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Why did Barren Island volcano erupt again?

February 26, 2017 03:03 am | Updated 01:47 pm IST

India’s only active volcano — the Barren Island volcano — in the Andaman and Nicobar Islands is again spewing lava and ash, according to a team of scientists from the Goa-based National Institute of Oceanography (NIO). They chanced upon it as part of an ocean expedition in January. While this may evoke apocalyptic images, scientists who have seen the fulmination say it’s fairly benign.

Abhay Mudholkar and B. Nagender Nath from the NIO, who saw the eruptions from a mile off the mountain, noted that the volcano was erupting in small episodes lasting 5-10 minutes.

Scientific expedition

During the daytime, they saw ash clouds, but after sundown, red lava fountains spewed from the crater into the atmosphere and hot lava streamed down the slopes. So far, the scientists have sampled the sediments and water in the vicinity of the volcano and recovered coal-like black pyroclastic material. They are preparing for a scientific expedition to the volcano to assess the ecological impact of the eruption.

The Barren Island, about 140 km from Port Blair, is a tourist destination and surrounded by waters ideal for scuba diving and is home to a wide variety of aquatic life. The island is open to visitors, with prior permission, and as the name suggests is uninhabited and devoid of any significant vegetation. It’s the only active volcano along a chain of volcanoes from Sumatra to Myanmar. The 354-metre-high island is the emergent summit of a volcano that rises from a depth of 2,250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km wide caldera (a volcanic crater) with walls 250-350 metres high.

Not dangerous

Historically, the first record of the volcano’s eruption dates back to 1787. It was known to have erupted at least five times over the next 100 years. Then there was silence for a century. In 1991, it spewed so massively that smoke billowed out for about six months. Ever since, there have been eruptions every two-three years, the last in February 2016. All of these recorded eruptions lie on the lowest end of the so-called Volcanic Explosivity Index that ranks volcanoes from 1-8 based on the quantity of volcanic material spewed and the strength with which it does so. The latest eruption was a mere ‘2’ on the scale.

However, detailed studies have shown that the volcano first erupted 1.6 million years ago and sits on a 106-million-year-old crust. However benign this may seem, the renewed volcanic activity over the past few decades has some scientists worried about the amount of unreleased pressure stored in the continental plates that support the volcano. An eruption in 2005 was linked to the previous year’s Indonesia-Sumatra earthquake that triggered the destructive tsunami that ravaged India’s southern coast.

In 1991, the volcano’s eruption was catastrophic for several animal species. According to a report from the Geological Survey of India, a scientific team visited Barren Island on April 8-9, 1993, to assess the impact of the 1991 eruption on the distribution, habit, and abundance of fauna. Gas emissions still seemed to be oozing. The eruption reduced the number of bird species and their population. Of the 16 previously reported species, only six were observed, of which the Pied Imperial Pigeon (Ducula bicolor) was the most abundant. A night survey encountered only one rat species (Rattus rattus) and 51 species of insects from eight orders.

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