The UK is known for being geologically stable and tectonically safe, with the last known volcanic eruption said to have been 60 million years ago when Britain was moving away from the tectonic boundaries and hotspots. Across the country, ancient volcanism is evident in the Lake District, Snowdonia, Northern Ireland, Southern Scotland, Western Scotland, the Scottish Isles, and even parts of Dartmoor. But, what many do not know is that just 81 miles from London, in the village of Warboys, Cambridgeshire, sits a volcano that dates back over 300 million years.

In the Sixties, experts at the British Geological Survey (BGS), detected magnetic and gravity anomalies due to variations in the physical properties of underlying rock formations. 

This led to an exploratory borehole being drilled to try to explain the source of the mysterious magnetic anomaly.

The team drilled through various sedimentary layers from the Middle and Lower Jurassic period until they encountered igneous rocks – formed by crystallisation of minerals from magma – at 217 metres. 

This led the BGS team to believe they had stumbled across the remnants of an ancient volcano that was active during the Hercynian Orogeny period around 300 million years ago.

30 years later, the Department of Earth Sciences at Cambridge University returned to carry out a Geophysics course for Physics undergraduates at Warboys to try and provide further data as part of their field studies. 

The team used gravimeters to measure the variations in the gravitational field around Warboys that would reveal changes in the density of the buried igneous rock.

Their analysis led to the discovery of the dense core of an extinct volcano, that they concluded extends for up to three miles horizontally and up to 600 metres vertically.

The researchers speculated that around 300 million years ago, during the Hercynian period, the volcano would have been active and covered several miles at its base. 

Over millions of years, the land surface around the volcano eroded leaving just the hard diorite core. 

During the Jurassic period, this sank beneath a shallow sea and was buried by deposits of sediment and later around 20,000 years ago.

Britons today need not worry about the volcano springing back to life and the closest active volcanos to the UK is a toss-up between Mount Vesuvius in Italy and Oraefajokull on the southeast coast of Iceland, both more than 1,000 miles from London.

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Vesuvius wins the prize by some 30 miles, but prevailing westerly winds in the UK mean that we are unlikely to be directly affected by an eruption.

But, Oraefajokull, which last erupted in 1728, is located in the East Volcanic Zone, a particularly active region that also includes the infamous Eyjafjallajokull and Grímsvotn volcanoes. 

Both of these have caused severe disruption to air travel in recent years and would cause great devastation in a future eruption.

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