The crater Kerið was formed about 6,500 years ago and lies at the northern end of a row of craters known as Tjarnarhólar. It is oval, about 270 m long, 170 m wide and 55 m deep: the depth of the water at the bottom varies between 7 and 14 m. According to an old tradition, a rise in the water level here is accompanied by a corresponding fall in the pond on Búrfell in Grímsnes and vice versa.
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Kerið lies in the Iceland´s Western Volcanic Zone, which runs through the Reykjanes peninsula and the glacier Langjökull. Traces of volcanism are not very obvious, since most of the eruption sites are low-lying and many of the craters are hidden by vegetation, but three craters in the Grímsnes area are clearly discernable and well-known features: Kerið, Seyðishólar and Kerhóll.