Two volcanic fissures lie from the sea onto land on the western side of Reykjanes and form a series of craters. These crater series have been named Stampar. The crater series are from two periods. This series lies in the SW-NE direction and follow thereby the most common fissure angle in Reykjanes.
The older formed in an eruption from a fissure that was just under 4 km long around 1,800 to 2,000 years ago. The younger Stampar crater series formed in the Reykjanes Fires in 1210-1240. The row of craters is around 4 km, and the area of the lava field they produced is approximately 4.6 km2. The two craters closest to the road, named Stampar, are at the north end of the crater row. Further south in the crater row are other sizeable craters such as Miðahóll hill, Eldborg the deeper and Eldborg the shallower. Fishermen in earlier times used all these craters as points of reference when out at sea. Most of the craters, however, are low-lying scoria cones and not very prominent.