Planetary and Space Science 111 (2015) 144–154

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Remnant buried ice in the equatorial regions of Mars: Morphologicalindicators associated with the Arsia Mons tropical mountain glacierdeposits

Kathleen E. Scanlon a,n, James W. Head a, David R. Marchant b

a Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI 02912, USAb Department of Earth & Environment, Boston University, Boston, MA 02215, USA

a r t i c l e i n f o

Article history:Received 30 September 2014Received in revised form25 March 2015Accepted 27 March 2015Available online 9 April 2015

Keywords:MarsMars surfaceMars climate

x.doi.org/10.1016/j.pss.2015.03.02433/& 2015 Elsevier Ltd. All rights reserved.

esponding author. Tel.: þ1 401 863 3485; faxail address: kathleen_scanlon@brown.edu (K.E

a b s t r a c t

The fan-shaped deposit (FSD) on the western and northwestern flanks of Arsia Mons is the remnant oftropical mountain glaciers, deposited several tens to hundreds of millions of years ago during periods ofhigh spin-axis obliquity. Previous workers have argued that the Smooth Facies in the FSD contains a coreof ancient glacial ice. Here, we find evidence that additional glacial ice remains preserved within severalother landforms in the Smooth Facies and Ridged Facies. These include landforms that we interpret askame and kettle topography on the basis of their distribution, size, and morphologies ranging progres-sively from knobs to degraded knobs to pits. We argue that some moraines in the Ridged Facies are ice-cored on the basis of their interactions with lava flows and the axial troughs at the crests of somemoraines. We also argue that dunes with axial troughs, found in and surrounding the FSD, are theremnants of sediment-covered snow dunes formed by reworking of snow or glacial ice, and that the axialtroughs form as tension cracks in the sediment and deepen by sublimation of the underlying ice. Long-term preservation of water ice in equatorial environments is assisted by a meters- to decameters-thickdebris cover (lag) formed from sublimation of dirty ice, as well as burial beneath volcanic tephra andaeolian deposits. This ancient ice could contain preserved biosignatures, provide information on Martianclimate and atmospheric history, and serve as a resource for human exploration.

& 2015 Elsevier Ltd. All rights reserved.

1. Introduction

The western and northwestern flanks of the equatorial TharsisMontes volcanoes were covered by cold based mountain glaciers asrecently as 125–220 million years ago (Kadish et al., 2014), as evi-denced by the morphology, stratigraphic relationships, and spatialdistribution of landforms in the fan-shaped deposits (FSDs) on eachvolcano (Williams, 1978; Lucchitta, 1981; Head and Marchant, 2003;Shean et al., 2005, 2007; Kadish et al., 2008a; Scanlon et al., 2014,2015). This geomorphologic evidence is bolstered by climate andglacial flow models that predict snow accumulation and ice flow inthose regions during periods of high spin-axis obliquity (Forgetet al., 2006; Fastook et al., 2008). Following a return to lowerobliquity and the resulting change in climate conditions, the glacialice ablated and returned to higher latitudes and the poles (Headet al., 2003, 2006a, b), leaving the Tharsis Montes fan-shapeddeposits. A major question is whether buried ice still remains in

: þ1 401 863 3978.. Scanlon).

some of these deposits, despite the peak insolation and relativelyhigh temperatures expected at equatorial latitudes now and in therecent past (e.g. Mellon and Jakosky, 1993, 1995; Mellon et al.,1997).

Morphological evidence for buried present-day water ice in thetropics and mid-latitudes of Mars can be generally divided intothree categories, as follows:

(1)

Surface textures attributed to partial removal of ice. Theseinclude sublimation pits or hollows (e.g. Mustard et al., 2001;Mangold, 2003; Kadish et al., 2008b), scalloped depressions(e.g. Lefort et al., 2010; Séjourné et al., 2011), sublimationpolygons and “brain terrain” (e.g. Levy et al., 2008, 2009), andother dissected terrains such as “basketball texture” (e.g. Headet al., 2003) or “ridge and valley texture” (Pierce and Crown,2003; Chuang and Crown, 2005).

(2)

Topographic profile. Lobate debris aprons (LDA), lineated val-ley fill (LVF), and concentric crater fill (CCF) on Mars have beeninterpreted as debris-covered glaciers with remnant ice cores,partially on the basis of the glacier-like convex upward topo-graphic profiles at their margins (e.g. Mangold and Allemand,

K.E. Scanlon et al. / Planetary and Space Science 111 (2015) 144–154 145

2001; Holt et al., 2008; Head et al., 2010; Levy et al., 2010).

(3) Unusual crater morphologies. “Ring-mold” craters (Kress and

Head, 2008) have been interpreted as resulting from impactsinto buried ice on the basis of their size-frequency distribution,which is consistent with smaller impacts not penetrating farenough to reach the buried ice; their annular moats, which area characteristic feature of experimental impacts into ice-richsubstrates; and the apparent degradation sequence representedby the range of ring-mold crater morphologies (Pedersen andHead, 2010). Pedestal craters, perched craters and excess ejectacraters (e.g. Kadish and Head, 2011) are interpreted to form byimpacts into an ice-rich substrate, where either the impactprocess itself (in the case of pedestal craters) or the excavationof rocky material from underneath the ice-rich layer (in the caseof perched and excess ejecta craters) creates a surface depositthat protects the ice-rich material immediately surrounding thecrater against sublimation.

Remnant ice at equatorial latitudes on Mars is of potentialinterest as an exploration target for several reasons. Gas bubblespreserved in terrestrial ancient ice can be used to develop timeseries for the molecular and isotopic composition of the atmo-sphere (e.g. Alley, 2000; Lüthi et al., 2008; Kobashi et al., 2011;Capron et al., 2012; Bazin et al., 2013; Rhodes et al., 2013). If areliable chronology and isotopic baseline could be developed forMars, then these data would be particularly useful, as they couldpotentially help constrain orbital parameter variations prior tothose that can be calculated a priori (Laskar et al., 2004). The ArsiaMons FSD has been suggested as a well-suited target for futurehuman missions (e.g. Levine et al., 2010), and ice deposits withinthe FSD would offer a potential water and fuel resource for humanexploration (e.g. Sridhar et al., 2004).

