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.