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Degassing process of Satsuma-Iwojima volcano, Japan: Supply of volatile components from a deep magma chamber


Satsuma-Iwojima volcano continuously releases magmatic volatiles from the summit of Iwodake, a rhyolitic lava dome. The temperature of fumaroles is high, between 800° and 900°C, and the water-rich composition of volcanic gases has not changed essentially over the past 10 years. Sulfur dioxide flux measured by COSPEC is almost constant with an average of 550 t/d since 1975. The present volcanic gas is likely degassed from a rhyolitic magma whose composition is similar to that erupted in 1934, 2 km east of Satsuma-Iwojima. Comparison of silicate melt inclusions and volcanic gas compositions indicates that the magma degassing pressure is very low, implying magma-gas separation at a very shallow level. The mass rate of magma degassing is estimated at 10 m3/s using the volatile content of the magma and the fluxes of magmatic volatiles. The rhyolitic parental magma is volatile-undersaturated in the deep magma chamber, as suggested by melt inclusion studies. Magma convection in a conduit, driven by the density difference between higher density degassed and lower density non-degassed magmas, explains the high emission rate of magmatic volatiles released at shallow depth from such a magma chamber, that is gas-undersaturated at depth. Model calculations require the conduit diameter to be greater than 50 m as a necessary condition for convection of the rhyolitic magma. Long-term convective degassing has resulted in the rhyolitic magma in the deep chamber to become depleted in volatile components. The melt-inclusion studies indicate that the rhyolitic magma responsible for discharging the present volcanic gas has been degassed during the long degassing history of the volcano and is now supplied with CO2-rich volatile components from an underlying basaltic magma. The total volcanic gas flux over 800 years requires degassing of 80–120 km3 of basaltic magma.


  1. Allard, P., Endogenous magma degassing and storage at Mount Etna, Geophys. Res. Lett., 24, 2219–2222, 1997.

  2. Allard, P., J. Carbobbelle, N. Metrich, H. Loyer, and P. Zettwoog, Sulfur output and magma degassing budget of Stromboli volcano, Nature, 368, 326–330, 1994.

  3. Burnham, C. W., Magmas and hydrothermal fluids, in Geochemistry of Hydrothermal Ore Deposits, edited by H. Barnes, 2nd ed., pp. 71–136, John Wiley & Sons, New York, 1979.

  4. Carroll, M. R. and J. D. Webster, Solubilities of sulfur, noble-gases, nitrogen, chlorine, and fluorine in magmas, Volatiles in Magmas, Rev. Mineral., 30, edited by M. R. Carroll and J. R. Holloway, pp. 231–279, Mineral. Soc. Am., Washington, 1994.

  5. Eichelberger, J. C., C. R. Carrigan, H. R. Westrich, and R. H. Price, Non-explosive silicic volcanism, Nature, 323, 598–602, 1986.

  6. Fogel, R. A. and M. J. Rutherford, The solubility of carbon dioxide in rhyolitic melts: a quantitative FTIR study, Am. Mineral., 75, 1311–1326, 1990.

  7. Hamasaki, S., Volcanic-related alteration and geochemistry of Iwodake volcano, Satsuma-Iwojima, Kyushu, SW Japan, Earth Planets Space, 54, this issue, 217–229, 2002.

  8. Hedenquist, J. W., M. Aoki, and H. Shinohara, Flux of volatiles and ore-forming metals from the magmatic-hydrothermal system of Satsuma Iwojima volcano, Geology, 585–588, 1994.

  9. Hirabayashi, J., T. Ohba, K. Nogami, and M. Yoshida, Discharge rate of SO2 from Unzen volcano, Kyushu, Japan, Geophys. Res. Lett., 22, 1709–1712, 1995.

  10. Kamada, M., Volcano and geothermy of Iwojima, Kagoshima prefecture, Jinetsu, 3, 1–23, 1964 (in Japanese).

  11. Kawanabe, Y. and G. Saito, Volcanic activity of the Satsuma-Iwojima area during the past 6500 years, Earth Planets Space, 54, this issue, 295–301, 2002.

  12. Kazahaya, K. and H. Shinohara, Excess degassing of active volcanoes: processes and mechanisms, Mem. Geol. Soc. Japan, 46, 91–104, 1996 (in Japanese with English abstract).

  13. Kazahaya, K., H. Shinohara, and G. Saito, Excessive degassing of Izu-Oshima volcano: magma convection in a conduit, Bull. Volcanol., 56, 207–216, 1994.

  14. Koyaguchi, T. and S. Blake, The dynamics of magma mixing in a rising magma batch, Bull. Volcanol., 52, 127–137, 1989.

  15. Lange, R. and I. S. E. Carmichael, Densities of Na2O-K2O-CaO-MgO-FeO-Fe2O3-Al2O3-TiO2-SiO2 liquids: new measurements and derived partial molar properties, Geochim. Cosmochim. Acta, 51, 2931–2946, 1987.

