Renewed lava eruption reported from the only active volcano in Barren Island of Andaman Group of Islands in the Indian subcontinent on 28.05.2005 after a gap of 10 years.

Introduction
Barren island volcano along with the extinct Narcondam sub-aerial volcano, also In Andaman Islands lie on a young (less than 65 million years before present) volcanic belt. This belt dotted with about 60 active volcanoes extends from the extinct volcanoes like Mt. Popa and Mt. Wuntho of Central Myanmar to the active volcanoes of Sumatra, Java and Bali of Indonesia in southeast . Mt. Krakatoa in Sunda Strait caused the biggest and ravaging volcanic eruption in 19th Century, while Mt. Toba is known for the earth's largest volcanic eruption_during the last 1.8 million years.

Location
The Barren Island (Latitude 12.29°N, Longitude 93.85°E) is located 135 km ENE of Port Blair. Its exposed area is 10 sq km and it has a maximum elevation of 335 m above sea level. Narcondam is located 140 km NNE of Barren Island. Besides, Alcock (60 km east of Barren) and Sewell (200 km east of Car Nicobar Island) seamounts (extinct submarine volcanoes) in Andaman Sea also belong to this volcanic arc. This volcanic belt is closely associated with the subduction zone of dynamic Indian plate going under the Burmese plate along a deep fracture zone inclined at about 45° towards east.

First Cycle: Apparently Pre-historic based on circumstantial evidences
Second Cycle: Historic, 1787-1832 with Intermittent eruption
Third Cycle:
Phase 1 : March - October,1991
Phase 2 : December,1994 - May, 1995
Phase 3 : Commenced on 28th May,2005

What Geological Survey of India has done

Geological Survey of India carried out systematic studies of this active volcano through geological mapping on (1 :25,000 scale), recording chronological account of the state of the volcano for 1st and 2nd phase of the third cycle, physical and chemical characters of the volcanic products, geothermal activity in and around the volcano, magnetic survey and bathymetric (sea floor depth measurement) survey around volcano.

The Barren Island volcano is marked by a prominent cone with a main central crater that underwent change in shape, size and position from time to time in response to the phases of volcanic activities. Lava composition and depth of lava source as well as composition of parent mantle material, partial melting of which led to lava generation also showed systematic change over time. The first cycle witnessed submarine volcanic eruption of thick massive basaltic lava followed by alternating bedded lavas and agglomerate (rock fragments, resulting from explosive volcanism embedded in subordinate lava/ash) flows, with intermittent ash beds. At least 9 such eruptions with 50 cm - 5 m thick flows are recorded. Eruptions characterized by weak (Hawaiian type) and violent (Strombolian type) alternated. Both the second and third cycles are sub-aerial. The second cycle developed a 305 m high cinder cone with 60 m wide crater at cauldron center and three subsidiary vents. From the craters and vents huge volume of cinder, ash, volcanic bombs, lava fragments and debris and molten basaltic lava that solidified as scoriaceous and massive bodies, were erupted. A part of the massive lava was fissured, clinkery with ropy surfaces. The second phase of third cycle witnessed pulsative ejection activity along all the three subsidiary vents and the main crater leading to ultimate blowing off the upper part of volcanic cone.

The crater (400 m wide and 200 m deep), connected to an underlying vertical conduit pipe became five times larger than the historic one. The eruption gradually changed from strombolian type to exceptionally violent ejective (Plinian) type. The second phase of third cycle developed two subsidiary cones on southern side of the main crater. Brown gas and white steam gushed out of crater to 800 m height. The eruption was mainly of strombolian type with occasional explosions. The lava composition of third cycle varies from basaltic to andesitic ones.
Mineral composition, texture, glassy component of the volcanic rocks and lava fluidity / viscosity also changed over time.

Study of chemical parameters also confirmed the association of lava with submarine deep fracture zone related to plate tectonics. Trend of chemical change is generally normal with occasional reversal. Isotopic studies Indicate progressive shift of lava source In mantle towards greater depth with varying degrees of crustal contamination. The change of lava composition is related to varying degrees of partial melting of mantle material at about 100 km depth with subsequent lava differentiation through crystal fractionation and crustal contamination in various degrees.

As expected average heat flow over Barren Island is also abnormally high, about 10-12 times greater than that in adjacent areas.

Proposal of monitoring programme for the current third phase of the third cycle of Barren volcanism with multidisciplinary Input by the department has been chalked out.
The first team is expected to leave for the Island soon.