When we think of dramatic volcanic activity (enormous volcanoes, eruptions, lava fields, geysers) often Iceland comes to mind. But the story of Iceland's volcanism actually extends far beyond the island itself. The Iceland plume, a massive upwelling of hot rock from deep within the Earth, has helped shape not only Iceland and the wider North Atlantic, but reached all the way to Britain and Ireland. And its influence is still being felt today!

Tracing the Iceland Plume's Effects in Britain and Ireland

Around 60 million years ago, a dramatic geological events started to reshape the North Atlantic region: the formation of the North Atlantic Igneous Province (NAIP), one of Earth's largest igneous provinces. Over relatively short periods of geological time, enormous volumes of magma erupted, altering the landscape and topography, building volcanoes, and leaving behind vast sheets of igneous rock. Events like this do not only change the surface, they can also affect the global environment and reshape Earth's climate and ecosystems, as the release of volcanic gases has in the past been linked to mass extinctions.

The formation of NAIP left its imprint across Greenland, Iceland, and western Europe, where outcrops with matching geochemical signatures, along with other geological evidence, reveal their common origin. In Northern Ireland, for example, it produced the Giant's Causeway (part of the extensive Antrim Lava Group), with its striking basalt columns formed as thick lava flows cooled and fractured. In Scotland, it shaped the dramatic Fingal's Cave on the Isle of Staffa, whose stunning interior inspired poets and composers (for istance, Felix Mendelssohn was inspired by when composing the Hebrides Overture). These scattered volcanic landmarks, along with many others in the region, are all originated from the same ancient episode. But what could have driven such widespread eruptions across thousands of kilometers?

The answer lies deep beneath our feet: the Iceland Plume, a rising column of hot rock from the deep mantle, not only supplied the heat and magma that built Iceland, but also spread laterally beneath the lithosphere, the Earth’s rigid outer shell. This lateral flow could explain why volcanism occurred not only in Iceland but also in more distant regions, such as Antrim and Staffa. Until recently, however, direct evidence for this process was scarce, and the topic remained a heated debate in the scientific community.

Peering Beneath the Surface

To tackle this mystery, we analyzed decades of seismic data, using vibrations from earthquakes recorded by hundreds of seismometers to look inside the Earth. To ensure high coverage beneath Britain and Ireland, we combined all publicly available stations in the region with additional instruments we deployed ourselves. Applying advanced imaging techniques, we then mapped the structure of the lithosphere and upper mantle.

The results were striking: regions of past uplift and volcanism align with areas where the lithosphere is unusually thin.

This is crucial. Where the lithosphere is thinner, hot plume material from the mantle can rise upward more easily, eroding the base of the plate. As the pressure drops, the rock melts to form magma, driving volcanism and surface uplift. The Iceland Plume not only built Iceland but created scattered volcanic centers hundreds of kilometres away, also in what we now call the British Isles.

Earthquakes Distribution Controlled by the Plate Thinning

What's even more surprising is that the plume's influence is not just ancient history. Modern earthquakes in Britain and Ireland are not evenly distributed, nor are they linked to major plate boundaries (unlike, for example, California's San Andreas Fault), which is why this type of seismicity is called intraplate seismicity. They do not follow the main regional faults, which mostly run southwest-northeast. Instead, they cluster in the same thin-lithosphere regions shaped by the plume millions of years ago, and in areas where the contrast between thin and thick lithosphere is pronounced.

This means that the Iceland Plume not only created volcanic landscapes, but it also altered the mechanical structure of the lithosphere, creating weak spots that still control where the Earth deforms and shakes today.

Understanding how deep Earth processes shape today’s seismicity is not only an academic topic; it also has real-world importance and societal impact. While major earthquakes are rare in the Britain and Ireland region, those that do occur can still disrupt communities and infrastructure. Intraplate earthquakes have caused serious damage in other regions: the 6.2 magnitude Christchurch earthquake in New Zealand in 2011, for example, devastated the city and claimed hundreds of lives. By linking today's earthquake patterns to the past activity of a plume, we can better understand where danger lies and take steps to reduce both human and financial losses.