The famous hexagonal basalt columns of the Giant's Causeway were not formed by a single eruption, but by a volcanic event so massive that scientists now call it globally significant.
New research published in the journal Geology reveals that the iconic rock formation in Northern Ireland was created by a series of volcanic pulses over a much shorter time frame than previously believed. The study, led by researchers from the University of Liverpool and the Geological Survey of Northern Ireland, used advanced dating techniques to analyze the basalt layers.
A volcanic chain reaction, not a single blast
The team collected samples from the 40,000 interlocking columns that rise from the coast of County Antrim. By measuring the decay of radioactive isotopes in the rock, they determined that the lava flows that formed the causeway occurred in rapid succession, possibly within just a few thousand years. Earlier estimates had suggested the eruptions spanned millions of years.
This concentrated volcanic activity, the scientists say, was part of a larger event linked to the opening of the North Atlantic Ocean around 60 million years ago. The same volcanic system also created similar formations in Scotland, Iceland, and Greenland. The researchers describe the event as a globally significant volcanic episode that reshaped the planet's geology.
Why locals and tourists should take note
The Giant's Causeway is Northern Ireland's most visited tourist attraction, drawing nearly one million visitors each year. It is also a UNESCO World Heritage site. For decades, the standard explanation for the columns was that they formed from a single, slow-cooling lava flow. The new findings rewrite that story.
Local tour guides and geologists have long debated the origins of the site, which is also central to Irish mythology. Legend says the columns were built by the giant Finn McCool as a bridge to Scotland. The new science does not contradict the legend, but it adds a dramatic natural history to the tale.
The research team used a technique called argon-argon dating, which measures the ratio of argon isotopes in the rock. This allowed them to date individual lava flows with far greater precision than before. They found that the flows happened in three distinct phases, each separated by only a few hundred or thousand years. In geological terms, that is almost instantaneous.
The discovery also helps explain why the columns are so uniform in shape. Rapid, repeated cooling of thick lava layers created the perfect conditions for the hexagonal cracks to form. The same process, the scientists note, is happening today in active volcanic regions like Iceland.
A new chapter for an ancient landmark
The findings do not change the way the causeway looks or how visitors experience it. But they do change how scientists understand the forces that shaped it. The study adds the Giant's Causeway to a short list of sites around the world that mark major turning points in Earth's geological history.
The research was funded by the Natural Environment Research Council and the Department for the Economy in Northern Ireland. The team plans to continue studying the site to learn more about how volcanic systems behave when they erupt in rapid succession.
