Lochaber truly has a fiery past! When plates collide with one another or when new ocean floor is created as plates split apart, enough heat can be produced to melt rocks in the Earth’s crust.
A caldera is formed when a volcano erupts and the magma chamber empties, leaving less behind to support the weight of the volcano’s summit. Gradually over time, the rocks that form the summit collapse inward to form a giant crater.
Lochaber is well known as a place where we can see ancient calderas up close.
Calderas can be seen from the roadside in Glencoe, and the rocks of Ben Nevis, though not as easily accessible, also show evidence of a complex collapse structure. The rocks which make up the highest summit in Scotland are only preserved today because they subsided more than 600m during the formation of a large caldera at the close of the Caledonian mountain-building period.
The lavas and granites of Ben Nevis, Glen Coe and Glen Etive are of outstanding geological interest. It was in these three locations that the geologists who first mapped the area a century ago discovered evidence of major caldera collapse structures. This was the first place in the world that such formations were identified.