Report on Miyakejima (Japan) — 16 May-22 May 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 16 May-22 May 2001
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2001. Report on Miyakejima (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 16 May-22 May 2001. Smithsonian Institution and US Geological Survey.
34.094°N, 139.526°E; summit elev. 775 m
All times are local (unless otherwise noted)
Based on information from the JMA, VRC reported that no ash clouds had been observed at Miyake-jima since the 19 March eruption. They also reported that steam plumes with abundant SO2 were continuously emitted from the summit caldera to 0.5-2 km above the caldera rim. Continuous SO2 emission released as much as 33,000 to 46,000 tons of SO2 per day. Low-level seismic activity continued and a M 2.8 earthquake occurred on 7 May. Global positioning system (GPS) measurements showed steady, continuous deflation of the volcano though the rate was lower than before September 2000. During air inspections very small collapses of the caldera rims were occasionally seen.
Geologic Background. 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.