Terrawatch: Taking a closer look at Ben Nevis

Ben Nevis, Britain’s tallest mountain, stands proud at 1,344 metres, and every year thousands of people make the pilgrimage to its summit. Most walkers are focused on getting to the top, but for those who take things more slowly the rocks around them tell the tale of how this mountain formed.

Around two-thirds of the way up there is sharp change, from red granite to dark grey andesite – a lava that erupted when the mountain was an active volcano hundreds of millions of years ago. Andesite is never normally found next to granite – a rock that forms slowly deep inside a magma chamber – and the traditional explanation for this unusual juxtaposition is that it was caused by a spectacular collapse 400m years ago, when the roof of the magma chamber failed, and the top of the volcano fell in.

But now geologists are not so sure. Last summer a team of climbers, geologists and botanists investigated previously unexplored nooks and crannies on the steep and forbidding and sheer 600-metre north face of Ben Nevis.

Dangling from ropes the scientists used state-of-the-art digital technology to photograph the rock and measure its orientation.

The extra detail suggests that the story of the mountain’s formation might be more complex, and perhaps it wasn’t the lava that crashed down, but instead the granite that rose up.

Over the next two summers the team will be going back to take more measurements to resolve the question. In the meantime a film of their adventures will be shown in February at the Fort William mountain festival. Kate Ravilious