Mareotis Fossae

The linear features in this VIS image are called Mareotis Fossae. They are part of a huge region of graben that comprise Tempe Terra. The graben of Mareotis Fossae trend to the northeast, parallel to the fossae of Alba Mons located just to the west of Tempe Terra. 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. Numerous sets of graben are visible in this THEMIS image, trending from northeast to southwest. Because the faults defining the graben are formed perpendicular to the direction of the applied stress, we know that extensional forces were pulling the crust apart in the northwest/southeast direction. Mareotis Fossae is 1907km long (1185 miles).