Outflow Channels of the Moon, Venus, and Mars

The Outflow Channels of the Inner Solar System

David Leverington
Assistant Professor of Geosciences

Overview

Among the landform types common to Venus, Mars, and the Moon are large channel systems formed by voluminous fluid flows from the subsurface. These channels are referred to here as "outflow channels".

Outflow channels generally head abruptly at topographic lows or ridged plains and extend downslope for distances of tens to thousands of kilometers. Lunar systems are relatively small, with channel widths of less than 10 km and typical lengths of less than 100 km. The largest of the Venusian and Martian outflow systems have widths of tens of kilometers and lengths of thousands of kilometers, and in many cases are characterized by complexly anastamosing reaches and large streamlined landforms.

In the material presented below, the basic characteristics and hypothesized formation mechanisms of outflow systems are outlined for the Moon, Venus, and Mars.

1 Outflow Channels of the Moon

Images generated by the Lunar Orbiter and Apollo missions have been used to identify a large number of lunar lava channels located in both mare and highland regions [e.g., Greeley, 1971a, 1976; Young et al., 1973; Zisk et al., 1977; Strain and El-Baz, 1977; Wilhelms, 1987]. The Apollo 15 mission involved direct investigation of one of these channels, Hadley Rille, as well as the surrounding basaltic mare units of Palus Putredinis [Swann et al., 1972; Howard et al., 1972; Spudis and Pieters, 1991].

The characteristics of lunar sinuous rilles can include inner channels [e.g., El-Baz et al., 1972], channel levees [e.g., El-Baz and Roosa, 1972; Hulme, 1974; Schaber, 1973; Schultz, 1976], channel terraces [e.g., Schultz, 1976; Leverington, 2004a; see also El-Baz et al., 1972], typical gradients of less than one degree [Strain and El-Baz, 1977], longitudinal profiles intermittently characterized by reverse gradients [e.g., Greeley, 1971a; Strain and El-Baz, 1977], and exposure of channel floors as a result of partial or complete drainage of late-stage lava pulses [e.g., Swann et al., 1972]. Rilles incised up to hundreds of meters into upland barriers across swaths as great as several kilometers exist on the Moon, with examples of incision located, e.g., at Rimae Herigonius [Greeley and Spudis, 1978; see also Young et al., 1973; Schultz, 1976; Leverington, 2006] and Rimae Prinz [Carr, 1974b; Schultz, 1976; Strain and El-Baz, 1977; Zisk et al., 1977; see also Masursky et al., 1978; Leverington, 2004a]. Some lunar channels contain streamlined landforms that appear to be erosional residuals [Leverington, 2004a].

Although once believed to be ancient river channels and valleys [e.g., Urey, 1967; Peale et al., 1968; Lingenfelter et al., 1968; see also Zimbelman, 2001], the volcanic character of the channels, and the absence of hydrous minerals in sampled lunar materials [e.g., Schmitt et al., 1970; Papike et al., 1991], together strongly suggest that sinuous lunar rilles did not form by water flow (or even in the presence of water). Sinuous lunar rilles share numerous characteristics with terrestrial lava tubes and channels, and are interpreted to have also formed by the flow of lava [e.g., Hackman, 1966; McCauley, 1967; Oberbeck et al., 1969, Greeley, 1971b, Cruikshank and Wood, 1972; El-Baz and Roosa, 1972; Young et al., 1973; Schaber, 1973; also see summaries in Leverington, 2004a, 2006, 2009b].

Figure 1: Oblique view of two channels of Rimae Prinz (figure center at ~27 degrees N, 44 degrees W), located north of lunar crater Prinz (P) [Leverington, 2004a]. As with many lunar outflow systems, these rilles commence abruptly at topographic depressions (d1 and d2); the rille associated with depression d1 crosses hills at h, suggesting structural control of channel position [Grolier, 1978], and/or incision processes that commenced prior to subsidence of mare materials [e.g., see Greeley and Spudis, 1978]. Scale is valid only in the upper-right corner of the image. Illumination is from the left. Apollo 15 Hasselblad frame AS15-93-12608.

Figure 2: Hadley Rille (Rima Hadley), located in the lunar volcanic plains of Palus Putredinus, southeast Mare Imbrium [Apollo 15 Panoramic frame 9924; see also, e.g., Hackman, 1966] [Leverington, 2006]. This channel was visited by the astronauts of Apollo 15 (see below). Image center is at ~2.5 degrees E, 25 degrees N. Illumination is from the right.

Figure 3: Oblique view of part of Rima Hadley (Hadley Rille), showing variable channel widths that may be related to the irregular collapse of a former channel roof along this segment [Apollo 15 Hasselblad frame AS15-87-11720; see also, e.g., Hackman, 1966; Leverington, 2006]. Scale is valid only in the top-left corner of the image. Image center is at ~3.5 degrees E, 26 degrees N. Illumination is from image bottom.

Figure 4: View of Hadley Rille from the ground. Apollo 15 astronauts David Scott and James Irwin used the first Lunar Rover to visit this and other sites in the Palus Putredinus region of eastern Mare Imbrium. About 77 kg of lunar samples were collected on this mission. The Apennine Front is visible in the distance, as is part of St. George crater (top-right corner). Apollo 15 Photo 82-11147.

Figure 5: Cross-sectional profiles of three lunar rilles: Rima Handel [after Strain and El-Baz, 1977]; Rima Beethoven [after Strain and El-Baz, 1977]; and Rima Hadley (Hadley Rille) [after Wu et al., 1972] [Leverington, 2006]. Profiles contain no vertical exaggeration. The width-to-depth ratios of lunar rilles can vary considerably within and between individual systems, with ratios of ~4:1 to 11:1 roughly describing the most common ranges that have been measured in past lunar studies based on high-resolution photogrammetric analysis of Apollo Panoramic-Camera images.

Figure 6: Highly sinuous lunar volcanic channels [Leverington, 2006]. a: Rima Diophantus, located north of crater Diophantus in southwestern Mare Imbrium. Image center is at ~35 degrees W, 28.75 degrees N (Apollo 15 Panchromatic frame 299); illumination is from the right. b: Sinuous rille located near the southern foot of Montes Agricola, north of Aristarchus Plateau in Oceanus Procellarum. Image center is at ~53.25 degrees W, 29.25 degrees N (Apollo 15 Panchromatic frame 349); illumination is from image bottom.

Figure 7: Oblique view of a lunar rille (part of the Rimae Herigonius system) that cross-cuts highland terrain located northeast of crater Gassendi [Greeley and Spudis, 1978] (Apollo 16 Hasselblad frame AS16-119-19170) [Leverington, 2006]. Scale is valid only in the bottom-right corner of the image. The rille crosscuts highlands at ~36.75 degrees W, 15.5 degrees S. Illumination is from the left.

Figure 8: Streamlined islands (arrows) inside a lunar rille located north of Aristarchus Plateau, Oceanus Procellarum (at ~29 degrees 30’N, 46 degrees 30’W) [Leverington, 2004a]. This channel extends westward from a breach in the wall of crater Krieger [e.g., Carr, 1974b; Leverington and Maxwell, 2004]. Illumination is from the right. Apollo 15 Panoramic frame 324.

