Report on Barren Island (India) — August 1991

Bulletin of the Global Volcanism Network, vol. 16, no. 8 (August 1991)
Managing Editor: Lindsay McClelland.

Barren Island (India) Basaltic andesite lava from flank vent reaches sea

Please cite this report as:

Global Volcanism Program, 1991. Report on Barren Island (India). In: McClelland, L (ed.), Bulletin of the Global Volcanism Network, 16:8. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN199108-260010.

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Barren Island

India

12.278°N, 93.858°E; summit elev. 354 m

All times are local (unless otherwise noted)


Lava production continued from the subsidiary vent on the NE face of the volcanic cone, 80 m below the main crater, during a visit on 26 June. Incandescent material was ejected in a pulsating fountain, to [80] m height, more intensely than during the previous visit on 16 May. Satellite monitoring had indicated a temperature of 1,100°C around the vent on 6 May. A dark plume rose 300-400 m from the crater of a large spatter cone that had formed at the eruptive vent. The main crater remained quiet. The lava flow observed in May had bifurcated, with one branch extending along the NW and W valleys, and a new branch extending S. By 26 June, lava had reached the sea at the boat landing near the NW corner of the island (~1.2 km from the vent); during the 16 May fieldwork, the lava front was still 200 m from shore. Vigorous boiling and thick jets of steam were observed for 100 m along the shore. Studies of water near the shore indicated a considerable decrease in pH, and visibility dropped to

The following is from a GSI report on lava chemistry and petrography. "Thirteen chemical analyses on samples of recent lava collected on 16 May indentify the rocks as basaltic andesites (table 1). They are porphyritic with phenocrysts of plagioclase (dominant; some grains show labradorite composition), with minor clinopyroxene (augite) and forsteritic olivine, set in a fluidal [intersertal] groundmass of brown glass, plagioclase microlites, and Fe-Ti oxides. The amount of mafic phenocrysts is relatively low. The average ratio between phenocryst and groundmass components is around 0.44. The volumetric composition of the phenocrysts indicates: 72% plagioclase, 17% clinopyroxene, and 11% olivine; while the groundmass consists of 43% plagioclase microlites, 37% glass, and 20% Fe-Ti oxides. The amount of glass in the groundmass is highly variable, exceeding 70% in some sections. There is a complete lack of amphibole grains, in both the phenocrysts and [in] the groundmass."

Table 1. Range and average compositions from 13 chemical analyses of recent lava erupted from Barren Island, collected 16 May 1991. Courtesy of the GSI.

Element Range (%) Average (%)
SiO2 54.96-56.33 55.64
TiO2 1.13-1.18 1.15
Al2O3 17.66-18.62 18.20
Fe2O3 5.39-9.44 6.32
FeO 0.36-4.23 2.36
MnO 0.18-0.19 0.185
MgO 3.29-3.59 3.39
CaO 7.52-7.93 7.79
Na2O 1.75-2.19 2.01
K2O 0.58-0.79 0.69
P2O5 0.14-0.18 0.16
L.O.I. 0.16-0.48 0.31

Geologic Background. 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-trending volcanic arc extending between Sumatra and Burma (Myanmar). The 354-m-high island 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; S. Acharya, SANE.