| |
A team of scientists from India and Italy carried out detailed geological, volcanological, geochemical and geothermal investigations in Barren Island between the 3rd and 6th of February, 2003. The scientific team led by D. Chandrasekharam, Department of Earth Sciences, Indian Institute of Technology, Bombay, India, consists of scientists from Italy - Piero Manetti, Director, Italian National Science Council (CNR) - Institute of Geosciences and Earth Resources (CNR-IGG), Orlando Vaselli, Department of Earth Sciences, University of Florence, Bruno Capaccioni, Institute of Volcanology and Geochemistry, Urbino University, and Mohammad Ayaz Alam, Research Scholar, Department of Earth Sciences, Indian Institute of Technology, Bombay, India. This is the first international scientific team ever camped in this uninhabited volcanic island.
The Journey
Indian Coast Guard vessel CGS Lakshmi Bai, commanded by Commander P. K. Mishra helped to ferry the team from Port Blair to Barren Island. This journey takes about five to six hours depending upon the condition of sea waves. Because of great depth of the sea around the island, it was not possible to anchor the vessel. The team, along with the field equipments and commodities, had to be ferried to the island from the vessel while it was still floating, by small motor driven rubber boat named “Gemini”. The Coast Guard Ship, after dropping us on the island left for the mainland and we were left alone to mend ourselves! The ship returned on 6th morning at 6 am to pick us back to the main land. On the way back a trip around the island was made by the vessel to see the steep seaward face of the prehistoric caldera wall, which was not accessible from the island.
Hot Dry Rock Province
Since the island is uninhabited, camping needs proper planning. There is no food or water available in the island. We took about 70 liters of drinking water, caned food, dry fruits, biscuits and fruits to support our stay for four days and three nights. We pitched two lightweight camp tents to rest during the night. One of us slept in the open, since the weather was quite pleasant. Dry plant roots and wood, which were washed ashore on the beach, became handy to make fire and cook our food. We had a psychological fear on the first night, since there is no possibility of getting any help what so ever, in the event of an emergency. There was no radio communication between us the mainland Coast Guard Office at Port Blair. We faced the problem of rats at night. There were more than a dozen rats around our camping site trying to steal our food and water. We managed to keep them away with our torchlights and campfire. But still there were occasions when one or two got into our tent, which created a nightmare for all of us! The night passed quietly and we regained 100% confidence the following day set out for fieldwork at 6.30 in the morning. Since the Island is located far in the east, the sun rises at about 4.30 a.m. giving us ample time to prepare our morning tea and breakfast and leave for field work early. We had bought all the required life supporting items at Port Blair the previous day of our journey. Since water was a very precious commodity, we were forced to ration water. At the end of our fieldwork just before getting into the ship we had about 5-6 liters of water left with us.
Fig. 1: Preliminary map of the Barren Island (Note: Detailed geological map is prepared and published in 2009)
The Island
Barren Island (Fig. 1) is the only active volcano in the Indian Subcontinent, located 135 km east of Port Blair in east Andaman Sea, and is a part of the Andaman and Nicobar chain of islands in the Indian Ocean. It lies on the Neogene Inner Volcanic Arc extending from the extinct volcanoes like Mt. Popa, Mt. Wuntho of Myanmar in the north to the active volcanoes of Sumatra and Java in the south ( Fig. 2).The volcano consists of a caldera, which opens towards the west, with a central polygenetic vent enclosing at least five nested tuff cones. Two spatter cones exist - one on the western flank of the central cinder cone and the other one on the southeastern flank of the central cone.
Fig. 2: Location of Barren Island over the volcanic arc (Modified after Rodolfo, 1969)
Volcanic Activity
The last volcanic activity in the island occurred during 1994-95. The lava flow of 1994-95 forms a tongue that extends up to a large distance into the sea (Photo 1) However, Indian Coast Guards informed the team of renewed activity (strong gas and, perhaps, lava emissions) in January 2000. Prior to 1994-95 eruptions, there was an eruption in 1991 after a prolonged period of quiescence (>200 years). During the historic time, this volcano erupted in 1852?, 1803-04, 1795, 1789, 1787. The island itself formed as a result of submarine eruption during Late Pleistocene time. The volcano is currently in a quiescent stage with continuing fumarolic activity. Steaming ground is visible at numerous places on the island.
