Report on Kavachi (Solomon Islands) — September 1976
Natural Science Event Bulletin, vol. 1, no. 12 (September 1976)
Managing Editor: David Squires.
Kavachi (Solomon Islands) Island formation on 7 September; lava and block eruptions
Please cite this report as:
Global Volcanism Program, 1976. Report on Kavachi (Solomon Islands) (Squires, D., ed.). Natural Science Event Bulletin, 1:12. Smithsonian Institution. https://doi.org/10.5479/si.GVP.NSEB197609-255060.
8.991°S, 157.979°E; summit elev. -20 m
All times are local (unless otherwise noted)
Much of the following information was received by R.B.M. Thompson from Solair pilots Bruce Kirkwood, Robert Snape, and Eric Cooper. Fountains of water and rock continued at least through 4 September, reaching about 60 m height. No information is available for 5 September.
6 September. A resident of Gatukai Island (NE of Kavachi) noted a change of the eruption column from white steam and spray to "smoke" during the afternoon (figure 2).
|Figure 2. Airphoto of Kavachi, taken 6 September 1976 (airplane wing at left of photo). Courtesy of R.B.M. Thompson.|
7 September. A morning overflight revealed that a rubble pile had reached the surface. Heavy swells were breaking over the rubble, which continuously emitted steam and "smoke", accompanied by bursts of rocks. The maximum height reached by the ejecta was about 90 m. By 1600, a cone, extruding lava, extended 1.5-3 m above the surface.
8 September. At 1300 the cone was about 9 m above sea level and 40 m across (at sea level). A red glow from the cone's central vent was clearly visible in bright sunlight. Lava was pouring over the NW rim, which was about 3 m lower than the rest of the cone. Eruptions of blocks, reaching more than 150 m height, occurred at approximately 1-minute intervals. Some of the blocks were fairly large and some were glowing. Brown and white "smoke" was emitted continuously.
9 September. At 1030 the volcano was less active than the day before. Lava surged up and down, overspilling the NW rim into the sea on the larger upsurges. Eruptions of blocks, ash, and vapor, occurring every 1-2 minutes, were less intense than on the 8th. The island appeared to be breaking up, most rapidly on the NW, the prevailing wave direction. The maximum height of the cone above sea level was about 6 m. The surrounding water was discolored by a brownish scum. Photographs were taken by seismological observer Deni Tuni (figure 3).
|Figure 3. Airphoto of Kavachi, taken 9 September 1976 by Deni Tuni. View is from the E. Note the bombs being emitted from the vent. Courtesy of R.B.M. Thompson.|
Geologic Background. Named for a sea-god of the Gatokae and Vangunu peoples, Kavachi is one of the most active submarine volcanoes in the SW Pacific, located in the Solomon Islands south of Vangunu Island about 30 km N of the site of subduction of the Indo-Australian plate beneath the Pacific plate. Sometimes referred to as Rejo te Kvachi ("Kavachi's Oven"), this shallow submarine basaltic-to-andesitic volcano has produced ephemeral islands up to 1 km long many times since its first recorded eruption during 1939. Residents of the nearby islands of Vanguna and Nggatokae (Gatokae) reported "fire on the water" prior to 1939, a possible reference to earlier eruptions. The roughly conical edifice rises from water depths of 1.1-1.2 km on the north and greater depths to the SE. Frequent shallow submarine and occasional subaerial eruptions produce phreatomagmatic explosions that eject steam, ash, and incandescent bombs. On a number of occasions lava flows were observed on the ephemeral islands.
Information Contacts: R. Thompson, Geological Survey, Honiara.