ARTICLE IN PRESS

0032-0633/$ - se

doi:10.1016/j.ps

�CorrespondE-mail addr

(W.C. Mahaney

jmd@hwr.arizo

(V.R. Baker), n

bermandc@psi.

Planetary and Space Science 55 (2007) 181–192

www.elsevier.com/locate/pss

Rock glaciers on Mars: Earth-based clues to Mars’ recentpaleoclimatic history

William C. Mahaneya,�, Hideaki Miyamotob, James M. Dohmc, Victor R. Bakerc,Nathalie A. Cabrold, Edmond A. Grind, Daniel C. Bermane

aQuaternary Surveys, 26 Thornhill Avenue, Thornhill, Ont., Canada L4J 1J4bLunar and Planetary Laboratory, University of Arizona and Department of Geosystem Engineering, University of Tokyo, Japan

cLunar and Planetary Laboratory, Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721, USAdSETI Institute/NASA Ames Research Center, Space Science Division, MS 245-3, Moffett Field, CA 94035-1000, USA

ePlanetary Science Institute, Tucson, AZ 85719, USA

Received 22 October 2004; received in revised form 11 April 2006; accepted 25 April 2006

Available online 28 July 2006

Abstract

The Mars Orbital Camera onboard the Mars Global Surveyor spacecraft, which is currently orbiting about Mars, has revealed

hundreds of pristine lobate and tongue-shaped flows that closely display the morphological characteristics of terrestrial rock glaciers,

both tongue- and lobe-shaped forms. Generally located between 301S and 471S latitude on Mars, these terrestrial-like flows have

important paleoenvironmental implications, including marking environmental change from current, present cold and dry desert martian

conditions to cold wetter climates in the past. Paleoenvironmental conditions, hypothesized to have significantly influenced the

dimensions of the terrestrial-like flows, is supported through a simple dynamic model with the power-law rheology. The presence of

periglacial landforms on Mars indicates the possible presence of permafrost and potential caches of water for future exobiological

exploration.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Mars; Rock Glacier Rheology; Paleoclimatology

1. Introduction

Hundreds of pristine mass flows resembling terrestrialrock glaciers are observed in a region on Mars between301S and 471S latitude using Mars Orbital Camera (MOC)imagery taken from the Mars Global Surveyor (MGS)spacecraft (Cabrol et al., 2001a; Cabrol and Grin,2002a, b). These Earth-like features, which typically occuron steep slopes and display an accumulation area, a flowsection, and a distal margin, have important environmentalimplications, including marking environmental changefrom current, cold and dry desert to cold wetter climates

e front matter r 2006 Elsevier Ltd. All rights reserved.

s.2006.04.016

ing author. Tel.: +1905 7317269.

esses: bmahaney@yorku.ca, arkose@rogers.com

), miyamoto@geosys.t.u-tokyo.ac.jp (H. Miyamoto),

na.edu (J.M. Dohm), baker@hwr.arizona.edu

cabrol@mail.arc.nasa.gov (N.A. Cabrol),

edu (D.C. Berman).

in the past (Baker, 2001; Cabrol et al., 2001a). We reflecton current information concerning terrestrial rock glaciersin order to better understand their potential martiancounterparts, including morphologic comparison andpaleoclimatic implications.

2. Background

2.1. Earth

Rock glaciers on Earth were first identified by Steenstrup(1883) in northern Greenland. In North America, Capps(1910) noted that some were composed of angular, blockymaterial derived from talus and/or moraine landforms andextending downvalley from cirque walls. Because somerock glaciers merge with moraines, Capps believed theywere related to wasting glaciers that had ablated leavingrock rubble with interstitial ice. About the same time,

ARTICLE IN PRESSW.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192182

Patton (1910) reported on rock glaciers observed in areasthat had never experienced glaciation. Other early researchon rock glaciers reported interstitial ice in the top fewmeters, an occurrence that sparked debate as to the originof ice and mechanisms of movement (Cross et al., 1905;Hole, 1912; Patton, 1910), a controversy that continuestoday.

