Report on Izu-Torishima (Japan) — 7 August-13 August 2002
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 7 August-13 August 2002
Managing Editor: Gari Mayberry
Please cite this report as:
Global Volcanism Program, 2002. Report on Izu-Torishima (Japan). In: Mayberry, G (ed.), Weekly Volcanic Activity Report, 7 August-13 August 2002. Smithsonian Institution and US Geological Survey.
30.484°N, 140.303°E; summit elev. 394 m
All times are local (unless otherwise noted)
On 11 August around 1530 a ship sailing near Tori-shima reported to the Japan Coast Guard that they observed white smoke rising from the summit of the volcano. JMA reported that an aerial inspection the following day during 1145-1245 revealed an ash-laden plume rising from the SW crater wall of the summit crater (Iwoyama) and white plumes emanating from the S to SE portion of the crater wall. Vigorous ash plumes rose 200-300 m above the crater every few minutes, drifted W, and ultimately reached a height of 1 km a.s.l. The summit area and the middle slope NNW of the summit were covered with ash-fall deposits. Discolored sea water extended 20 km W of the island. Tori-shima is not inhabited by humans, but an endangered albatross species lives there.
Geologic Background. The circular, 2.7-km-wide island of Izu-Torishima in the southern Izu Islands is capped by an unvegetated summit cone formed during an eruption in 1939. Fresh lava flows from this eruption form part of the northern coastline of the basaltic-to-dacitic edifice. The volcano is referred to as Izu-Torishima to distinguish it from the several other Japanese island volcanoes called Torishima ("Bird Island"). The main cone is truncated by a 1.5-km-wide caldera that contains two central cones, of which 394-m-high Ioyama is the highest. Historical eruptions have also occurred from flank vents near the north coast and offshore submarine vents. A 6-8 km wide submarine caldera lies immediately to the north.