A vast, complex system of interconnected canyons stretching for c.4000 km/2500 mi around Mars; located just S of the equator, and extending from near the summit of a region of extensive volcanism (Tharsis) to the E until it merges with a region characterized as chaotic terrain. Generally the canyons are over 3 km/1½ mi deep and over 100 km/60 mi wide; in the central section they are over 7 km/4 mi deep and 600 km/350 mi wide. There are giant landslides in places along their steep walls. They were discovered by Mariner 9 orbiter in 1972, and studied in detail by Viking orbiters.
Valles Marineris (Latin for Mariner Valleys, named after the Mariner 9 Mars orbiter of 1971-72 which discovered it) is a vast canyon system that runs along the Martian equator just east of the Tharsis region. At 4,500 km long, 200 km wide and up to 5.7 km deep, the Valles Marineris rift system compares to Grand Canyon of Arizona's 800 km length, 30 km width and up to 1.8 km depth, and is the largest known crevice in the solar system.
The Valles Marineris is located along the equator of Mars, on the east side of the Tharsis Bulge, and stretches for nearly a quarter of the planet’s circumference. The Valles Marineris system starts in the west with the Noctis Labyrinthus, proceeds east to Tithonium and Ius Chasmata, then Melas and Ophir Chasmata, proceeding to Coprates Chasma, then Ganges, Capri and Eos Chasmata, finally emptying out into an outflow channel composed of chaotic terrain and finally Chryse Planitia. Most researchers agree that Valles Marineris is a large tectonic "crack" in the Martian crust, forming as the planet cooled, affected by the rising crust in the Tharsis region to the west, and subsequently widened by erosional forces.
Formation
There have been many different theories about the formation of Valles Marineris that have changed over the years. The most agreed upon theory today is that the Valles Marineris was formed by rift faults like the East African Rift Valley, later made bigger by erosion and collapsing of the rift walls.
Because the Valles Marineris is thought to be a large rift valley, its formation is closely tied with the formation of the Tharsis Bulge. Finally the crust failed to hold up the Tharsis and the radial fractures, like Valles Marineris, was formed. Tharsis volcanism is a very low viscosity magma forming shield volcanoes similar to the Hawaiian Island chain, but, because there are no active plate tectonics on Mars, the hotspot activity kept loading the same spot over and over, creating some of the biggest volcanoes in the solar system, including the biggest: Olympus Mons (Cattermole, 103-104).
Oudemans Crater, the trigger
Between the Valles Marineris proper and the Noctis Labyrinthus, slightly to the south is Oudemans Crater. This might have been the trigger for some of the features of Valles Marineris because this could have heated up the permafrost turning the carbon dioxide to liquid and then further decompression of the carbon dioxide ice could flow out of the Noctis Labyrinthus, causing a catastrophic flood of carbon dioxide liquid and gas into the northern plains. North of Oudemans in the Valles Marineris itself, there is a large area on the floor composed of grooved floor material with irregular troughs and pits interpreted as alluvial deposits or contraction by the removal of ice or fluid. This only comprises about two-thirds of the floor area north of Oudemans, the other third is composed of more rough and smooth floor material. (USGS I-2010)
Regions of Valles Marineris
Noctis Labyrinthus
The Noctis Labyrinthus, on the western edge of the Valles Marineris Rift System, north of the Syria Planum and east of Pavonis Mons, is a jumbled terrain composed of huge blocks which are heavily fractured. Most of the upper parts of the blocks are composed of younger fractured material thought to be of volcanic origin associated with the Tharsis Bulge. The other tops are composed of older fractured material thought also to be volcanic in origin, but differentiated from the younger material by more ruggedness and more impact craters. The sides of the blocks are composed of undivided material thought to be basement rock. The space between the blocks is composed mainly of either rough or smooth floor material. The rough floor material tends to be in the eastern portion of the Noctis Labyrinthus and is thought to be debris from the walls or maybe eolian features covering rough topography and landslides. The smooth floor material is thought to be composed of fluvial material and/or eolian features covering an otherwise rough and jumbled terrain (USGS I-2010).
Ius and Tithonium Chasmata
Further to the east from Oudemans, Ius and Tithonium Chasmata are located parallel to each other, Ius to the south and Tithonium to the north. The floor of Ius Chasma is mostly composed of slide material that is really just a bunch of pristine landslides covering each other; Tithonium Chasma is very similar to Ius, except it is lacking the sapping features on the south side and contains a small portion of floor that is similar to the smooth floor features except that it appears to be an ash fall that has been eroded by the wind forming eolian features. Between the two canyons, the surface is composed of younger fractured material of lava flows and faults from crustal extension of the Tharsis Bulge. (USGS I-2010)
Melas, Candor and Ophir Chasmata
The next portion of Valles Marineris to the east are three chasmas, that from south to north are Melas, Candor and Ophir Chasmata. The floor of Melas Chasma is about 70% younger massive material that is thought to be volcanic ash whipped up by the wind into eolian features. It also contains rough floor material from the erosion of the canyon walls. Also, in these central chasmas there is a portion of the floor that is higher than the rest of the floor, most likely left by the continued dropping of the other floor material. Around the edges of Melas is also a lot of slide material as seen in Ius and Tithonium Chasmas (USGS I-2010). This is also the deepest part of the Valles Marineris system at eleven kilometers deep from the surrounding surface, from here to the outflow channels are about a 0.03 degree slope upward to the northern plains, which means that if you filled the canyon with fluid, would have a lake with a depth of one kilometer before the fluid would flow out onto the northern plains. (Cattermole, 105)
On the floor of the canyon system between Candor and Melas Chasmata is a grooved floor material that is interpreted to be alluvial deposits and/or material that has collapsed or contracted by the removal of ice or water. There are also portions of older and younger massive floor material of volcaniclastic origin only separated in age by crater distribution. Also there is etched massive floor material that is like the younger and older massive material except that it has wind erosional features on it. There are also a few spires of undivided material composed of the same material as the canyon walls (USGS I-2010).
Coprates Chasma
Further to the east, the canyon system runs into Coprates Chasma, which is very similar to Ius and Tithonium Chasmas, except geographical location. Also Coprates differs from Ius is the eastern end which contains alluvial deposits and eolian material (USGS I-2010). These deposits pre-date the Valles Marineris system, suggesting erosion and sedimentary processes later cut by the Valles Marineris system. Newer data from Mars Global Surveyor suggest that the origin of this layering is either just a succession of landslides, one over another, volcanic in origin, or it may be the bottom of a basin of either liquid or solid water ice suggesting that the peripheral canyons of the Valles Marineris system could have been at one time isolated lakes formed from erosional collapse. Another possible source of the layered deposits could be wind-blown, but the diversity of the layers suggests that this material is not dominant.
Eos and Ganges Chasmata
Further to the east, lie Eos and Ganges Chasmata. Eos Chasma’s western floor is mainly composed of an etched massive material composed of either volcanic or eolian deposits later eroded by the Martian wind. This is interpreted to be stream-carved plateau deposits and material transported and deposited by flowing fluid. The floor of Gangis is mainly composed of alluvial deposits from the canyon walls (USGS I-2010).
Chryse region
East of Eos and Ganges, the Valles Marineris empties out into the Chryse region of the northern plains of Mars at an elevation of only one kilometer above the deepest point of the Valles Marineris in Melas Chasma.
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