Memnonia and Mangala Fossae

Fossae are long linear depressions called graben and are formed by extension of the crust and faulting. When large amounts of pressure or tension are applied to rocks on timescales that are fast enough that the rock cannot respond by deforming, the rock breaks along faults. In the case of a graben, two parallel faults are formed by extension of the crust and the rock in between the faults drops downward into the space created by the extension. The graben in this VIS image are part of Mangala Fossae (top, in crater) and Memnonia Fossae (bottom of image). Memnonia Fossae, Mangala Fossae and Sirenum Fossae are all long graben systems that stretch from eastern Terra Sirenum into western Daedalia Planum. Mangala Fossae is 828 km long (514 miles). Memnonia Fossae is 1585 km long (985 miles).