![Three outflow channels located near the eastern edge of the giant impact basin Hellas, in a view …[Credits : NASA/JPL/Malin Space Science Systems]](http://media-2.web.britannica.com/eb-media/19/75419-004-4935DE5E.jpg)
Three outflow channels located near the eastern edge of the giant impact basin Hellas, in a view obtained by Mars Global Surveyor on September 13, 2000. Running diagonally from upper left to lower right, they are (left to right) Dao Vallis, Niger Vallis (which joins Dao Vallis near the centre of the image), and Harmakhis Vallis. They are believed to have been incised into the Martian surface by floodwaters moving downslope (toward the bottom of the image) into Hellas. The channels are roughly 1 km (0.6 mile) deep and vary along their courses from about 40 km (25 miles) to about 8 km (5 miles) in width.
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