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The volcano that blew 74,000 years ago

7 November 2012

At http://phys.org/print271337921.html … acidity spikes in Greenland and Antarctic ice cores, calculated to date back to around 74,000 years ago, are thought to mark the eruption of a supervolcano, Toba in Sumatra. A paper in the journal Climate of the Past claims the eruption left a crater 50km in diameter and when it blew it expelled lava to the equivalent of two volumes of Mount Everest. The eruption, it is claimed, was 5000 times bigger and more violent than Mount St Helens which erupted in the 1980s. Toba is said to be the largest volcanic explosion on Earth during the last 2 million years. Clouds of ash and sulphuric acid blasted into the atmosphere and spread around the whole globe and fell down as acid rain. It is this acid rain that has been found in the ice cores.

Obviously, the volcano has attracted a lot of hyperbole over the years, but contradictions are known. Modelling shows that such a big eruption could cause cooling of up to 10 degrees in global temperatures for many years afterwards. The temperature curve in the ice cores do not show this – and the spikes are spikes that rise up suddenly and fall back down again just as suddenly a few years later. The ice cores do not show a general cooling – but ocean sediment cores may differ. The ice cores seem to show that any global cooling as a result of the Toba spike was short-lived, and fairly muted. A layer of ash has been found in some parts of Asia. It is thought, or rather it is part of the grand thesis, that humans were affected by eruption – and it may even have sparked the great migration the Out of Africa people are so fond of pontificating on, hampering legitimate research into alternative scenarios. The Out of Africa hypothesis is so deeply ingrained into anthropological studies that this study might seem a blessing to them – contrived or othrwise. Archaeologists, or some of them, say they have found no evidence that Toba greatly bothered humans. There is evidence of human activity before and after the layer of ash that is attributed to Toba, particularly in India. Nevertheless, it seems that scientists are united following the discovery the Toba spike is not only evident in Greenland ice but also in Antarctic ice, at the same point in time, 74,000 years ago. We may note this is probably not the last word on the subject. Could another volcano have erupted at 74,000 years ago and what exactly ties Toba in with the ice core data? Was the concept of a supervolcano a theory that became a fact simply as a result of being repeated so often. Is it foible rather than solid fact? 

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