Relevance: prelims/mains: G.S paper I: Indian physical Geography, Important Geophysical phenomena such as volcanic activity, geographical features and their location.
Barren Island, one of the most easterly of the Andaman Islands, is the only confirmed active volcano in India. The island along with the rest of the Andamans is the the Andaman & Nicobar Islands, and lies some 135 kms northeast of the territory’s capital, Port Blair.
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.
VOLCANO
- It is a rupture in the crust of a planetary-mass object (like Earth), that causes hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
- On Earth, volcanoes are generally found where tectonic plates (like Eurasian, Pacific, Somali, etc) diverge or converge. Examples- volcanoes occurring in mid-oceanic ridge and Ring of Fire.
- Eruption of volcanoes can be hazardous for humans and other lives living in its vicinity and volcanic ash may be a threat to aircrafts. Volcanoes can also cause
- Large volcanic eruptions inject water vapour (H2O), Carbon Dioxide (CO2), Sulphur Dioxide (SO2), ash, etc into the stratosphere to heights of 16-32 km.
- A volcano is considered to be “active” if it has erupted in the last 10,000 years. Examples – Kilauea (Hawaiian Islands), Mount Etna (Italy), etc.
- Extinct volcanoes are unlikely to erupt again as the volcano no longer has a magma supply. Examples – Volcanoes on Hawaiian Emperor seamount chain in the Pacific Ocean, Shiprock in New Mexico, etc.
Volcanic Explosivity Index (VEI)
- The Volcanic Explosivity Index(VEI) is a relative measure of the explosiveness of volcanic eruption. It was devised by chris Newhall of the United states geological survey and Stephen Self at the University of Hawaii in 1982.
- Volume of products, eruption cloud height, and qualitative observations (using terms ranging from “gentle” to “mega-colossal”) are used to determine the explosivity value.
- The scale is open-ended with the largest volcanoes in history given magnitude 8.
- A value of 0 is given for non-explosive eruptions, defined as less than 10,000 m3(350,000 cu ft) of tephra ejected; and 8 representing a mega-colossal explosive eruption that can eject 0×1012 m3 (240 cubic miles) of tephra and have a cloud column height of over 20 km (66,000 ft)
- The scale is logarithmic, with each interval on the scale representing a tenfold increase in observed ejecta criteria.
BARREN ISLAND (ANDAMAN ISLANDS)
- Barren Island is located in Andaman Sea, about 140 km from Port Blair.
- It is a part of Indian Union Territory of Andaman and Nicobar Islands.
- Barren volcano in the region is the only confirmed active volcano in South Asia (along a chain of volcanoes from Sumatra to Myanmar)
- The oldest subaerial lava flows of the volcano are calculated to be 1.6 million years old.
Recent eruptions in Barren island:
1991: The eruption occurred after about 150 years of dormancy. It lasted for about 6 months and caused considerable damage, particularly to the island’s fauna.
1995: Eruption reported
2004-05: Eruption recorded and linked to 2004 Indian Ocean earthquake.
2017: Volcano was spotted. They were a continuation of eruption in 2005, as per a study by Indian Space Research Organisation (ISRO).
2018: Volcanic eruptions reported and linked to 28 September 2018 earthquakes in Sulawesi, Indonesia.
CONCLUSION
Volcanoes are phenomenon which can cause a lot of damage if it occurs in the vicinity of populations living in the region. Barren islands are quite far away from human habitations, but can disrupt the paths of flights travelling in the region. Volcanoes, Earthquakes, etc are natural phenomenon but early predictions and preparations can reduce the possible hazards.