Activity has been observed at six submarine volcanoes in the Volcano Island chain in 1978 and 1979 (figure 1). Discolored water has often been visible . . . during frequent overflights by JMSDF and JMSA aircraft. [Discolored water was noted, in an included table of observations, by almost every overflight during January 1978-July 1979 (see table 1 below).]

Figure 1. Map showing Japan and the Volcano Island chain. Volcanoes active in 1978 or 1979 are indicated by black squares. Courtesy of JMA.

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: JMSA, Tokyo; JMA, Tokyo.