Gerðuberg is a cliff of dolerite, a coarse-grained basalt rock, located on the western peninsula of Snæfellsnes in Iceland. It is a row of perfectly shaped hexagonal basalt columns that run along the cliff for over a kilometer. The columns are between 7 and 14 meters tall and up to 1.5 meters wide.
Gerðuberg was formed by a process called columnar jointing. When lava cools, it contracts. This contraction can cause the lava to break into a series of regular polygons, such as hexagons or pentagons. The size and spacing of the columns depends on the rate of cooling and the composition of the lava. In the case of Gerðuberg, the lava was cooled rapidly by the sea. This rapid cooling caused the lava to break into hexagonal columns with very regular spacing. The columns are also very tall because the lava was thick when it flowed.
The most unusual thing about Gerðuberg is how the columns are so geometrically symmetrical that they seem to be carved by hand. Such features are rare around Iceland and the rest of the world, but easily explained by science. Gerðuberg is so flat on top because the lava that formed it cooled very evenly. Also, the columns have been eroded by the wind and rain. The wind has blown away the loose material between the columns, leaving a smooth, flat surface.
Gerðberg is usually the first major site visitors to the Snӕfellsnes Peninsula see as they as they approach it from Reykjavík, and travel along its southern side. The cliffs with these strange columns runs adjacent to the road and sea, making them impossible to avoid.
According to the Internet