It's as tall as a high-rise and as wide as a lorry, with a vaulted entrance as high as a cricket pitch. Is it any wonder Fingal's Cave was once thought to be the work of an ancient warrior-giant?
That warrior-giant, it's said, was Fionn mac Cumhaill – also known as "Finn McCool" or "Fingal. Legend has it that he built a path from Giant's Causeway in Northern Ireland to the Isle of Staffa in the Inner Hebrides. His mission: to walk the 83 miles between them to confront his rival, the Scottish giant Benandonner.
These days, few people believe this origin story. Instead, the formation of this spectacular sea cave on the uninhabited island of Staffa is attributed to the slow, slow workings of lava and water.
The cave's cathedral-like structure is made up of towering basalt columns. These impressive columns are a remarkable example of naturally occurring hexagons.
Fingal's Cave is a feast for the ears as well as the eyes. Its unique acoustic properties amplify the crashing waves all around it. It's no surprise that this wonder of the natural world has inspired composers, poets and painters.
So, how was it formed? It all began 60 million years ago.
How was it formed?
Let's rewind to the Palaeocene period. The dinosaurs were gone, the world was largely tropical and the continents we know today were still forming.
Huge volcanic eruptions spewed forth thick, flowing basaltic lava. As it cooled, it contracted and cracked into fascinatingly symmetrical hexagonal patterns.
Thousands of years passed. The Atlantic Ocean battered its waves against the basalt, washing away loose rocks and ash from underneath the towering pillars.
Over time, the ocean's natural chisel carved out the arched ceiling and deep chasm we see today.
In this sense, Fingal's Cave has something in common with the caves here at Stump Cross Caverns. Like so many other natural rock formations, they're made by the working of water and time against rock. Simple – yet the results are breathtaking in their natural intricacy.
Fingal's Cave is one-of-a-kind. But there are other sea caves carved into columnar basalt – most notably the Giant's Causeway in Northern Ireland.
Our ancestors were right to notice the similarity. But whereas they believed both formations were the work of a warrior-giant, we now believe they were formed from the exact same lava flow.
There are similar formations on the neighbouring islands of Ulva and Gometra. And on the other side of the Atlantic, the Sea Lion Caves in Oregon tell a similar geological story.
Why are the columns hexagonal?
One of the most amazing things about Fingal's Cave is its naturally occurring hexagonal basalt columns – the result of a process called "columnar jointing".
Essentially, the lava flow cooled into rock, and the rock began to shrink. As it shrank, it cracked into a geometric pattern where three fractures intersect at 120-degree angles.
The result? Perfect six-sided columns.
This has something in common with other naturally occurring hexagons – often driven by a fundamental principle of physics where surface area is minimised to relieve stress.
Take honeycombs, where bees use the least amount of beeswax to store the maximum volume of honey. You can even see naturally occurring hexagons in foam, where surface tension causes bubbles to flatten against each other and form efficient, hexagon-like shapes.
Other naturally occurring hexagons include snowflakes and the eyes of insects like dragonflies and flies.
How are sea caves formed?
