Hverfjall is a tuff ring type of volcano crater in northern Iceland. It is located to the east of Lake Mývatn. It is one of the best preserved volcanic craters in the world. It errupted about 2900 years ago.
It is about 140 metres deep and 1km in diameter which makes it one of the largest of its kind in the world. A landslide occurred in the south part of the crater during the eruption, which accounts for the disruption to the round shape of the mountain.