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Pseudokarst on Mars: the evolution of the Hephaestus Fossae and Hebrus Vallis Systems, Utopia Basin

Pseudokarst on Mars: the evolution of the Hephaestus Fossae and Hebrus Vallis Systems, Utopia Basin.

Principal Investigator:           Dr. Mary C. Bourke, PSI

Co-Investigators:                   Dr. Les Bleamaster, PSI

                                                Mr. Dan Berman, PSI

                                                Dr. Michael Manga, UC Berkeley, CA.

                                                Professor Paul Williams, University of Auckland

Funding: NASA, Mars Data Analysis Program (2005-2008

Project summary

The subsurface of Mars has been an important source for most of the large-scale surface channels (Carr, 1996). It is also potentially the greatest reservoir of solid and liquid water on Mars (Clifford, 1993). Martian groundwater-fed channels cover a broad spectrum of temporal and spatial scales, and are hypothesized to be triggered by a range of geological processes including collapse, fissure formation, dike intrusion, permafrost melting and groundwater piping. Of the many types of groundwater-fed channels identified on Mars, those associated with significant subsurface collapse require further investigation. Understanding the origin, age and process dynamics of these fluvial systems is paramount for determining volatile reservoir location, magnitude and stability.

Areas of karst and have been hypothesized for Mars. The origin of these areas has been variably attributed to the solution of carbonates (i.e. true karst), tectonic stresses and magma-cryosphere interactions. Chaos regions have been attributed to the catastrophic evacuation of a confined aquifer and subsequent surface collapse (Cabrol et al., 1997). Others have proposed that surface collapse is an expression of extensive underground cavernous system where the intrusion of dikes (mostly non emergent) in ground ice resulted in the removal of the ice-binding matrix  (Rodriguez et al., 2003).

Pseudokarst is a term used to describe topography, landform assemblages or features developed on non-carbonate or non-evaporite rocks which exhibit a morphology similar to those characteristic of carbonate or evaporite karst terrains. They have formed through processes that are not dominated by dissolution or dissolution-induced subsidence or collapse. They include thermokarst, volcanic karst and piping in soils (Doerr and Wray, 2004).

Figure 1:  Viking mosaic showing the location of Hebrus Vallis and Hephaestus Fossae.                                              

Figure 2. Mola data (1/128 pixel/degree grid) stretched to emphasize the structural features close to Hebrus Vallis.

We study two hypothesized groundwater-flow channels in the south east of  Utopia Planitia (20°N; 235°W).  These systems are located in an impact basin, close to the volcanic provenance of Elysium Mons and lie in a hypothesized permafrosted, paleolacustrine environment. Hebrus Vallis is to the north east and the Hephaestus Fossae is to the south west (Fig 1). Both systems are initiated at single large pits, both trend with the regional gradient to the north west. Both have patterns that include sinuous sections, apparent ‘anabranching’, and both terminate in the northern plains (Figs. 3 & 4). We use high resolution MOC, THEMIS and MOLA data sets to determine the discharge regime, describe the range of associated geomorphic landforms, and in particular to establish the likely triggers for both the surface collapse and the release of water at the surface.

Figure 3 Streamlined forms and channel patterns along Hebrus Vallis (location marked as Fig. 2 in Fig. 1)                    

Carr and Malin (2000) propose that the Hebrus Valles and Hephaestus Fossae were formed by either solution, subsurface erosion (piping) or faulting. They observe that the Hebrus Vallis system changes from a continuous surface channel upstream (with streamlined islands) to discontinuous lines of depressions downstream (Fig. 1) and suggest it was formed by a combination of surface and subsurface flow. They note that the geometry is similar to that of terrestrial karst regions where solution of limestone enables large-scale sub-surface flow. They suggest that faulting alone is unlikely and hypothesize that subsurface drainage is the result of solution, as is common in terrestrial limestone regions. They propose that the perplexing absence of a carbonate signature at the surface may be explained by the burial of those deposits. We aim to gain a greater understanding of the cryosphere-hydrosphere volatile pathway and the importance of pseudokarst as a geomorphic process on Mars. We hypothesize that the evolution of Hephaestus Fossae and Hebrus Vallis involved a strong component of pseudokarst. We nominate the following four potential processes: a) volcanic karst, b) tectonic processes, c) polygon karst and d) magma-cryosphere interaction.

Figure 4.  THEMIS VIS image of Hebrus Vallis (location marked as Fig. 6 in Fig. 1).                                      

1. pits,

2. shallow, older channel pattern,

3. larger incised channel,

4. streamlined islands indicating flow towards the top of the image,

5. Mesas on adjacent surface,

6. Potential ‘sinkhole as fluvial channel disappears into trough.

References

Cabrol, N. A., Grin, E. A., and Dawidowicz, G. (1997). A Model of Outflow Generation by Hydrothermal Underpressure Drainage in Volcano-Tectonic Environment, Shalbatana Vallis (Mars). Icarus 125, 455-464.

Carr, M. H. (1996). "Water on Mars." Oxford University Press, New York.

Carr, M. H., and Malin, M. C. (2000). Meter-scale characteristics of Martian channels and valleys. Icarus 146, 366-386.

Clifford, S. M. (1993). A model for the hydrologic and climate behaviour of water on Mars. Journal of Geophysical Research 98, 10,973-1,016.

Doerr, S. H., and Wray, R. (2004). Pseudokarst. In "Encyclopedia of Geomorphology." (A. Goudie, Ed.), pp. 814-816. Routeledge.

Rodriguez, J. A. P., Sasaki, S., and Miyamoto, H. (2003). Nature and hydrological relevance of the Shalbatana complex underground cavernous system. Geophysical Research Letters 30, doi:10.1029/2002GL016547.

 

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