Channels on Mars have been found in many locations and across all possible scales, indi-cating presence of flowing water in the past. Several hypotheses for the formation of these channels have been proposed, including a role for groundwater. In this study we explored the morphology formed by three types of groundwater systems, all three previous-ly hypothesized as possible Martian scenarios: 1) seep-age from a regional groundwater system [1], 2) seep-age from local precipitation [2] and 3) groundwater release from a pressurized aquifer (varying from sub- to super-lithostatic pressure) [3]. Here we present the results of analogue scale models which were focused on characteristic morphological elements, which we compare to Martian cases

Conway, S.J.

Hauber, E.

Kleinhans, M.G.

Marra, W.A.

McLelland, S.J.

Murphy, B.J.

Parsons, D.P.

NARCIS 

Diagnostic morphology for Martian groundwater outflows from flume experiments

Institute of Transport Research:Publications

DIAGNOSTIC MORPHOLOGY FOR MARTIAN GROUNDWATER OUTFLOWS FROM FLUME EXPERIMENTS.  W.A. Marra1, M.G. Kleinhans1, E. Hauber2, S.J. McLelland3, B.J. Murphy3, D.P. Parsons3 and S.J. Conway4, 1Fac. of Geosciences, Utrecht University, the Netherlands, w.a.marra@uu.nl; 2Institute of Planetary Research - DLR Berlin, Germany; 3Dep. of Geography Environment and Earth Sciences, University of Hull, United Kingdom; 4Dep. of Physical Sciences, The Open University, Milton Keynes, United Kingdom.  Introduction:  Channels on Mars have been found in  many locations and across all possible scales, indi-cating presence of flowing water in the past. Several hypotheses for the formation of these channels have been proposed, including a role for groundwater. In this study we explored the morphology formed by three types of groundwater systems, all three previous-ly hypothesized as possible Martian scenarios: 1) seep-age from a regional groundwater system [1], 2) seep-age from local precipitation [2] and 3) groundwater release from a pressurized aquifer (varying from sub- to super-lithostatic pressure) [3]. Here we present the results of analogue scale models which were focused on characteristic morphological elements, which we compare to Martian cases. Experimental setup:  We performed a series of scale experiments to study the morphological devel-opment of different scenarios. Several experiments were conducted in a setup of 1x3x0.25 m (width x length x depth, at Utrecht University) and in a large setup of 4x6x1 m (in the Total Environmental Simula-tor at University of Hull). Lightweight plastic sediment was used in the small setup and sand in the large setup, both poorly sorted. To simulate the three hydrological conditions mentioned in the introduction, 1) a constant sub-surface hydraulic head was applied using a header tank connected to the sediment, 2) a series of rainfall simulator nozzles were used (UoH setup only) and 3) a super-surface hydraulic pressure was applied to a per-forated pipe beneath the sediment. The two scales of experiments allow us to assess the scalability to real-world conditions. We collected detailed DEMs and time-lapse imagery of the morphological development of the sediment surface. Results:  In the regional groundwater experiments (Fig. 1a), elongated valleys with circular, steep-walled, heads developed with depths down to the groundwater table. Valley heads and sides developed as result from mass wasting processes; within the valley material was transported by fluvial processes. Multiple parallel valleys formed initially, but one or two eventually capture most of the outflow and became much larger compared to the pirated valleys. In the precipitation-fed seepage experiments (Fig. 1b), groundwater flowed from all directions into valleys rather than just from upslope. Again, multiple parallel valleys with semi-circular heads formed but the valleys were shallower and wider compared to the regional groundwater sys-tem experiment. For the pressurised groundwater re-lease (Fig. 1c), channel formation was significantly faster and initially formed sieve deposits flanking a small channel, as the sediment downstream of the source was not yet saturated. With increasing pressure, pits developed in the source area as sediment was  Fig. 1 Examples from the three types of experiments: a) regional groundwater source, in action; b) precipitation-fed seepage, in action; and c) pressurized groundwater (super-lithostatic), final dried morphology, subsurface source indi-cated. In all cases flow is from left to right. 