News

New island in Andaman sea?

K. S. Jayaraman

doi:10.1038/nindia.2009.131 Published online 11 May 2009

The Barren Island volcano.

© Indian Navy

After remaining quiet for a year, the Barren Island volcano in the Andaman sea has started spewing lava and ash, according to Indian geologists who have returned from a field trip six weeks ago.

Lava falling into the sea is actually building a new island, Hetu Sheth, a geologist at the Indian Institute of Technology in Mumbai and a member of the expedition team told Nature India. "The island is growing but imperceptibly slowly."

"Barren Island is evidently a very active volcano meriting close study," says Jyotiranjan Ray, a geochemist at the Physical Research laboratory (PRL) in Ahmedabad. Ray, another team member, had earlier led two field trips to the volcano in January 2007 and April 2008.

The researchers said that rising steam plume can be seen from a distance of 6 km. Also visible are dark ashes bursting out of the central cone and the glowing lava, at a few places on the slope, particularly at dark. About 135 km from Port Blair and hardly three kilometres across, Barren Island is the only active volcano in Indian territory (Narcondam Island also in Andaman Sea is not known to have been active in recent times).

The submarine volcano rises about 2.5 km above the sea floor with only a 400 meter 'cone' visible above sea level.Despite its name, the island is not all barren — it has a lush jungle on its southern and eastern sides with some freshwater springs and goats grazing. But it is uninhabited by man. From the first recorded eruption in 1787, Barren Island volcano is known to have erupted 30 times until 1832. Geologists were surprised when it began to smoke in 1991 after a long gap of 160 years.

Two more eruptions in rapid succession in 1994-95 and 1995-96 and a fourth on-going one 'suggest considerable excitement in store for the volcanological community', the scientists reported1. "If activity persists, new lava flows are not unexpected," they said.

In an eye witness account of their latest observation on 30 March 2009, the scientists report," The volcano's central cinder cone was continuously emitting dark ash clouds every few seconds from its central crater. The pre-existing valley between the cinder cone and the northern caldera wall has been filled up by deposition of new ash in the past year, which has enabled the new, active lava flow to completely abandon the westerly route (taken by all historic and recent lava flows) and to reach the sea over the northern caldera wall. The new, channelised lava flow is currently descending at a steep angle over the northern caldera wall's outer cliff face, and into the sea."

The new lava flow has built a structure resembling an alluvial fan along the shore. The scientists said they were able to reach this fan to collect lava samples 'in an inflatable rubber boat carefully circumventing the steam plume and through seawater which was very hot (an estimated ~60–70°C)'. Ray said the sample studies will form the subject of their next paper. "We would like to find out how old the volcano is. We will analyse the rock fragments using different isotopes to see geochemical changes that have taken place inside the Earth's mantle. We will know if the eruptions are of explosive nature or not, and the magma coming from the bowels of the Earth rises continuously to the top or makes a stopover on the way."

Indian geologists are concerned why Barren Island has suddenly become active in the last few years after being dormant since 1832. The Andaman Trench, the birth place of vicious earthquakes, is only 250 km west of the volcano, Ray said. "We would like to know how the renewed activity of the volcano would affect the tectonics of this region."

The researchers report that their study of the volcanology and eruptive styles of the Barren Island volcano would lay the ground for detailed geochemical and isotopic work. "It would help us with clues to the future eruptive activity of the volcano as well as potential volcanic hazards," they said.

Sheth notes there have been very few studies on the Barren Island volcano, because access to the place is possible only with help of the Indian Coast Guards' vessels as the sea is almost always rough. Scientists from the Geological Survey of India (GSI) have been occasionally visiting the area after the first eruption in 1991 but there is no continuous monitoring, said Ray. The volcano has quite low visibility among international scientists as it falls in restricted zone and foreigners are prohibited, he said.

The scientists acknowledge that while their three field trips have provided 'the first volcanological synthesis of Barren Island volcano, there is ample scope for detailed work when current accessibility and logistic issues become less daunting.'

They recommend that besides geochemical and isotopic work on Barren Island volcanics — that is already in progress in their labs — future research in this region should include (i) more-continuous monitoring of the volcano by government agencies (ii) dredging and possibly drilling its undersea bulk and (iii) precise age-dating of its eruptive products with radioisotopic techniques.


References

  1. Sheth, H. C. et al. Volcanology and eruptive styles of Barren Island: an active mafic stratovolcano in the Andaman Sea, NE Indian Ocean. Bull. Volcanol. doi:  10.1007/s00445-009-0280-z