Photo 1 : Flow of 1994-95 eruptions formed a tongue that extends up to the sea (Photo:D.Chandrasekharam)
The Work
According to the present observation, the structure of the central polygenetic cinder cone appears to have been developed during the 1994-95 activity, which left, as mentioned above, two visible spatter cones on its southern-eastern and western flanks. From these vents two lava flows (aa-type) were outpoured, both reaching the sea, during two distinct eruptive phases, separated by an ash-fallout. On the 5th of February we climbed the summit of the central cinder cone that shows strongly fumarolized (but not presently active) areas with layers of sulphur deposits (photo 2). The ascent to the crater was relatively difficult since the material is loose cinder and slope of the central cone is very steep (photo 3), neither magma nor gas emissions were observed at the bottom of the different cones. From the middle to the upper part of the western cone, the ground temperature is relatively high (>40oC) and steaming grounds are clearly visible at different sites. The fumarolic activity, with temperature up to 101oC, is mainly concentrated in the upper-inner part of the southern-western cone. Blue colour fumes (indicative of the presence of SO2) and smells of acid gases such HCl were not recorded.
Photo 2: Fumaroles deposit on top of the central cinder cone (Photo: D.Chandrasekharam)
Photo 3: Central cinder cone showing steep slope (Photo:D.Chandrasekharam)
From a volcanological point of view, the pre-caldera deposits are characterized by the presence of more than five lava flows (prehistoric?) separated by scoria fall beds and minor ash tuff and cinder deposits. The lava flows vary in thickness from 2 to 3 meters, while the other volcanic materials vary in thickness from one to four meters. These flows can be clearly seen towards the northern part of the main caldera. Towards the southeastern part of the inner caldera a 5 m wide, NNE-SSW trending dyke is observed. This feeder dyke is fine to medium grained and contains buff coloured olivine, green pyroxene and plagioclase phenocrysts. The northern and north-western part of the caldera has been mantled by a ~50 m thick monotonous sequence of breccias and tuff representing sin/post-caldera phreatic and hydromagmatic activities, whereas the products of a small littoral cone occur mainly towards the western side close to the camping site. The flows of the main caldera are highly porphyritic with phenocrysts of green pyroxene (~3 cm) and plagioclase feldspars. Several steam vents can be seen within the 1994-95 lava flows, some of these vents have been dried out and no steam is emanating at present.
Life on the Island
The outer and part of the inner caldera contains thick vegetation, which escaped the fury of the recent eruptions. Feral goats and rats dominate the island. Large number of rats lives in the island and become a menace at night. There have been reports on the life of the feral goat of this island. Earlier reports indicate that these goats adapted to a different kind of life and drink seawater to meet their water requirement. But during the present expedition two fresh water springs have been discovered towards the southeastern part of the caldera (N 12°15´55.3´´; E 93°51´05.5´´). This is possibly the fresh water source for the goats living in this island. The water from the springs is potable as indicated by the chemical analysis of the water samples collected from these springs.
Volcano Profile
Barren Island Volcano (12.29° N, 93.87° E), Andaman Islands, Indian Ocean (India). Summit elevation 305 m. Eruptions of Barren Island Volcano: 2000 (?), 1994-95, 1991, 1852 (?), 1803-04, 1795, 1789 and 1787.
Remarks
The longitude shown by all the earlier maps of the island appearing on various websites and published literature is wrong. Based on the current work a revised detailed geological map is being prepared and will be published later.
Post Script
What makes this expedition unique is that it was the first time that a team of international scientists camped on the Barren Island and carried out the investigations during their stay. One needs several security clearances from several Departments in the Government to visit in the island. The only mode of transport to the island is through the Indian Coast Guard vessels. For the present team it took nearly one year to get such clearances. Further since no team camped in the Island, any one does not know logistic problems, which are foreseen. All earlier expeditions to this island were one-day exercise - the geologists (mainly from the Geological Survey of India) travel by night, reach the Island in the morning, carry out the fieldwork and return to the ship by evening. Food, water and security are in hand from the ship. Due to short stay of the earlier workers on the Island the published works based on the island are incoherent and inconsistent, which demanded a detailed investigation of the island. Apart from this it is first time that a joint team of scientists from two different countries collaborated in the expedition.
Top
|
|
