BackgroundOshima-Oshima is the small emergent summit of two overlapping basaltic-to-andesitic stratovolcanoes: Higashi-yama at the east end of the island is cut by a 2-km-wide caldera covered on its west side by Nishi-yama volcano.
The western cone partially collapsed during an eruption in 1741, creating a large horseshoe-shaped caldera breached to the north and extending from the summit down to the sea floor at the base of the volcano. This event produced a mostly submarine debris avalanche that traveled 16 km distance, and triggered a large tsunami. The tsunami devastated the coasts of Hokkaido, western Honshu, and as far as Korea, causing nearly 1500 fatalities.
The 1741 eruption was the largest in historical time at Oshima-Oshima and ended with the construction of a basaltic cinder cone at the head of the breached caldera. No eruptions have occurred since the last eruption in 1790, but seismic unrest under the volcano occurred in 1996.
See also: Sentinel hub | Landsat 8 | NASA FIRMS