Figure 9: Anastamosing volcanic channels located in Mare Imbrium (~24 degrees N, 31 degrees W), northwest of lunar crater Euler [see also, e.g., Schaber, 1973] [Leverington, 2004a]. Illumination is from the right. Apollo 15 Metric frame AS15-M3-1701.

Figure 10: Oblique view of the distal valley and nested channel of lunar Vallis Schroteri (figure center at ~25 degrees N, 52 degrees 40’ W), which extend onto Oceanus Procellarum (OP) from a large topographic depression that marks the main channel source on the Aristarchus Plateau [Leverington, 2004a]. Scale is valid only in the upper-right corner of the image. Illumination is from the left. Apollo 15 Hasselblad frame AS15-93-12628.

Figure 11: Terraces in one of the channels of Rimae Prinz (~27 degrees N, 44 degrees 20’ W), located north of lunar crater Prinz [Leverington, 2004a]. Illumination is from the right. Apollo 15 Panoramic frame 318.

2 Outflow Channels of Venus

The existence and diversity of volcanic channels on Venus were first recognized in images generated by the Magellan mission [Saunders and Pettengill, 1991]. These channels, believed to have formed through a variety of mechanisms involving both constructive and erosive processes, are widely associated with volcanic features such as coronae, shield volcanoes, and rift zones [e.g., Baker et al., 1992; Komatsu et al., 1992, 1993; Gregg and Greeley, 1993; Komatsu and Baker, 1994]. Though many Venusian systems are readily classifiable as outflow channels, some channels are associated with flows that appear to head at or under the ejecta blankets of impact craters [e.g., Asimow and Wood, 1992; Chadwick and Schaber, 1993].

Many Venusian channels are relatively simple in form, consisting of long channels with few or no tributraries, and having general morphologies that are similar to those of simple sinuous lunar rilles [Baker et al., 1992, 1997; Head et al., 1992; Komatsu and Baker, 1994] (see lunar section above). Simple channels on Venus generally head at topographic depressions, and have relatively constant widths of ~1 to 2 km and lengths of tens to hundreds of kilometers [Baker et al., 1992, 1997; Head et al., 1992]. The longest recognized channel on Venus, located mostly on lava plains located north of Rusalka Planitia, has a total length of 6800 km [Baker et al., 1992]. Features associated with simple channels on Venus include meander cutoffs, abandoned channel segments, and levees [Baker et al., 1992; Head et al., 1992]. The meanders of simple Venusian channels are suggestive of modification of original flow patterns by erosional channel widening during lava flow [Komatsu and Baker, 1994]. As with their lunar counterparts, there are numerous examples of simple Venusian channels that cut across irregular topography, suggesting that formation of these channels involved erosive processes [e.g., Komatsu and Baker, 1994].

Complex channels, which in numerous cases possess large braided patterns that define streamlined islands, are also found on Venus [Baker et al., 1992]. Many of these channels head at topographic depressions, and a minority of channels have large delta-like distributary systems at their mouths [Baker et al., 1992]. A prominent complex Venusian channel, Kallistos Vallis, is located in the northern region of Lada Terra, east of Lavinia Planitia. Kallistos Vallis is over 1200 km long and up to 30 km wide, and heads at a collapse feature on the flank of a large volcanic construct [Baker et al., 1992; Komatsu et al., 1993]. This collapse feature is morphologically similar to the regions of chaotic terrain that acted as sources for many outflow channels on Mars [Baker et al., 1992] (see below).

Liquid water is unstable on Venus [e.g., Kargel et al., 1993], and although water may have been abundant very early in the planet’s history, it is only present today in trace amounts as water vapor [e.g., Donahue and Russell, 1997]. Partly on this basis, the channels of Venus are believed to have formed in the essential absence of water [Baker et al., 1992]. The X-ray fluorescence and gamma-ray measurements made by seven Venera and Vega landers are consistent with mafic volcanic compositions such as tholeiitic basalt [e.g., Surkov, 1983; Surkov et al., 1987; Kargel et al., 1993; Fegley et al., 1997]. A volcanic origin for Venusian outflow systems is widely favored based on the volcanic nature of associated Venusian landforms, the character of the Venusian surface (including the absence of Venusian landforms suggestive of widespread aqueous surface runoff in the past), and environmental and geochemical considerations [e.g., Baker et al, 1992, 1997; Nimmo and McKenzie, 1998].

Venusian channels are hypothesized to have formed by the flow of mafic or ultramafic silicate lavas, or possibly by the flow of lavas of exotic compositions such as sulfur or carbonatite [e.g., Baker et al., 1992; Komatsu et al., 1993; Kargel et al., 1994]. Although some workers have hypothesized that formation of complex channels on Venus may have been a consequence of the planet’s high surface temperatures and of particular fluid chemistries such as liquid sulfur or ultramafic compositions, appeals to special rock chemistries and environmental conditions to justify the existence of Venusian channels may be unnecessary. A simpler interpretation of Venusian channels involves a recognition that basaltic lava, erupted in sufficiently large volumes and at sufficiently low viscosities, is capable of formation of large channels through processes that include erosion. This interpretation is consistent with measurements returned by the Venera and Vega landers [e.g., Surkov, 1983; Surkov et al., 1987; Kargel et al., 1993; Fegley et al., 1997], the seemingly basaltic nature of volcanic landforms on Venus [Head et al., 1992], and the nature of basaltic landforms on the Moon.

Figure 12: Simple Venusian rille located at ~2 degrees S, 273 degrees 18’ E, in Phoebe Regio [Leverington, 2004a]. Lava flows that formed this channel emerged from topographic depressions at d, flooding small basins and cutting northwestward across tesserae [Komatsu and Baker, 1994]. Microwave illumination is from the left. Magellan FMAP Left-Look SAR mosaic.

Figure 13: Belisama Vallis, a 350-km-long Venusian channel system located in Ishtar Terra, heads at a 42-km-long topographic depression (S) [Leverington, 2009b]. An associated pit (P) is located south of the main depression, and the orientation of both depressions is approximately concentric with prominent structural features in the region (arrows). Further downslope, southeast of the depicted region, this system broadens to a width of ~10 km and anastamoses complexly about streamlined landforms with long axes of up to ~10 km [Baker et al., 1992]. Magellan FMAP left-look Synthetic Aperture Radar (SAR) mosaic; the slight vertical offset of the rightmost quarter of the figure is a mosaic artifact. SAR illumination is from the left. Figure center: 22 degrees 08’ E, 50 degrees 30’ N.

Figure 14: Examples of streamlined landforms of the largest Venusian outflow system, Kallistos Vallis [Leverington, 2009b]. Located north of Lada Terra and southeast of Alpha Regio, this system is part of the Ammavaru volcanic complex and is over 1000 km long [Baker et al., 1992, 1997; Komatsu et al., 1993]. The system heads in a region of chaotic terrain located northwest of the depicted area. In this figure, the channel extends downslope from bottom left to middle right. Magellan FMAP left-look SAR mosaic. SAR illumination is from the left. Figure center: 22 degrees 55’ E, 51 degrees 00’ S.

