A seasick twenty-year-old German climbed into a small boat off the Isle of Mull in August 1829, and orchestras have been dealing with the consequences ever since.
His destination was Staffa, an uninhabited slab of basalt sitting a few miles out into the Atlantic. Waiting for him was a sea cave that runs some 70 metres into the island and stands 18 metres high, walled entirely in hexagonal stone columns, with the ocean washing straight through the floor, as Live Science describes it. Felix Mendelssohn spent much of the crossing being violently ill. He got the tune anyway.
How the rock cracked itself into columns
Staffa is what’s left of something enormous. Lava flows on the island belong to the Palaeogene Mull volcanic centre, one node in a chain of North Atlantic volcanism that also produced Skye, Arran, Ardnamurchan and Rum, as the Geological Society of London records. Only the earliest flows in that sequence cracked into tidy columns.
Cooling is what makes a column. Hot rock contracts as it loses heat, tension builds, and the cheapest way to release that tension is to split. Cracks link into a rough honeycomb at the surface, then travel inward as the cooling front retreats, leaving long prisms behind. Most come out six-sided. Plenty come out five- or seven-sided instead.
Lucas Goehring, L. Mahadevan and Stephen Morris tested that mechanism with cornstarch, of all things. Their paper in the Proceedings of the National Academy of Sciences found that starch dried in a laboratory cracks into columns about a hundred times smaller than basalt ones, yet geometrically similar to the fracture patterns at the Giant’s Causeway in Northern Ireland. Both sets of measurements collapse onto a single scaling curve, which points to one dynamical law running the show in a kitchen cupboard and in a lava flow alike. That is one line of experimental work, not a settled consensus: the researchers were blunt that centuries of study had never produced a comprehensive physical account of how these patterns get their scale.
The sea did the rest
So how does a cliff full of neat prisms end up with a hole through it?
Staffa carries at least nineteen sea caves. The National Trust for Scotland, which owns the island as a national nature reserve, sets out the method: heavy ocean swells find the crevices between columns and snap off great pieces of basalt, then pick the broken blocks back up and hammer the cliffs with them. Every joint in the rock was a pre-cut line of weakness. The Atlantic just followed them.
How a Hebridean rock became a destination
Joseph Banks was not looking for a cave. Fresh off Captain Cook’s first voyage, and having fallen out with Cook badly enough to mount his own expedition to Iceland, the botanist called in at the Hebrides in 1772 and was floored by a basalt cavern that already had a name in Gaelic. He’d brought an artist along, who drew it on the spot. Banks gave English readers a different name for the cave: Fingal, borrowed from the hero of James Macpherson’s Ossian poems. He never wrote up his own account of the day, so it reached the public secondhand, inside Thomas Pennant’s tour of the Hebrides two years later, engravings and all, as the Linda Hall Library tells it in its history of volcanic science.
Publication did the rest. Poets and painters started arriving, then steamers full of everybody else.
Why it sounds like that
Its Gaelic name is An Uamh Bhinn, the melodious cave, which rather gives the game away.
Basalt is hard and those columns are angular, so a sound entering the cave gets flung back from many directions at once instead of returning as a clean echo. Writing in the VIEW Journal of European Television History and Culture, Shona Noble of the Glasgow School of Art calls the result a diffuse reverberant field: reflections arriving from everywhere, fading slowly, filling the space like an organ chord held past its welcome.
Measuring any of this is awkward. Noble worked from an acoustic fingerprint recorded inside the cave in 2014 by the Historical Archaeology Research Project on Staffa, a collaboration between the art school and the Trust. Wind and waves keep the background noise so high that a simple recorded pulse would be swamped, so the team instead played a sine sweep climbing from 20Hz to 20kHz and worked backwards from what came out the other end. That one recording later let people in a headset hear their own voice as the cave would hand it back.
Twenty-one bars in a letter
Mendelssohn’s method was quicker and involved no equipment.
He wrote home to say the Hebrides had affected him extraordinarily, and copied out what had arrived in his head: twenty-one bars in piano score, tempo and dynamics already settled, orchestration sketched in, strings opening, woodwinds joining after the fourth bar, trumpets at the close of the fragment. The letter survives, as documented by Art and Music in Britain, an exhibition mounted at Yale.
He first called the piece The Lonely Island. Three years of revision later it had become the Hebrides overture, Op. 26, the work most people simply call Fingal’s Cave. Its final autograph draft score sits in Oxford, bought by the Bodleian Library in 2002 with lottery and donor money.
Noble raises one caveat worth carrying out of the cave. Any such measurement only describes a room from the exact spot the microphone stood in, so a single recording captures the cave about as well as one photograph captures a walk.
Which makes the cave Mendelssohn heard entirely his own: that tide, that swell, that patch of wet basalt, on a day he could barely stand upright. Every visitor since has been handed a different room. The overture is a transcript of one of them.
