Excessive degassing of Izu-Oshima volcano: magma convection in a conduit |
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Authors: | Kohei Kazahaya Hiroshi Shinohara Genji Saito |
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Affiliation: | (1) Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, 305 Ibaraki, Japan |
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Abstract: | 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. |
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Keywords: | Izu-Oshima volcano degassing magma convection conduit volatile flux reservoir |
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