Figure 15: Magellan synthetic aperture radar image of a Venusian channel located northeast of Ozza Mons, eastern Aphrodite Terra [Leverington, 2007]. This channel, interpreted as volcanic, is characterized by complexly-anastamosing reaches that define numerous streamlined islands that are kilometers to tens of kilometers across; these islands appear to be erosional residuals [Komatsu et al., 1993]. Some lineations in the radar imagery (e.g., L) could correspond to channel lineations, the banks of inner channels, or channel terraces. Flow along this reach was from south to north (figure bottom to top). Magellan FMAP left-look Synthetic Aperture Radar (SAR) mosaic; microwave illumination is from the left. Figure center is at ~211 degrees 40’ E, 11 degrees 40’ N.

3 Outflow Channels of Mars

The outflow channels of Mars are mainly located equatorward of ~30 degrees latitude [Mars Channel Working Group, 1983], and are characterized by a variety of sizes, morphologies, ages, and relationships with surrounding terrain features [e.g., Masursky et al., 1977]. The largest outflow channel, Kasei Valles, has a length of ~3000 km, and maximum width of ~230 km. The attributes of individual outflow channels are variable: some channels have features such as large tributaries or streamlined bedforms, whereas others do not; some channels originate from very broad regions, whereas others originate more locally [e.g., Milton, 1973; Masursky et al., 1977; Carr, 1981; Mars Channel Working Group, 1983; Tanaka and Chapman, 1990; Zimbelman et al., 1992; Baker et al., 1992; Komatsu and Baker, 1997; Nelson and Greeley, 1999; Burr et al., 2002; see summaries in Leverington, 2004a, 2007, 2009b].

The largest outflow channels typically commence abruptly and at full width in regions of chaotic terrain, and are associated with features such as streamlined islands [e.g., Baker, 1978; Baker and Kochel, 1978ab, 1979] and longitudinal grooves [e.g., Baker and Milton, 1974; Carr, 1979; Baker, 1978; Baker and Kochel, 1979]. Most of the largest outflow channels head in regions adjacent to Chryse Planitia [e.g., Mars Channel Working Group, 1983]. Smaller channels located elsewhere on Mars, such as Dao Vallis and Harmakhis Vallis in eastern Hellas [e.g., Crown and Greeley, 1993] and the channels of Elysium [e.g., Wilson and Mouginis-Mark, 2003], share many of the characteristics of the largest outflow channels, including abrupt commencement at topographic depressions and association with features such as streamlined islands.

The anastamosing reaches of some Martian outflow channels have previously been interpreted by many workers as evidence in support of aqueous origins [e.g., McCauley et al., 1972; Masursky, 1973; Milton, 1973]. On the basis of their strong morphological similarity to terrestrial features known to have been produced by catastrophic floods [see, e.g., McCauley et al., 1972; Milton, 1973; Baker and Milton, 1974; Baker, 1978], streamlined features of Martian outflow channels are widely believed to have formed by relatively rapid releases of large volumes of groundwater [e.g., Masursky, 1973; Milton, 1973; Baker and Milton, 1974; Masursky et al., 1977; Baker, 1978; Baker, 1979; Mars Channel Working Group, 1983; Baker, 2001; Coleman, 2003; Manga, 2004]. Aqueous origins for the outflow channels would be consistent with the confirmed modern presence of water ice at high latitudes [Kieffer et al., 1976], and the hypothesized development of older (Noachian) valley networks by aqueous processes [Craddock and Maxwell, 1993].

Determination of realistic mechanisms by which these floods might have occurred has been problematic, however [Leverington, 2004a, 2007, 2009ab]. It has been recognized, for example, that the volumes of water that could have been produced solely from regions of chaos at the heads of many Martian channels would likely have been insufficient to form the outflow channels, necessitating multiple releases (dozens to thousands) each involving large volumes of water [e.g., Baker, 1982; Manga, 2004]. In order to have taken place, these releases would seem to have required the existence of unusual conditions at and near the Martian surface, such as 1) a global cryosphere that could be locally and repeatedly breached and re-sealed, and confined regional aquifers that could supply and convey large amounts of water under high artesian pressures to breached areas [e.g., Carr, 1979; Clifford, 1993; Clifford and Parker, 2001]; or 2) large surface lakes from which water could be repeatedly released catastrophically [e.g., McCauley, 1978; Robinson and Tanaka, 1990; Scott et al., 1992].

The aqueous hypothesis for development of the outflow channels of Mars suffers from further basic weaknesses [Leverington, 2009ab] including an inability to account for the relatively high elevations of the heads of the largest outflow systems of Mars. Given the widespread capacity for volcanism to have breached hypothesized cryospheric caps across all Martian elevations during the Hesperian, a cryospherically-confined aquifer system with dynamics driven partly or entirely by hydrostatic pressures should have favored outbursts at relatively low elevations rather than at elevated terrain located deep within the southern highlands [Carr, 2002].

Since the mineral olivine is readily altered in the presence of water, it is not clear that the existence of pristine olivine-rich units along Martian outflow channels [Koeppen and Hamilton, 2008] is consistent with aqueous models of channel development involving the long-term presence of massive groundwater stores and water-saturated cryospheric seals, and recurring releases of large volumes of water to the surface [Leverington, 2009b]. Indeed, olivine-rich units spanning a wide range of ages are preserved across much of the surface of Mars [e.g., Koeppen and Hamilton, 2008]. Small grains of olivine should be especially susceptible to alteration by water, but are nevertheless known to comprise a significant fraction of the sediment cover of locales including the Spirit landing site at Gusev Crater [e.g., Morris et al., 2004]. The widespread preservation of olivine on Mars, and the restriction of mineralogical evidence for limited "wet" surface processes mainly to the earliest stages in the planet’s history [e.g. Chevrier and Mathe, 2007; Koeppen and Hamilton, 2008], bring aqueous interpretations of the Martian outflow channels further into question.

Importantly, hypotheses for the catastrophic aqueous development of Martian outflow systems continue to be weakened by the absence of satisfactory analog processes for the sudden release of large volumes of water from the subsurface [Leverington, 2007, 2009b]. Although terrestrial landscapes such as the Channeled Scabland of Washington and the flood systems of the Mongolian plateau have been cited as a possible analogs to the terrain that characterizes outflow systems on Mars [e.g., Baker and Milton, 1974; Sharp and Malin, 1975; Komatsu et al., 2004; Andrews-Hanna and Phillips, 2007], the mechanisms of formation of terrestrial systems may offer little in the way of insight into the root causes of outflow-channel formation on Mars [Leverington, 2007]. Whereas the Martian outflow systems developed as a result of voluminous flow from the subsurface, the widely-cited landforms of the Channeled Scabland formed in response to entirely different processes related to the release of floodwaters from an ice-dammed lake [e.g., Bretz et al., 1956; Baker, 1978a; Smith, 1993]. In the near term, substantial progress in our understanding of Martian outflow systems may depend upon identification of genuine analog processes to those that initiated development of these systems.

