Sulfur dioxide emissions during the 2011 eruption of Shinmoedake volcano, Japan

Sulfur dioxide flux of the 2011 Shinmoedake eruption, which started in January 2011, was measured repeatedly throughout its activity. The SO2 flux, which was greater than 10,000 ton/day during the earlier stages, quickly decreased to below 1,000 ton/day over the following two weeks. The flux decreased gradually thereafter to about 200 ton/day by the second half of March 2011. It continued at that level until April 2012. To evaluate the amount of SO2 emitted during the 2011 eruption, daily SO2 flux was estimated based on direct observations and other information. The total SO2 emissions were about 280 kt, with nearly two-thirds emitted during the first two weeks. The degrees of excess degassing estimated for the lava accumulation stages were low (2.3-2.9), suggesting a small pre-eruptive bubble content in the magma. High SO2 flux observed immediately after the sub-Plinian eruptions and before rapid lava effusion is probably related to the extensive degassing of magma in the conduit, which probably played a role in the transition from explosive to effusive eruption. An abrupt and large flux decrease occurred around February 8, 2011, which might be attributable to depletion of pre-eruptive bubbles in the magma.