Kasei Valles, Mars - Interpretation of canyon materials and flood sources

Kasei Valles form the most immense outflow channel system on Mars. Here, the materials that make up the canyon walls and floors of Kasei Valles are investigated along with the sources of the flood waters. It is proposed that the geological sequence of plateau materials through which Kasei Valles cuts is capped by ridged plains material overlying relatively weak Noachian plateau materials that increase in resistance to erosion below 1000 m depth. Flooding began in the Late Hesperian, probably originating from the Tharsis rise, here volcanotectonic activity produced high ground-water pressures. Ground water sluiced through hydrofractures above the resistant zone at 1000 m depth and erupted in northern Kasei Valles, forming mostly northeast-trending troughs of Sacra Fossae and etching joints in the ridged plains material. Some of the flood water invaded the upper weak zone of the Noachian plateau materials, producing chaotic and knobby terrains of low relief.