Flow structures in rock glaciers (Fig. 1) have beenattributed to many causes, including: slow deformation ofthe material (Howe, 1909), rapid landslide with alterationby ice growth on a small scale, and/or slow deformationproduced by surface freeze thaw mechanisms of a diurnalnature (Patton, 1910). Direct observations by Capps (1910)of rates of rock glacier movement led to a theory ofupwelling of ground water, which would subsequentlyfreeze at the surface and produce expansion-relateddeformation (Tyrrell, 1910). Observation of glacial ice atthe base of a rock glacier through which a tunnel had beenconstructed (Brown, 1925) provided a link with glaciation,a connection that prompted Kesseli (1941) to conclude thatrock glaciers are nearly always glacial in origin, aconclusion reached by other workers (Whalley, 1974).Additional observations by Behre (1933) and Ives (1940)reinforced the notion that rock glaciers were principallyproducts of glaciation.

Following World War II, the seminal work of Wahr-haftig and Cox (1959) provided a substantial corpus ofobservations and analysis on rock glaciers in Alaska thatlooked at flow structures and mechanics concluding thatrock glaciers were not principally derived from glaciers andthat movement was mostly the result of interstitial icedeformation. Outcault and Benedict (1965) took issue with

Fig. 1. Terrestrial tongue-shaped rock glaciers: (A) Lobes of the Jaw Rock Gla

to the north with a source in talus and moraine (3230m a.s.l.) to the south in

advance of Neoglaciation (5–3 ka; JAW3) to the Audubon advance (2–1 ka; JA

way of pronounced pressure ridges, to the Gannett Peak advance (0.5–0.2 ka; JA

of the rock glacier moraines of Late Glacial age dam Jaw Lake approximate

Prominent rock glacier in Valhalla Canyon below the Grand Teton with a prom

and left) flowing north into Cascade Canyon. The toe of the flow is 250m abo

and spotty unfrozen soil cover up to thicknesses of �50 cm. The area around

Wahrhaftig and Cox (1959) arguing that some rock glaciersresult from choking of ice glaciers with rock materialfollowed by ablation or wastage and Østrem and Arnold(1970) believed some rock glaciers were possibly derivedfrom ‘‘runaway moraines.’’ However, on some mountains,rock glaciers may override moraines and consist almostexclusively of mass wasted debris (e.g. Mt. Sopris, CO;Birkeland, 1973; Colorado Front Range; Benedict, 1968).The contrasting theories of rock glacier origin, combined

with various mechanisms of movement proposed in theearly stages of research on rock glaciers in North America(Foster and Holmes, 1965) has led to research in otherareas of the world, principally in the Alps (Haeberli,1983; Hollermann, 1983; Vietoris, 1972), the Pyrenees(Hollermann, 1983), Asia (Gorbunov, 1983; Cui, 1983),South America (Corte 1976), and New Zealand (Jeanneret,1975). While relatively rare, rock glaciers are even found ontropical mountains such as Mt. Kenya (5119m a.s.l.) andIthanguni (3894m a.s.l.) in East Africa (Mahaney, 1980,1990a); despite the presence of collapse features, interstitialice has never been observed in them (Mahaney, 1980).Most of the examples are clear indicators that rock glaciersoften respond to climatological activity and water.One school of thought on terrestrial rock glaciers holds

that they are exclusively phenomena of permafrost, and aregenetically distinct from true glaciers (Barsch, 1996). Theother school considers rock glaciers to be part of acontinuum that leads from true glaciers to debris-coveredglaciers, with remobilized talus or till as permafrostfeatures (Clark et al., 1998). The continuum school holdsthat environmental change may promote debris-coveredglaciers by the shrinkage of accumulation zones as

cier, Teton Range, Wyoming. The toe of the flow (2720m a.s.l.) is oriented

Jaw Cirque. A succession of pressure ridges date from the Indian Basin

W2) where the mass of material is coarse clastic material with little in the

W4), the source coming from a prominent moraine ridge. Below the snout

ly 100m above Paintbrush Canyon (see Mahaney and Spence, 1984). (B)

inent source (3290m a.s.l.) in talus (bottom) and moraine material (center

ve the canyon floor at 3020m a.s.l. Both rock glaciers carry discontinuous

the base of both rock glaciers is unfrozen in summer to depths of �1.0m.

