Mt. Hverfjall (Hverfell) is a beautifully formed 2500 years old tephra crater. The crater is about 1 km in diameter and 140 meters deep. The round shape of the crater is disrupted by a landslide that occurred at the south edge of the crater during the eruption.
In the Settlement period, lava flowed from "Svortuborgir" almost encircling Hverfjall (Hverfell). At the same time, "Mt. Dalfjall" erupted.
Craters of the same type as Hverfjall are uncommon in the world, but there is another crater, "Ludentarskal" crater, which is much older, southeast of Mt. Hverfjall (Hverfell).
A great eruption occurred in a 12-km-long fissure south of Mt. Hverfjall (Hverfell) 2300 years ago.
Several bizarre formations are in this lava, which has been called the "Younger-Laxarhraun" lava field. A great row of craters called "Ludentarborgir" was formed on the fissure. "Threngslaborgir" is the name of two prominent craters towards the south of the fissure.
The "Younger-Laxarhraun" flowed over most of Myvatns district and covered and destroyed a large lake. The lava then flowed on through "Laxardalur valley", reaching the sea through "Adaldalur valley". Wherever the lava encountered lakes and wetland, steam explosions formed craters. Such craters are called pseudocraters since they are not outlets for lava but steam.
There are clusters of beautiful pseudocraters all around Myvatn and also in "Laxardalur" and "Adaldalur" valleys. Many of the craters are double and some even triple. The largest are found near "Mt. Vindbelgur".