Miyake-jima has remained restless since its summer eruption in 2000, with robust degassing ongoing through the week of 16-22 April. The SO2 gas output (flux) remained high (about 5,000-10,000 tons/day) as of March 2003. All people who lived on Miyake-jima island have been evacuated since September 2000 and SO2 fluxes around that time had reached extremely high values, over 80,000 tons/day. Although high SO2 flux continues, thus far in 2003 there has been no eruption.

Geological Summary. The circular, 8-km-wide island of Miyakejima forms a low-angle stratovolcano that rises about 1,100 m from the sea floor in the northern Izu Islands about 200 km SSW of Tokyo. The basaltic volcano is truncated by small summit calderas, one of which, 3.5 km wide, was formed during a major eruption about 2,500 years ago. Parasitic craters and vents, including maars near the coast and radially oriented fissure vents, dot the flanks of the volcano. Frequent historical eruptions have occurred since 1085 CE at vents ranging from the summit to below sea level, causing much damage on this small populated island. After a three-century-long hiatus ending in 1469, activity has been dominated by flank fissure eruptions sometimes accompanied by minor summit eruptions. A 1.6-km-wide summit caldera was slowly formed by subsidence during an eruption in 2000; by October of that year the crater floor had dropped to only 230 m above sea level.

Source: Akihiko Tomiya, Senior Research Scientist, Geological Survey of Japan