Ring furrows: Inversion of topography in Martian highland terrains

Ring furrows are flat-floored trenches, circular in plan view, surrounding a central, flat-topped, mesa or plateau. The internal plateau is about the same elevation or lower than the plain outside the ring. The outer wall is often breached by valley drainage or opened to low, degraded surfaces. Related landforms range from ring furrows with fractured central plateaus to those with isolated circular mesas without depressed rings. Ring furrows are superposed on many types of materials, but they are most common on cratered plateau-type materials which are interpreted as volcanic flows overlying ancient cratered terrain. Most rings occur in or near regions of fretted terrain. Ring furrows are formed by preferential removal of the exposed rims of partially buried craters. Ground ice decay and sapping followed by fluvial erosion are proposed for removal of the least resistant rim materials. Thus, differential erosion has caused an inversion of topography in which the originally elevated rim is reduced to negative relief.