During an overflight on 9 March the Japan Coast Guard (JCG) noted continuous activity from the central vent at Nishinoshima, including an ash plume rising as high as 1 km. Ejected material landed near the cone’s base. Lava from the NE side of the central vent flowed 1 km N and into the sea. Steam plumes rose along the E coast where lava entered the sea. Lava also effused from a vent on the SW flank of the cone. Discolored yellow-green water was visible offshore to the W, N, and E. Sulfur dioxide emissions had increased since 17 February measurements. The marine exclusion zone was defined as a radius of about 2.6 km from the island.

Geological Summary. The small island of Nishinoshima was enlarged when several new islands coalesced during an eruption in 1973-74. Another eruption that began offshore in 2013 completely covered the previous exposed surface and enlarged the island again. Water discoloration has been observed on several occasions since. The island is the summit of a massive submarine volcano that has prominent satellitic peaks to the S, W, and NE. The summit of the southern cone rises to within 214 m of the ocean surface 9 km SSE.

Source: Japan Coast Guard