The GSI visited . . . again on 11 May. At that time only the central conduit was vigorously active, with continuing phreatomagmatic eruptions. The vents near the S crater wall and S foot of the volcanic cone, sites of strong activity on 8 March (20:04), were inactive. Seawater temperature at the only landing site ranged widely from 38 to 70°C, and atmospheric temperatures were 70 and 55°C at distances of ~10 and 15 m, respectively, from the advancing lava front.

Fire fountains from the central vent rose to a height of ~150 m. Dark fumes sometimes attained a height of ~400 m. The eruption column was ~100 m across and fed a mushroom-shaped cloud over the crater region. Approximately 90% of the activity from the main conduit was explosive, but eruptive pulses occurred without rumbling sounds. Eruption column fall-out consisted of profuse quantities of cinder, ash, and rock debris.

A new vent at the W foot of the cone, ~1.5 km ESE of the landing site, exhibited continuous emission of very liquid lava and bluish fumes, but no explosive activity. The lava erupted from this vent formed a 15-m-high and 70-m-wide flow front that was slowly advancing W towards the landing site, threatening to engulf it. The lava flow was advancing at a rate of ~2 m/hour on 11 May.

The 1995 lava is a basalt (50.4-52.3% SiO₂ and 2.5-3.1% Na₂O + K₂O) with mega-xenocrysts of plagioclase, clinopyroxene, and olivine in decreasing abundance. The groundmass is composed of glass, plagioclase microlites, and Fe-Ti oxides showing intersertal to very rare fluidal texture. The 1995 lava differs from the lava erupted in 1991 in its absence of wall-rock xenoliths, its greater abundance of mega-xenocrysts, and its groundmass texture. Major elements were determined for ten samples of January 1995 lava. Compared to 1991 lavas (13 samples), the 1995 basalt is deficient in SiO₂ and K₂O (although total alkali values are similar), but enriched in Al₂O₃, CaO, and MgO.

Geological Summary. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

Information Contacts: Director General, GSI; Deputy Director General, GSI Eastern Region.