Report on Miyakejima (Japan) — 14 February-20 February 2001
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 February-20 February 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, 14 February-20 February 2001. Smithsonian Institution and US Geological Survey.
34.094°N, 139.526°E; summit elev. 775 m
All times are local (unless otherwise noted)
The National Coordination of Volcanic Eruption Prediction committee reported on the status of Miyake-jima on 5 February. They stated that eruptions had not occurred since October 2000. High SO2 emission rates, ranging from 20 to 50 kilotons per day, continued to be detected. Most of the SO2 is considered to be from degassing magma. The temperature of the active crater increased in December 2000 and returned to normal by late January. Very little ground deformation has been detected. Seismic activity had been low since September, until low-frequency earthquakes occurred in late-January. Due to the high SO2 emission rates and the threat of lahars, volcanologists continue to closely monitor the volcano.
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.