June 21, 2021

I, Science

The science magazine of Imperial College

The Giant’s Causeway: World Heritage site, celebrity of ‘Visit Ireland’ publicity campaigns, subject of myth and legend

Its beautiful, sculpted steps are iconic, but it may shock people to realise the lavas which formed this stunning landscape are only 60 million years old, produced in what’s known as the Paleogene period. To give an idea of how recent this was, these eruptions occurred over five million years after the last dinosaur was made extinct. Ok, so still unimaginable, but it’s barely a smudge on the Earth’s timeline. At the time, Ireland (or the land which would eventually form it) was closer to the Equator, very hot and humid, still attached to America, and tiny dog-sized horses (with toes instead of hooves) roamed the land.

The stepped columns shown in the photo represent several individual eruptions. The middle eruption, of three, formed the hexagonal stones when the lava was forced to cool extremely quickly. This still happens in Hawaii, as you’ll see if you’re ever lucky enough to visit. When the lava is erupted it instantly encounters water, which causes it to crack and crystallize. This was what happened to form the Causeway. The columns sit on still older rocks, containing fossils of sea-creatures and dinosaurs, which are the not-so-pretty rocks in the picture, further into the water. The eruptions were so huge that the same formation can be seen at Scotland’s Fingal’s Cave as well.

Due to the stepping-stone-like nature, it of course prompted a different account of its formation, one of human creation. Legend has it that Fionn mac Cumhaill, an Irish warrior, built the causeway as a bridge to battle his Scottish enemy, Benandonner. One version of the legend tells that Fionn, one can only assume exhausted from building the Sistine Chapel of bridges, fell asleep before he got across.

When he did not arrive, the much larger Benandonner crossed the bridge looking for him. To protect Fionn, his wife Oonagh laid a blanket over him so he could pretend that he was actually their baby son, which, shockingly, worked. When Benandonner saw the size of the ‘infant’, he assumed the alleged father, Fionn, must be gigantic indeed. Therefore, Benandonner fled home in terror, ripping up the Causeway in case Fionn followed him.

I’ll leave it with you to decide which theory is more feasible, but personally, I’d much rather a giant baby built it than a measly volcano.

Image: Douglas Heaven