A network of lava tubes as the origin of Labyrinthus Noctis and Valles Marineris on Mars

• I reassess the role of collapsed lava tube networks to explain the origin of Labyrinthus Noctis and Valles Marineris on Mars.
• I explain how chasmata and pit chains are not of tectonic but of volcanic origin.
• I favour the role of lava over that of water for the evolution of pit chain to chasmata.
• I explain the origin of chaos terrains doubting the role of water (ice) in their formation.

The role of lava tube networks and lava channels is reassessed as the primordial stage of the volcano-erosional processes that formed the Labyrinthus Noctis–Valles Marineris system instead of a tectonic origin. The combined use of CTX, CRISM, HiRISE imagery, and MOLA profiles has provided valuable insight in the evolution of pit chains into fossae first and then chasmata later due to mass wasting processes caused by the erosional effect of the lava flows that draped Valles Marineris and other outflow channels. Although a quantitative evaluation of eruption rates is difficult even with digital terrain models (DTMs) because of the mixing between new flows and paleoflows, a comparison with Elysium and other Tharsis outflow channels suggests that the availability of lava supply is correlated to their widths. The images of ubiquitous lava flows rather than sporadic light-toned deposits strengthen the role of lava over that of water in the erosional processes that formed Labyrinthus Noctis and carved Valles Marineris like many other outflow channel on Mars. The erosional evolution of the outflow channels shows an increasing trend of age and a decreasing trend of depth from the sources on Tharsis to the mouths at Chryse Planitia. This finding, coupled with the observation of lava flows mantling Chryse Planitia, may have profound implications for the water inventories thought to have filled the lowlands with an ocean.