British geologists have discovered a huge ancient volcano buried beneath the east coast of England, an eruption they say took place 454.4 million years ago and was several times more powerful than Mount Etna is today. The findings were reported by BBC Science Focus.
The volcano lies beneath the counties of Norfolk and Lincolnshire. When it erupted, the blast is estimated to have released energy equal to several thousand hydrogen bombs going off at once, with ash scattering as far as Scandinavia.
Scientists believe the eruption produced what is known as the Kinnekulle tephra, a vast layer of volcanic ash still found today in Norway, Sweden, the Baltic states, Belarus and Poland.
Tim Pharaoh, a geophysicist and author of the study, said the discovery changes understanding of England's deep geological past.
Mount Etna, on the Italian island of Sicily, is one of the most active volcanoes in the world and a frequent benchmark for measuring the scale of eruptions elsewhere.
Traces found in two boreholes
Researchers found evidence of the buried volcano in rock samples taken from two boreholes in Norfolk and Lincolnshire, 65 kilometres apart. The team said the volcano itself could have covered a much larger area than the borehole sites suggest.
Dan Condon, a co-author of the study, said it was probably not a simple cone-shaped volcano. He said the evidence pointed to a large and complex volcanic system with several caldera-like depressions stretching for tens of kilometres above a substantial magma reservoir.
Dating the eruption with zircon crystals
To pin down the volcano's age, the scientists examined tiny zircon crystals embedded in the ancient volcanic rock, which allowed them to date the eruption with what they described as the highest precision currently available.
Condon said zircon crystals work like small natural clocks. As zircon crystallises out of magma, uranium becomes trapped in its structure and gradually decays into lead over time.
By measuring the rate of that decay, Condon's team established that the rock from the English volcano and the Scandinavian tephra formed at the same time. The chemical fingerprint of the samples also matched completely.
Awakening after half a millennium
Volcanic activity has been surprising scientists not only in the deep geological past but also in the present, as dormant systems reawaken. Kamchatka's Krasheninnikov volcano had been silent for more than 500 years, but a magnitude 8.8 megaquake last year stirred ancient magma chambers beneath the peninsula, sending up an ash column roughly 6 kilometres high.
Scientists have dubbed such a state "hidden critical", meaning a volcano is already primed to erupt while showing no visible warning signs.
