JMSA [and JMSDF have] continued frequent monitoring flights over several known submarine volcanoes (table 1). On almost all overflights discolored sea water was seen around Fukutoku-Okanoba, the most active submarine volcano in this area.

Table 1. Volcanic activity at three sites (Fukutoku-Okanoba, Minami-Hiyoshi, and Fukujin) in the Volcano Islands, January 1978-December 1982, detected by JMSA and JMSDF monitoring flights. Activity indicated as D = Discolored water; N = No discolored water, - = No overflight, ? = not reported. This table combines data from reports in 1979 (4:7), 1980 (5:4, 5:11, and 5:12), 1981 (6:10), and 1982 (7:9, plus additional data not published in the Bulletin).

Geological Summary. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the island of Minami-Ioto. Water discoloration is frequently observed, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.

Information Contacts: JMA, Tokyo.