Smithsonian Institution, Bulletin of the Global Volcanism Network Volume 21, Number 1, January 1996 Sakura-jima (Japan) Explosive eruptions and ashfalls continue Sakura-jima Kyushu, Japan 31.58 N, 130.67 E; summit elev. 1,117 m Minami-dake crater was slightly active throughout January. The monthly total number of eruptions was 60, including 42 explosive ones. At the seismic station 2.3 km NW of Minami-dake crater (Station B), 601 earthquakes and 684 tremors were recorded. The highest ash plume of the month rose 2,300 m above the summit crater on the 21st. Ashfall measured at the Kagoshima Local Meteorological Observatory, 10 km W form the crater, was 41 g/m^2. The VRC noted that there were more than 200 eruptions in 1995; total amount of erupted material was estimated at 3-4 million tons by the Sakurajima Volcanological Observatory, Kyoto University. The latter has been observing continuous uplift on the N side of the volcano, implying accumulation of magma beneath the volcano. Sakura-jima volcano, located within the Aira Caldera, lies in the N half of Kagoshima Bay. The volcano formed an island that was joined to the Osumi Peninsula during an eruption in 1914. Frequent historical eruptions have deposited ash on the city of Kagoshima, which is located across Kagoshima Bay 7 km W of the summit. Sakura-jima=FEs frequent eruptions present a significant hazard to air transportation using Kagoshima=FEs airport. Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1- 3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan; VRC (see Suwanose- jima). Smithsonian Institution, Bulletin of the Global Volcanism Network Volume 21, Number 1, January 1996 Kuju (Japan) Earthquake swarm and eruptions on 13-14 January; continuous plume Kuju Kyushu, Japan 33.08 N, 131.25 E; summit elev. 1,788 m Frequent earthquakes during the night of 13 January and through the next morning were centered 3-4 km NW of the Hosho dome near Sujiyu spa; eruptions caused minor ashfall around the volcano. Instruments recorded 526 earthquakes during the 13-14 January episode, some of which were felt by local residents. Some earthquakes on 27 January were centered SW of the active dome. Overall, there were 861 earthquakes detected in January, but no tremor. The plume height remained at 100-300 m throughout most of the month. Scientists at the University of Tokyo noted that vesiculated glass was again observed in the 13 January material, and deflation near the crater area was continuing. The Kuju volcano group consists of more than 10 stratovolcanoes and lava domes NE of Aso caldera. Hosho lava dome is situated near the center of the 20 x 15 km complex. The Geological Survey of Japan reports historical phreatic or hydrothermal eruptions at Kuju in 1662, 1675, and 1738. Molten sulfur effusion may have occurred in 1675 and 1738. The youngest known magmatic activity, ~1.7 ka, produced the Kuro-dake lava dome at the E end of the complex, accompanied by pyroclastic flows. Information Contacts: JMA (see Sakura-jima); VRC (see Suwanose- jima). Smithsonian Institution, Bulletin of the Global Volcanism Network Volume 21, Number 1, January 1996 Fukutoku-okanoba (Japan) Discolored seawater observed for the second time in three months Fukutoku-okanoba Volcano Islands, Japan 24.28 N, 141.52 E; summit elev. -14 m (submarine) On 12, 22, and 23 January, an aviator from the Japan Marine Safety Agency (JMSA) reported distinct discoloration of seawater to yellowish green. Similar discoloration was seen during 25-28 November 1995 (Bulletin v. 20, no. 11/12). Prior to that, discolored seawater was last seen at this location in September 1993. Water discoloration has often been observed at Fukutoku-okanaba (Shin-Iwo-jima), 5 km NE of Minami-Iwo-jima island. Eruptions produced ephemeral islands in 1904, 1914, 1974, and 1986. A dark plume rose above the water surface in November 1992, and floating pumice was observed. Information Contact: JMA (see Sakura-jima). Smithsonian Institution, Bulletin of the Global Volcanism Network Volume 21, Number 1, January 1996 Minami-Hiyoshi (Japan) Discolored seawater plume 6 km long Minami-Hiyoshi Volcano Islands, Japan 23.507 N, 141.905 E; summit elev. -30 m (submarine) On 12 January, an aviator from the JMSA observed seawater discolored to yellowish green in an area 500 m wide and 6 km long, flowing from Minami-Hiyoshi seamount to the S. Discolored water was last observed in February 1992 (Bulletin v. 17, no. 2). Periodic water discoloration and water-spouting has been reported over this submarine volcano since 1975, when detonations and an explosion were also reported. Located 90 km SE of Minami-Iwo- Jima, Minami-Hiyoshi lies near the SE end of a coalescing chain of youthful seamounts, and is the only historically active vent. The morphologically youthful seamounts Kita-Hiyoshi and Naka- Hiyoshi lie to the NW, and Ko-Hiyoshi to the SE. Information Contact: JMA (see Sakura-jima). Smithsonian Institution, Bulletin of the Global Volcanism Network Volume 21, Number 1, January 1996 Unknown Submarine Activity (W Pacific Ocean) Acoustic signals in late January; source not locatable Unknown Submarine Activity western Pacific Ocean The JMA Ocean Bottom Seismograph off the Boso Peninsula (E of Tokyo) detected T-phase-like signals after 22 January, and clear T-phase signals on 27 January (figure 8). According to tentative analyses of arrival times at the detectors, the signals were interpreted to have propagated from the S. As of mid-February, JMA had not determined a specific source for these signals. However, discolored seawater was observed above two submarine volcanoes in the Volcano Islands during January: Minami-Hiyoshi on 12 January, and Fukutoku-okanoba on 12, 22, and 23 January. Information Contact: JMA (see Sakura-jima). Figure 8. Example of T-phase signals (spikes) detected by the Ocean Bottom Seismograph off the Boso Peninsula, Japan, 27 January 1996. Courtesy of JMA.