Report on Kavachi (Solomon Islands) — March 1977
Natural Science Event Bulletin, vol. 2, no. 3 (March 1977)
Managing Editor: David Squires.
Kavachi (Solomon Islands) Eruptive activity observed in October 1976 and February 1977
Please cite this report as:
Global Volcanism Program, 1977. Report on Kavachi (Solomon Islands). In: Squires, D. (ed.), Natural Science Event Bulletin, 2:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.NSEB197703-255060.
8.991°S, 157.979°E; summit elev. -20 m
All times are local (unless otherwise noted)
Captain Stewart Evans approached Kavachi at 1500 on 13 October observing subsurface activity, but no island. He reports: "There was a definite eruption cycle during the first 2 hours of observation. Eruptions were fairly regular at approximately 15-minute intervals, and every 4th or 5th eruption was of noticeably greater magnitude. The cycle broke down about 1730. Frequent tremors were then heard and felt from the government survey vessel Wakio, stationed about 1 km from the vent. The tremors were felt at 5-10 minute intervals, but eruptions became less frequent and less violent. No eruptions were sighted for a 40-minute period while steaming away from the area at about 1800.
"The crest of the volcano was estimated to be less than 15 m below the surface and the sea was stained brown over an area approximately l00 m in diameter. The average height attained by ejecta (water and volcanic debris) was 10-15 m above the sea surface. The maximum height attained following the highest ejection was estimated at 30 m. Small waves were generated by each eruption. The average wave was 1 m high and radiated to about 500 m from the volcano. No bottom was found in a 365-m range on the echo sounder around a 1-km perimeter of the volcano."
"On 23 October, I observed a circular area of shallow (yellow-blue) sea surrounding a deep (dark blue) area, from an airplane above Kavachi. A yellow-blue area looking like a reef extended to the SE."
A study of 8 mm movies taken 9, 14, and 30 September, 1976 shows that red-hot blocks reached a maximum dimension of more than 1 m.
No other activity was reported until 0945 on 22 February, 1977 when Solair Chief Pilot Bruce Kirkwood reported plumes of spray and rock debris thrown upwards to about 60 m at intervals of 10 minutes.
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.