The Old Man of Storr, a dramatically isolated pinnacle on the Isle of Skye in Scotland, is an iconic natural feature known globally for its rugged appearance. This geological monument draws its distinctive character from its core material. It is composed of an igneous rock known as basalt. The Storr is a remnant of ancient volcanic activity that created the entire Trotternish Ridge where the formation stands.
The Volcanic Composition
The foundation of the Storr is entirely volcanic, originating from vast flows of lava that erupted approximately 60 million years ago during the Paleogene period. This molten rock solidified into the dark, fine-grained basalt that now dominates the landscape. Basalt is extremely hard and dense, allowing it to resist erosion and weather much more effectively than the materials beneath it.
This durable basalt functions as a heavy “caprock” that overlies much softer sedimentary deposits, primarily mudstone and sandstone from the earlier Jurassic period. The contrast in rock strength is a defining feature of the area’s geology. Within the basalt layers, gas bubbles trapped during cooling formed spherical cavities called amygdales. These cavities later filled with secondary minerals such as calcite and various zeolites, creating amygdaloidal basalt.
The Mechanism of Formation
The unique, jagged appearance of the Storr resulted from a precise sequence of geological events. After the basalt caprock formed, its tremendous weight pressed down onto the underlying, weaker layers of sedimentary rock. This pressure created an unstable geological structure highly susceptible to movement.
The primary force that shaped the Storr was the massive post-glacial landslip, known as the Trotternish landslip. Following the retreat of the ice sheets, the removal of glacial weight combined with water seeping into the rock layers caused the underlying softer material to fail. This resulted in the largest continuous area of landslides in Britain, causing the entire eastern side of the ridge to slump toward the sea.
The landslip carried large sections of the basalt caprock down the hillside, but the most resistant fragments—like the Old Man pinnacle—were left standing exposed. This massive movement and subsequent erosion isolated the hard basalt sections, leaving them as spiky monoliths. Continuous erosion by wind, rain, and freeze-thaw cycles continues to refine the shape of these exposed remnants.
Distinguishing Features of the Storr
The Old Man of Storr pinnacle, standing approximately 55 meters tall, is a detached fragment of the larger Storr plateau characterized by its fractured structure. This basalt rock displays evidence of columnar jointing, a feature common in cooled lava flows. Columnar jointing occurs as the thick lava cools and contracts, forming a network of geometric cracks, often with four to six sides, that extend vertically through the rock mass.
These vertical joints give the Storr and surrounding formations their distinctive, spiky, and pillar-like appearance. The pinnacle itself is a massive column separated from the main cliff face by the landslip and weathering. Nearby, smaller rock spires, such as the Needle Rock, further highlight how the columnar nature of the basalt was exploited by erosional forces to create these isolated structures.