Explore the story of mountain building and thrust faulting, told through sculpture and interactive exhibits at Knockan Crag
Unlock the mysteries of the amazing landscape in and around the Knockan Crag NNR in the North West Highlands UNESCO Geopark. Here, you can walk right up to and touch the strange, internationally famous geological phenomenon known as the ‘Moine Thrust’. This is the place where crystalline metamorphic rocks sit on top of a sequence of undisturbed sedimentary rocks which have not been affected by the activity that deformed the overlying rocks. Read on to find out why!
Geologists first learned that rocks can move vast distances when continents collide through studying the rocks of the North West Highlands. We now know that when two land-masses collide (such as India and Asia today), mountains are pushed up. Deep underground, the rocks are buckled, bent, fractured and heated – the process of metamorphism, when rocks are changed by heat and pressure. The rocks at the top of Knockan Crag are called the Moine metamorphic rocks, they started as billion-year-old sedimentary rocks and were affected by metamorphism in several stages up to about 450 million years ago, during the formation of the Caledonian mountain range.
Knockan Crag is a window into conditions 420 million years ago, at the edge of the Caledonian mountains, demonstrating that how great slabs of rock can be pushed to the surface and sideways over adjacent rocks in ‘thrust sheets’. The Moine metamorphic rocks have ended up on top of limestone, and at the Moine Thrust at Knockan Crag you can put your hands on these two very different rocks.
For more than 100 years geologists have used Knockan Crag to help demonstrate this, and now their theories are applied to understanding mountain building and tectonic plates across the world. However, this was far from a straight-forward development of theory, and some of the early ideas were incredibly controversial at the time. The first geologists to study the sequence here, Roderick Murchison and Archibald Geikie, thought they were a simple sedimentary succession with the oldest rocks to the west and the youngest to the east. They were fooled by the nature of the lower part of the Moine rocks: their layered nature was later identified as the result of thrust faulting, a type of rock first described and named ‘mylonite’ by Charles Lapworth at Loch Eriboll in the North West Highlands.
Text contributed by Laura Hamlet & Pete Harrison, North West Highlands UNESCO Global Geopark.
Find out more
Learn more at nature.scot/Knockan-Crag and driftingapart.ccght.org or come visit us! The site has good car parking, toilet facilities and an interpretation centre. Trails around the site give spectacular views, allow 1-2 hours for the circular walk around these spectacular crags.
This web page is published by the Scottish Geodiversity Forum under a Creative Commons ‘Attribution Non-commercial’ (CC BY-NC) licence, which permits non-commercial reuse provided the original work is properly cited.