For centuries, the tale has been passed from generation to generation: how the Irish giant Finn McCool built the Giant's Causeway in Northern Ireland to fight Benandonner, his Scottish rival, by hurling chunks of the Antrim coastline into the sea.
Scientific Discovery Challenges Legend
Now, scientists have revealed it was intense geological activity during a "major globally impacting volcanic event" – and not a legendary battle between two destructive giants – that led to the formation of the coastline's 40,000 distinctive interlocking basalt columns about 60 million years ago.
Geochronologists investigating how the Giant's Causeway was created have discovered volcanic events in the region formed rocks, including the Causeway, in just 5.5 million years – 8 million less than previously estimated.
The discovery demonstrated that the processes that formed the Giant's Causeway were linked to a globally significant volcanic event recorded in rocks as far away as Greenland.
Linking Volcanic Systems
"While we knew generally the volcanic story of the Giant's Causeway, what we can now do is link its timing to other volcanic systems in the region at an unprecedented level," said Dr Simon Tapster, a geochronologist at the British Geological Survey (BGS).
"Before this event, Greenland was joined to the crust of the north of the UK – and at the end of this event, the North Atlantic sea had started to open between them," he added.
For the first time, scientists at the Geological Survey of Northern Ireland and BGS were able to definitively connect the first lava flows on the Northern Irish plateau to the same volcanic activity that formed the giant basalt columns in Fingal's Cave on the Scottish Hebridean island of Staffa – rocks that were previously thought to have formed millions of years after the Causeway.
Rock formations on the nearby Mourne mountain range and on the Hebridean isle of Rùm, as well as magmatic activity on Skye, can also be linked to this volcanic activity, placing the formation of the Giant's Causeway within a more precise, global geological context for the first time and enabling scientists to create a new timeline for volcanic activity across Northern Ireland.
Reassessing Timescales
Tapster said: "Fundamentally, what we've done is by piecing together this tapestry of volcanic rocks all across the North Atlantic, but focusing on Northern Ireland, we have been able to reassess a major globally impacting volcanic event.
"In doing that, and in reassessing the timescales, we have shown that actually it occurred in a much shorter duration."
The Giant's Causeway is a Unesco world heritage site and has been named one of the greatest natural wonders of the UK. According to Irish folklore, Finn McCool created the causeway so he could cross to Scotland to confront Benandonner, who was threatening his homeland – but retreated back to the island of Ireland, chased by his Scottish rival, when he saw the Scot was a much larger and more impressive giant.
Legend of Finn McCool
Legend has it that it was Oonagh, Finn's quick-thinking wife, who then saved the day. She disguised Finn as a giant baby so that Benandonner, scared into believing the infant's father would be large enough to beat him in a fight, rushed back across the causeway to Scotland – destroying as much of the crossing as he could on his way.
Although visitors to the dramatic landscape may prefer to believe the legend, scientists have shown the Causeway was formed when thick molten rock rose through cracks in the Earth's crust. As the lava cooled and contracted, stress and tension built up in the rock, forcing it to fracture into mostly hexagonal columns, although some of the rocks have four, five, seven or more sides.
Tapster's research is part of a wider initiative at the BGS to improve the understanding of the UK's geology through better quantifying geological time in the rocks around us.
He said: "By looking at the timescales and the high-resolution timeline, we're able to match it up with various other locations, particularly in the Inner Hebrides in Scotland, the volcanics of Mull, Rum, the Isle of Skye, and taking a bigger view, looking at Greenland and the Faroe Islands."
