Post contributed by Dr. Wouter Marra, Faculty of Geosciences, Universiteit Utrecht.
There are many water-worn features on the planet Mars, which contribute to the reconstruction of former hydrological conditions. For example, dendritic valley networks show that there was precipitation in the Noachian, the oldest epoch on Mars more than 3.7 billion years ago (Craddock and Howard, 2002). In contrast, fluvial morphologies in younger terrains seem to originate from groundwater (e.g. Baker and Milton, 1974). These are valleys that appear suddenly in the landscape, for example the large outflow channels (e.g. Mangala Vallis and Kasei Vallis) and theatre-headed valleys (such as Nirgal Vallis). However, such systems and their implications are poorly understood. To better understand the formation of such landscapes, I performed several scale-experiments focused on the fundamental process and resulting morphology.
Theater-headed valleys can form by groundwater seepage due to undercutting at the valley head where the groundwater comes to the surface. In a set of experiments I studied the effect on landscape development as result of groundwater from local or distal sources (Marra et al., 2015). In case of seepage from groundwater that first has to travel some distance, groundwater flow converges to only a few valleys (time-lapse video: http://figshare.com/articles/Video_1_Distal/1326217). As a result, small valleys get abandoned and only the larger ones continue to develop, which results in a sparsely dissected landscape with several small and only a few large valleys (Image 1). On the other hand, seepage from nearby infiltrated groundwater, results in a landscape with many valleys as seepage is not influenced by the convergence of flow (time-lapse video: http://figshare.com/articles/Video_2_Local/1326218). The valleys of Louros Valles on Mars show properties of sapping by a local source and Nirgal Vallis shows evidence of a distant source (Image 1).
In a second set of experiments (Marra et al., 2014), I studied groundwater under pressure. These experiments show that distinct outflow processes and morphologies result from different pressures. Low groundwater pressure results in a shallow surface lake and a channel when the lake overflows (time-lapse: http://figshare.com/articles/Video_1_Low_Pressure/1326226). At intermediate groundwater pressures, fissures form and groundwater flows out more rapidly (time-lapse: http://figshare.com/articles/Video_2_Medium_Pressure/1326227). At even higher pressures, the groundwater initially collects in a subsurface reservoir that grows due to flexural deformation of the surface. When this reservoir collapses, a large volume of water is expulsed to the surface (time-lapse: http://figshare.com/articles/Video_3_High_Pressure/1326225). Fissures, holes and cracks are at the source of many fluvial features on Mars, for example as show for Ganges Catena (Image 2). On Mars, these fissures relate the regional tectonic structure, which likely triggered the outflow the fissure ruptured a confining layer. The more extreme bulging from very high pressures can explain the enigmatic chaotic terrains that are the source of many large outflow channels, for example as shown for Maja Valles (Image 2).
Baker, V. R., and D. J. Milton (1974), Erosion by catastrophic floods on Mars and Earth, Icarus, 23(1), 27–41, doi:10.1016/0019-1035(74)90101-8.
Craddock, R. A., and A. D. Howard (2002), The case for rainfall on a warm, wet early Mars, J. Geophys. Res., 107(11), 5111, doi:10.1029/2001JE001505.
Marra, W. A., E. Hauber, S. M. de Jong, and M. G. Kleinhans (2015), Pressurized groundwater systems in Lunae and Ophir Plana (Mars): Insights from small-scale morphology and experiments, GeoResJ, accepted manuscript, doi:10.1016/j.grj.2015.08.001.
Marra, W. A., E. Hauber, S. J. McLelland, B. J. Murphy, D. R. Parsons, S. J. Conway, M. Roda, R. Govers, and M. G. Kleinhans (2014), Pressurized groundwater outflow experiments and numerical modeling for outflow channels on Mars, J. Geophys. Res. Planets, 119, 2668–2693, doi:10.1002/2014JE004701.
Marra, W. A., S. J. McLelland, D. R. Parsons, B. J. Murphy, E. Hauber, and M. G. Kleinhans (2015), Groundwater seepage landscapes from distant and local sources in experiments and on Mars, Earth Surf. Dyn., 3(3), 389–408, doi:10.5194/esurf-3-389-2015.
Marra, W. A. (2015), Martian groundwater outflow processes and morphology – reconstruction of paleohydrology using landscape evolution experiments, PhD Thesis, Universiteit Utrecht. ISBN: 978-90-6266-393-4, http://dspace.library.uu.nl/handle/1874/311674.