A prominent collapse feature [box 1] can be seen in Phoenicis Lacus. It is a long pit with a depth of about 3 km below the surrounding terrain. In the central fault zone, there are uplifted blocks [box 2], showing that significant tectonic deformation has taken place in this region. A crater can be seen [box 3]. This impact structure was elongated during the spreading of the region and evolved from a circular to an ellipsoidal form.