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

• Kazahaya Kohei

  Geological Survey of Japan, AIST

• Shinohara Hiroshi

  Geological Survey of Japan, AIST

• Saito Genji

  Geological Survey of Japan, AIST

Bibliographic Information

Other Title

• Degrassing process of Satuma-Iwojima volcano, Japan: Supply of volatile components from a deep magma chamber

Abstract

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.

Journal

• Earth, Planets and Space

  Earth, Planets and Space 54 (3), 327-335, 2002

  Society of Geomagnetism and Earth, Planetary and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan , The Geodetic Society of Japan , The Japanese Society for Planetary Sciences

Keywords

• Space and Planetary Science
• Geology

Details

• CRID: 1390001206513020288
• NII Article ID: 10008634908
• NII Article ID: 130003956298
• NII Book ID: AA11211921
• DOI: 10.1186/bf03353031
• COI: 1:CAS:528:DC%2BD38XjtVKjur4%3D
• ISSN: 18805981
• ISSN: 13438832
• ISSN: http://id.crossref.org/issn/13438832
• NDL BIB ID: 6263038
• Web Site: https://ndlsearch.ndl.go.jp/books/R000000004-I6263038
• Web Site: https://link.springer.com/content/pdf/10.1186/BF03353031.pdf
• Web Site: https://link.springer.com/article/10.1186/BF03353031/fulltext.html
• Web Site: http://link.springer.com/content/pdf/10.1186/BF03353031
• Text Lang: en
• Data Source:
  • JaLC
  • NDL
  • Crossref
  • CiNii Articles
• Abstract License Flag: Disallowed