At �166,000 km2 in area, the Arsia Mons FSD (Head andMarchant, 2003; Shean et al., 2005, 2007; Scanlon et al., 2014,2015) is the largest of the Tharsis Montes FSDs (Fig. 1). Cratercounts indicate that the FSD has been in place for �210 Ma(Kadish et al., 2014). The Smooth Facies, one of the geomorpho-logic units in the FSDs (Zimbelman and Edgett, 1992; Scott andZimbelman, 1995), has been interpreted as remnant alpine-likedebris-covered glaciers (Head and Marchant, 2003). Likewise,Shean et al. (2007) suggest that lineated debris displaying con-centric ridges and partially filling tectonic graben higher up thevolcanic edifice is also cored by glacier ice. The convex topographyof these deposits (Shean et al., 2007), as well as the morphologicindicators of active flow (Head and Marchant, 2003; Marchant andHead, 2007) and the unique morphology of superimposed craters(Head and Weiss, 2014), suggest that buried ice 100–300 m thickmay still be present at depth. In this contribution, we expand thesearch for buried ice and review several other classes of landformsin the FSD that have not been previously described, and whosemorphology indicates that remnant ice may still be present.

2. Data and methods

Images in this study are from the Mars Reconnaissance Orbiter(MRO) Context Camera (CTX), with �5 m per pixel resolution (Malinet al., 2007), augmented with images from the High ResolutionStereo Camera (HRSC) at 10–30 m per pixel resolution (Neukum andJaumann, 2004). Topographic data is from the Mars Orbital LaserAltimeter (MOLA) at �463 m per pixel resolution (Zuber et al., 1992;Smith et al., 1999) and, where available, HRSC-derived Digital Ele-vation Maps (DEMs) with �100 m per pixel resolution (Dumkeet al., 2008). Contour maps were created using the Spatial Analysttoolkit in ArcMap 10.0.

3. Landforms interpreted to be indicative of remnant ice

On Earth, remnant patches of buried glacier ice may occurwherever overlying debris is sufficiently thick to retard ice ablation.Examples include ice-cored moraines, detached blocks of ice buriedbeneath proglacial sediment, and remnant, stagnant ice buriedbeneath thick sublimation till (e.g. Hambrey, 1984; Marchant et al.,2002; Evans, 2009; Swanger et al., 2010; Irvine-Fynn et al., 2011;Lacelle et al., 2011; Monnier et al., 2008).

In the coldest and driest region of the Mars-like Antarctic DryValleys, 40Ar/39Ar ages of volcanic ash deposits indicate thatunderlying remnant glacier ice has been preserved for millions ofyears (Sugden et al., 1995; Marchant et al., 2002; Kowalewski et al.,2006, 2012). We propose that the morphology of several land-forms adjacent to Arsia Mons suggests that ice millions of yearsold is also present in the Arsia Mons FSD.

3.1. Pit-and-knob terrain

Near the northern edge of the FSD is a field of mounds(“knobs”) and shallow topographic depressions (“pits”; Figs. 1 and2). Each knob is up to 1 km in diameter. Interspersed among theknobs are pits of similar size and shape to the knobs (Figs. 2 and3). The pits and knobs are generally aligned, and the lines onwhich they fall are concentric with the outline of the SmoothFacies (Figs. 1 and 2) and with drop moraines left by a relativelyyoung debris-covered glacier extending from a nearby graben(Shean et al., 2007). Many of the smaller knobs are surrounded byshallow annular depressions (“moats”), and some pits have whatappear to be degraded knobs at their centers (Fig. 3). We proposethat the pit-and-knob terrain is ice-cored and that the landformsrepresent a progression in which gradual loss of ice via sublima-tion causes topographic inversion, with knobs becoming moatedknobs, then pits with degraded knobs, and finally pits (Fig. 4).

In terrestrial zones of rapid ice retreat, blocks of ice detachedfrom the retreating edge of a glacier may become partially buriedbeneath glacial outwash (Thwaites, 1926; Price, 1969; Fay, 2002;Russell et al., 2010; Evans, 2011; Knight, 2012). When the blockseventually melt, they leave “kettle holes” where the blocks for-merly stood. Fields of pits interpreted as kettle holes have beenobserved on Mars in the circumpolar Dorsa Argentea Formation(Dickson and Head, 2006). The morphological evidence suggeststhat the Arsia FSD pit-and-knob terrain may have resulted frombackwasting of ice in the Smooth Facies and subsequent burial ofthe isolated ice blocks, analogous to the formation of terrestrialkettled outwash plains (Fig. 5). This evidence comprises (1) thesimilarity in size and shape between the pits and knobs, (2) thegenetic relationship implied by the presence of knobs with moats,and (3) the co-alignment of the pits and knobs with the outline ofthe Smooth Facies and with lineations in the Smooth Facies(Fig. 6). Because of the cold Amazonian climate, however, the iceblocks would have sublimed rather than melted to leave the pitsbehind, and the sediment that embayed them would have beenvolcanic tephra, englacial debris, or aeolian sediment, rather thanglacial outwash as in terrestrial kettled plains. The concentricfractures surrounding many of the pits (Fig. 3) suggest that near-surface sediment, possibly cemented by pore ice, moved down-slope toward pit centers as underlying ice sublimed; similar pat-terns can be observed on Earth where the removal of blocks ofburied ice causes concentric fractures to form in the overlyingsediment (Sanford, 1959; Dickson and Head, 2006). This sedimentcover could have armored some of the ice blocks against furthersublimation, leaving the present-day knobs.

Alternatively, the pit-and-knob terrain may have formed in amanner analogous to terrestrial “controlled moraine” (e.g. Evans,2009; Szuman and Kasprzak, 2010; Bennett and Evans, 2012; Lakeman

Fig. 1. Geomorphological unit map of the Arsia Mons fan-shaped deposit (FSD), after Zimbelman and Edgett (1992) and Scott and Zimbelman (1995); reproduced from Scanlonet al. (2014) and annotated. Red lines denote large volcanic graben, white lines denote contacts between units, and black lines denote the outlines of glaciovolcanic landforms(Scanlon et al., 2014) and landforms characteristic of volcanism-induced wet-based glacial conditions (Scanlon et al., 2015). Closed and open green circles in the Smooth Faciesdenote pits and knobs, respectively. The regions where moraines and dunes with linear troughs (Sections 3.2 and 4, respectively) are located are marked by shaded black andwhite ellipses, respectively. The area shown in Fig. 2 is denoted by a white box. THEMIS 100 m/pixel daytime image mosaic. This and all other images in this paper are orientedwith north toward the top of the image. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2. Pit (white arrow) and knob (black arrow) terrain in the Arsia Mons fan-shaped deposit (see Fig. 1 for location). Pits and knobs form lines concentric to theborder of the Smooth Facies. The area shown in Fig. 3 is denoted by a white box.Some knobs appear to be surrounded by moats (red arrow), implying a progressionfrom knob to pit (see also Fig. 4). CTX image P08_004056_1741_XI_05S125W. (Forinterpretation of the references to color in this figure legend, the reader is referredto the web version of this article.)

