Mars Geology

Valles Marineris

The largest tectonic feature on Mars is Valles Marineris, a mammoth system of troughs that extends eastward from Tharsis. It is actually a coalesced system of a dozen smaller troughs. Each is about 5 kilometers (3 miles) deep and around 160 kilometers (100 miles) across. High resolution images of the canyon walls show thousands of layers, attesting to a long and rich geologic history preserved in stratigraphic cross-section. Many of these layers seem volcanic, but, as is discussed below, CRISM shows that clays are also common. Parts of the floors of the chasma system are intermediate-elevation plateaus made of sediments rich in sulfates that may have accumulated in water.

Valles Marineris is as large and deep as Earth's Mediterranean Sea without the water. (Image credit NASA/USGS.)