ARTICLE IN PRESSW.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192 183

temperatures rise or accumulation declines (Ackert, 1998).In extreme cases, debris-covered ice may be cut off fromthe glacial ice accumulations source. However, mass canstill be added by rockfalls, and water can move in thesubsurface by active-layer processes in the permafrost (forfurther discussion on rock glaciers on Earth and theirpossible martian counterparts, see Whalley and Azizi,2003).

2.2. Mars

Since the discovery of networks of fluvial valleysdissecting the ancient cratered uplands of Mars, it hasbeen recognized that past environmental conditions musthave been very different than those prevailing today(Masursky, 1973). With an atmospheric pressure of onlyabout 7mb at its lowest elevations, and mean dailytemperatures ranging from 220 to 150K, the currentatmospheric state will not allow the precipitation andrunoff necessary to produce the valleys. Because theheavily cratered uplands of Mars probably formed priorto about 3.5 billion years ago (Tanaka, 1986), mostresearchers concluded that the age of major environmentalchange was also ancient, presuming that the fluvialdissection was approximately coincident (Carr and Clow,1981). Despite the Viking-spacecraft-based documentationof much younger fluvial (Gulick and Baker, 1989) andglacial (Kargel and Strom, 1992) landforms, this paradigmof a ‘‘warm-wet’’ early Mars (Pollack et al., 1987)continued through the initial study of data from thecurrent Mars Global Surveyor (MGS) mission. However,recently released, high-resolution MOC images (Malin andEdgett, 2000) from that mission are revealing spectacularuncratered or very lightly cratered surfaces on whichgeologically youthful landforms pose striking anomalies inregard to the above paradigm (Baker, 2001). The prevailingparadigm indicating that Mars was early warm and wetand later transitioned into a cold and dry dead planet hasbeen further challenged by recent Odyssey findingsthat show water-enriched regions (Boynton et al., 2002;Feldman et al., 2002) consistent with the geologic andgeomorphic evidence on the surface of Mars (Scott et al.,1995; Baker, 2001).

A diverse suite of very recent, water-related, globallydistributed landforms can be recognized on Mars, includ-ing pristine mass flows that resemble terrestrial rockglaciers (also see Whalley and Azizi, 2003). Other featuretypes have been interpreted to be fluvial (Malin and Edgett,2000; Ferris et al., 2002), lacustrine (Scott et al., 1995;Cabrol et al., 2001b, c), periglacial (Baker, 2001), andglacial in origin (Baker, 2001; Cabrol et al., 2001a; Cabroland Grin 2002a, b). Earth counterparts are produced byprocesses operating under a relatively dense atmospherealong with related transport and precipitation of water.The anomalous character of these landforms in regard tothe very cold, dry present-day martian conditions maybe explained by short-duration climatic perturbations

(perhaps 103–104 yr), triggered by locally extensive volcan-ism and associated outburst flooding of groundwater(Baker, 2001; Dohm et al., 2001a, b). The ‘‘MEGAOUT-FLO’’ hypothesis (Baker et al., 2000) first proposed byBaker et al. (1991) genetically links such activity torelatively short-lived, magmatic-driven climatic changesfrom a common cold and dry Mars (e.g., short-termhydrological cycles), which includes enhanced erosion byprecipitation, landslides/mass wasting (both land andsubmarine), glacial activity, and the presence of largestanding bodies of water such as the Amazonian-agedOceanus Borealis (also see Fairen et al., 2003). In addition,though the migration of ice from the south pole can not berelated to the current obliquity cycle (Haberle et al., 2000),obliquity-related activities may have been optimal forstimulation of recent environmental change and associatedgrowth of rock glaciers (Cabrol et al., 2001a).Whether endogenic—and/or exogenic-triggered, recent

