Scientists have discovered the remains of a massive volcano, thousands of times more powerful than Mount Etna, deep beneath England's east coast.

The supervolcano, centred under The Wash and extending into Norfolk and Lincolnshire, measured at least 65km (40 miles) across and erupted with the force of several thousand hydrogen bombs 454 million years ago.

Experts at the British Geological Survey (BGS) believe it explains a huge layer of volcanic ash spread across Norway, Sweden, the Baltic region, Belarus and Poland.

Dr Tim Pharaoh of the BGS said the discovery was a "fantastic result", changing "our understanding of England's deep geological past".

The term supervolcano is given to those that have erupted more than 1,000 cubic km (240 cubic miles) of material.

There are 30 in the world today, with Campi Flegrei, near Naples, Italy, the nearest to the UK.

The last to erupt was Toba in Indonesia, 74,000 years ago, which genetic evidence suggests wiped out all but a few thousand people on Earth.

The Wash supervolcano, which is now under a large estuary and extends beneath one of England's flattest landscapes, was active roughly 200 million years before dinosaurs walked the planet.

Its eruption was one of the largest in history, throwing hundreds of cubic km of the Earth's crust into the stratosphere.

An eruption on the same scale today would likely threaten the existence of humanity.

But Pharaoh, the principal author of the research paper outlining the discovery, said: "Unlike faults, which can be seismically reactivated, a volcano can't.

"Once it's gone extinct, that's it. Nobody needs to worry about the supervolcano erupting again."

The Wash supervolcano was discovered following fresh analysis of rock samples taken 80 years ago from boreholes hundreds of metres deep in North Creake, Norfolk, and Claxby, near Horncastle, Lincolnshire, and kept by the BGS at its archives in Keyworth, Nottinghamshire.

During the Covid lockdown, scientists began to look again at their existing samples, using new equipment and techniques.

By examining tiny zircon crystals about the width of a human hair, formed within molten magma before a volcano erupts, they found the Norfolk and Lincolnshire samples were formed at the same time, about 454.4 million years ago, and were from the same volcano.

This matched the age of material analysed by the University of Oslo, suggesting that ash from the eruption was blown over to what is now Scandinavia and settled on the sea floor.

Pharaoh said there was no evidence of the supervolcano on the surface.

But he said throughout his 40-year career at BGS, he had thought about earlier work by University of East Anglia scientists.

They had identified a geophysical anomaly beneath The Wash region, and concluded it was underlain by lighter rocks, most likely granite.

"It's only now that we've got these precise ages we can make these bold statements and assertions.

"It's extremely satisfying to come up with this very precise result."

Prof Jenni Barclay, a University of Bristol volcanologist, said the new findings were fascinating.

"This work is an important step forward in piecing together the geological history of the UK, and understanding that subsurface is important for lots of reasons linked to our sustainable use of resources, like water and minerals," she said.

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