[3] One of the first major networks of stream channels, called Warrego Valles, were discovered here by early orbiters.

Various measurements and calculations show that liquid water could exist in aquifers at the usual depths where gullies begin.

[10] One variation of this model is that rising hot magma could have melted ice in the ground and caused water to flow in aquifers.

[12] As for the next theory, much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust.

[13][14][15] This ice-rich mantle, a few yards thick, smooths the land, but in places it has a bumpy texture, resembling the surface of a basketball.

An excellent view of this mantle is shown below in the picture of the Ptolemaeus Crater Rim, as seen by HiRISE.

[20] Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from polar regions down to latitudes equivalent to Texas.

The water comes back to ground at lower latitudes as deposits of frost or snow mixed generously with dust.

[25] Very few gullies are found in the Thaumasia region; however, a few are present in the lower elevations like the one pictured below in Ross Crater.

During a warmer climate, the first few meters of ground could thaw and produce a "debris flow" similar to those on the dry and cold Greenland east coast.

[26] Since the gullies occur on steep slopes only a small decrease of the shear strength of the soil particles is needed to begin the flow.

Mariner 9 and Viking Orbiter images, showed a network of branching valleys in Thaumasia called Warrego Valles.

[32] The density of impact craters is used to determine the surface ages of Mars and other solar system bodies.

Water from the melting ice dissolves minerals, and then deposits them in cracks or faults that were produced with the impact.

Primitive organisms may have developed in such lakes; hence, some craters may be prime targets for the search for evidence of life on the Red Planet.

[48][49][50][51] Indeed, a study published in June 2017, calculated that the volume of water needed to carve all the channels on Mars was even larger than the proposed ocean that the planet may have had.