Summit at 2-3 m depth; no visible fumarolic activity; sulfur odor

"Kuwae is a mainly submarine caldera (~10 x 5 km) that, according to ¹⁴C ages, Tongan folklore, and reconnaissance fieldwork (Garanger, 1972; Crawford, 1988), is probably very young (~1,500 A.D.). The caldera is located between Epi, Laika, and Tongoa islands in the central part of Vanuatu. During the ORSTOM-CALIS cruise in May 1991, detailed bathymetric and magnetic surveys of the collapse structure were made, and data are presently under analysis. August fieldwork was carried out on Tongoa and Laika Islands in order to study caldera eruption products, their composition, and their age. Several ignimbrite units, including non-welded ash and pumice flow deposits, and thick, complex sequences of poorly-welded to densely-welded tuffs, have been discovered. C14 ages will be determined for charcoal samples from these deposits.

"During the last century, the caldera's active Karua volcanic cone has emerged at least six times, in 1897, [1901], . . . 1948, [1949], 1959, and 1971. Each period of activity was accompanied by explosions. The ephemeral island reached a maximum size of 100 m tall and 1.5 km in diameter in 1949. On 6 August, during a visit by speedboat, the submerged summit area was 50-70 m large at 2-3 m depth. No fumarolic activity was observed despite a strong sulfur smell." [Turbulence and discolored sea water were observed in 1971-74 and 1977.]

References. Crawford, A.J., 1988, Circum-Pacific Council for Energy and Mineral Resources: Earth Science Series, v. 8.

Garanger, J., 1972, Publication de la Société Océanistes, no. 30.

Information Contacts: C. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM,Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.

Information is preliminary and subject to change. All times are local (unless otherwise noted)

February 1971 (CSLP 23-71)

Explosive eruption on 22 February builds island

Card 1137 (24 February 1971) Explosive eruption on 22 February builds island

The following cable was received . . . on 23 February. "Submarine volcano Karua . . . erupted strongly 22 February 1971. Eruption commenced with explosions at about 0730 local time. Activity increased throughout afternoon. Eruption occurring from three closely spaced vents from which a mushrooming ash cloud rose strongly through the cloud base at about 1,000 m. Some large blocks of rock thrown up by explosions occurring several times each minute. Activity still strong at 1740 local time, but no visible sign of activity from village 5 km away at 1800. By 1030 23 February no activity at all except very minor water turbulence. Island of cinders about 200 x 70 m built to about 1 m above high tide mark. Surface of island studded with angular blocks up to 6 m³."

Information Contacts: D.I.J. Mallick, New Hebrides Geological Survey, Port Vila, New Hebrides.

March 1971 (CSLP 23-71)

Eruption ends quickly; felt seismicity

Card 1142 (01 March 1971) Eruption ends quickly; felt seismicity

"Although activity of . . . 22 February was reported to be much stronger than the last time an island was formed in 1959, eruption ceased quickly after only 1.5 hours. No recurrence of volcanic activity to 1000 local time 26 February, but series of earthquakes felt on Tongoa 5 km S of Karua. First shock about 2100 local time 24 February, intensity MM 6-7, duration half-minute. Some damage to older native houses, cracking of at least one sunken concrete water tank and collapse of section of coastal cliff. No casualities reported. Second shock about 2115 duration 10 seconds. Series of smaller shocks during night 24/25 February. Aerial reconnaissance 23 February regrettably made after all activity ceased."

Information Contacts: D.I.J. Mallick, New Hebrides Geological Survey, Port Vila, New Hebrides.

July 1971 (CSLP 23-71)

Report of island visit 10 days after 22 February eruption

Card 1247 (02 July 1971) Report of island visit 10 days after 22 February eruption

"On 22 February 1971, at about 0800, a known area of crustal instability began to erupt [at Karua], giving off clouds of steam and shooting black masses of cinder, ash, and pre-solidified crust up to 600 feet into the air. The activity intensified during the day with increasingly frequent explosions and clouds of dust being formed. At the height of the activity the eruption covered an area over one mile in diameter. Accompanying the volcanic explosions was tremendous thunder and lightning, precipitated by the intense heat of the eruption which led to condensation and great atmospheric instability. Then, very suddenly, at about 1800, the activity died away.

"Ten days after the eruption, I went to the newly-formed land mass and found an almost moon-like terrain. The islet was flat with large boulders strewn about the surface. A few hot water pools were in evidence and there was a distinct smell of sulphur in the air. Underfoot the ground was still warm and when kicked smoke appeared from the ash and cinders of which the island was composed. On one side the sea was shallow for some distance but too hot to touch. This is the actual crater and the nucleus of all the activity. I estimate the island to be over half a mile wide and in the opinion of local pilots is easily large enough to land a light plane upon.

Information Contacts: Richard J. Ellis, c/o B.D.A. Lakatoro, Lakatoro, New Hebrides.

February 1977 (BVE 17)

Bubbling and water discoloration

"Increased activity at this submarine was reported on 1 February when the sea above was apparently bubbling and a yellow discoloration was evident. However, when visited on 25 February only a greenish stain on the surface of the sea and a faint sulphurous odour were noted."

Reference. Volcanological Society of Japan, 1979, Bulletin of volcanic eruptions no. 17: Annual report of the world volcanic eruptions in 1977: International Association of Volcanology and Chemistry of the Earth's Interior, IUGG, p. 27.

Information Contacts: A. MacFarlane, Geological Survey Department, Vila, New Hebrides.

July 1991 (BGVN 16:07) Cite this Report

Summit at 2-3 m depth; no visible fumarolic activity; sulfur odor

"Kuwae is a mainly submarine caldera (~10 x 5 km) that, according to ¹⁴C ages, Tongan folklore, and reconnaissance fieldwork (Garanger, 1972; Crawford, 1988), is probably very young (~1,500 A.D.). The caldera is located between Epi, Laika, and Tongoa islands in the central part of Vanuatu. During the ORSTOM-CALIS cruise in May 1991, detailed bathymetric and magnetic surveys of the collapse structure were made, and data are presently under analysis. August fieldwork was carried out on Tongoa and Laika Islands in order to study caldera eruption products, their composition, and their age. Several ignimbrite units, including non-welded ash and pumice flow deposits, and thick, complex sequences of poorly-welded to densely-welded tuffs, have been discovered. C14 ages will be determined for charcoal samples from these deposits.

"During the last century, the caldera's active Karua volcanic cone has emerged at least six times, in 1897, [1901], . . . 1948, [1949], 1959, and 1971. Each period of activity was accompanied by explosions. The ephemeral island reached a maximum size of 100 m tall and 1.5 km in diameter in 1949. On 6 August, during a visit by speedboat, the submerged summit area was 50-70 m large at 2-3 m depth. No fumarolic activity was observed despite a strong sulfur smell." [Turbulence and discolored sea water were observed in 1971-74 and 1977.]

References. Crawford, A.J., 1988, Circum-Pacific Council for Energy and Mineral Resources: Earth Science Series, v. 8.

Garanger, J., 1972, Publication de la Société Océanistes, no. 30.

Information Contacts: C. Robin and M. Monzier, ORSTOM, New Caledonia; M. Lardy and C. Douglas, ORSTOM,Vanuatu; C. Mortimer, Dept of Geology, Mines, and Rural Water Supply, Vanuatu; J. Eissen, ORSTOM, France.