Gargantuan valleys on Mars have always raised questions about their formation. Were they formed by catastrophic floods under a climate more temperate than today, where liquid water was stable? The issue is that these floods usually have not left marks in the northern hemisphere's plains because they are often covered with sedimentary deposits subsequent to the ice-dam ruptures. The Hebrus Valley, southeast of Utopia Planitia, is unique due to its relatively young age (under 3 billion years) and its complex network of interconnected orthogonal surface channels and underground cavities.
The Hebrus Valley. This large flow channel shows numerous characteristic signs indicating that massive amounts of water flowed through this area, notably teardrop-shaped islands and streamlined contours.
Image NASA/JPL-Caltech/MSSS An international research team, which includes scientists from the CNRS Earth & Universe (see inset), has just completed an unparalleled study on the role of underground conduits in the conveyance of major floods such as those of the Hebrus Valley on Mars. The scientists analyzed images from the HRSC camera aboard the European Mars Express mission of this Hebrus Valles outburst flood.
The mapping revealed an ancient surface flow network disappearing in favor of cavities where water could have infiltrated and flowed underground. Next, experimental simulation experiments were carried out in a laboratory replicating an underground network composed of tunnel-like structures in a water-saturated sandy matrix. These surface flows caused localized terrain collapses from which water infiltrated deep down, mimicking the interconnected network of subsurface channels observed on Mars.
Top image: interconnected orthogonal surface channels connected to underground cavities in the Hebrus Valley on Mars (HRSC image, Mars Express, ESA).
Bottom image: Laboratory simulation of an underground cavern system in an environment simulating a water-saturated subsoil. Our laboratory simulation suggests that caves along the Hebrus valleys are preferential conduits through which water and sediments have been captured.
© Costard et al.
These experiments confirm that discontinuities in the subsurface of Mars would have favored the formation of an extensive, interconnected, and functional underground flow network, potentially directing floodwaters from the Hebrus Valley deluges to the depths of Martian subsoil. Their experiments also show that cavities effectively contribute to the "disappearance" of floodwaters from the Hebrus outburst flood valley. Lastly, Hebrus is an exceptionally interesting region, as a future landing site for exploring underground cavities in Mars's northern hemisphere plains.
Reference:
F. Costard, J.A.P. Rodriguez, E. Godin, A. Séjourné and J. Kargel (2024).
Deciphering Martian Flood Infiltration Processes at Hebrus Valles: Insights from Laboratory Experiments and Remote Sensing Observations.
JGR Planets.