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Scientists Concerned About the Eruption Potential of Toba Super Volcano
Lake Toba in Sumatra, Indonesia is part of a massive caldera left when Mount Toba last blew its top 74,000 years ago. Mount Toba produced the largest volcanic eruption in the last 2 million years.
Lake Toba in Sumatra, Indonesia is part of a massive caldera left when Mount Toba last blew its top 74,000 years ago. Mount Toba produced the largest volcanic eruption in the last 2 million years. The caldera is 18 x 60 miles (30 by 100 km) and has a total relief of 5,100 feet (1700 m). The caldera probably formed in stages. Large eruptions occurred 840,000, about 700,000, and 75,000 years ago.
During its last eruption, Toba spewed out an amazing 2,800 cubic km of material. Pyroclastic flows covered over 7,000 square miles to a depth of over 500 feet. The ash fall from the eruption covered an area of over one and a half million square miles, an area about half the size of the continental United States.
The area is seismically active. The last major earthquake occurred in 1987. Running alongside Lake Toba is the Sumatran fault line, and that is what’s worrying the scientists. The dormant, but not extinct volcano still contains a magma chamber.
The Indonesian Geographical Society used tomography, the same as used for medical imaging but on a much grander scale, to locate the magma chamber. It almost straddles the Sumatran fault.
The Sumatran fault line runs through Sumatra, running from Aceh in the northwest to Lampung in the south, passing right through Mount Toba. Should the fault rupture, the sudden change in pressure could force the magma to rise resulting in an eruption.
Adding to the problem is the Sumatran Trench, a tectonic plate margin that is moving towards Sumatra at a rate of 5.5cm a year. The Australian plate is forcing its way under the Sunda plate, making the margin a subduction zone, which are known for producing the strongest earthquakes on the planet.
As the Australian plate moves under the Sunda Plate, the sediments, rock and debris that is scrapped off it as it moves, piles up forming the small islands off the coast of Sumatra.
Although Earthquakes can’t be predicted, Indonesia is a very active part of the ‘Ring of Fire’. With the subduction zone being so geographically close to the Sumatran fault, it is perfectly feasible that a major subduction earthquake could trigger a slip along the fault line, which in turn could alter the shape, and the pressure in the Toba magma chamber.
There are 129 active volcanoes in Indonesia, many of them laying like a string of pearls in an arc along the edge of Sumatra and the islands to its south. Scientists are looking at all of them, some of which are incredibly close together. It has been suggested that some of the magma chambers may be linked to each other, with magma traveling from one to another depending on the surrounding pressures from the fault and plate movement.
More research is needed before any firm conclusions can be arrived at, but the thought of Toba coming back to life makes that research vitally important for all of us, not least the millions of people that live in its shadow.
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