Lake Missoula had covered parts of Idaho and western Montana. Thus, the floods generated by the formation of the Martian channels may have carried more than 100 times as much water as the largest known floods on Earth. The minimum estimates for the total volume of water necessary to have carved the Martian outflow channels is at least 6 million cubic km, enough to make a global ocean 40 m deep. Valley Networks Valley networks are the most common drainage system on Mars. The formation of such valley networks normally assumes warm and wet climatic conditions, but this may be much to simplistic.
Most valley networks are no wider than a few km.
Most valley networks appear to have formed by the process of groundwater sapping, in which the water source is underground and the valleys from by the collapse of the surface as it is undermined by the movement of water underground. Thus, it is possible that few or none of these valleys require a warm, wet Mars. One valley network on Mars is Nirgal Vallis , as seen by Viking and later by the Mars Global Surveyor. Another is found in the Thaumasia region . Terra Meridiani valley network near the martian Equator.