An Alternative Volcanic Interpretation of the Outflow Channels of Mars

An alternative, volcanic, interpretation of the Martian outflow channels has recently been suggested [Leverington, 2004a, 2007, 2009b; see also Schonfeld, 1979]. This interpretation does not involve development of channels through aqueous diluvial processes, and thus does not rely upon the past existence of massive near-surface volatile reservoirs, the past action of exotic outflow processes that defy recognized constraints upon aquifer permeabilities or that lack meaningful analogs, or dramatic changes in climate from the Hesperian to the present. Instead, the Martian outflow systems are interpreted as the products of volcanic processes broadly analogous to those hypothesized to have formed outflow systems on the Moon and Venus. Volcanic interpretations of Martian outflow systems are made partly on the basis of 1) the strong association between Martian outflow channels and major volcanic provinces; 2) the widespread mantling of Martian outflow channels and outlet basins by volcanic flows; 3) the consistency between basic channel characteristics and those of terrestrial, lunar, and Venusian systems interpreted as volcanic; 4) the consistency between basic outburst processes and recognized analog processes involving voluminous effusion of magma from the subsurface; and 5) the consistency between non-aqueous volcanic origins and the mineralogical record of the Martian surface for the Hesperian and Amazonian, the timeframe over which virtually all outflow systems of Mars were formed.

Formation of large outflow channels on Mars by flowing lava is consistent not only with the gross morphologies of Martian landforms but also with general global geographic relations on that planet between channels, source regions, and basins of accumulation. Many outflow channels on Mars are within or proximal to Tharsis and Elysium [Mars Channel Working Group, 1983; Baker et al., 1992; Carr, 1995], volcanic provinces that contain the largest volcanic rises in the solar system [Carr, 1973]. The largest outflow channels head in the vicinity of Valles Marineris, an immense rift in volcanic units of the Tharsis bulge [e.g., Scott and Tanaka, 1986; McEwen et al., 1999]. The topographic depressions from which Martian outflow channels emerge are located in regions of recognized volcanic activity; indeed, most competing hypotheses of channel formation that involve catastrophic releases of water from confined aquifers rely entirely upon a contemporaneous association between local igneous activity and channel-formation processes [e.g., Masursky et al., 1977; Baker et al., 1991; Tanaka and Chapman, 1990; Wilson and Head, 2002; Burr et al., 2002; Wilson and Mouginis-Mark, 2003; Russell and Head, 2003; Head et al., 2003; Rodriguez et al., 2003; Manga, 2004]. As with lunar and Venusian volcanic channels, the volcanic plains onto which Martian outflow channels extend are among the largest known [see e.g., Head et al., 2002].

The landing sites of the Viking 1 [e.g., Binder et al., 1977; Greeley et al., 1977], Pathfinder [e.g., McSween et al., 1999; Chapman and Kargel, 1999], and Spirit [e.g., McSween et al., 2004] spacecraft, all of which are located near the mouths of prominent Martian outflow channels, are plains with properties that are entirely consistent with volcanic origins [Leverington, 2004a]. In a manner similar to that of lunar volcanic plains visited by the Luna, Surveyor, and Apollo landers [e.g., Shoemaker et al., 1966, 1968, 1970; Schmitt and Cernan, 1973; Vaniman et al., 1991; Horz et al., 1991], surface materials at the three Martian landing sites appear to consist primarily of the remnants of volcanic units subjected to extensive reworking by impacts. As on the Moon, formation of a surface regolith layer at these sites has resulted in the reduction of original volcanic units to block fields consisting of rock fragments and fines.

Consistent with a volcanic origin for the largest outflow channels, smaller outflow channels that head in highland regions outside of Tharsis and Elysium (e.g., those in Memnonia, Aeolis, and Hellas) are typically associated with structural features formed by crustal extension [e.g., Memnonia Fossae: Tanaka and Chapman, 1990; Zimbelman et al., 1992; and high-elevation systems near Valles Marineris: Coleman et al., 2007], volcanic rises [e.g., Tyrrhena Patera: Greeley and Crown, 1990], and large volcanically-emplaced plains units [e.g., see Scott and Tanaka, 1986; Greeley and Guest, 1987; Smith et al., 2003]. As with larger outflow features, channels in these regions ultimately flow onto extensive volcanic plains. Even relatively small Hesperian sinuous valleys located in the Martian highlands [e.g., Goldspiel et al., 1993; Carr, 1995; Carr and Malin, 2000] appear in some cases to have characteristics that are more consistent with volcanic than fluvial or sapping origins [e.g., Leverington and Maxwell, 2004; Leverington, 2004ab, 2006], suggesting a possible consistency in the origins of many Hesperian-aged Martian channels across a wide range of scales.

In the absence of supporting evidence for the action of past aqueous processes in the Hesperian and Amazonian, the simplest interpretation of Martian outflow channels that extend from volcanic source regions onto volcanic plains is as conduits formed by volcanic flows. Volcanic processes operate under an extremely wide range of environmental conditions, and thus can account for channel formation without appeals to more complex scenarios involving substantial past changes in Martian climate or concepts such as hemispheric aquifers confined under a global cryosphere. Channel-formation hypotheses requiring major changes in the properties of the Martian atmosphere or involving repeated catastrophic flow of water from features such as volcanic rifts appear needlessly exotic alongside the igneous hypothesis for channel formation. This hypothesis requires only that large flows of lava have a capacity for erosion and for formation of streamlined landforms and anastamosing channels, a capacity that is implied by the nature of lunar and Venusian volcanic landforms. Crude estimates for Martian outflow system Mangala Valles [Leverington, 2007] suggest that formation of that channel system through thermal mechanisms of lava incision could have taken place through eruption of ~2 x 10⁵ km³ of lava, a volume that under some conditions would involve an average eruption rate of ~4 x 10⁶ m³/s over a total event duration of almost 600 days (though likely taking place through multiple events over geological timescales). A smaller volume of lava would be required if mechanical processes of erosion were also substantially involved [Leverington, 2007].

The origin of the Martian outflow channels is of central importance to our understanding of the geology and climate history of Mars. Aqueous interpretations of outflow systems have motivated hypotheses for the past existence of oceans and large lakes on Mars, as well as for the past occurrence of major changes or oscillations in global climate [e.g., Baker et al., 1991]. Aqueous interpretations have also served as a basis for inferences of Martian volatile abundances [e.g., Carr, 1996]. A non-aqueous volcanic origin for the outflow systems of Mars would undermine conclusions drawn from aqueous models, and would instead be consistent with maintenance of predominantly dry Martian conditions throughout the Hesperian and Amazonian epochs [Leverington, 2009b]. A volcanic origin for the outflow systems of Mars would also be congruous with interpretations of Hesperian drainage systems and "crater lakes" as the products of regional volcanic resurfacing [Leverington and Maxwell, 2004; Leverington, 2004b, 2006], and would be consistent with the constraints imposed by Martian mineralogy upon the past nature of aqueous surface processes [e.g., Goetz et al., 2005; Bibring et al., 2006; Chevrier and Mathé, 2007; Koeppen and Hamilton, 2008].

Figure 16: Oblique view of Martian outflow channels Dao Vallis (D) and Harmakhis Vallis (H), located in eastern Hellas on the flanks of Hadriaca Patera and Tyrrhena Patera [Leverington, 2004a; see also, e.g., Crown and Greeley, 1993]. Niger Vallis (N) joins Dao Vallis near the center of the figure (figure center is at ~271 degrees 18’W, 38 degrees S). Scale is valid only in the upper-right corner of the image. Illumination is from the left. Mars Orbiter Camera wide-angle frame M1900826.

