Gigantic SO2 emission from Miyakejima volcano, Japan, caused by caldera collapse

• DOI: 10.1130/g20399.1
• Publication Date: 2004-04-20T16:57:36Z
• Authors: Kohei Kazahaya; Hiroshi Shinohara; Kozo Uto; Masanobu Odai; Yasuhiro Nakahori; Hirokazu Mori; Hideki Iino; Makoto Miyashita; Junichi Hirabayashi

An extremely large amount of volcanic gas has been released since mid-August 2000 from the volcanic island of Miyakejima, Japan, after formation of a summit caldera of 1.6 km diameter. The volcanic gas emission was continuous with very little extrusive magma activity. Variation of the SO 2 emission rate was monitored by repeated measurements with an airborne correlation spectrometer. In December 2000, the SO 2 emission rate averaged for the month peaked at 54 kt/d, which is twice the global SO 2 emission rate from nonerupting volcanoes evaluated before this activity. The SO 2 emission rate gradually decreased, almost linearly when plotted on a log scale, to 7 kt/d by the end of 2002, and then remained constant until at least December 2003. The total SO 2 emission amounts to 18 Mt, comparable to the emission of a large explosive eruption such as Pinatubo in 1991. A theoretical evaluation, based on the model of magma convection in a conduit, suggests that extremely large volcanic gas emissions can be caused by formation of a magma pathway with a slightly larger diameter than exists in common systems, because the magma-transport rate is proportional to the fourth power of the conduit radius. Because volcanic gas emissions were initiated by formation of a summit collapse caldera of 1.6 km diameter, the creation of a large magma-conduit system through fractures formed during caldera collapse is likely the underlying cause of the extremely large volcanic gas emissions from the volcano.