A smaller volcanic system lies to the north-west of the glacier in the Arnarvatnsheiði, north of the glacier Eiríksjökull. About 1,000 years ago, the craters of this system produced the lava field Hallmundarhraun which extends some 50 km westward into the valley of the Hvítá, and is traversed by underground streams which emerge at the beautiful waterfalls of Hraunfossar not far from Húsafell.