The Japan Meteorological Agency (JMA) reported that the number of small volcanic earthquakes at Miyakejima decreased after a peak on 17 June that led to an Alert Level change. On 17 June the number of small volcanic earthquakes with epicenters directly below the summit crater totaled 59, and uplift near the summit was detected in tiltmeter data. During 18-23 June the number of daily earthquakes decreased to 0-4 earthquakes per day and no changes in tilt were detected after 18 June. The Alert Level remained at 2 (on a 5-level scale) and the public was warned to be cautious in areas inside the Oyama Ring Road.

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. Numerous craters and vents, including maars near the coast and radially oriented fissure vents, are present on the flanks. Frequent eruptions have been recorded 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 CE, activity has been dominated by flank fissure eruptions sometimes accompanied by minor summit eruptions. A 1.6-km-wide summit crater was slowly formed by subsidence during an eruption in 2000.

Source: Japan Meteorological Agency (JMA)