Gemini-Oscostar Volcano — Vanuatu

The submarine Gemini-Oscostar volcanic field lies near the southern end of the Vanuatu (or New Hebrides) Volcanic Arc, ~100 km S of Aneityum Island. Water discoloration and bursts of very dark water were observed from Oscostar seamount (also known as Eastern Gemini) from a passing ship on 18 February 1996. Overflights as late as 22 February noted periodic explosions that ejected black material to about 20 m above sea level. It consists of an elongated NNE-SSW-trending ridge of submarine volcanoes with satellitic cones. Several basaltic samples and one andesitic rock dredged in 1989 were described as glassy, vesicular, and extremely fresh.