Why a volcanic doomsday is closer than we think
INDONESIA: Some 75,000 years ago part of the island of Sumatra blew up so violently that the explosion propelled about 2900 cubic kilometres of searing ash into the sky.
The Toba catastrophe plastered half a continent with a 15cm layer of debris and brought about a decade-long winter that may have wiped out most of the human race.
Today the world is more or less due another ‘‘super-eruption’’, according to scientists who have calculated that these events happen more frequently than was previously thought.
Researchers used to think that eruptions capable of blasting out more than a billion tonnes of detritus - enough, according to some estimates, to cast humanity back into a ‘‘pre-civilisation’’ state - happened only once every few hundred thousand years.
New calculations from the University of Bristol, however, suggest that they actually tend to occur every 17,000 years or so. The last one, which ripped a large hole in the North Island of New Zealand, was about 26,000 years ago.
‘‘On balance, we have been slightly lucky not to experience any super-eruptions since then,’’ Jonathan Rougier the university’s professor of statistical science, said.
‘‘But it is important to appreciate that the absence of supereruptions in the last 20,000 years does not imply that one is overdue. Nature is not that regular.
‘‘What we can say is that volcanoes are more threatening to our civilisation than previously thought.’’
Rougier and his team examined the geological record of the past
100,000 years for signs of eruptions that had expelled at least 300 million tonnes of mass. They used a new statistical approach to work out how often the largest of these could be expected to strike.
Although they found nearly
1400 eruptions, they also inferred that many others had not been recorded.
This suggests that the ‘‘return period’’ for Toba-like eruptions measuring eight on the volcanic explosivity index is between 5000 and 50,000 years.
Independent experts said the conclusions were credible but contained a great deal of uncertainty. Marc Reichow, lecturer in igneous and metamorphic geochemistry at the University of Leicester, said the work was ‘‘robust’’ and could help to predict future cataclysmic eruptions, but it was only the foundation for more detailed research.
‘‘Nature, including volcanic eruptions, does not necessarily work as clockwork,’’ he said. ‘‘To fully understand the frequency and hazards of volcanic eruptions, we have to closely monitor active volcanoes ... and investigate extinct volcanic systems where an entire ‘life-cycle’ of a volcano is exposed.’’