Nili Fossae

The linear depressions in today's VIS image are part of Nili Fossae. Nili Fossae is a collection of curved faults and down-dropped blocks of crust between the faults called graben. Graben 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 Nili Fossae graben lie northeast of the large volcano Syrtis Major and northwest of the ancient impact basin Isidis Planitia. The troughs, which can be almost 500 meters (1,600 feet) deep , make concentric curves that follow the outline of Isidis Planitia. The graben likely formed as the crust sagged under the weight of lava flows filling the Isidis Planitia impact basin.