Exploring the Planets

Deltas and Layers

Some ancient impact craters and canyons contain sedimentary deposits that resemble river deltas.

In Eberswalde Crater, river meanders grew and cut off their loops as meandering rivers do on Earth. Wind has slowly blown away the floodplain sediments, leaving the channel beds behind as ridges. Dozens of valley deposits with steep outer margins have been found on Mars, but few appear as dramatic as this.

Mars Orbiter Camera mosaic
NASA/JPL/Malin Space Science Systems image

Eberswalde Crater, Mars

Some impact craters have deep alcoves eroded into their rims, and thick deposits of gravelly sediment (called alluvial fans) deposited along the base of the inner wall.

Mars Odyssey, THEMIS
NASA/JPL/Arizona State University image

Alluvial Fans on Mars

Some craters and basins have alternating dark- and light-colored, thinly layered deposits exposed by excavation and erosion on their floors and walls, as here in Holden Crater. They probably formed by a combination of volcanic and sedimentary processes.

Mars Odyssey, THEMIS
NASA/JPL/Arizona State University image

Holden Crater, Mars

The best-preserved valley networks on Mars are often the youngest. These dense valleys formed on the plateau and canyon walls of Valles Marineris between 1.8 and 3.5 billion years ago. Possible deltas formed where valleys drained into a basin near the canyon bottom.

Mars Odyssey, THEMIS; NASA/JPL/Arizona State University image
Mars Global Surveyor, MOC; NASA/JPL/Malin Space Science Systems image

Valles Marineris, Mars