Iceland, June 2014, Overseas Adventure Travel (OAT) trip.
Basalt column formation of Gerðuberg.
Basalt with its varieties is the most common volcanic rock type. Nevertheless basalt columns are really rare. They are formed during the cooling of the lava under certain conditions. Lava shrinks and breaks during the cooling process. Basalt is cooling down quite rapidly and by doing so it starts shrinking. This shrinking process starts at the surface, which mostly is cool air. The shrinking process slowly develops into the depth, forming longer and longer columns. These can grow to many meter length, depending on the thickness of the original basalt lava flow. Beautifully shaped basalt lava columns are almost always formed vertically as you find them here Gerðuberg. Most of these basalt columns are hexagonal, but there are also pentagonal and heptagonal columns. They look a little bit like enormous pencils.