Exploratour - The Surface of Mars
Outflow Channels
On the Martian surface are a number of large, tear-drop shaped channels such as the one shown in this image. Most of these are found on the slopes of the Martian volcanoes. They seem to start from a hole in the ground, and quickly develop their shape, 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. The most plausible explanation for these is that they are eruptions of ground water. There is no water left in these channels today.