The Giant’s Causeway in Northern Ireland is consistently one of the top geologically fascinating places in the world. The hexagon, systematically spaced columns protrude out from the sea and have fascinated many of locals and tourists for many years. I recently got the chance to quickly stop over here and check out the columns for myself!
In this short blog post I’ll describe how they were formed (geologically) and a little of the folk-lore around them. Spoiler alert – Giants may or may not be involved…
How it formed?
The Giant’s Causeways consists of over 40,000 basalt hexagonal columns, pretty much all systematically uniform in their shape. What caused this is actually not so unique to this windy coast of Northern Ireland. It is a common feature when a hot, mafic (basalt or dolerite) volcanic rock (either lava at the surface or shallow magma just below the surface) cools and contracts into a hexagonal columns (e.g., Kantha, 1981; Gray, 1986; Budkewitsch and Robin, 1994). The rapidly cooling lava cools from the outside toward the centre which causes contractions, and differences in the way it cools leads to the formation of hexagonal, prismatic column shapes (termed columnar jointing).
New understandings
Relatively new studies have deciphered more of the science on how these columns formed. For example, it is estimated that the temperature of incipient “jointing”, or cracking, happens at 840 – 890°C, according to Lamur et al. (2018) and studies from basalt of the Eyjafjallajökull volcano in Iceland. It has also been worked out recently (by computer models and physics) as to why the columns take on the hexagonal form (Hofmann et al., 2015). The initial simulated “lava” cools and cracks at right-angles (90°) initially, then as it cools it rearranges to change to 120° angles, thus forming the angles of the hexagons. It cools and takes the shape of the hexagon, and then the lava around also cools and tends to form around more hexagonal shapes.
GIANT’s Causeway history
Here at the Giant’s Causeway in Northern Ireland the pillars formed approximately 50 to 60 million years ago. The region consisted of chalk sedimentary beds which were then subjected to volcanic activity, forming a lake of lava that cooled relatively rapidly, forming the shapes we see now.
Another version of the story goes back to an old folk tale involving an Irish giant named Finn McCool. According to the tale, Mr. McCool built the crossing from Northern Ireland to Scotland by throwing boulders in the sea in order to bring his Scottish girlfriend over and confront his Scottish rival.
Not so unique…
Columns like this can be seen in many other place in the world actually, though probably none as famous as the ones at Giant’s Causeway. For example, Tasmania has many amazing exposures of columnar dolerite, such as seen at Cape Hauy and Raoul. Iceland also hosts some spectacular basalt columns where cascading waterfalls makes for quite the photos.
But wait, also… Game of Thrones 🙂
As an aside, the popular (and one of my favorite) TV series, Game of Thrones, did some of their filming nearby this area in Northern Ireland (though not right on the Giant’s Causeway). I stopped by a few sites in Northern Ireland, including the Dark Hedges, also known as “The Kingsroad” in Game of Thrones. This road is lined by >200 year old beech trees, forming a pretty stunning tree tunnel which happens to make a good filming backdrop for Game of Thrones (i.e., season 2).
Another filming site is the stunning Dunluce castle, situated at the edge of a prominent basalt outcrop. Dunluce castle is a 17th century medieval castle ruins in Northern Ireland and also was used (though heavily CG’d) as “Castle Pyke” of the Iron Islands in Game of Thrones.
Final thoughts
The Giant’s Causeway is a spectacular, natural wonder in the UK. Even though the hexagonal basalt columns are not themselves a unique phenomenon, the history/legend behind the area and the rugged and accessible setting on the north coast of Northern Ireland makes it truly cool site to visit. Something about seeing these beautiful hexagonal columns makes you really appreciate how neat rocks can be sometimes – well at least that is what I think, haha 😉
-Stephanie
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[…] enhancements) as Pyke Castle, home to the House of Greyjoy in Game of Thrones. And then we got to the Causeway. And wow was it breathtaking! I would have to say it was the most unique and interesting geological […]
Great stuff. I am a Canadian who is teaching in Huonville at the high school. I am currently teaching geology to year 8’s and if you have time for a one hour visit sometime, they’d love to meet you to hear your stories. Call the school if you are willing and able
Hi Jason, thanks for the message. Huonville is a cool place, I have been there a few times when I was in Tassie. I would love to come to the school for a visit, however, I no longer live in Tassie (I am currently in Canada). But if I ever find myself back down there I will give the school a call for sure 🙂
Hello from Huonville
Wow! Nothing like that around here! We do have some neat things but they’re not nearly so obvious and can take some hunting to find.
Thanks for the comment and reading the blog post 🙂 Yes the exposure here is quite spectacular indeed!
Great explanation Stephanie, great photos also. I have seen columns of over 2 m across inland from Innisfail in North Queensland where there appears to have been a lava pool caused by a gorge in the pre lava landscape. Pretty spectacular, cut through by the main highway but not highlighted/signposted/mentioned by anyone.
Thanks Peter. That sounds neat (and quite large at 2 m across)! Yeah the columns are more common around the world but often not highlighted as much as here at the Giant’s Causeway. Cheers 🙂