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and England, 2012). When variable concentrations of debris within oron top of glaciers (e.g. Mackay et al., 2014) are shaped into belts byglacial flow, bands of debris can isolate patches of stagnant ice as the

glacier retreats. Incomplete loss of this dead ice results in lineararrangements of mounds and kettle holes, with the continuity andlinearity of the mounds breaking down as the removal of ice continuesto completion. As with the “backwasting” formation model, the knob-to-pit progression (Fig. 4), the linearity of the remaining knobs(Figs. 1, 2 and 6), and the concentric fractures surrounding pits (Fig. 3)suggest that these features had ice cores at formation and that theremoval of ice from these features has not proceeded to completion.This “controlled moraine” model (Fig. 7) accounts for the lineararrangement of the pits and knobs without requiring widespreadaccumulation of ice blocks to have occurred at the ice margins. Wetherefore favor this model of pit-and-knob terrain development.

3.2. Drop moraines with linear troughs

At the northwestern edge of the deposit, some of the dropmoraines (Head and Marchant, 2003) in the Ridged Facies havelinear troughs along their crests (Fig. 8). These moraines aretypically �100 m wide, and some are continuous for over 100 km.Other nearby moraines have similar dimensions but lack thecharacteristic crest troughs. We interpret these moraines to havedeveloped their trough morphology by the loss of ice via sub-limation. In terrestrial settings, ice-cored moraines can develop atthe margins of glaciers when bands of debris within a glacierisolate small masses of ice from the main body of ice as the glacierretreats (e.g. Evans, 2009).

The hypothesis that moraines in the FSD may contain remnantice is also supported by the lone subaerial lava flow in the RidgedFacies, which has a chaotic texture interpreted to have resulted

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from interactions between the lava flows and ice in and aroundthe moraines at the time of flow emplacement (Scanlon et al.,2014). If ice was present in the moraines when lava flowed overthem, the lava would be expected to interact with it by meltingand collapse (e.g. Edwards et al., 2012), as well as explosively (e.g.Belousov et al., 2011), imparting a chaotic texture to the flows.

4. Postglacial ice-related landforms

Dispersed throughout the northwestern edge and surroundingsof the Arsia FSD are relatively short (�2 km, but some as much as

Fig. 3. Pit-and-knob terrain: (a) Closeup view of pits and knobs outlined by the white bFig. 3a; pits are shown in red, knobs in yellow, and fractures in blue. (For interpretatioversion of this article.)

Fig. 4. Examples of knobs (a), moated knobs (b), pits with remnant knobsP16_007392_1743_XN_05S126W.

9 km) elongate ridges with axial troughs (Fig. 11). The width of theridges in any one population of ridges is highly uniform, buttypical widths vary between regions from �100 m to �350 m.Their distribution is not restricted to any underlying unit of theFSD, and they often appear superposed on and draping the con-tacts and features of the underlying FSD units (Fig. 10). In contrastto the characteristics of the concentric drop moraines of theRidged Facies, they are consistently oriented southwest-to-north-east wherever they occur, and they are straight rather than curvedin plan view. They are also continuous over much shorter distan-ces than the drop moraines with linear troughs. They are often

ox in Fig. 2. CTX image P08_004056_1741_XI_05S125W. (b) Sketch map of area inn of the references to color in this figure legend, the reader is referred to the web

(c), and pits (d), from CTX images P08_004056_1741_XI_05S125W and

Fig. 5. Comparison of kettle hole formation process on Earth (right) and a “backwasting”model of pit and knob terrain formation in the Arsia Mons fan-shaped deposit (left).As a glacier (a) recedes, blocks of ice separate from its terminus (b). In a warm-based, terrestrial glacier, outwash from the receding glacier will partially bury (or in somecases, not shown, completely bury) these blocks; on Amazonian Mars, atmospheric dust or volcanic tephra covers the ice blocks before they fully sublime (c). When the icefully melts or sublimes, shallow pits are left behind in the sediment; in the case of Mars, some ice has been armored by debris fall and remains as debris-covered knobs (d).

Fig. 6. Pits and knobs fall along lines concentric to the boundaries of the Smooth Facies. (a) THEMIS image mosaic. (b) Sketch map; the Smooth Facies is shown in orange, theKnobby Facies in blue, pits as filled green circles, and knobs as open green circles. (For interpretation of the references to color in this figure legend, the reader is referred tothe web version of this article.)

K.E. Scanlon et al. / Planetary and Space Science 111 (2015) 144–154148

K.E. Scanlon et al. / Planetary and Space Science 111 (2015) 144–154 149

concentrated in local topographic lows rather than being uni-formly located within a particular unit. In general, they appeardune-like in nature, but are distinguished from typical dune formsin having a trough along their long axis.

On the basis of the physical proximity of these features to theArsia Mons glacier deposits, and the likelihood that at least somesnow and ice is deposited in the Tharsis FSD regions wheneverspin-axis obliquities measurably increase from current values(Forget et al., 2006; Schon, Head, 2012), we suggest that thismorphology results from the sublimation of ice along the crests ofice-rich dunes. Pedestal craters found throughout the Tharsisregion and dated to 12–13 Ma (Schon and Head, 2012) suggest that

Fig. 7. A “controlled moraine” model of pit-and-knob terrain formation in the Arsia Mona debris-covered glacier (or thickens bands of debris atop the glacier, resulting in similar vdebris isolate masses of ice, concentric to the outlines of the glacier. (c) As ice removalmounds. Complete removal of ice in some mounds (by sublimation) results in the form

Fig. 8. Candidate ice-cored moraines. (a) Some moraines in the Ridged Facies near the Noimage mosaic. (b) Close view of the drop moraine with linear trough, highlighted by tw

several meters of ice covered the Tharsis region in a recent phaseof moderately high obliquity. Due to the superposition of thedunes upon the other units of the Arsia Mons FSD, we propose thatdeposits such as this later ice cover may have been the source ofthe ice that formed the dunes displaying linear troughs. Thegreater density of dunes within the FSD (Fig. 10) suggests that thedunes may also have been built by reworking of the ice and debrisfrom the FSD itself.