Figure 17: Streamlined island located at the mouth of Martian outflow channel Ares Vallis, at ~20 degrees 12’ N, 31 degrees 15’ W [Leverington, 2004a]. Illumination is from the left. Themis daytime thermal frame I02560002.

Figure 18: Part of Hrad Vallis, a Martian outflow channel located on the distal flanks of Elysium Mons, at ~34 degrees N, 218 degrees 15’ W [Leverington, 2004a; see also, e.g., Wilson and Mouginis-Mark, 2003]. The channel commences abruptly at a complex topographic depression (d). Illumination is from the right. Viking Orbiter frame 541A10.

Figure 19: The Allegheny Vallis and Walla Walla Vallis systems are relatively small Martian outflow channels that head at elongate topographic depressions (A and B, respectively), and extend northward and eastward to the western rim of Ganges Chasma (top right) [Leverington, 2009b; see also, e.g., Coleman et al., 2007; Komatsu et al., 2009]. A third elongate depression (C) is located along the southern interior rim of a 40-km-diameter impact crater; effusion of fluids from this depression may have played a role in development of the shallow lowlands that extend northward from the impact crater to Allegheny Vallis. THEMIS daytime-infrared mosaic courtesy of Arizona State University. Figure center: 53 degrees 55’ W, 9 degrees 20’ S.

Figure 20: Large systems of longitudinal features developed in lava flows at Martian outflow channel Athabasca Valles (a) are partly composed of both equant and elongate classes of cone-like features (b and c), each mound partly defined by upturned layers. Longitudinal ridge systems of the Cerberus plains are also partly formed by lineate exposures of upturned layer edges, as at Lethe Vallis (d). All of these landforms appear to be primary volcanic features developed during emplacement of associated flows [Jaeger et al., 2007, 2008], suggesting a capacity for development of longitudinally-oriented features by large channelized lava flows. HiRISE image PSP_008344_1895 (a and b), HiRISE image PSP_002226_1900 (c), HiRISE image PSP_006762_1840 (d). Approximate figure centers: a, 156 degrees 07’ E, 9 degrees 30’ N; b, 156 degrees 09’ E, 9 degrees 36’ N; c, 156 degrees 26’ 30” E, 9 degrees 39’ N; d, 155 degrees 26’ 30” E, 3 degrees 43’ N [Leverington, 2009b].

Figure 21: Aromatum Chaos, Mars (~43 degrees 8’ W, 1 degree 7’ S) [Leverington, 2004a]. The outflow channel feeds into Hydroates Chaos, ultimately extending onto the plains of Chryse Planitia through Simud Vallis and Tiu Vallis. Illumination is from the right. Viking MDIM mosaic.

References Cited

Andrews-Hanna, J. C., R. J. Phillips (2007), Hydrological modeling of outflow channels and chaos regions on Mars, J. Geophys. Res., 112, E08001, doi:10.1029/ 2006JE002881.

Asimow, P.D., and J.A. Wood (1992), Fluid outflows from Venus impact craters: analysis from Magellan data, J. Geophys. Res., 97 (E8), 13,643-13,665.

Baker, V.R. (1978), A preliminary assessment of the fluid erosional processes that shaped the Martian outflow channels, Proc. Lunar Planet. Sci. Conf. 9th, 3205-3223.

Baker, V. R. (1982), The Channels of Mars, University of Texas Press, Austin, TX.

Baker, V.R. (1979), Erosional processes in channelized water flows on Mars, J. Geophys. Res., 84, 7985-7993.

Baker, V.R. (2001), Water and the Martian landscape, Nature, 412, 228-236.

Baker, V. R., and D. J. Milton (1974), Erosion by catastrophic floods on Mars and Earth, Icarus, 23, 27-41.

Baker, V. R., and R. C. Bunker (1985), Cataclysmic late Pleistocene flooding from glacial Lake Missoula: A review, Quaternary Science Reviews, 4, 1-41.

Baker, V. R., and R. C. Kochel (1978a), Morphometry of streamlined forms in terrestrial and martian channels, Proc. Lunar Planet Sci. Conf., 9th, 3193-3203.

Baker, V. R., and R. C. Kochel (1978b), Morphological mapping of martian outflow channels, Proc. Lunar Planet Sci. Conf., 9th, 3181-3192.

Baker, V. R., and R. C. Kochel (1979), Martian channel morphometry: Maja and Kasei Valles, J. Geophys. Res., 84, 7961-7983.

Baker, V.R., and G. Komatsu (1999), Extraterrestrial fluvial forms, in Varieties of Fluvial Form, edited by A.J. Miller and A. Gupta, pp.11-30, John Wiley & Sons Ltd.

Baker, V. R., R. G. Strom, V. C. Gulick, J. S. Kargel, G. Komatsu, and V. S. Kale (1991), Ancient oceans, ice sheets, and the hydrological cycle on Mars, Nature, 352, 589-594.

Baker, V. R., G. Komatsu, T. J. Parker, V. C. Gulick, J. S. Kargel, and J. S. Lewis (1992), Channels and valleys on Venus: Preliminary analysis of Magellan data, J. Geophys. Res., 97 (E8), 13,421-13,444.

Baker, V. R., G. Komatsu, V. C. Gulick, and T. J. Parker (1997), Channels and valleys, in Venus II, edited by S.W. Bougher, D.M. Hunten, and R.J Phillips, pp. 757-793, Univ. of Ariz. Press, Tucson.

Bibring, J-P., et al. (2006), Global mineralogical and aqueous Mars history derived from OMEGA/Mars Express Data, Science, 312, 400-404.

Binder, A.B., R.E. Arvidson, E.A. Guinness, K.L. Jones, E.C. Morris, T.A. Mutch, D.C. Pieri, and C. Sagan (1977), The geology of the Viking Lander 1 site, J. Geophys. Res., 82, 4439-4451.

Bretz, J. H., H. T. U. Smith, and G. E. Neff (1956), Channeled scabland of Washington: New data and interpretations, Bull. Geol. Soc. Am., 67, 957-1049.

Burr, D.M., A.S. McEwen, and S.E.H. Sakimoto (2002), Recent aqueous floods from the Cerberus Fossae, Mars, Geophys. Res. Lett., 29, No. 1, 1013, 10.1029/2001GL013345.

Carr, M. H. (1973), Volcanism on Mars, J. Geophys. Res., 78, 4049-4062.

Carr, M. H. (1974a), Tectonism and volcanism of the Tharsis region of Mars: J. Geophys. Res., 79(26), 3943-3949.

Carr, M. H. (1974b), The role of lava erosion in the formation of lunar rilles and Martian channels, Icarus, 22, 1-23.

Carr, M. H. (1979), Formation of martian flood features by release of water from confined aquifers, J. Geophys. Res., 84, 2995-3007.

Carr, M.H. (1981), The Surface of Mars, Yale University Press, New Haven, Conn.

Carr, M.H. (1995), The martian drainage system and the origin of valley networks and fretted channels, J. Geophys. Res., 100, 7479-7507.