environmental changes are recorded by a diverse suite ofwater-related, globally distributed landforms on Mars(Baker, 2001), and in particular as reported here, flowfeatures resembling rock glaciers of Earth. The features onMars are recognized to have attributes similar to terrestrialrock glaciers, including: (a) lobate debris aprons, (b)lineated valley fill, and (c) concentric crater fill, dependingon their respective spatial association with (a) mountainsand mesas, (b) canyons and valleys, and (c) craters (Carrand Schaber, 1977; Squyres, 1978, 1989; Lucchitta, 1984;Squyres and Carr, 1986; Whalley and Azizi, 2003; Bermanet al., 2005).

3. Internal and surface structures

3.1. Earth

Rock glaciers on Earth form in any rock type in areasfavorable for, but not necessarily limited to, permafrostdevelopment (Figs. 1 and 2). Large angular blocks ofmaterial provide void space that inhibits warming ofsurface layers by providing insulation. Boulders dominateon the surfaces of many rock glaciers (Barsch, 1996), but inreality, there is often a distribution of pockets rich in sand,silt, and clay; the finer sizes of material are sometimes heldin place by the sporadic distribution of plants (Mahaney,1980). The boulder mantle, common on most rock glaciers,often reflects the local lithology with larger boulders41.0m derived from crystalline rocks; and those o1.0mderived from sedimentary sources.Finer grained material found in lower beds of rock

glaciers is probably the result of the down drainage of finematerial washed from the surface and possibly also fromretention of fines at depth due to ice growth and frostheave. Certainly the presence of collapse pits and drunkenforests on rock glacier surfaces (Mahaney, 1990a,b) suggestthe past occurrence of ice (either of frozen pore water orglacial ice) that supports the many observations of aboulder mantle overlying a finer subsurface.

ARTICLE IN PRESS

Fig. 2. Terrestrial lobe-shaped rock glacier free of ice cores in the Cottian

Alps, north of the Col de la Traversette on the northwest flank of Mt.

Granero, Italy. Several lobes of rock rubble date from the Little Ice Age

(o500BP). The source of the rock glacier is at 2950m a.s.l.; the toe at

2750m a.s.l.. No ice was observed in the upper layers of the open network

of boulders despite its position within the lower established limit of

discontinuous permafrost (Fabre et al., 2003).

W.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192184

Relative to ice glaciers where clast fabrics are often usedto infer flow direction (Mahaney, 1990a) fabric studies onrock glaciers are rare (Evin and Assier, 1983; Jakob, 1992;Nicholas, 1994), but the trend and plunge of long angularclasts shows a nonrandom orientation different to what isfound in till (Mahaney, 1990b, 1995), presumably aresponse to flow vectors of the rock glacier.

Internally, ice lenses with thicknesses of several metershave been identified from tunnels (Brown, 1925), boreholes(Barsch et al., 1979; Haeberli et al., 1988), and geophysicaldata (Vonder Muhll and Haeberli, 1990; Potter, 1968,1972). Meltwater is known to flow from surface layersacross the surfaces of buried ice lenses in some instances,while in others no ice lenses have been identified evenwhere an over-steepened front argues for an active rockglacier (Mahaney, 1980, 1990a; Mahaney and Spence,1984). Therefore, active rock glaciers may not contain anactive layer of permafrost despite claims to the contrary(Barsch, 1996). The topography of rock glaciers is similarto that of lava flows with longitudinal ridges stretching

from the detrital source area to the toe of the rock glacier(Wahrhaftig and Cox, 1959; see Fig. 1). These ridges areoften traced to talus cones in the source area withintervening spaces or troughs in the rock glacier surfacetraceable to inter-talus spaces against adjoining ridges.Various other fissures and sinkholes are sometimesapparent in rock glaciers that have undergone melting ofinterstitial ice, the resulting collapse resembling karsttopography. Melting of buried snow and ice may alsoexplain clasts, often observed to have little dip on ridgetops, to exhibit increased plunge in troughs.Longitudinal ridges and furrows on the surface of a rock

