Exploratour - Water on Mars
Outflow Channels
This is one example of an outflow channel. It has a large, tear-drop shape. Most of these are found on the slopes of the Martian volcanoes. They seem to start from a hole in the ground. The water quickly carved a channel, as if whatever came out of the ground came out full steam.
The channels are typically 10 m to 100 m deep (about the depth of a football field), 40 km across, and filled with rubble. Mars Pathfinder landed on a channel such as this called Ares Valles.
The most plausible explanation for these is that they are eruptions of ground water. There is no water left in these channels today.