  16. Melnik, O. and R. S. J. Sparks, Nonlinear dynamics of lava dome extrusion, Science, 402, 37–41, 1999.

  17. Miyagi, I., H. Yurimoto, and E. Takahashi, Water solubility in albiteorthoclase join and JR-1 rhyolite melts at 1000°C and 500 to 2000 bars, determined by microanalysis with SIMS, Geochem. J., 31, 57–61, 1997.

  18. Nakada, S. and Y. Motomura, Petrology of the 1991–1995 eruption at Unzen: effusion pulsation and groundmass crystallization, J. Volcanol. Geotherm. Res., 89, 173–196, 1999.

  19. Ohkita, T., M. Kawamura, and S. Takagi, Amount of SO2 emission from Satsuma-Iwojima volcano, Kazan, 22, 107, 1977 (abstract in Japanese).

  20. Ohminato, T. and D. Ereditato, Broadband seismic observation at Satsuma-Iwojima, Japan, Geophys. Res. Lett., 24, 2845–2848, 1997.

  21. Ono, K., T. Soya, and T. Hosono, Geology of Satsuma-Io-jima district, Quadrangle series, Scale 1:50,000, 2, Geol. Surv. Japan, 80 p., 1982 (in Japanese with English abstract).

  22. Persikov, E. S., The viscosity of magmatic liquids: experiment, generalized patterns, a model for calculation, applications, in Physical Chemistry of Magmas, edited by L. L. Perchuk and I. Kushiro, pp. 1–40, Springer-Verlag, 1990.

  23. Saito, G., K. Kazahaya, H. Shinohara, J. Stimac, and Y. Kawanabe, Variation of volatile concentration in a magma system of Satsuma-Iwojima volcano deduced from melt inclusion analyses, J. Volcanol. Geotherm. Res., 108, 11–31, 2001.

  24. Saito, G., J. A. Stimac, Y. Kawanabe, and F. Goff, Mafic-felsic magma interaction at Satsuma-Iwojima volcano, Japan: Evidence from mafic inclusions in rhyolites, Earth Planets Space, 54, this issue, 303–325, 2002.

  25. Shinohara, H., W. F. Giggenbach, K. Kazahaya, and J. W. Hedenquist, Geochemistry of volcanic gases and hot springs of Satsuma-Iwojima, Japan: Following Matsuo, Geochem. J., 27, 271–285, 1993.

  26. Shinohara, H., K. Kazahaya, and J. B. Lowenstern, Volatile transport in a convecting magma column: Implications for porphyry Mo mineralization, Geology, 23, 1091–1094, 1995.

  27. Shinohara, H., K. Kazahaya, G. Saito, N. Matsushima, and Y. Kawanabe, Degassing activity from Iwodake rhyolitic cone, Satsuma-Iwojima volcano, Japan: Formation of a new degassing vent, 1990–1999, Earth Planets Space, 54, this issue, 175–185, 2002.

  28. Snyder, D. and S. Tait, The imprint of basalt on the geochemistry of silicic magmas, Earth Planet. Sci. Lett., 160, 433–445, 1998.

  29. Stevenson, D. S. and S. Blake, Modelling the dynamics and thermodynamics of volcanic degassing, Bull. Volcanol., 60, 307–317, 1998.

  30. Stolper, E. and J. R. Holloway, Experimental determination of the solubility of carbon dioxide in molten basalt at low pressure, Earth Planet. Sci. Lett., 92, 107–123, 1988.

  31. Wallace, P. J., Volcanic SO2 emissions and the abundance and distribution of exsolved gas in magma bodies, J. Volcanol. Geotherm. Res., 108, 85–106, 2001.

  32. Wallace, P. J., A. T. Anderson, and A. M. Davis, Quantification of preeruptive exsolved gas contents in silicic magmas, Nature, 377, 612–616, 1995.

  33. Westrich, H. R. and J. C. Eichelberger, Gas-transport and bubble collapse in rhyolitic magma—an experimental approach, Bull. Volcanol., 56, 447–458, 1994.

  34. Yoshida, M. and T. Ozawa, Abundance of some chemical elements produced by Satsuma-Iwo-Jima Volcano in relation to their provenance, Bull. Volcanol. Soc. Japan, 26, 25–34, 1981.

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Correspondence to Kohei Kazahaya.

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Kazahaya, K., Shinohara, H. & Saito, G. Degassing process of Satsuma-Iwojima volcano, Japan: Supply of volatile components from a deep magma chamber. Earth Planet Sp 54, 327–335 (2002).

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  • Magma Chamber
  • Basaltic Magma
  • Summit Crater
  • Rhyolitic Magma
  • Magma Degas