The phrase “hidden supervolcano” sounds a bit like an oxymoron, doesn’t it? Supervolcanoes are notoriously conspicuous, what with their enormous size and penchant for spewing massive amounts of lava, ash, and rock into the sky. This one, however, has quietly been buried off the east coast of England for millennia.
Its discovery, detailed in a recent study published by the GSA Bulletin, answers a question that has puzzled geologists for decades. The authors believe that some 454 million years ago, this long-extinct supervolcano produced one of the largest eruptions known to scientists, creating the Kinnekulle tephra. The origin of this expansive volcanic ash layer—spread across Norway, Sweden, the Baltic region, Belarus, and Poland—was a mystery until now.
“It’s only now that we’ve got these precise ages we can make these bold statements and assertions,” principal author Tim Pharaoh, a geophysicist at the British Geological Survey, told the BBC. “It’s extremely satisfying to come up with this very precise result.”
Reconstructing an ancient supereruption
Pharaoh and his colleagues at the BGS and the University of Oslo re-examined tiny zircon crystals about the width of a human hair, extracted 80 years ago from boreholes 40 miles (65 kilometers) apart in Lincolnshire and Norfolk, England. These crystals form within molten magma before a volcano erupts.
Zircon contains trace amounts of uranium, a radioactive metal that decays into lead isotopes. Analyzing these isotopes allowed the researchers to precisely date the crystals, and the results showed that they formed around the same time, dating back approximately 454.4 million years. This indicated that they were deposited by the same eruption—one that occurred roughly 200 million years before dinosaurs walked the Earth.
In a previous study, researchers at the University of Oslo obtained almost exactly the same age for the Kinnekulle tephra in the Oslo Region. This suggests that ash from the eruption in what is now eastern England blew across the Tornquist Sea (which separated England and Scandinavia at the time) and settled on the seafloor of ancient Scandinavia.
The eruption must have been enormous, according to the researchers. They estimate that it blew tens to hundreds of cubic miles (several hundred to 1,000 cubic kilometers) of Earth’s crust into the stratosphere with a force equivalent to several thousand hydrogen bombs. But from the surface, the supervolcano that produced it was nowhere to be seen.
That’s because it is now buried deep underground. Centered beneath the Wash, an estuary off England’s east coast, the supervolcano extends beneath one of the nation’s flattest landscapes. Interestingly, geophysical data suggests it’s not alone. In fact, it appears to be part of an extensive caldera system that the researchers call the “Wash Igneous Complex.” While it is incapable of erupting today, its explosive potential was once incredible.
These findings not only solve the longstanding mystery of the Kinnekulle tephra’s origin but also provide new insight into England’s geological history. There’s no telling what else researchers may uncover as they continue to investigate this complex subsurface region.
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