Researchers have identified a 454-million-year-old volcanic complex buried beneath The Wash in eastern England, providing a long-sought source for the massive Kinnekulle ash layer spread across northern Europe. Scientists used borehole crystals to date the ancient activity.
An ancient volcanic system that erupted more than 454 million years ago has finally found its geological address. Beneath the flat landscapes and shallow waters surrounding The Wash on England’s east coast, scientists have uncovered the remains of a massive buried volcanic complex.
The discovery solves a decades-old puzzle in European geology. For years, researchers knew that a colossal ash layer blanketed Scandinavia and the Baltic region during the Late Ordovician period, but the volcanic engine powerful enough to drive it across an ancient sea had remained entirely hidden.
Borehole Crystals Reveal a 454-Million-Year-Old Timeline
The breakthrough emerged from rock samples recovered from deep boreholes drilled at Claxby in Lincolnshire and North Creake in Norfolk. Although these drilling sites sit about 65 kilometers apart, tiny zircon crystals inside the rocks recorded near-identical ages.
Zircon serves as a natural radioactive clock for geologists. As the mineral forms from molten magma, uranium enters its crystal structure and decays into lead over immense spans of time. Measuring these specific isotopes lets researchers calculate the precise moment crystallization occurred.
The microgranite from Claxby yielded an age of roughly 454.40 million years, while an older population of zircon from the North Creake volcanic breccia dated to about 454.45 million years. Teams from the British Geological Survey and the University of Oslo noted that these numbers closely match high-precision dates previously obtained for the Kinnekulle Metabentonite in Scandinavia, where samples from Denmark and Norway place the ash layer at approximately 454.4 million years old.
Using cutting-edge analytical techniques at BGS’s laboratories, scientists have been able to examine zircon crystals, which form within molten magma before a volcano erupts. Over time, uranium within the zircon slowly decays into lead isotopes, analysis of which enables the age of eruption to be precisely determined. The research reveals that the zircon crystals at both sites were formed at approximately the same time, about 454.4 million years ago.
Researchers from the British Geological Survey and the University of Oslo studied tiny crystals preserved in rock samples from boreholes in Norfolk and Lincolnshire. The crystals helped them date the eruption to about 454.4 million years ago.
Crossing the Tornquist Sea
During the Late Ordovician, the geography of Europe looked entirely different. The landmass that would eventually become England was then part of Avalonia and lay near an active zone of volcanic activity, separated from Scandinavia by the Tornquist Sea. A belt of active volcanoes extended from what is now northern England toward continental Europe.
454.45 million years ago several hundred to a thousand cubic kilometres of the Earth’s crust were thrown into the stratosphere by eruptions with a force equivalent to several thousand H-bombs, one of the largest eruptions in recorded Earth history. The scientists believe that the near-identical ages suggest that ash from the eruption plume in what is now eastern England was blown across the Tornquist Sea, which separated England and Scandinavia.
The Kinnekulle tephra, about 130 cm thick in the Oslo region, represents the fall-out from an Ultra-plinian volcanic eruption in eastern England 454.45 million years ago. Volcanic rocks of comparable age comprise the rugged topography of Eryri (Snowdonia) and the Lake District.
To confirm the connection beyond simple chronology, researchers compared the chemistry of apatite crystals in the English samples with material from the ash layer. The similarities strengthen the proposed link between the buried volcanic complex and the tephra.
Scale and Legacy of the Wash Igneous Complex
The origin of the Kinnekulle tephra, a huge volcanic ash layer spread across Norway, Sweden, the Baltic region, Belarus and Poland, has long been a mystery. The complex lies beneath The Wash and surrounding parts of eastern England, concealed by hundreds of millions of years of geological change.
The landscape above the suspected source gives almost nothing away today, and the researchers describe the Wash Igneous Complex as a leading candidate rather than a confirmed source. Over millions of years, the volcano was buried beneath younger layers of rock and sediment.