The morphology of these ridges suggests the removal of avolatile component. There are two possibilities for the nature ofthe dust-ice mixture that could give rise to the troughs at the crestof the ridges. First (Fig. 11a), the ridges could have formed as

s fan-shaped deposit. (a) Glacial flow concentrates debris into discrete bands withinariable preservation of the underlying ice). (b) As downwasting occurs, the bands ofproceeds, the ice-cored ridges become less continuous and form knobs or elongateation of collapse pits.

rthwest Plateau (Scanlon et al., 2014; see Fig. 1) have troughs along their crests. CTXo arrows in Fig. 8a. CTX image P17_007814_1773_XI_02S129W.

K.E. Scanlon et al. / Planetary and Space Science 111 (2015) 144–154150

mixed snow-ice dunes formed during snow deposition at higherobliquity. When the spin-axis obliquity lowered such that ice wasno longer stable at the equator (e.g. Jakosky and Carr, 1985; Mellonand Jakosky, 1993), the snow component would have sublimedand the dust component would have become concentrated in theoutermost layers (Fig. 11b), analogous to the development processof the martian latitude-dependent mantle and some types of ter-restrial loess (Mustard et al., 2001; Head et al., 2003).

If the sides of the dunes were sufficiently steep, these dry outerlayers would have slumped down the ridge sides, forming debris-rich piles at either side of the crest and exposing more ice tosublimation (Fig. 11c). A similar process helps drive topographicinversion cycles in ice-cored moraines and creates ring-shaped“circular moraine features” from sufficiently tall debris-covereddead ice blocks on Earth (Ebert and Kleman, 2004). In concert withthis mechanism, continued wind shear could cause dust to beremoved from the crest, exposing buried ice-rich material topreferential sublimation.

Second, the ridges could have formed as snow dunes that werelater covered by a layer of dust or tephra (Fig. 12a and b). Becausethe least compressive stress in a topographic ridge is orientedhorizontally away from the axis of the ridge (Fiske and Jackson,1972; McTigue and Mei, 1981; Dieterich, 1988; Rubin and Rubin,2013), long tensile cracks aligned with the dune crests could beexpected to form in the sediment cover (Fig. 12c). This tendencycould be further enhanced if the surface sediment layer was notfrozen to the underlying snow and ice, in which case it couldslump to either side of the ridge crest. Fractures are observedalong the crests of debris-covered snow ripples in the AntarcticDry Valleys (compare Figs. 9 and 13) and develop parallel totopographic contours on niveo-aeolian dunes and beds in Alaskaas their snow component melts (Koster and Dijkmans, 1988).These fractures in the protective dust cover would enhance sub-limation directly beneath them by exposing the underlying snow(Mangold, 2003; 2011), eventually leaving a hollow along the ridgeaxis (Fig. 12d and e). On the basis of the similarity of these featuresto terrestrial debris-covered snow dunes, and the fact that plau-sible heights for the ripples are lower than the ice block heightsthat form ring-shaped circular moraines on Earth (and are thusmore likely to create a single ridge of debris than two parallelridges; Ebert and Kleman, 2004), we currently favor this latterinterpretation. High-resolution topographic data will help distin-guish between these mechanisms more conclusively by con-straining the height and side slopes of individual ridges.

Unlike the drop moraines described in Section 3, there are nodunes in the FSD that are similar in shape, size, and distribution tothe crest-trough dunes but which lack the troughs. This suggests

Fig. 9. Typical dunes with linear troughs, found throughout the western extent ofthe Arsia Mons fan-shaped deposit. CTX image P19_008605_1772_XI_02S129W.

that ice removal in the dunes may have proceeded to completion.By analogy with the Antarctic debris-covered snow ripples, icemay still be present beneath the dunes, but this cannot be deter-mined from image data alone. The primary importance of theselandforms is therefore not as a likely reservoir of present-day ice,but rather as an additional indicator of the extent and aeoliantransport of equatorial ice in a recent high-obliquity excursion.

5. Discussion

How much ice remains within the FSDs, what data aside fromgeomorphologic observations indicate the presence of this ice, andwhere does this remnant ice fit in the timeline of Amazonian cli-mate change? For comparison, the best-studied deposits of non-polar Amazonian ice are the Lobate Debris Aprons (LDAs), whichare mid- to late-Amazonian aged debris-covered remnant glaciersfound throughout the mid-latitudes of Mars (e.g. Head et al.,2010). Radar data is consistent with the hypothesis that LDAs arecomposed of massive water ice covered by a layer of debris 0.5–10 m thick (Holt et al., 2008; Plaut et al., 2009). If the age of theFSD and the LDAs are similar, and the temperature and humidity ofthe environments surrounding them (and hence the stability of icein those environments) are also similar, then the depth to massiveice would be expected to be somewhat greater for landforms inthe equatorial FSDs than for the mid-latitude LDAs (e.g. Schor-ghofer and Forget, 2012). Many of our proposed ice-cored featuresat Arsia Mons are several times greater than 10 m in height, suchthat a debris cover thick enough to preserve an ice core couldremain. The fact that the characteristic crest troughs are mostevident in the relatively small moraines and dunes may in fact bedue to their smaller size; the debris cover on larger features maybe sufficient that no significant volume of ice has yet beenremoved, or that the thick surface debris masks topographyassociated with underlying ice loss.

The elevated concentration of hydrogen on the western sides ofArsia and Pavonis Mons relative to their eastern sides (as indicatedby local minima in epithermal neutron fluxes; Boynton et al.,2002; Elphic et al., 2005) is also consistent with the hypothesisthat some ice remains in the FSDs. Elphic et al. (2005), making thesimplifying assumption that the hypothesized ice-rich deposits arepure ice overlain by dry sublimation till in order to obtain a firstorder estimate, calculated that ice could lie �60 cm below thesurface. Since the widespread dunes in the FSD suggest recent orongoing aeolian activity, it is possible that wind has removeddebris from the deposit such that the thickness of debris currentlyoverlying any ice in the deposit is less than the amount that wasrequired to preserve it to the present day.

Radar data could potentially bolster the geomorphologicalevidence for remnant ice in the FSDs, but have not been clear. Forexample, it has also been suggested that the Pavonis Mons FSDcontains remnant ice in its Smooth Facies deposits (Shean et al.,2005). Recent SHARAD radar profiles, however, did not detectstrong reflections in this unit as they did for the LDAs, and aswould be expected for an internally layered ice core (Campbellet al., 2013). Head and Weiss (2014) presented geomorphologicevidence for up to several hundred meters of present-day iceunder aZ16 m thick debris cover in the Smooth Facies at Pavonisand Arsia Mons. They suggest that the lack of strong radarreflections could be explained if any ice in the Smooth Facies isintermingled with volcanic tephra. Due to the proximity of theArsia Mons volcano, tephra would be expected to be more abun-dant in the FSD than in the LDAs.

