Report on Miyakejima (Japan) — 18 February-24 February 2004
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 February-24 February 2004
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2004. Report on Miyakejima (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 18 February-24 February 2004. Smithsonian Institution and US Geological Survey.
34.094°N, 139.526°E; summit elev. 775 m
All times are local (unless otherwise noted)
Relatively high amounts of gas discharge continued at Miyake-jima through 22 February. The sulfur-dioxide emission rate has been nearly constant (4,000-9,000 tons per day) since October 2002. Due to volcanic unrest, residents of the volcanic island have been evacuated since September 2000.
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.
Source: Geological Survey of Japan