Outflow channels

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Outflow channels are extremely long, wide swathes of scoured ground on Mars.^[1] They extend many hundreds of kilometers in length and are typically greater than one kilometer in width. They are thought to have been carved by huge outburst floods.

Crater counts indicate that most of the channels were cut since the early Hesperian,^[2] though the age of the features is variable between different regions of Mars. Some outflow channels in the Amazonis and Elysium Planitiae regions have yielded ages of only tens of millions of years, extremely young by the standards of Martian topographic features.^[3] The largest, Kasei Vallis, is around 3,500 km (2,200 mi) long, greater than 400 km (250 mi) wide and exceeds 2.5 km (1.6 mi) in depth cut into the surrounding plains.

The outflow channels contrast with the Martian channel features known as "valley networks", which much more closely resemble the dendritic planform more typical of terrestrial river drainage basins.

Outflow channels tend to be named after the names for Mars in various ancient world languages, or more rarely for major terrestrial rivers.^[1] The term outflow channels was introduced in planetology in 1975.^[4]