Hverfjall is a tephra cone or tuff ring volcano in northern Iceland, to the east of Mývatn. It erupted in 2500 BP in the southern part of the Krafla fissure swarm. The crater is approximately 1 km in diameter. Tephra has been carried from Hverfjall all over the Mývatn area. A landslide apparently occurred in the south part of the crater during the eruption, which accounts for the disruption to the round shape of the mountain.