The total amount of ice potentially remaining in the landformsdescribed in this paper cannot be estimated at present due to theabsence of topographic data that can resolve the smaller classes of

K.E. Scanlon et al. / Planetary and Space Science 111 (2015) 144–154 151

potentially ice-cored landforms, e.g. Ridged Facies moraines. Thescale of the kettle pits and hypothesized ice-cored knobs (Section3.1) is larger, however, and these landforms are resolved in HRSCDEMs (Fig. 14). Within the area of HRSC DEM coverage, knobsstand �15–80 m high, whereas pits are typically 5–10 m deep. Ifthis height difference is entirely caused by the removal of volatiles,and if these dimensions are typical for the pits and knobs notcovered by HRSC DEMs, the hundreds of knobs remaining in theFSD could each contain a body of ice 20–90 m thick at their cores.

6. Conclusions

The geomorphology of three classes of landform in the ArsiaMons FSD suggests that the deposit contains more remnant icethan previously thought. Evidence for extant ice in the bulk of theSmooth Facies has been described by previous researchers (Sheanet al., 2007; Head and Weiss, 2014); the evidence we present forextant ice in some Ridged Facies drop moraines and in small

Fig. 10. The majority of the ridges with linear troughs, here interpreted as dunes, are otopographic lows rather than being associated with a specific stratigraphic level in themoraines highlighted in blue, and white arrows indicating locations where dunes are cothe references to color in this figure legend, the reader is referred to the web version o

Fig. 11. The dunes with linear troughs may have formed from dust-ice dunes (a). Upon aof the dunes (b). Over time, this dry material would slump down the dune sides, exposin

landforms at the margins of the Smooth Facies increases the totalvolume of proposed ice in the FSD. Trough morphologies suggestthat ice has been removed from some but not all of the glacialmoraines in the deposit, and the chaotic surface texture of volcanicflows to the northwest of the deposit suggests that they interactedwith ice-cored moraines. The size and morphology of pits andknobs near the northern edge of the FSD suggest that the knobscontain ice that is armored by debris. These deposits should beadded to the volumes of sequestered ice mapped throughout themid-latitudes (Levy et al., 2014). Fields of dunes with lineartroughs along their crests suggest that windblown snow waswidespread across the region in the Amazonian.

The knobs and moraines examined in this study represent apotential reservoir of buried, present-day equatorial ice, in addi-tion to the ice previously estimated (Shean et al., 2007; Head andWeiss, 2014) to remain in the Smooth Facies. These features arepresent in several regions of the deposit, near other landforms ofclimatological, volcanological, and possible astrobiological interest(Scanlon et al., 2014, 2015). Because of its location near the

riented southwest-to-northeast wherever they occur, and are concentrated in localdeposit. (a) CTX image mosaic. (b) CTX mosaic with dunes highlighted in red, dropncentrated in the local topographic lows between lava flows. (For interpretation off this article.)

change from the climate in which they formed, ice would sublime from the surfaceg fresh ice-cemented material at the dune center (c) to continuing sublimation (d).

Fig. 12. The dunes with linear troughs may have formed from snow dunes (a) that gained a dust cover (b), e.g. from a pyroclastic eruption. Such a cover would slump awayfrom the dune crest over time (c), forming cracks at the crest and exposing the snow beneath to sublimation (d). As the snow sublimed, dust would fall in to fill the space leftbehind (e).

Fig. 13. Dust- and sand-covered ripples in the McMurdo Dry Valleys. Boxes on left images indicate the areas shown in right images. (a) Small dust- and sand-covered snowripples in the Dry Valleys develop cracks in the dust cover along their crests. (b) An alternate view of the debris-covered ripples shows bare ground between them. Darkcentral bars on scale card are 10 cm long. Photos taken by D. M. Hollibaugh Baker, 11/11/2010.

K.E. Scanlon et al. / Planetary and Space Science 111 (2015) 144–154152

Fig. 14. Topography of a region of pits (examples highlighted with white arrows)and knobs (examples highlighted with red arrows). Topographic contours fromHRSC DEM, superimposed on DEM-shaded CTX imagery. Contour interval is 5 m;bold contour every 20 m. (For interpretation of the references to color in this figurelegend, the reader is referred to the web version of this article.)

K.E. Scanlon et al. / Planetary and Space Science 111 (2015) 144–154 153

equator, the Arsia Mons FSD may be a good target for humanmissions to study martian ice while avoiding the logistical diffi-culties of a polar mission (e.g. Cockell, 2001).

Acknowledgments

We gratefully acknowledge support from the NASA Graduate Stu-dent Researchers Program (Grant NNX12AI39H) to KES, from the MarsData Analysis Program (Grant NNX11AI81G) and the Mars ExpressHigh-Resolution Stereo Camera (HRSC) Investigation Team (JPL1488322) to JWH, and from NSF Polar Programs (Grant ANT-0944702)to DRM. We thank David Hollibaugh Baker for the use of his photo-graphs in Fig. 13, and an anonymous reviewer for their constructivesuggestions.

References

Alley, R.B., 2000. Ice-core evidence of abrupt climate changes. Proc. Natl. Acad. Sci.97 (4), 1331–1334.

Bazin, L., et al., 2013. An optimized multi-proxy, multi-site Antarctic ice and gasorbital chronology (AICC2012): 120–800 ka. Clim. Past. 9, 1715–1731.

Belousov, A., Behncke, B., Belousova, M., 2011. Generation of pyroclastic flows byexplosive interaction of lava flows with ice/water-saturated substrate. J. Vol-canol. Geotherm. Res. 202, 60–72.

Bennett, G.L., Evans, D.J.A., 2012. Glacier retreat and landform production on anoverdeepened glacier foreland: the debris-charged glacial landsystem atKvia rjökull, Iceland. Earth Surf. Process. Landf. 37, 1584–1602.

Boynton, W.V., et al., 2002. Distribution of hydrogen in the near surface of Mars:evidence for subsurface ice deposits. Science 297 (5578), 81–85.

Campbell, B.A., Putzig, N.E., Carter, L.M., Morgan, G.A., Phillips, R.J., Plaut, J.J., 2013.Roughness and near-surface density of Mars from SHARAD radar echoes.J. Geophys. Res.: Planets 118, 436–450.

Capron, E., Landais, A., Chappellaz, J., Buiron, D., Fischer, H., Johnsen, S.J., Jouzel, J.,Leuenberger, M., Masson-Delmotte, V., Stocker, T.F., 2012. A global picture of

the first abrupt climatic event occurring during the last glacial inception.Geophys. Res. Lett. 39, L15703.

