Ismenius Lacus Quadrangle - Fretted Terrain

Fretted Terrain

The Ismenius Lacus quadrangle contains several interesting features such as Fretted terrain, parts of which are found in Deuteronilus Mensae and Protonilus Mensae. Fretted terrain contains smooth, flat lowlands along with steep cliffs. The scarps or cliffs are usually 1 to 2 km high. Channels in the area have wide, flat floors and steep walls. Many buttes and mesas are present. In fretted terrain the land seems to transition from narrow straight valleys to isolated mesas. Most of the mesas are surrounded by forms that have been called a variety of names: circum-mesa aprons, debris aprons, rock glaciers, and Lobate Debris Aprons. At first they appeared to resemble rock glaciers on Earth. But scientists could not be sure. Even after the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) took a variety of pictures of fretted terrain, experts could not tell for sure if material was moving or flowing as it would in an ice-rich deposit (glacier). Eventually, proof of their true nature was discovered by radar studies with the Mars Reconnaissance Orbiter showed that they contain pure water ice covered with a thin layer of rocks that insulated the ice.

• Fretted terrain of Ismenius Lacus showing flat floored valleys and cliffs. Photo taken with Mars Orbiter Camera (MOC)on the Mars Global Surveyor, under the MOC Public Targeting Program.

• Enlargement of the photo on the left showing cliff. Photo taken with high resolution camera of Mars Global Surveyor (MGS), under the MOC Public Targeting Program.