Waw an Namus is a , caldera, which has a small relief outwards but a steep margin inwards. During its formation, over of rock were displaced. Another crater lies northwest from Waw an Namus. That vent was formed by overlapping craters which feature no volcanic rocks and which have produced salty mud; this may have been a site of phreatic activity and of volcanic degassing. The caldera contains ash deposits and some dunes, but also a humid zone with reeds.