Slumping is a landslide in which rocks and soil slide as a single unit. Sapping is when groundwater breaks the surface and undermines rock and sediment, causing them to collapse. It can cause the progressive collapse of rocks and soil resulting in the headward retreat of a canyon. The Martian surface has many prominent features resulting from the flow of subsurface water. Subsidence is the sinking of the ground surface due to the removal, dissolving or shrinkage of material below that ground surface.
Rocks dissolve slowly, such as over thousands, millions and billions of years.
The Martian surface has many prominent features resulting from subsidence. Students try to explain the formation of the largest, most complex rift valley on Mars by applying what they learned earlier in the module about processes that alter a planet's surface. Valles Marineris is a network of valleys, each showing evidence of a variety of geological processes. There are many competing hypotheses about the formation of Valles Marineris. Valles Marineris is immense.