Ben Nevis is all that remains of a Devonian volcano that met a cataclysmic end in the Carboniferous period around 350 million years ago. Evidence near the summit shows light-coloured granite (which had cooled in subterranean chambers several kilometres beneath the surface) lies among dark basaltic lavas (that form only on the surface). The two lying side-by-side is evidence the huge volcano collapsed in on itself creating an explosion comparable to Thera (2nd millennium BC) or Krakatoa (1883).