Dyngjufjöll, a cluster of mountains around the Askja caldera, forming a square about 24 km a side, rising 600–700 m above the surrounding plateau and 100–200 m above the bottom of Askja. Evidence suggests that these mountains are the remnants of a huge volcanic zone from the ice age, that collapsed. There are many younger lava streams, almost no vegetation and geothermal heat in many places. The highest peak is Þorvaldstindur (1510 m) on the south rim, named for the 19th century geologist Þorvaldur Thoroddsen. The main passes into Askja are Suðurskarð on the south, Jónsskarð on the northwest and Öskjuop on the northeast, where the road–track is.