This lava field is among the most rugged AA-lava fields of the country. It was created by a fissure eruption 3600-4000 years ago (a sign by the craters sais 3000 years ago) and is vegetated with woolly fringe moss, heather, birch, and willow. The largest of the three craters situated on a volcanic fissure with a northwesterly and southeasterly direction is Grabrok.
The craters were declared inviolate in 1962 after decades of exploitation for construction material and the lava field is a nature reserve. A hike to the top of the Grabrok crater is very rewarding on a fine day because of the magnificent scenery and surroundings and people are urged to stay on the path.

There are interesting hiking trails all over the area, along the fine salmon river Nordura and Lake Hredavatn and further for those who might want to spend the whole day walking.