Chuang, F.C., Crown, D.A., 2005. Surface characteristics and degradational history ofdebris aprons in the Tempe Terra/Mareotis fossae region of Mars. Icarus 179,24–42.

Cockell, C.S., 2001. Martian polar expeditions: problems and solutions. ActaAstronaut. 49 (12), 693–706.

Dickson, J.L., Head, J.W., 2006. Evidence for an Hesperian-aged south circum-polarlake margin environment on Mars. Planet. Space Sci. 54, 251–272.

Dieterich, J.H., 1988. Growth and persistence of Hawaiian volcanic rift zones. J.Geophys. Res.: Solid Earth 93 (B5), 4258–4270.

Dumke, A., Spiegel, M., Schmidt, R., Neukum, G., 2008. High-resolution digital ter-rain models and ortho-image mosaics of Mars: generation on the basis of Mars-express HRSC data. Presented at Lunar and Planetary Science ConferenceXXXIX. Abstract #1910.

Ebert, K., Kleman, J., 2004. Circular moraine features on the Varanger peninsula,northern Norway, and their possible relation to polythermal ice sheet coverage.Geomorphology 62 (3–4), 159–168.

Edwards, B., Magnússon, E., Thordarson, T., Guđmundsson, M.T., Höskuldsson, A.,Oddsson, B., Haklar, J., 2012. Interactions between lava and snow/ice during the2010 Fimmvörðuháls eruption, south-central Iceland. J. Geophys. Res.: SolidEarth 117, B04302.

Elphic, R.C., Feldman, W.C., Prettyman, T.H., Tokar, R.L., Lawrence, D.J., Head, J.W.,Maurice, S., 2005. Mars odyssey neutron spectrometer water-equivalenthydrogen: comparison with glacial landforms on Tharsis. Presented at Lunarand Planetary Science Conference XXXVI. Abstract #1805.

Evans, D.J.A., 2009. Controlled moraines: origins, characteristics and palaeoglacio-logical implications. Quat. Sci. Rev. 28 (3–4), 183–208.

Evans, D.J.A., 2011. Glacial landsystems of Satujökull, Iceland: a modern analoguefor glacial landsystem overprinting by mountain icecaps. Geomorphology, 129;pp. 225–237.

Fastook, J.L., Head, J.W., Marchant, D.R., Forget, F., 2008. Tropical mountain glacierson Mars: altitude-dependence of ice accumulation, accumulation conditions,formation times, glacier dynamics, and implications for planetary spin-axis/orbital history. Icarus 198 (2), 305–317.

Fay, H., 2002. Formation of kettle holes following a glacial outburst flood (jökulh-laup), Skeidarársandur, southern Iceland In: Snorrason, A., Finnsdóttir, H.P.,Moss, M.E. (Eds.), The Extremes of the Extremes: Extraordinary Floods. Inter-national Association of Hydrological Sciences, Wallingford, Oxfordshire, Eng-land, pp. 205–210.

Fiske, R.S, Jackson, E.D., 1972. Orientation and growth of Hawaiian volcanic rifts: theeffect of regional structure and gravitational stresses. P. Roy. Soc. Lond. A. 329,299–326.

Forget, F., Haberle, R., Montmessin, F., Levrard, B., Head, J., 2006. Formation ofglaciers on Mars by atmospheric precipitation at high obliquity. Science 311(5759), 368–371.

Hambrey, M.J., 1984. Sedimentary processes and buried ice phenomena in the pro-glacial areas of Spitsbergen glaciers. J. Glaciol. 30 (104), 116–119.

Head, J.W., Marchant, D.R., 2003. Cold-based mountain glaciers on Mars: WesternArsia Mons. Geology 31 (7), 641–644.

Head, J.W., Mustard, J.F., Kreslavsky, M.A., Milliken, R.E., Marchant, D.R., 2003.Recent ice ages on Mars. Nature 426, 797–802.

Head, J.W., Marchant, D.R., Agnew, M.C., Fassett, C.I., Kreslavsky, M.A., 2006a.Extensive valley glacier deposits in the northern mid-latitudes of Mars: evi-dence for Late Amazonian obliquity-driven climate change. Earth Planet.Sci. Lett. 241, 663–671.

Head, J.W., Nahm, A.L., Marchant, D.R., Neukum, G., 2006b. Modification of thedichotomy boundary on Mars by Amazonian mid-latitude regional glaciation.Geophys. Res. Lett. 33, L08S03.

Head, J.W., Marchant, D.R., Dickson, J.L., Kress, A.M., Baker, D.M.H., 2010. Northernmid-latitude glaciation in the late Amazonian period of Mars: criteria for therecognition of debris-covered glacier and valley glacier landsystem deposits.Earth Planet. Sci. Lett. 294, 306–320.

Head, J.W., Weiss, D.K., 2014. Tropical mountain glacier deposits on Mars: pre-servation of ancient ice at Pavonis and Arsia Mons. Icarus 103, 331–338.

Holt, J.W., Safaeinili, A., Plaut, J.J., Head, J.W., Phillips, R.J., Seu, R., Kempf, S.D.,Choudhary, P., Young, D.A., Putzig, N.E., Biccari, D., Gim, Y., 2008. Radarsounding evidence for buried glaciers in the southern mid-latitudes of Mars.Science 322, 1235–1238.

Irvine-Fynn, T.D.L., Barrand, N.E., Porter, P.R., Hodson, A.J., Murray, T., 2011. Recenthigh-Arctic glacial sediment redistribution: a process perspective using air-borne lidar. Geomorphology 125 (1), 27–39.

Jakosky, B.M., Carr, M.H., 1985. Possible precipitation of ice at low latitudes of Marsduring periods of high obliquity. Nature 315 (6020), 559–561.

Kadish, S.J., Head, J.W., Parsons, R.L., Marchant, D.R., 2008a. The Ascraeus Mons fan-shaped deposit: volcano–ice interactions and the climatic implications of cold-based tropical mountain glaciation. Icarus 197 (1), 84–109.

Kadish, S.J., Head, J.W., Barlow, N.G., Marchant, D.R., 2008b. Martian pedestal cra-ters: marginal sublimation pits implicate a climate-related formationmechanism. Geophys. Res. Lett. 35, L16104.

Kadish, S.J., Head, J.W., 2011. Impacts into non-polar ice-rich paleodeposits onMars: excess ejecta craters, perched craters and pedestal craters as clues toAmazonian climate history. Icarus 215, 34–46.

