Gerðuberg Cliffs are one of the most striking examples of columnar basalt on the Snæfellsnes Peninsula. These columns up to 46 feet high form an unusually straight, regular wall of dark volcanic rock on the southern side of the peninsula, near the western edge of the Hnappadalur valley. When a thick body of basaltic lava cooled, it contracted. That contraction produced fractures that propagated through the rock, creating the characteristic vertical columns. Hexagons are particularly common because they efficiently accommodate the stresses created during cooling.