gas geothermometry indicates a reservoir temperature of 260–320°C. The intracaldera hydrothermal reservoir in Alcedo is probably capable of producing up to 150 MW; however, environmental concerns as well as lack of infrastructure and power users will limit the development of this resource.

Galapagos Volcanic gases Gas geochemistry Isotope geochemistry Geothermal systems Sierra Negra Alcedo 

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Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • Fraser Goff
    • 1
  • Gary M. McMurtry
    • 2
  • Dale Counce
    • 1
  • James A. Simac
    • 3
  • Alfredo R. Roldán-Manzo
    • 4
  • David R. Hilton
    • 5
  1. 1.Los Alamos National Laboratory, Los Alamos, NM 87545, USAUS
  2. 2.SOEST University of Hawaii, Honolulu, HI 96822, USAUS
  3. 3.Unocal Corporation, Philippines, 14141 Southwest Freeway, Sugar Land, TX 77478, USAUS
  4. 4.INDE, Guatemala City, GuatemalaGT
  5. 5.Department of Earth Sciences, Vrije Universiteit, HV1081 Amsterdam, The NetherlandsNL

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