The Kerið Crater was formed 6,500 years ago and lies at the northern end of a row of craters known as Tjarnarhólar. It is part of the Western Volcanic Zone which also includes the Reykjanes peninsula and Langjökull Glacier. The caldera is approximately 55 m deep, 170 m wide, and 270 m across, and is made up of a unique red volcanic rock.

Visitors to Kerið will be able to hike down one of its sloping walls blanketed with deep green moss, and admire the stunning aquamarine lake at the bottom. The lake is shallow, but its vivid color is due to minerals from the soil.

Kerið was not formed by a volcanic explosion, but rather a cone volcano that erupted and emptied its magma reserve. The weight of the cone then collapsed into the empty magma chamber, creating the current crater. The water in the bottom of the crater is at the same level as the water table and is not caused by rainfall.