I just got aware recently that Barren Island volcano (Andaman Islands) is erupting again since – at least – 17 March 2015. According to the Darwin VAAC from 27 April, a pilot observed an ash plume from Barren Island that rose to an altitude of 3 km (10,000 ft) a.s.l. but ash was not identified in satellite images. However, on checking the MODIS volcanic hotspot data from the University of Hawaii (MODVOLC), I found that heat sources on the volcano were recorded from mid-March through April. The strongest were on March 18 and 28 with lava flows apparently reaching the sea on the NE side. Or – is that a pyroclastic surge travelling out on the water??
Edit May 5th: There were no further hotspots visible since April 29, so it may or may not still be erupting.
Left: MODIS volcano hotspots (MODVOLC) from 18 and 28 March, and a Google Maps image for comparison.
BARREN ISLAND VOLCANO
The Andaman and Nicobar Islands (belonging to India) are geographically part of South-East Asia and tectonically they are related to Sumatra in Indonesia. Barren Island is located about 135 km NE of the capital Port Blair, and it is the northernmost active volcano of the Great Indonesian volcanic arc. The volcano is associated with the subduction of the NE-moving Indian Plate beneath the Burmese Plate along the Andaman Trench. The 354-m-high island is just the top of a stratovolcano that rises from a depth of about 2250 m. In 2013, scientists Jyotiranjan S Ray et al. determined its age by studying a 4m-long core of marine sediments collected from the Andaman Sea about 30 km away from Barren Island. The core was analysed with the help of the Argon dating facility at IIT-Bombay. The results were that the volcano would be at least 1.8 million years old.
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. Using tephrachronology, eruptions have been dated back to ~8060 BCE (Before the Common Era = BC). Historical eruptions, recorded since 1787, 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.
The volcano erupted for the first time in the 20th century beginning in April 1991 after a dormant period of 152 years. Strombolian eruptions from the central cone produced clouds of ash and incandescent ejecta, and a lava flow reached the west coast of the island. By the time of September 25 of that year, all subsidiary vents had merged with an enlarged summit crater.
This was followed by the 1994–95 and 2005–06 eruptive periods. Thereafter, eruption cycles occurred every 1-3 years, and the present period started in Oct. 2013.
As the island is uninhabited, eruptions are often overlooked by the public. Sometimes fishermen, coast guard, the Navy or pilots report a plume or visible lava flows, then the media takes notice of an eruption. Other eruptions might go unnoticed, as long as the Geological Survey of India does not publish them. However, it seems that Barren Island erupts far more frequently: The crew of the Infiniti Live Aboard dive boat noted that there was a plume visible during each of their six visits to the island between January and April 2014 (source: GVP).
NEW BREACH THROUGH THE CALDERA WALLS IN THE NE – OR A PF?
As far as I can see, in all recent eruptions the lava flowed out towards the sea through the breach in the western part of the caldera wall. Once it was mentioned that the activity had “shifted to the north”, but that referred to the location of new vents on the NE slopes of the cinder cone inside the caldera. All later reports have the western sea entry again. However, looking at the new satellite hotspot images (above), it appears that this time the lava has found a way to the north-east of the island and into the sea on that side, through either a new breach through the caldera walls or buildup of new cinder cones inside that reach over the walls. OR it could also have been a pyroclastic flow that the camera has captured, if so, that would have been a very great coincidence! This suggests either that the morphology of the Island has further changed in recent activity periods, or that a great pyroclastic surge has taken place to the NE, which is not a common occurence with a volcano that produces mostly VEI 1 or 2 strombolian type eruptions… and that the behaviour of the volcano is far from being settled, well known or understood.
If even a scientist “felt that since Barren Island is not inhabited so such studies have no societal relevance” (quote from the minutes of the 39th Annual Session of the Indian National Committee for IGCP, 30th January, 2014, concerning studies of submarine landslides around the Barren volcano, which could cause tsunamis), it appears that there is a general lack of support for geological/volcanological studies in that region.
Given that the volcano is only some 500 km from the Myanmar coast, 135 km from Port Blair, and just 80 km from the nearest inhabitated island of the Andamans, and seeing that caldera-forming events have taken place before, it seems that more research would be necessary to fully understand possible threats going out from Barren Island or its geological neighbors (like the dormant Narcondam, another island volcano some 70 km north of it).
Enjoy! – GRANYIA
SOURCES and FURTHER READING
– Barren Island on GVP
– Barren Island – Wikipedia
– MODVOLC Hawaii
– Volcano World, OSU
– Volcanology and eruptive styles of Barren Island:… (2009) Highly recommended read!
– “The Hindu”: Barren Island could be 1.8 million years old