Everything We Knew About The Giant's Causeway Was WRONG

A Familiar Landscape With an Unfamiliar Story

The Giant’s Causeway is one of those places people think they already understand. You hear “cooling lava,” you see the neat hexagons, and it all feels satisfyingly explained. But the more geologists have looked at this place, the more they’ve realised that the familiar story barely scratches the surface. Something about this landscape refuses to line up with the old explanations, and for decades nobody noticed. The rocks give away just enough to suggest that something unusual happened here — unusual enough that the accepted story eventually had to be torn apart and rebuilt from the ground up.

Part of the reason this site became so famous is because it seems straightforward at a glance. A clean row of hexagonal columns stretching into the sea feels like a simple, tidy geological process frozen in stone. But if you walk the coastline long enough, the cliffs begin to hint that something isn’t quite right. Certain layers behave oddly. Heights don’t match. Patterns bend where they shouldn’t. And once you spot these inconsistencies, it becomes difficult to shake the sense that the Causeway is hiding a much deeper story just beneath its surface.

For a long time, hardly anyone questioned any of this. It was easier to assume the Causeway was exactly what it appeared to be — a photogenic example of volcanic geometry — rather than a puzzle with missing pieces. But eventually, someone did question it. They noticed a detail that didn’t fit the established explanation, then another, and then another still, until cracks began spreading through the old story like fractures in cooling basalt. What looked like a simple landscape was suddenly anything but.

Only once that sense of unease has settled in do we have enough footing to start pulling at the threads. And when you pull at the rocks of the Giant’s Causeway, the first thing that begins to unravel is the idea that this landscape formed under ordinary volcanic conditions. Because if you strip away the columns and the ocean and the tourists climbing over the stones, what you’re left with is a geological problem that should never have been overlooked in the first place.

The Basalts Beneath and the Origin of the Traditional Model

The Causeway sits inside a massive sequence of ancient basalt flows known as the Antrim Lava Group. These lavas erupted around sixty million years ago during the Paleocene, when the North Atlantic was in the process of tearing open. That rifting — the technical term for the stretching and thinning of Earth’s crust — allowed huge volumes of magma to rise toward the surface. “Magma” simply means molten rock stored beneath the ground. When magma erupts, it becomes lava. It’s a distinction based entirely on whether the molten rock is underground or above it.

*Image depicts the Antrim Basalt Layer

The older part of this volcanic sequence is called the Lower Basalt Formation. These older flows line the cliffs surrounding the Causeway, and at first glance they look unremarkable. But these are the layers that store the evidence of what really happened. They hold the shape of the landscape before the famous columns formed, and it’s this shape — the dips, the tilts, the angles — that quietly contradicts the traditional story.

*Image depicts the Antrim Lava layer (red) and the Older Volcanics (Yellow)

For nearly a century, the accepted explanation was that the Causeway’s columns are so thick here because the lava filled a valley. A valley carved by rivers, deepened over time, and eventually buried beneath a massive sheet of molten rock. This process is called fluvial incision. “Fluvial” means river-related, and “incision” means cutting down into the land. The idea was comfortable, familiar, and easy to visualise. It made sense. A valley is low; lava flows downhill; thicker lava gathers in depressions. It explained the thickness. And because it explained the thickness, no one questioned it.

The Evidence That Destroyed the Old Interpretation

But the rocks beneath the Causeway do not behave like a valley. They do not dip in a smooth, predictable direction. They lean inward. They curve toward a single, central point beneath the Causeway itself. This inward convergence is not a signature of erosion. It’s the signature of something the landscape did not inherit — but something it experienced.

A valley carved by water has walls and a floor. It has debris, sediment, and the scars of erosion. Yet the surface beneath the Causeway lava contains none of these things. Instead, it preserves a layer of deep reddish soil known as laterite, which forms under intense tropical weathering when rainwater strips away soluble minerals and leaves behind iron and aluminium-rich material. Laterite is delicate. It shouldn’t survive the carving of a valley. But there it is: intact, undisturbed, still in place right where the valley was supposed to have been.

This is the moment where the old story begins to collapse under its own weight. If rivers carved a valley, the laterite should be gone. If water collected in that valley, the lava should contain glassy debris from the moment it hit the water. If time passed between valley formation and lava eruption, there should be sediment layers. But none of these things are present. The lava rests directly on the laterite, as though nothing happened between the soil forming and the lava arriving.

That leaves only one possibility: the feature beneath the Causeway was not carved. It formed another way.

The more you follow this idea, the more the pieces fall into place. The inward-dipping older lavas resemble a bowl rather than a valley. The lack of sediment suggests no time passed between the formation of this depression and the arrival of lava. The remarkable thickness of the Causeway lava suggests that whatever formed the depression happened quickly, creating space that was immediately filled with molten rock.

