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New theory for the Giant's Causeway's formations revealed

A new theory as to why the Giant’s Causeway’s extraordinary geological features are found at sea-level only has been revealed this UNESCO International Geodiversity Day on October 6th. The interpretation is the first time in more than 80 years that existing theories have been brought into question and has been put forward by Dr Mike Simms, our Curator of Natural Sciences.

Giants Causeway - Credit National Trust (1095 x 616)
Ulster Museum
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Although folklore might suggest that the Giant’s Causeway was built by Finn McCool to cross the North Channel to Scotland, the scientific explanation - widely accepted for decades - is that a river valley was filled with lava that ponded to a greater depth than normal. As the thick layer of lava cooled and solidified it formed these regular columns.

However, Dr Simms has put forward the idea that if this lava-filled hollow was a valley it would have cut through old layers of lava beneath. He has identified layers of old lava on the shore either side of the Giant’s Causeway sloping inward where older layers have not eroded away.

Dr Simms explains in more detail:

“An analogy I find helpful when explaining this involves cake. Eroding a river valley is rather like cutting through a layer cake to reveal layers beneath the surface. In my interpretation, what we actually see are layers of older rock sloping towards the Causeway – more like a badly baked cake that has sunk in the middle.

“I believe the ground subsided as lava moved up and erupted at the surface. The lava filled the depression creating the conditions for the columns to form. This event likely took just a few days rather than the many thousands of years that would be needed for erosion to create a river valley.”

A deserted Giant’s Causeway, June 2020
Interestingly it was during a field trip Dr Simms was leading at the Giant’s Causeway that he first thought there may be an alternative explanation.  

Dr Simms continued:

“I owe a particular debt of gratitude to another geologist, a young Brazilian man who was on a field trip I was leading in 2012. He questioned how long it would take to erode the supposed river valley, and it was this that opened my eyes to the evidence before me. I had visited the Giant’s Causeway many times before and until that moment, I had just accepted the previous theory. It goes to show that even at world famous landmarks such as this, new discoveries can be made from a simple observation.”

The Giant’s Causeway is Northern Ireland's only UNESCO World Heritage Site and is operated by the National Trust which has acknowledged Dr Simms’ discovery.

Max Bryant, General Manager at Giant’s Causeway and Carrick-a-Rede said:

“This new interpretation demonstrates that even at a site as well-known and well-studied as the Giant’s Causeway, there can always be new possibilities and perspectives waiting to be discovered. It highlights just how marvellous, magnificent and mysterious a geological formation we have here in Northern Ireland to share with the world.”

National Museums NI is the custodian of significant natural sciences collections and natural habitats. It is also home to CEDaR, Northern Ireland’s environmental record centre - a partnership between National Museums NI and the Northern Ireland Environment Agency. For decades these organisations have worked together, and in partnership with other scientists, to progress research and further understanding of our natural world.

Kathryn Thomson, Chief Executive of National Museums NI, said:

“I’m proud to support Mike’s findings. I think it’s wonderful he has showcased the expertise of our team and how important museums are. Yes, we provide spaces for people to explore and learn, but our teams also make meaningful contributions elsewhere. As a knowledge-based organisation, our staff are uniquely placed to present research and ideas. By using our vast natural science collections, for instance, we can support new discoveries and promote responsible and ethical action when it comes to our natural world.”