Iani Chaos and Ares Vallis
This image, taken by the High Resolution Stereo Camera (HRSC) aboard ESA's Mars Express spacecraft, shows a large depression called Iani Chaos and the upper reaches of a large outflow channel called Ares Vallis. North is to the left.
Image strips were taken in October 2004, during three orbits from a 350-kilometre altitude, with a resolution of 15 metres per pixel. The strips have then been matched to a mosaic that covers an area from 17.5° western longitude to 3° North. The Iani Chaos depression – 180 kilometres long and 200 kilometres wide – is connected to the beginning of Ares Vallis by a 100-kilometre wide transition zone.
From here, Ares Vallis continues its course for about 1400 kilometres through the ancient Xanthe Terra highlands, bordered by valley flanks up to 2000 metres high. Eventually Ares Vallis empties into Chryse Planitia.
Ares Vallis is one of several big outflow channels on Mars in this region that formed billions of years ago. Many surface features suggest that erosion of large water flows had carved Ares Vallis in the Martian landscape.
Most likely gigantic floods ran downhill, carving a deep canyon into Xanthe Terra. Rocks eroded from the valley flanks were milled into smaller fractions and transported in the running water.
Finally this sedimentary load was deposited far north at the mouth of Ares Vallis in the Chryse plains.
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