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

Carr, M. H. (2002), Elevations of water-worn features on Mars: Implications for circulation of groundwater, J. Geophys. Res., 107, doi:10.1029/ 2002JE001845.

Carr, M. H., R. Greeley, K. R. Blasius, J. E. Guest, and J.B. Murray (1977), Some Martian volcanic features as viewed from the Viking Orbiters, J. Geophys. Res., 82, 3985-4015.

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

Chadwick, D.J., and G.G. Schaber (1993), Impact crater outflows on Venus: Morphology and emplacement mechanisms, J. Geophys. Res., 98 (E11), 20,891-20,902.

Chapman, M.G., and J.S. Kargel (1999), Observations at the Mars Pathfinder site: Do they provide “unequivocal” evidence of catastrophic flooding?, J. Geophys. Res., 104 (E4), 8671-8678.

Chevrier, V., and P. E. Mathé (2007), Mineralogy and evolution of the surface of Mars: A review, Planetary and Space Science, 55, 289-314.

Clifford, S.M. (1993), A model for hydrologic and climatic behavior of water on Mars, J. Geophys. Res., 98 (E6), 10,973-11,016.

Clifford, S.M., and T.J. Parker (2001), The evolution of the Martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains, Icarus, 154, 40-79.

Coleman, N.M. (2003), Aqueous flows carved the outflow channels on Mars, J. Geophys. Res., 108(E5), 5039, doi:10.1029/2002JE001940.

Coleman, N. M., C. L. Dinwiddie, and K. Casteel (2007), High outflow channels on Mars indicate Hesperian recharge at low latitudes and the presence of canyon lakes, Icarus, 189, 344-361.

Craddock, R.A., and T.A. Maxwell, Geomorphic evolution of the martian highlands through ancient fluvial processes. Jour. Geophys. Res., 98, 3453-3468.

Crown, D.A., and R. Greeley (1993), Volcanic geology of Hadriaca Patera and the eastern Hellas region of Mars, J. Geophys. Res., 98 (E2), 3431-3451.

Cruikshank, D.P., and C.A. Wood (1972), Lunar rilles and Hawaiian volcanic features: Possible analogues, Moon, 3, 412-447.

Donahue, T.M., and C.T. Russell (1997), The Venus atmosphere and ionosphere and their interaction with the solar wind: an overview, In Venus II (S.W. Bougher, D.M. Hunten, and R.J Phillips, Eds.), The University of Arizona Press, Tucson, Arizona, pp.3-31.

El-Baz, F. (1972), New geological findings in Apollo 15 lunar orbital photographs, Proc. Lunar Sci. Conf., 3rd, 39-61.

El-Baz, F., and S.A. Roosa (1972), Signficant results from Apollo 14 lunar orbital photography, Proc. Lunar Sci. Conf. 3rd, 63-83.

El-Baz, F., and A.M. Worden (1972), Orbital science investigations: Part A, Visual observations from lunar orbit, in Apollo 15 Preliminary Science Report, NASA Spec. Publ., SP-289, 25-1 – 25-27.

El-Baz, F., A.M. Worden, and V.D. Brand (1972), Astronaut observations from lunar orbit and their geological significance, Proc. Lunar Sci. Conf., 3rd, 85-104. Fegley, Jr., B., G. Klingelh?fer, K. Lodders, and T. Widemann (1997), Geochemistry of surface-atmosphere interactions on Venus, In Venus II (S.W. Bougher, D.M. Hunten, and R.J Phillips, Eds.), The University of Arizona Press, Tucson, Arizona, pp.591-636.

Goetz, W., et al. (2005), Indication of drier periods on Mars from the chemistry and mineralogy of atmospheric dust, Nature, 436, 62-65.

Goldspiel, J. M., Squyres, S. W., and Jankowski, D. G. (1993), Topography of small Martian valleys, Icarus, 105, 479-500.

Greeley, R. (1971a), Lava tubes and channels in the lunar Marius Hills, The Moon, 3, 289-314.

Greeley, R. (1971b), Lunar Hadley Rille: Considerations of its origin, Science, 172, 722-725.

Greeley, R. (1976), Modes of emplacement of basalt terrains and an analysis of mare volcanism in the Orientale Basin, Proc. Lunar Sci. Conf. 7th, 2747-2759.

Greeley, R., E. Theilig, J.E. Guest, M.H. Carr, H. Masursky, and J.A. Cutts (1977), Geology of Chryse Planitia, J. Geophys. Res., 82, 4093-4109.

Greeley, R., and P. D. Spudis (1978), Mare volcanism in the Herigonius region of the Moon, Proc. Lunar Planet. Sci. Conf. 9th, 3333-3349.

Greeley, R., and Guest, J. E. (1987), Geologic map of the eastern equatorial region of Mars, scale 1:15,000,000, U.S. Geol. Surv. Misc. Invest., Map I-1802-B.

Greeley, R., and D.A. Crown (1990), Volcanic geology of Tyrrhena Patera, Mars, J. Geophys. Res., 95 (B5), 7133-7149.

Gregg, T. K. P., and R. Greeley (1993), Formation of Venusian canali: Considerations of lava types and their thermal behaviours, J. Geophys. Res., 98, 10,873-10,882.

Grolier, M.J. (1978), Caption to Figure 193, in Apollo Over the Moon: A View From Orbit (H. Masursky, G.W. Colton, and F. El-Baz, Editors), p.186.

Hackman, R. J. (1966), Geologic map of the Montes Apenninus region of the Moon, in Geologic Atlas of the Moon, I-463 (LAC-41), U.S. Geological Survey.

Head, J.W., L.S. Crumpler, J.C. Aubele, J.E. Guest, and R.S. Saunders (1992), Venus volcanism: classification of volcanic features and structures, associations, and global distribution from Magellan data, J. Geophys. Res., 97, 16,055-16,067.

Head, J.W., M.A. Kreslavsky, and S. Pratt (2002), Northern lowlands of Mars: Evidence for widespread flooding and tectonic deformation in the Hesperian Period, J. Geophys. Res., 107 (E1), 5004, 10.1029/2000JE001445.

Head, J.W., L. Wilson, and K.L. Mitchell (2003), Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryosphereic cracking, and confined aquifer groundwater release, Geophys. Res. Lett., 30, 1577, doi: 10.1029/2003GL017135.

Horz, F., R.Grieve, G. Heiken, P. Spudis, and A. Binder (1991), Lunar surface processes, In Lunar Sourcebook (G.H. Heiken, D.T. Vaniman, and B.M. French, Eds.), Cambridge University Press, 61-120.

Howard, K. A., J. W. Head, and G. A. Swann (1972), Geology of Hadley Rille, Proc. Lunar Sci. Conf., 3rd, 1-14.

Kargel, J.S., G. Komatsu, V.R. Baker, and R.G. Strom (1993), The volcanology of Venera and VEGA landing sites and the geochemistry of Venus, Icarus, 103, 253-275.

Kargel, J.S., R.L. Kirk, B. Fegley Jr., and A.H. Treiman (1994), Carbonate-sulfate volcanism on Venus?, Icarus, 112, 219-252.

Kieffer, H., S. Chase, T. Martin, E. Miner, F. Palluconi (1976), Soil and surface temperatures at the Viking landing sites, Science, 194, 1341-1344.

