A discolored belt was observed on the sea surface at this site on 27 and 28 March. Similar activity had been reported at Minami-Hiyoshi beginning 10 January, but had declined by 24 January.

[The JMA provided additional chronological information on the 1977 discolorations. They were observed by the crew of JMSA aircraft on 10-14, 17-18, 21, 26, and 28-29 January, and 3-4, 11, 18, and 24-25 February. JMSDF crews continued to see them on 10, 11, and 17 March, but saw no discolorations on 18, 19, 21, 23, and 25 March. Discolorations were again visible on the next 3 days (26-28 March) during JMSDF flights, but were not seen on 6 April by a JMSA flight nor by any subsequent flights that year.]

Geological Summary. Periodic water discoloration and water-spouting have been reported over the Minami-Hiyoshi submarine volcano since 1975, when detonation sounds and an explosion were also reported. It lies near the SE end of a coalescing chain of youthful seamounts, and is the only vent with recorded activity. The reported depth of the summit of the trachyandesitic volcano has varied between 274 and 30 m. The morphologically youthful seamounts Kita-Hiyoshi and Naka-Hiyoshi lie to the NW, and Ko-Hiyoshi to the SE.

Information Contacts: JMA, Tokyo.