Geology GEÓLAS Glen Nevis is widely recognised as one of the most beautiful and spectacular glens in Scotland. It is bordered by more than twenty different mountain peaks including mighty Ben Nevis but how did this extraordinary place come into being? What shaped and formed the glen and mountains we see today? The story behind the scenery is as dramatic and exciting as the landscape itself. While it is relatively easy to imagine that ice played a big part in the shaping of Glen Nevis, the story revealed by the rocks themselves is even more astonishing. Most of the rocks seen in the glen were originally laid down as sediments on the sea floor some seven-hundred million years ago. Layers of quartz, sand and mud were buried and turned into sandstone and siltstone. Then, at a later date, these rocks were squeezed and crumpled on a huge scale. This massive squeeze caused by two great ‘plates’ colliding resulted in the formation of the Caledonian Mountain chain with huge peaks up to 6000m high. Soon after the Caledonian Mountains had been uplifted, huge quantities of magma formed within the Earth’s crust. Some of this magma escaped to the surface and poured out as lava. Remains of these lavas can be seen forming the upper half of Ben Nevis. The large rock fragments which cover the ground on the upper part of the mountain are all made of these grey volcanic lavas. Two huge magma chambers developed in the Glen Nevis area, one in the Mamores and another formed directly beaneath what is now the summit of Ben Nevis. In a cataclysmic event, which would have blasted vast quantities of ash into the atmosphere, a great mass of crust collapsed 600m into the magma chamber and a huge circular crater called a caldera was formed. The rocks we see today represent the roots of that ancient mountain chain. It is estimated that the rocks in Glen Nevis were at one time buried some 20km below the surface, so enormous amounts of material must have disappeared to reveal the rocks as they are now.