Geopark Rock Route 3 - Trislaig
The interpretation board is located in the car park of the village hall in Trislaig. The interpretation board is sited to provide fine views of the Ben Nevis Range (Aonach Mor, Car Mòr Dearg and Ben Nevis), as well as Cow Hill and Fort William. The board describes the formation of the Ben Nevis Range, involving laying down of sedimentary rock, the collision of continents, metamorphism and volcanic activity over vast geological time scales.
The board tells the fascinating story of the origins and geology of the Ben Nevis Range; a complex sequence of events illustrated through a series of diagrams. Diagrams depict the formation of Ben Nevis Range, which resulted from a series of eruptions, the first around 410 million years ago to form a volcano and a large lava field (of andesite lava). The lava erupted onto the pre-existing schists and other metamorphic rocks that formed the remains of the Caledonian mountain chain.
Later, a large mass of magma rose and solidified in a magma chamber beneath the surface to form the coarse grain outer granite of Nevis Range. This was followed by another upsurging of magma, followed by the collapse of the roof of the magma chamber. The collapse of the roof led to the sinking of a cylindrical block of rocks above (andesite lava and schists) into the magma chamber; an event accompanied by further eruptions of ash, gases and lavas. A large crater (caldera) was formed as a result. The magma in the chamber eventually solidified to form the pink fine grained inner granite of the Nevis range.
The formation of the caldera, followed by later erosion of the lava field and surrounding schists, resulted in the distinctive geology of the Ben Nevis Range as seen today with the upper slopes consisting mainly of outer granite and inner granite, and the lower slopes dominated by quartz diorite, quartzite and schists, with dykes variously cutting through the granites. The summit of Ben Nevis is composed of volcanic breccias and andesite lava, the remains of the eroded caldera. Erosion, uplift and glaciation events have all left their distinctive marks.
The board is located in the car park at Trisaig Village Hall just south of Camusnagaul ferry terminal.
This information board provides a great opportunity to familiarise yourself with the geology and topography of the Ben Nevis Range, with the ancient caldera volcano of Ben Nevis dominating the landscape, at a height of 1344 m.