View of the source region of an apparent flood. The channel starts full scale in a region of chaos enclosed by cliffs. Possible mechanisms for producing such a relation are rapid release of water from buried aquifers or the melting of ground ice by volcanism. The flow emerges under pressure and with a very high-discharge rate. The image is about 140 km across.
North is to the upper right.
The lower image is a typical segment of a Martian valley network formed by sapping processes. In such case, the discharge is likely low, and the enlargement of the valley is mostly due to mass-wasting.