1899.pdf44th Lunar and Planetary Science Conference (2013)washed out and distinct features of converging flow were observed in the source area towards the resulting channel.  Martian cases:  Both short and long channels with semi-circular heads have been identified on Mars which are attributed to seeping groundwater. Mega-outflow channels on Mars have been attributed to pres-surized groundwater, but smaller features such as sand volcanoes and pitted dome-features also require a super-surface water pressure to form.  Ophir Cavus has been identified as the source area for the connected Allegheny Vallis [4] (Fig. 2a). Ophir Cavus is a large pit in a chain of many similar pits. These pits have been attributed to subsidence as mate-rial sinks into a void caused by a dilating fault [4], however our experiments show that similar pits de-velop when sediment is removed due to super-lithostatic pressure. The relatively low elevation of this area near the higher Tharsis region makes this area a potential candidate for a pressurized aquifer. A fault could promote the break of a pressurized aquifer and at the same time act as a preferential flow path with both mechanisms focussing the outflow at the fault location. The key similarities between this area and our experi-ment (Fig. 1c) are the elongated pit, an area of flow convergence toward the channel and incisional ter-races.  In several places, pitted features are observed in the vicinity of a chaotic terrain, for example North-West of Aromatum Chaos (Fig. 2b). Multiple pits and con-nected channels observed in this area are truncated by the chaos, and probably pre-dates chaotization. A val-ley with a semi-circular head and no source pit resem-bles the morphology observed during our sapping experiments (Fig. 1a) and likely post-dates chaotiza-tion and earlier channels.  Discussion and conclusion:  The observed pitted morphologies that result from super-lithostatic pressure are likely to be observed at areas with other systems attributed to pressurized water, for example mega-outflow channels and chaotic terrains. Also, a combi-nation of pressurized groundwater and sapping induced morphologies in the same area can be the result of a single event. As local super-surface groundwater pres-sure will result in sub-surface groundwater pressure at a distance and during a later stage of the event as the water pressure decreases.  Generally, we show that channels require very di-verse timescales to form by the different sources of groundwater (ranging over several orders of magni-tude). Correct identification of the process and water source is therefore key when assessing the formative timescales of Martian channels. Discriminative proper-ties, that are unique for different sources of groundwa-ter, are evident in the final valley morphology (break in slope, valley shape), regional characteristics (drain-age density) and several non-channel morphologies (features in source area, preserved initial-stage depos-its).  References: [1] Howard A.D. & McLane C.F. (1988) WRR 24(1), 1659-1674. [2] Kite E.S. et al. (2011) JGR 116, E07002. [3] Andrews-Hanna J.C. & Phillips R.J. (2007) JGR 112, E08001. [4] Coleman N. et al. (2007) Icarus 201(2), 344-361.  Acknowledgements. All technicians from the FG-LAB at UU provided great work. Leiping Ye, Tjalling de Haas & Steven de Jong helped with the UoH experiments, Anne Baar helped with the UU experiments (several other helped too, but minor). WAM is supported by a grant of the Netherlands Organisation for Scientific Research (ALW-GO) to MGK.  Fig. 2 Possible pressurized groundwater induced landforms on Mars. a) Ophir Cavus (large elongated pit) and Allegheny Vallis (~W55°, S9.8°). This structre is part of a regional chain of similar features. b) pits and channels NW of Aroma-tum Chaos (~W43.5°, S0.9°). Similar and larger pits exist in this area. The interior channel resembles the morphology observed in the sapping experiments. Scale bars are 10 km. 1899.pdf44th Lunar and Planetary Science Conference (2013)

Diagnostic Morphology for Martian Groundwater Outflows from Flume Experiments

Utrecht University Repository

Diagnostic Morphology for Martian Groundwater Outflows from Flume Experiments

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