Giants and Geology


Often in my travels, I encounter cool geology. This isn’t particularly surprising given that as a geologist, it’s one of the main reasons I travel in the first place. What I don’t find as often, however, is cool geology built by giants. You might be skeptical, and rightly so, but after an evening of Guinness and Irish folklore, it will all start to fit into place. Welcome, friends, to Giant’s Causeway.


In the morning light, it’s easy to see why the formation is a UNESCO World Heritage Site, referred to in any guidebook as one of the natural wonders of the world. Located in the northern tip of Northern Ireland, the Causeway is composed of tens of thousands of rock columns, linking to form a structure almost like a cobblestone highway that runs across the beach and into the sea. The tops of the columns form regular geometric shapes – most with 5, 6, or 7 sides. Almost a million visitors a year travel to the remote Antrim Coast to experience this display of geology at its finest. But the Causeway is more than just a marvel for hungry eyes and cameras; it tells a story – a story that begins some 60 million years ago.


A quick trip back in time takes us to a landscape much different than today. The Atlantic Ocean had just begun to form, its edges marked by chains of volcanoes. Northern Ireland was one of these volcanic coastlines. Eruption after eruption spilled a sea of hot lava onto the landscape; as the lava was exposed to air, it cooled and hardened into basalt – the black rock that makes up the columns we see today. Upon cooling, the rock contracted and cracked. The top layer, exposed directly to the air, cooled fastest and cracked the most, leaving behind little more than a jumble of rocky debris. The lava below cooled more slowly, forming vertical fissures that divided the rock into columns. Many eruptions occurred during this period, forming a basalt layer more than 100 metres thick.


At one time, the columns would have been hidden from view by layers of younger material, deposited in the millions of years that came afterwards. However, over the years, waves, rain, wind and glaciers have worn away those units, exposing the pillars we see today. But the Causeway continues to erode, accelerated by the footsteps of hundreds of thousands of eager tourists a year. Its present form is only a small remnant of the structure created 60 million years ago; in another few million years, the Causeway will have worn away completely.


My Earth Ring – either for scale or as ‘one ring to rule them all’

The Irish have their own version of events, steeped in centuries of folklore and Guinness. As the story goes, once upon a time, the Irish giant Finn MacCool decided to challenge the Scottish giant BenandonnerWhile Finn could easily have crossed the sea to Scotland, he hated getting his feet wet and chose instead to build a bridge. Crossing over the causeway, he glimpsed Benandonner in the distance and, terrified by his size, ran back to Ireland. There he asked his wife, Una, to hide him. Quickly, Una dressed her husband as an infant and laid him down in a cradle. Soon after, Benandonner crossed the causeway looking for Finn and came upon his house. There he found Una and the ‘baby’. Imagining how large Finn himself must be, Benandonner retreated across the sea, shattering the causeway behind him. To this day, identical columns can be found on the Scottish isle of Staffa.


Even the visitor’s centre is designed to echo the landscape

Whichever story you prefer, Giant’s Causeway remains one of the geological marvels of the world. One word of warning if you do decide to visit: be antisocial! Visiting during tourist season guarantees that the backdrop of all your photos will be people, not landscapes.


Be warned: you may have just sustained a lethal dose of mostly harmless science

If you enjoyed this article or have suggestions for future posts, please comment below! I’d love for you to follow me on WordPress or on Twitter @harmlessscience (just click Follow on the right sidebar). Thanks for reading!

Cover photo courtesy of Chris Lofqvist, Flickr Creative Commons. This article is modified from an earlier article I wrote for The Wanderer


7 responses to “Giants and Geology

    • Check out some of the photography of Giant’s Causeway on Google. Especially when the mist comes in, it’s just stunning.

  1. Pingback: The Yellowstone Supervolcano: A Disaster in the Making? | Mostly Harmless·

  2. Since getting to Northern Ireland I’ve already been twice and am planning another trip back. Love the post! Especially your pictures since there were gale warnings and some rain both times I was there.

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