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How was Giant’s Causeway in Northern Ireland formed: Geology vs. Irish Myths

Imagine stepping onto a landscape straight out of a fantasy novel, where thousands of hexagonal columns fit together like the world's most intricate jigsaw puzzle. Welcome to Giant’s Causeway in Northern Ireland, an intriguing site that seems to have been carved by ancient giants. But was it really built by mythical creatures? Or can science offer a more plausible explanation?

In this post, we're diving into the spectacular Giant’s Causeway in Northern Ireland. I love, love, LOVE Ireland, and on my last visit, I became by fascinated by the Giant’s Causeway. As someone who’s passionate about science, and about Irish myths and legends, I just knew I had to uncover Giant’s Causeway's secrets and share them with the world.

Geological history of Giant’s Causeway in Northern Ireland

Giant's Causeway Northern Ireland

The creation of Giant’s Causeway was marked by several significant stages.

Its inception dates back to the early Paleogene period. The Paleogene period stretched over a period of about 43 million years, between 66 and 23 million years ago. The Giant’s Causeway started forming about 60 million years ago, around the time when Laurasia started fragmenting, causing the formation of the North Atlantic Ocean. Laurasia was an ancient continent that comprised North America, Europe, and part of Asia.

The splitting of this ancient continent triggered intense volcanic activity across the region that comprises the nowadays north coast of Ireland and western Scotland. The lava flowing onto this region built up the foundational layers of the Giant’s Causeway. And we can find a similar geological formation in Scotland, called the Fingal’s Cave, another impressive geological wonder of our planet.

After this period of violent eruptions, the volcanic activity subsided, and a long period of inactivity followed. During this dormant period, the topmost layer of lava was subjected to severe weathering, eventually leading to the formation of a rich, iron and aluminum-laden red layer known as the Interbasaltic Formation, and the landscape turned into a lush, hilly forest.

But the fireworks weren’t over yet! A second period of volcanic activity began, filling the valleys with deep lakes of lava that slowly cooled to form the iconic basalt columns of the Giant’s Causeway. After another quiet period, came the grand finale of eruptions, the Upper Basalt Formation. Lava carved its way up through existing fissures, adding further layers to the geological formations that comprise the Giant's Causeway today.

The Giant's Causeway columns and their shape

First, let’s get better acquainted with the columns at Giant’s Causeway. The site, which is a UNESCO World Heritage Site, consists of about 40,000 columns made up of dark, fine-grained basalt.

Basalt columns at Giant's Causeway in Northern Ireland

The columns have different heights, diameters, and shapes. They can be as high as 12 meters and 30 - 60 cm wide. While the most predominant shape we observe in the columns at Giant’s Causeway is hexagonal, we can find columns with other number of sides, anywhere from three to eight.

Why are most of the columns hexagonally shaped?

The columns formed as the molten basaltic lava cooled and solidified. The lava cooled rapidly from the outside in causing it to contract and form cracks on the surface.

Hexagonal basalt columns at Giants Causeway Northern Ireland

Recent computational studies have shown that these initial cracks formed at right angles (90-degree angles), but as the cooling process continued, they shifted to 120 degree angles, which are typical of hexagons. The cooling lava is thus molded into hexagonal shapes. With the continued cooling and contraction of the lava, the cracks then propagated downwards, thus creating the tall hexagonal columns we see today.

These lengthy geological processes culminated in the magnificent landscape we get to enjoy today at Giant’s Causeway in Northern Ireland. But, there is an alternative story to the creation of Giant’s Causeway, one rooted deep into the Irish mythology.

The Giant's Causeway Mythology

A Story of Two Giants: Finn McCool vs. Benandonner

Once upon a time, in ancient Ireland, the mighty giant Finn McCool (Fionn MacCumhaill) got into a fight with the Scottish giant, Benandonner, who fancied Ireland as his own. The nerve of that guy! Angry with the Scottish giant, Finn started throwing boulders into the sea off the Antrim coast, creating a rocky bridge all the way to Scotland’s Isle of Staffa, where Benandonner resided. With his newly formed Giant’s Causeway, Finn, pretty sure of himself, took off to Scotland to challenge the Scottish giant to a duel.

However, upon crossing the causeway and seeing Benandonner, Finn immediately started regretting his decision. Benandonner was not just a giant; he was huge even for a giant! Realizing he was in way over his head, Finn rushed back across the causeway to Ireland to try to find another way of defeating the giant. His quick-witted wife, Sadhbh, helped disguise him as an enormous baby. When Benandonner arrived at Finn’s home, his wife presented him with Finn’s enormous child. Imagining the father to be even larger, Benandonner lost all courage.

Fingal's Cave in the Island of Staffa in Scotland

Terrified of the super-giant he now believed Finn to be, Benandonner “turned about and gallantly he chickened out”, to quote Monty Python and the Holy Grail. He retreated back to Scotland and on his way ripped up portions of the causeway, tossing them into the sea to ensure Finn couldn't follow. He retreated back to the Isle of Staffa, in Fingal’s Cave, the geological twin of Giant’s Causeway.

Whether it was geological processes or ancient giants, the Giant’s Causeway is an exquisite wonder of our planet and a significant site of cultural heritage, and I highly encourage you to visit the site if you travel to Ireland.

And if you’re interested in exploring even more of these interesting basalt columns, you can also find them in other sites, like the Devils Postpile National Monument in California, USA, at the Svartifoss waterfall in Skaftafell, Iceland, the Organ Pipes National Park in Victoria, Australia, and at Los Prismas Basálticos waterfalls at Huasca de Ocampo in Mexico. Isn’t it amazing how awesome and interesting our planet is?

Which origin story do you like more? As a scientist I enjoyed learning about the geological history of the Giant’s Causeway, but as a Sci-Fi/Fantasy writer, and someone who loves Irish mythology, I enjoyed more the story of the two giants.


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