Koeppen, W.C., and V.E. Hamilton (2008), Global distribution, composition, and abundance of olivine on the surface of Mars from thermal infrared data, J. Geophys. Res., 113, E05001, doi:10.1029/2007JE002984.

Komatsu, G., P. E. Geissler, R. G. Strom, and R. B. Singer (1993). Stratigraphy and erosional landforms of layered deposits in Valles Marineris, Mars, J. Geophys. Res., 98, 11,105-11,121.

Komatsu, G., V. R. Baker, V. C. Gulick, and T. J. Parker (1993), Venusian channels and valleys: distribution and volcanological implications, Icarus, 102, 1-25.

Komatsu, G., and V. R. Baker (1994), Meander properties of Venusian channels, Geology, 22, 67-70.

Komatsu, G., and V.R. Baker (1997), Paleohydrology and flood geomorphology of Ares Vallis, J. Geophys. Res., 102 (E2), 4151-4160.

Komatsu, G., J. M. Dohm, and T. M. Hare (2004), Hydrogeologic processes of large-scale tectonomagmatic complexes in Mongolia-southern Siberia and on Mars, Geology, 32, 325-328.

Komatsu, G., G. Di Achille, C. Popa, S. Di Lorenzo, A.P. Rossi, and J.A.P. Rodgriguez (2009), Paleolakes, paleofloods, and depressions in Aurorae and Ophir Plana, Mars: Connectivity of surface and subsurface hydrological systems, Icarus, 201, 474-491.

Leverington, D. W. (2004a), Volcanic rilles, streamlined islands, and the origin of outflow channels on Mars, J. Geophys. Res., 109, E10011, doi:10.1029/2004JE002311.

Leverington, D. W. (2004b), Volcanic resurfacing as an alternative mechanism for formation of Martian “crater lake” features, Eos Trans. AGU, 85(17), Jt. Assem. Suppl., Abstract P33D-08.

Leverington, D. W. (2006), Volcanic processes as alternative mechanisms of landform development at a candidate crater-lake site near Ytrrhena Patera, Mars, J. Geophys. Res., 111, E11002, doi:10.1029/2004JE002382.

Leverington, D. W. (2007), Was the Mangala Valles system incised by volcanic flows? J. Geophys. Res., 112, E11005, doi:10.1029/2007JE002896.

Leverington, D.W. (2009a), Potential implications of a common origin for outflow systems on Venus, Mars, and the Moon, International Conference on Comparative Planetology: Venus – Earth – Mars, European Space Agency, ESTEC, Abstract P2.06.

Leverington, D.W. (2009b), Reconciling channel formation processes with the nature of elevated outflow systems at Ophir and Aurorae Plana, Mars, J. Geophys. Res., 114, E10005, doi:10.1029/2009JE003398.

Leverington, D. W., and T. A. Maxwell (2004), An igneous origin for features of a candidate crater-lake system in western Memnonia, Mars, J. Geophys. Res., 109, E06006, doi: 10.1029/2004JE002237.

Lingenfelter, R.E., S.J. Peale, G. Schubert (1968), Lunar rivers, Science, 161, 266-269.

Manga, M. (2004), Martian floods at Cerberus Fossae can be produced by groundwater discharge, Geophys. Res. Lett., 31, L02702, doi:10.1029/2003GL018958.

Mars Channel Working Group (1983), Channels and valleys on Mars, Geological Society of America Bulletin, 94, 1035-1054.

Masursky, H. (1973), An overview of geological results from Mariner 9, J. Geophys. Res., 78, 4009-4030.

Masursky, H., J.M. Boyce, A.L. Dial., G.G. Schaber, and M.E. Strobell (1977), Classification and time of formation of Martian channels based on Viking data, J. Geophys. Res., 82, 4016-4038.

Masursky, H., G.W. Colton, and F. El-Baz (Eds.) (1978), Apollo Over the Moon: A View From Orbit, NASA Spec. Publ., SP-362, 184.

McCauley, J.F. (1967), Geologic Map of the Hevelius Region of the Moon, U.S. Geological Survey, Map I-491 (LAC-56).

McCauley, J.F. (1978), Geologic Map of the Coprates Quadrangle of Mars, U.S. Geol. Survey Misc. Inv. Ser. Map I-897.

McCauley, J.F., M.H. Carr, J.A. Cutts, W.K. Hartmann, H. Masursky, D.J. Milton, R.P. Sharp, and D.E. Wilhelms (1972), Preliminary Mariner 9 report on the geology of Mars, Icarus, 17, 289-327.

McEwen, A. S., M. C. Malin, M. H. Carr, and W. K. Hartmann (1999), Voluminous volcanism on early Mars revealed in Valles Marineris, Nature, 397, 584-586.

McSween, H.Y., S.L. Murchie, J.A. Crisp, N.T. Bridges, R.C. Anderson, J.F. Bell III, D.T. Britt, J. Br?ckner, G. Dreibus, T. Economou, A. Ghosh, M.P. Golombek, J.P. Greenwood, J.R. Johnson, H.J. Moore, R.V. Morris, T.J. Parker, R. Rieder, R. Singer, and H. W?nke (1999), Chemical, multispectral, and textural constraints on the composition and origin of rocks at the Mars Pathfinder landing site, J. Geophys. Res., 104 (E4), 8679-8715.

McSween, H., R. Arvidson, J. Bandfield, J. Bell, D. Blaney, W. Calvin, P. Christensen, B. Clark, J. Crisp, T. Economou, W. Farrand, A. Ghosh, K. Herkenhoff, J. Johnson, G. Klingelh?fer, S. McLennan, J. Moersch, R. Morris, R. Rieder, S. Ruff, C. Schroeder, P. Souza, S. Squyres, H. Wanke, M. Wyatt, J. Zipfel, and the Athena Science Team, 2004, Preliminary mineralogy and geochemistry results at the MER-A landing site in Gusev, 35th Lunar and Planetary Science Conference, Abstract #2167.

Milton, D.J. (1973), Water and processes of degradation in the Martian landscape, J. Geophys. Res., 78, 4037-4047.

Morris, R.V., et al. (2004), Mineralogy at Gusev Crater from the Mossbauer Spectrometer on the Spirit Rover, Science, 305, pp.833-836.

Nelson, D.M., and R. Greeley (1999), Geology of Xanthe Terra outflow channels and the Mars Pathfinder landing site, J. Geophys. Res., 104 (E4), 8653-8669.

Nimmo, F., and D. McKenzie (1998) Volcanism and tectonics on Venus, Annu. Rev. Earth Planet. Sci., 26, 23-51.

Oberbeck, V.R., W.L. Quaide, and R. Greeley (1969), On the origin of lunar sinuous rilles, Mod. Geol., 1, 75-80.

Papike, J., L. Taylor, S. Simon (1991), Lunar minerals, In Lunar Sourcebook (G.H. Heiken, D.T. Vaniman, and B.M. French, Eds.), Cambridge University Press, 121-181.

Peale, S.J., G. Schubert, and R.E. Lingenfelter (1968), Distribution of sinuous rilles and water on the Moon, Nature, 220, 1222-1225.

