Abstract
Rahway Vallis sits within a shallow basin (the “Rahway basin”) in the Cerberus Plains of Mars containing a branching network of channels converging on the basin floor. Using topographic cross-profiles of the channels we have found that they are set within broader, subtly-expressed, valleys. These valleys are shallow (around 15 m vertically compared to several kilometres in the horizontal) and have convex to rectilinear slope profiles that are consistent in form across the whole Rahway basin. Both channels and valleys descend and deepen consistently from west to east. The channels typically widen down-slope and increase in width at confluences. The morphology and topology of this channel system are consistent with formation by contributory fluid flow, generated from many distributed sources. The transition between the older heavily cratered terrain and the floor of the Rahway basin is bounded by near-horizontal continuous topographic terraces. Plotting the elevation of the terraces shows that they conform to a plane with a height difference of around 100 m east to west for the 300 km width of the Rahway basin. We calculate that the volume of material needed to fill the topography up to the level of the plane best fit by the terraces is ∼1500 km3. Bordering the channels are sinuous ridges, typically several kilometres long, 20 m across, with heights on the order of 10 m. They sometimes form branching networks leading into the channels, but also occur individually and parallel to the channels. The multiple tilted terraces, the channel/valley network with many fluvial-like characteristics, and the distributed source regions, suggest that the landforms within the Rahway basin are unlikely to have formed through purely volcanic processes. Rather, the channels within the Rahway basin are consistent with a genesis requiring the flow of liquid water, and the sinuous ridges with melting of a static ice body that occupied the basin. We suggest a hypothesis of rapid basin filling by fluvial flooding, followed by lake drainage. Drainage could have occurred as a consequence of an ice or debris-dam failure within (or during the formation of) the large, nearby fluvial flood channel Marte Vallis. If the lake was partly or largely frozen prior to drainage, this offers a possible explanation for the sinuous ridge systems. Hence, although the sinuous ridges provide some of the most compelling morphological analogues of terrestrial eskers yet observed, we conclude that the contextual evidence for this interpretation in Rahway Vallis is not strong, and instead they are better explained in the context of a frozen or partially frozen lake or cryolacustrine model.
Highlights
Rahway Vallis, located at 10°N 175°E, is a valley network within the Cerberus Plains in the Elysium Planitia region of Mars (Fig. 1)
The majority of the boundary is determined by where the Cerberus Plains meets the outliers of Nepenthes Mensae Unit (HNn; Tanaka et al, 2005; grouped into the Hesperian and Noachian transition unit, HNt, in the global map Tanaka et al, 2014); the southern boundary is defined as where Marte Vallis truncates the Rahway basin and tracing along the Cerberus Fossae
The Cerberus Fossae have been identified as a possible source of both lava and water outbursts onto the Cerberus Plains (Balme et al, 2010; Berman and Hartmann, 2002; Burr et al, 2002a, 2002b; Head and Kreslavsky, 2001; Jaeger et al, 2010; Page, 2010; Plescia, 2003; Thomas, 2013) and could provide the source for the formation of Rahway Vallis, either as point sources of ground water release or vents for highly mobile lava flows
Summary
Rahway Vallis, located at 10°N 175°E, is a valley network within the Cerberus Plains in the Elysium Planitia region of Mars (Fig. 1). Plescia (2003) determined that the valley network was older than AEc3 due to cross-cutting relationships and identifies ‘‘several major branches forming a well-defined dendritic pattern’’. Best described as a branching valley network that is around 450 km in length and 300 km wide and which is amongst the youngest terrain features in the area. The majority of the boundary is determined by where the Cerberus Plains meets the outliers of Nepenthes Mensae Unit (HNn; Tanaka et al, 2005; grouped into the Hesperian and Noachian transition unit, HNt, in the global map Tanaka et al, 2014); the southern boundary is defined as where Marte Vallis truncates the Rahway basin and tracing along the Cerberus Fossae. The fossae boundary is somewhat arbitrary and has been mainly used as an aid to describing this area as opposed to the Cerberus Plains in general
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