Bulletin of Volcanology

, Volume 56, Issue 3, pp 207–216

Excessive degassing of Izu-Oshima volcano: magma convection in a conduit


  • Kohei Kazahaya
    • Geological Survey of Japan
  • Hiroshi Shinohara
    • Geological Survey of Japan
  • Genji Saito
    • Geological Survey of Japan

DOI: 10.1007/BF00279605

Cite this article as:
Kazahaya, K., Shinohara, H. & Saito, G. Bull Volcanol (1994) 56: 207. doi:10.1007/BF00279605


Excess degassing of magmatic H2O and SO2 was observed at Izu-Oshima volcano during its latest degassing activity from January 1988 to March 1990. The minimum production rate for degassed magma was calculated to be about 1×104 kg/s using emission rates of magmatic H2O and SO2, and H2O and S contents of the magma. The minimum total volume of magma degassed during the 27-month period is estimated to be 2.6×108 m3. This volume is 20 times larger than that of the magma ejected during the 1986 summit eruption. Convective transport of magma through a conduit is proposed as the mechanism that causes degassing from a magma reservoir at several kilometers depth. The magma transport rate is quantitatively evaluated based on two fluid-dynamic models: Poiseuille flow in a concentric double-walled pipe, and ascent of non-degassed magma spheres through a conduit filled with degassed magma. This process is further tested for an andesitic volcano and is concluded to be a common process for volcanoes that discharge excess volatiles.

Key words

Izu-Oshima volcanodegassingmagma convectionconduitvolatile fluxreservoir

Copyright information

© Springer-Verlag 1994