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.