Kadish, S.J., Head III, J.W., Fastook, J.L., Marchant, D.R., 2014. Middle to Late Ama-zonian tropical mountain glaciers on Mars: the ages of the Tharsis Montes fan-shaped deposits. Planet. Space Sci. 91, 52–59.

K.E. Scanlon et al. / Planetary and Space Science 111 (2015) 144–154154

Knight, J., 2012. Glaciotectonic sedimentary and hydraulic processes at an oscil-lating ice margin. Proc. Geol. Assoc. 123, 714–727.

Kobashi, T., Kawamura, K., Severinghaus, J.P., Barnola, J.-M., Nakaegawa, T., Vinther,B.M., Johnsen, S.J., Box, J.E., 2011. High variability of Greenland surface tem-perature over the past 4000 years estimated from trapped air in an ice core.Geophys. Res. Lett. 38, L21501.

Koster, E.A., Dijkmans, J.W.A., 1988. Niveo-aeolian deposits and denivation forms,with special reference to the great Kobuk Sand Dunes. Northwestern Alaska,Earth Surf. Processes 13, 153–170.

Kowalewski, D.E., Marchant, D.R., Head, J.W., Jackson, D.W., 2012. A 2D model forcharacterizing first-order variablility in sublimation of buried glacier ice, Ant-arctica: assessing the influence of polygon troughs, desert pavements, andshallow-subsurface salts. Permafrost Periglac. Process. 23, 1–14. http://dx.doi.org/10.1002/ppp.731.

Kowalewski, D.E., Marchant, D.R., Levy, J.S., Head III, J.W., 2006. Quantifying lowrates of summertime sublimation for buried glacier ice in Beacon Valley, Ant-arctica. Antarct. Sci. 18, 421–428.

Kress, A.M., Head, J.W., 2008. Ring-mold craters in lineated valley fill and lobatedebris aprons on Mars: evidence for subsurface glacial ice. Geophys. Res. Lett.35, L23206.

Lacelle, D., Davila, A.F., Pollard, W.H., Andersen, D., Heldmann, J., Marinova, M.,McKay, C.P., 2011. Stability of massive ground ice bodies in University Valley,McMurdo Dry Valleys of Antarctica: using stable O–H isotope as tracers ofsublimation in hyper-arid regions. Earth Planet. Sci. Lett. 301 (1–2), 403–411.

Lakeman, T.R., England, J.H., 2012. Paleoglaciological insights from the age andmorphology of the Jesse moraine belt, western Canadian Arctic. Q. Sci. Rev. 47,82–100.

Laskar, J., Correia, A.C.M., Gastineau, M., Joutel, F., Levrard, B., Robutel, P., 2004. Longterm evolution and chaotic diffusion of the insolation quantities of Mars. Icarus170 (2), 343–364.

Lefort, A., Russell, P.S., Thomas, N., 2010. Scalloped terrains in the Peneus andAmphitrites Paterae region of Mars as observed by HiRISE. Icarus 205, 259–268.

Levine, J.S., Garvin, J.B., Head, J.W., 2010. Martian geology investigations: planningfor the scientific exploration of mars by humans, Part 2. J. Cosmol. 12,3636–3646.

Levy, J., Head, J.W., Marchant, D.R., Kowalewski, D., 2008. Identification of sub-limation-type thermal contraction crack polygons at the proposed NASAphoenix landing site: implications for substrate properties and climate-drivenmorphological evolution. Geophys. Res. Lett. 35, L04202.

Levy, J.S., Head, J.W., Marchant, D.R., 2009. Concentric crater fill in Utopia Planitia:history and interaction between glacial “brain terrain” and periglacial mantleprocesses. Icarus 202, 462–476.

Levy, J.S., Head III, J.W., Marchant, D.R., 2010. Concentric crater fill in the northernmid-latitudes of Mars: formation processes and relationships to similar land-forms of glacial origin. Icarus 209, 390–404.

Levy, J.S., Fassett, C.I., Head, J.W., Schwartz, C., Watters, J.L., 2014. Sequesteredglacial ice contribution to the global martian water budget: geometric con-straints on the volume of remnant, mid-latitude debris covered glaciers.J. Geophys. Res.: Planets 119 (8), 2188–2196.

Lucchitta, B.K., 1981. Mars and Earth-comparison of cold-climate features. Icarus45 (2), 264–303.

Lüthi, D., et al., 2008. High-resolution carbon dioxide concentration record650,000–800,000 years before present. Nature 453, 379–382.

Mackay, S.L., Marchant, D.R., Head, J.W., Lamp, J.L., 2014. Cold-based debris-coveredglaciers: evaluating their potential as climate archives through studies ofground-penetrating radar and surface morphology. J. Geophys. Res. Earth Surf.119. http://dx.doi.org/10.1002/ 2014JF003178.

Malin, M.C., et al., 2007. Context camera investigation on board the Mars recon-naissance orbiter. J. Geophys. Res.: Planets 112 (E05).

Mangold, N., Allemand, P., 2001. Topographic analysis of features related to ice onMars. Geophys. Res. Lett. 28, 407–410.

Mangold, N., 2003. Geomorphic analysis of lobate debris aprons on Mars at Marsorbiter camera scale: evidence for ice sublimation initiated by fractures.J. Geophys. Res.: Planets 108 (E4), 2-1–2-13.

Mangold, N., 2011. Ice sublimation as a geomorphic process: a planetary perspec-tive. Geomorphology 126 (1), 1–17.

Marchant, D.R., Lewis, A., Phillips, W.C., Moore, E.J., Souchez, R., Landis, G.P., 2002.Formation of patterned-ground and sublimation till over Miocene glacier ice inBeacon valley, Antarctica. Geol. Soc. Am. Bull. 114, 718–730.

Marchant, D.R., Head, J.W., 2007. Antarctic dry valleys: microclimate zonation,variable geomorphic processes, and implications for assessing climate changeon Mars. Icarus 192 (1), 187–222. http://dx.doi.org/10.1016/j.icarus.2007.06.018.

McTigue, D.F., Mei, C.C., 1981. Gravity-induced stresses near topography of smallslope. J. Geophys. Res.: Solid Earth 86 (B10), 9268–9278.

Mellon, M.T., Jakosky, B.M., 1993. Geographic variations in the thermal and diffusivestability of ground ice on Mars. J. Geophys. Res.: Planets 98 (E2), 3345–3364.

Mellon, M.T., Jakosky, B.M., 1995. The distribution and behavior of martian groundice during past and present epochs. J. Geophys. Res.: Planets 100 (E6),11781–11799.