Robinson, M.S., and K.L. Tanaka (1990), Magnitude of a catastrophic flood event at Kasei Valles, Mars, Geology, 18, 902-905.

Rodriguez, J.A.P, S. Sasaki, and H. Miyamoto (2003), Nature and hydrological relevance of the Shalbatana complex underground cavernous system, Geophys. Res. Lett., 30, 1304, doi:10.1029/2002GL016547.

Russell, P. S., and J. W. Head III (2002), The martian hydrosphere/cryosphere system: Implications of the absence of hydrologic activity at Lyot crater, Geophys. Res. Lett., 29(17), 1827, doi:10.1029/2002GL015178.

Russell, P.S., and J.W. Head (2003), Elysium-Utopia flows as mega-lahars: A model of dike intrusion, cryosphere cracking, and water-sediment release, J. Geophys. Res., 108 (E6), 5064, doi:10.1029/2002JE001995.

Saunders, R. S., and G. H. Pettengill (1991), Magellan: Mission summary, Science, 252, 247-249.

Schaber, G.G. (1973), Lava flows in Mare Imbrium: Geologic evaluation from Apollo orbital photography, Proc. Lunar Sci. Conf. 4th, 73-92.

Schmitt, H.H., G. Lofgren, G.A. Swann, and G. Simmons (1970), The Apollo 11 samples: Introduction, Proceedings of the Apollo 11 Lunar Science Conference, Vol. 1, pp.1-54.

Schmitt, H.H., and E.A. Cernan (1973), A geological investigation of the Taurus-Littrow valley, In Apollo 17 Preliminary Science Report, NASA Special Publication 330, pp.5-1 – 5-21.

Schonfeld, E. (1979), Origin of Valles Marineris, Proc. Lunar Planet. Sci. Conf. 10th, 3031-3038.

Schultz, P. H. (1976), Moon Morphology, University of Texas Press, Austin.

Scott, D. H., and K. L. Tanaka (1986), Geologic Map of the Western Equatorial Region of Mars, scale 1:15,000,000, Miscellaneous Investigations Series, NASA Map I-1802-A.

Scott, D.H., M.G. Chapman, J.W. Rice, and J.M. Dohm (1992), New evidence of lacustrine basins on Mars: Amazonis and Utopia Planitia, Proc. Lunar Planet. Sci. Conf. 22nd, 53-62.

Sharp, R. P., and M. C. Malin (1975), Channels on Mars, Bull. Geol. Soc. Am., 86, 593-609.

Shoemaker, E.M., R.M. Batson, K.B. Larson (1966), An appreciation of the Luna 9 pictures, Astronautics and Aeronautics, May 1966, 40-50.

Shoemaker, E.M., E.C. Morris, R.M. Batson, H.E. Holt, K.B. Larson, D.R. Montgomery, J.J. Rennilson, and E.A. Whitaker (1969), Television observations from Surveyor, In Surveyor Project Final Report, Part II. Science Results, Jet Propulsion Laboratory Technical Report 32-1265, Pasadena, pp. 21-136.

Shoemaker, E.M., M.H. Hait, G.A. Swann, D.L. Schleicher, D.H. Dahlem, G.G. Schaber, and R.L. Sutton (1970), Lunar regolith at Tranquility Base, Science, 167, 452-455.

Smith, G. A. (1993), Missoula flood dynamics and magnitudes inferred from sedimentology of slack-water deposits on the Columbia Plateau, Washington, Bull, Geol. Soc. Am., 105, 77-100.

Smith, D., G. Neumann, R.E. Arvidson, E.A. Guinness, and S. Slavney (2003), Mars Global Surveyor Laser Altimeter Mission Experiment Gridded Data Record, MGS-M-MOLA-5-MEGDR-L3-V1.0, NASA Planet. Data Syst., Washington D.C.

Spudis, P., and C. Pieters (1991), Global and regional data about the Moon, In Lunar Sourcebook (G.H. Heiken, D.T. Vaniman, and B.M. French, Eds.), Cambridge University Press, New York, pp.595-632.

Strain, P.L., and El-Baz, F. (1977), Topography of sinuous rilles in the Harbinger Mountains region of the Moon, The Moon, 16, 221-229.

Surkov, Y.A. (1983), Studies of Venus rocks by Veneras 8, 9, and 10. In Venus (D.M. Hunten, L. Colin, T.M. Donahue, V.I. Moroz, Eds.), The University of Arizona Press, Tucson, Arizona.

Surkov, Y.A., F.F. Kirnozov, V.N. Glazov, A.G. Dunchenko, L.P. Tatsy, and O.P. Sobornov (1987), Uranium, thorium, and potassium in the Venusian rocks at the landing sites of Vega 1 and 2, J. Geophys. Res., 92 (B4), E537-E540.

Swann, G. A., and 19 co-authors. (1972), Preliminary geologic investigations of the Apollo 15 landing site, in Apollo 15 Preliminary Science Report, NASA Spec. Publ., SP-289, 5-1 to 5-112.

Tanaka, K.L., and M.G. Chapman (1990), The relation of catastrophic flooding of Mangala Valles, Mars, to faulting of Memnonia Fossae and Tharsis volcanism, J. Geophys. Res., 95 (B9), 14,315-14,323.

Urey, H.C. (1967), Water on the Moon. Nature, 216, 1094-1095.

Vaniman, D., R. Reedy, G. Heiken, G. Olhoeft, and W. Mendell (1991), The lunar environment, In Lunar Sourcebook (G.H. Heiken, D.T. Vaniman, and B.M. French, Eds.), Cambridge University Press, 27-60.

Wilhelms, D. E. (1987), The Geologic History of the Moon, U.S. Geological Survey Professional Paper 1348, Washington, DC.

Wilson, L., and J.W. Head III, (2002), Tharsis-radial graben system as the surface manifestation of plume-related dike intrusion complexes: Models and implications, J. Geophys. Res., 107 (E8), 5057, 10.1029/2001JE001593.

Wilson, L., and P.J. Mouginis-Mark (2003), Phreatomagmatic explosive origin of Hrad Vallis, Mars, J. Geophys. Res., 108 (E8), 5082, doi:10.1029/2002JE001927.

Wu, S.C., Schafer, F.J., Jordan, R., Nakata, G.M., and Derick, J.L. (1972), Photogrammetry of Apollo 15 photography, in Apollo 15 Preliminary Science Report, NASA Spec. Publ., SP-289, 25-36 to 25-48.

Young, R.A., W.J. Brennan, R.W. Wolfe, and D.J. Nichols (1973), Analysis of lunar mare geology from Apollo photography, Proc. Lunar Sci. Conf. 4th, 57-71.

Zimbelman, J.R. (2001), Image resolution and evaluation of genetic hypotheses for planetary landscapes, Geomorphology, 37, 179-199.

Zimbelman, J.R., R.A.Craddock, R. Greeley, and R.O. Kuzmin (1992), Volatile history of Mangala Valles, Mars, J. Geophys. Res., 97 (E11), 18,309-18,317.

Zisk, S.H., C.A. Hodges, H.J. Moore, R.W. Shorthill, T.W., Thompson, E.A. Whitaker, and D.E. Wilhelms (1972), The Moon, 17, 59-99.