Morphology of the Marte Valles Channel System, Mars

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Sven C. Moller, Pomona College; Kate E. Poulter, Colorado College

Introduction:

We are interested in the origins and evolution of the fluvial channels of Marte Valles, which is located along the southeastern edge of Orcus Patera in the Elysium region of Mars (Fig. 1). Although ancient highland fluvial networks and the dramatic outflow channels such as Kasei Valles on the dichotomy boundary have been intensively studied (e.g., Baker, 1982; Komatsu and Baker, 1997), relatively little effort has been devoted to studying some of the low-relief drainage systems in the northern lowlands. The features are subtle and available topography and images were insufficient for much quantitative work prior to the Mars Global Surveyor (MGS) mission. The high-resolution topography data from the Mars Orbiter Laser Altimeter (MOLA) (Zuber et al., 1992; Smith et al., 1998) allow us to more carefully study lowland channels that were difficult or impossible to distinguish with USGS topography.

The Marte Valles channel system looks similar in shape if not in scale to the outflow channels of Kasei Valles, which are hypothesized to be the result of catastrophic flooding. Baker and Milton (1974) propose the Channeled Scabland of Washington, site of the glacial Lake Missoula outburst floods, as a terrestrial analogue for the Martian outflow channels. More recent study, however, suggests evidence of repeated flooding over a greater period of time (Williams et al., 2000). From the Scabland analogy starting point, subsequent research has suggested several possible source mechanisms: episodic aquifer release (Carr, 1979), a pluton-driven hydrothermal system (Gulick, 1998), or volcanic-induced localized precipitation (Plescia, 1993). Marte Vallesí proximity to both Elysium Mons and to the dichotomy boundary (Fig. 1), combined with the probable presence of ground ice (Brakenridge, 1990; Carr, 1996), makes any of these mechanisms plausible. With high-resolution MOLA data now available, detailed study allows us to measure channel morphology, estimate channel bankfull cross-sectional areas, and better constrain possible methods of formation.

Conclusion:

The Marte Valles channel system, although similar in appearance to a catastrophic outflow channel, was not formed by this mechanism entirely. We hypothesize the formation of a local lake in the upper channel region, confined by a wrinkle ridge. The failure of this confining structure caused a massive flood through the lower channel region, not merely carving out the channels currently visible but resurfacing a broad area to either side. Subsequent to this flood, repeated episodes of volcanism and water release resulted in the interfingered deposits now evident in the channels. Although we did not identify an origin for the water, Elysium Mons and the Cerberus Rupes vents are likely sources of volcanic-ground ice interactions. The relationship between the two volcanic features is not sufficiently clear to discriminate between their effects on the study area; Cerberus Rupes has been tentatively cited, but not proven, to be the source of the Marte Valles lava flows. The morphology of the channels, with increasing cross-sectional area downstream, suggests multiple sources of input. Before a complete chronology can be established, more study of the cause-and-effect relationship between volcanism and channel modification is necessary.

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