A failure of foundation
The unusual topography of Fairy Glen is a direct result of a massive, post-glacial landslip. The entire Trotternish peninsula, where the glen is located, contains the largest continuous area of landslides in Great Britain, extending for 23 kilometers and covering nearly 40 square kilometers. The geological setup for this instability began around 60 million years ago, during the Palaeogene period, when extensive volcanic activity covered the region in thick lava flows.
These flows formed a heavy cap of dense basalt rock, approximately 300 meters thick, over much older and weaker sedimentary rocks from the Jurassic period. This underlying foundation consists of layers of mudstones, shales, and sandstones. After the last ice age, when glaciers retreated and meltwater saturated the ground, the immense weight of the basalt layer overwhelmed the soft Jurassic strata beneath it. The weaker rock sheared, and huge sections of the basalt-capped hillside slumped and slid slowly towards the sea. This was not a single, sudden event; some major slides along the peninsula have been dated to between 6,000 and 7,000 years ago.
Rotational slumping on a vast scale
The distinctive shapes within Fairy Glen are examples of rotational slumping. As the blocks of land slid, they tilted backward against the slope, a motion that created the glen's signature conical hills and hummocky ground. The process fractured the basalt cap into individual masses, which now appear as scattered, contorted outcrops.
The most prominent feature is a natural basalt outcrop known as Castle Ewen, which has the appearance of a decaying fortress. This is not a man-made structure but a large, resistant block of basalt that remained more cohesive than its surroundings as the landmass around it moved and collapsed. The entire miniature landscape of small, steep hills, circular mounds, and little lochans (ponds) is the result of this deep-seated geological movement. The grassy, uneven terrain shows soil and vegetation have since covered the raw features of the ancient landslip.