Mellon, M.T., Jakosky, B.M., Postawko, S.E., 1997. The persistence of equatorialground ice on Mars. J. Geophys. Res.: Planets 102 (E8), 19357–19369.

Monnier, S., Camerlynck, C., Rejiba, F., 2008. Ground penetrating radar survey andstratigraphic interpretation of the Plan du Lac rock glaciers, Vanoise Massif,Northern French Alps. Permafr. Periglac. Proces 19 (1), 19–30.

Mustard, J.F., Cooper, C.D., Rifkin, M.K., 2001. Evidence for recent climate change onMars from the identification of youthful near-surface ground ice. Nature 412(6845), 411–414.

Neukum, G., Jaumann, R., 2004. HRSC: The High Resolution Stereo Camera of MarsExpress In: Wilson, A. (Ed.), Mars Express: The Scientific Payload. EuropeanSpace Agency, The Netherlands, pp. 17–35.

Pedersen, G.B., Head, J.W., 2010. Evidence of widespread degraded Amazonian-agedice-rich deposits in the transition between elysium rise and Utopia planitia,Mars: guidelines for the recognition of degraded ice-rich materials. Planet.Space Sci. 58, 1953–1970.

Pierce, T.L., Crown, D.A., 2003. Morphologic and topographic analyses of debrisaprons in the eastern Hellas region, Mars. Icarus 163, 46–65.

Plaut, J.J., Safaeinili, A., Holt, J.W., Phillips, R.J., Head, J.W., Seu, R., Putzig, N.E., Frigeri,A., 2009. Radar evidence for ice in lobate debris aprons in the mid-northernlatitudes of Mars. Geophys. Res. Lett. 36, L02203.

Price, R.J., 1969. Moraines, Sandar, kames and Eskers near Breidamerkurjökull,Iceland. Trans. Inst. Br. Geogr. 46, 17–43.

Rhodes, R.H., Faïn, X., Stowasser, C., Blunier, T., Chappellaz, J., McConnell, J.R.,Romanini, D., Mitchell, L.E., Brook, E.J., 2013. Continuous methane measure-ments from a late holocene Greenland ice core: atmospheric and in-situ signals.Earth Planet. Sci. Lett. 368, 9–19.

Rubin, D.M., Rubin, A.M., 2013. Origin and lateral migration of linear dunes in theQaidam Basin of NW China revealed by dune sediments, internal structures,and optically stimulated luminescence ages, with implications for linear duneson Titan: discussion. Geol. Soc. Am. Bull. 125, 1943–1946.

Russell, A.J., Tweed, F.S., Roberts, M.J., Harris, T.D., Gudmundsson, M.T., Knudsen, O.,Marren, P.M., 2010. An unusual jökulhlaup resulting from subglacial volcanism,Solheimajökull, Iceland. Q. Sci. Rev. 29, 1363–1381.

Sanford, R.A., 1959. Analytical and experimental study of simple geologic struc-tures. Geol. Soc. Am. Bull. 70, 19–51.

Scott, D., Zimbelman, J., 1995. Geologic map of Arsia Mons Volcano. Mars USGeological Survey Miscellaneous Gteologic Investigation Map I-2480.

Scanlon, K.E., Head, J.W., Wilson, L., Marchant, D.R., 2014. Volcano–ice interactionsin the Arsia Mons tropical mountain glacier deposits. Icarus 237, 315–339.

Scanlon, K.E., Head, J.W., Marchant, D.R., 2015. Local, volcanism-induced wet-basedglacial conditions recorded in the Late Amazonian Arsia Mons tropical moun-tain glacier deposits. Icarus 250, 18–31.

Schon, S.C., Head III, J.W., 2012. Decameter-scale pedestal craters in the tropics ofMars: evidence for the recent presence of very young regional ice deposits inTharsis. Earth Planet. Sci. Lett. 317-318, 68–75.

Schorghofer, N., Forget, F., 2012. History and anatomy of subsurface ice on Mars.Icarus 220, 1112–1120.

Séjourné, A., Costard, F., Gargani, J., Soare, R.J., Fedorov, A., Marmo, C., 2011. Scal-loped depressions and small-sized polygons in western Utopia Planitia, Mars: anew formation hypothesis. Planet. Space Sci. 59, 412–422.

Shean, D.E., Head, J.W., Marchant, D.R., 2005. Origin and evolution of a cold-basedtropical mountain glacier on Mars: the Pavonis Mons fan-shaped deposit. J.Geophys. Res.: Planets 110 (E5).

Shean, D.E., Head, J.W., Fastook, J.L., Marchant, D.R., 2007. Recent glaciation at highelevations on Arsia Mons, Mars: implications for the formation and evolution oflarge tropical mountain glaciers. J. Geophys. Res.: Planets 112 (E3).

Smith, D.E., et al., 1999. The global topography of Mars and implications for surfaceevolution. Science 284 (5419), 1495–1503.

Sridhar, K.R., Iacomini, C.S., Finn, J.E., 2004. Combined H2O/CO2 solid oxide elec-trolysis for Mars in situ resource utilization. J. Propul. Power 20 (5), 892–901.

Sugden, D.E., Marchant, D.R., Potter Jr., N., Souchez, R.A., Denton, G.H., Swisher III, C.C.,Tison, J.-L., 1995. Preservation of Miocene glacier ice in East Antarctica. Nature376, 412–414.

Swanger, K.M., Marchant, D.R., Kowalewski, D.E., Head, J.W., 2010. Viscous flowlobes in central Taylor valley, Antarctica: origin as remnant buried glacial ice.Geomorphology 120, 174–185. http://dx.doi.org/10.1016/j.geomorph.2010.03.024.

Szuman, I., Kasprzak, L., 2010. Glacier ice structures influence on moraine devel-opment (Hørbye Glacier, Central Spitsbergen). Quaest. Geogr. 29, 65–73.

Thwaites, F.T., 1926. The origin and significance of pitted outwash. J. Geol. 34 (4),308–319.

Williams, R., 1978. Geomorphic processes in Iceland and on Mars: a comparativeappraisal from orbital images. Geol. Soc. Am. Abstr. Progr. 10, 517.

Zimbelman, J.R., Edgett, K.S., 1992. The Tharsis Montes, Mars – comparison ofvolcanic and modified landforms. Presented at Lunar and Planetary ScienceConference XXII, pp. 31–44.

Zuber, M.T., Smith, D.E., Solomon, S.C., Muhleman, D.O., Head, J.W., Garvin, J.B.,Abshire, J.B., Bufton, J.L., 1992. The Mars-observer laser altimeter investigation.J. Geophys. Res.: Planets 97 (E5).