The New Model: Magma Chambers, Collapse, and Lava Ponding

This points to a geological mechanism very different from erosion — one rooted in the behaviour of magma chambers beneath Earth’s crust. The modern picture that geologists now recognise is that a shallow magma reservoir once sat beneath this stretch of Paleocene Ireland. At some point, magma was being added to it from below, causing the crust to swell slightly. This swelling is called inflation. It’s the same process seen today in volcanic areas like Hawaii and Iceland, where the ground subtly rises when magma forces its way into shallow chambers.

But inflation doesn’t last forever. When magma drains from a chamber — either by erupting at the surface or by moving elsewhere in the crust — the support disappears. The roof of the chamber begins to sag. Not dramatically, not like a sinkhole, but enough to fracture and tilt the rocks above. This sinking is known as subsidence. And the shape it produces in the landscape matches precisely what geologists have now mapped beneath the Causeway.

This would have created a sudden basin in the landscape. Not carved slowly. Not shaped by water. But produced directly by volcanic movement under the ground. The basin likely formed quickly, perhaps in a matter of weeks or months, although in geological terms it could have been even faster. Crucially, it formed so rapidly that there was no opportunity for sediment to accumulate or for water to transform it into a lake. The land dropped — and before anything could change, lava arrived.

When that lava flowed in, it did so as a thick, searing-hot flood of tholeiitic basalt. “Tholeiitic” describes basalt formed from low-alkali magma, which tends to erupt in widespread, sheet-like flows. This chemically simple lava cools at a very predictable rate, and when it cools slowly and evenly through a large thickness, it contracts in a way that forms columnar joints — the hexagonal patterns for which the Causeway is famous.

The lava cooled from the top down and the bottom up simultaneously. As the contraction cracks began forming at the cooling surfaces, they propagated downward and upward, creating tall pillars separated by hexagonal cracks. Because the lava here was so unusually thick — due to the subsidence basin beneath it — the columns grew exceptionally tall and exceptionally regular. Their shape is not accidental. It is the consequence of slow, uninterrupted cooling inside a deep pool of molten rock.

Why the New Interpretation Changes Everything

What makes the new interpretation so compelling is that it explains everything the old model struggled with. It explains the basin shape. It explains the lack of erosion. It explains the thickness. It explains the columns’ perfection. And most importantly, it explains why this phenomenon is so localised to the Causeway itself. The depression created by subsidence was centred right here, not along the entire coast. This is why the columnar-jointed basalt is thicker at the Causeway than anywhere else along the Antrim cliffs.

The beautiful irony is that this revelation didn’t come from exotic technology or complex computer models. It came from geologists walking the cliffs, looking closely at the dip of the rocks and asking whether the old explanation still held. It came from noticing the absence of sediment, the survival of the laterite, and the precise angles of the older basalt flows. The Causeway had been studied for centuries, but the details that held the truth were small, quiet, and easily overlooked. Sometimes geology advances not through grand theories, but through simple questions with uncomfortable answers.

And when all the evidence is brought together, the story becomes clear. The Giant’s Causeway was not formed inside an ancient valley. It was formed inside a volcanic collapse. A shallow magma chamber beneath Paleocene Ireland drained rapidly, the ground above it sagged, and the resulting depression was immediately filled with molten basalt. As that lava cooled slowly, it fractured into columns. Those columns stood through the ages, long after the volcanoes went extinct and the North Atlantic continued its expansion. Millions of years later, the sea carved away the softer rock around them, revealing the geometric landscape we see today.

Understanding this changes the way you see the Causeway. What once looked like a tidy example of volcanic cooling becomes the frozen aftermath of a geological failure — a moment when Earth’s crust adjusted to the sudden loss of support beneath it. The columns are the final stage of a chain reaction that began miles underground, in a magma body that no longer exists. And the tourists walking across the stones today are unknowingly exploring the floor of a long-lost volcanic basin.

It also changes the way you think about familiar landscapes. The Causeway teaches us that even the most photographed, most interpreted, most visited geological sites can still withhold their secrets. It reminds us that geology is alive with revision and discovery. That a single observation — a tilted layer here, an absence of sediment there — can rewrite decades of certainty.

The Giant’s Causeway has always been a place where myth and geology collide. But the truth buried beneath it is stranger still. It is a landscape built not by giants, nor by rivers, but by the sudden breath and collapse of a Paleocene magmatic system that shaped Northern Ireland at the dawn of the North Atlantic. It is a story that sat in plain sight for nearly a century, waiting for someone to look again.

And now that we know the real story, the Causeway becomes more than a beautiful oddity. It becomes a geological moment captured in stone — a moment of collapse, eruption, cooling, and preservation that reveals just how dynamic Earth’s crust can be, even in places that appear timeless.

Here's the video we made on this on the OzGeology YouTube Channel:

Link to the study used to construct this article:

Subsidence, not erosion: Revisiting the emplacement environment of the Giant's Causeway, Northern Ireland