JMSA [and JMSDF have] continued frequent monitoring flights over several known submarine volcanoes (table 1). No discolored sea water has been observed near Minami-Hiyoshi since March 1978.

Table 1. Volcanic activity at three sites 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 4:7, 5:4, 5:11, 5:12, 6:10, and 7:9, plus additional 1982 data not published in the Bulletin.

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: JMSA, Tokyo; JMA, Tokyo.