glacier, which are sometimes observed on large-scaletopographic maps, intersect with cross-glacier pressureridges similar in form to ogives or Alaskan bands on anice glacier. These intersecting ridges and troughs reveal astreamlined-flow pattern connecting source areas with thetoe of the rock glacier (for example, see Figs. 1 and 2),which is most apparent in tongue-shaped rock glaciers. Theshape of the surface texture of a rock glacier is oftencontrolled by the underlying topography, steepness of slope,volume of interstitial ice in the system and ice-melt collapse.The rock glaciers shown in Figs. 1 and 2 are at nearly

identical elevations in the middle latitudes and are withinthe zone of sporadic permafrost (see Mahaney, 1981, fordetails on sporadic permafrost at 3200m a.s.l. in the RockyMountains of western Wyoming), possibly also discontin-uous permafrost, although precise ground thermal mea-surements are not available for either area. In both casesinternal ice lobes were not observed in the field althoughcollapse features are know in all deposits. The groundsubstrate surrounding the rock glaciers is free of perma-frost to a depth of �1.0m. Despite recent glacierinventories of the Central Italian Alps (Seppi et al., 2003)and estimations (Fabre et al., 2003) of the lowerdiscontinuous permafrost elevation (2600m a.s.l.) in theMaritime Alps (south of the Cottian Alps example inFig. 2), it appears that either ice is buried deep within therock mass or that the rock rubble is free of ice altogetherand may constitute relict forms. The rock glacier in Fig. 2,situated between the Maritime Alps to the south and theSwiss Mountains to the north, is in a location where GIS-based energy-balance models of permafrost distributionhave yet to be worked out. In any case with climaticwarming affecting all mountain areas on Earth limits ofdiscontinuous and sporadic permafrost are shifting tohigher elevations. The lobe-shaped rock glacier shown inFig. 2 bears a striking relationship to similar forms onMars (Mangold and Allemand, 2001) and while thepresence/degree of ice in either example is unknowncross-feature ridges and troughs, coarse textured surfaces,and 10–201 down slope angles are similar.

3.2. Mars

Pristine mass flows on Mars, resembling terrestrialdebris-covered glaciers and rock glaciers, typically display

ARTICLE IN PRESSW.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192 185

an accumulation area, a flow section, and a distal margin.The distinction between rock glaciers and debris-coveredglaciers, using remotely sensed data, is often difficult evenfor terrestrial cases where field investigations are oftennecessary to confirm feature type. Based on terrestrialstudies (Clark et al., 1998; Humlum, 1996), the flow lobesare used to make the distinction between landform types,including rheology and potential ice content.

Accumulation areas are observed to occur in elevateddepressions on Mars. They show longitudinal striationsand grooves converging toward the valleys (for example,see Figs. 3A–C). Topographically controlled changes indirection of the striations and grooves within accumulatedmaterial at the bottom of the depressions show evidence forflow. The flows develop over several kilometers withsurfaces characterized by blocks that can reach up to20m in size, but generally average 5–10m, much largerthan in terrestrial rock glaciers. There is no specific sorting

Fig. 3. (A) Mars Mosaicked Digital Image Model (MDIM) and Digital Terr

images m0000210 (Fig. 3C) and m0807937 (Fig. 3D) with respect to significant

(USGS Web Graphical Access footprint chart of MOC images) showing loca

respect to impact craters and Reull Valles (RV), a valley that contains lineate

covered glacier about 10 km wide (Mahaney et al., 2001). (C) MOC image m000

that linears become less organized at the confluence of the two valleys. (D) M

of the blocks from upstream to downstream. They arecemented in a matrix of finer sediments that formundulating waves along the slopes. The flows showtransversal sections with arched lobes convex in thedownstream direction. Block alignments are observed inplaces where valleys merge. The distal margins arecharacterized by tongues of material with fewer largeblocks and finer material deposited on the floor of thecraters. Berman et al. (2005), for example, present evidencefor the flow of glaciers or rock glacier materials down thewalls of craters between �2 and 30 km in diameter in thesouthern mid-latitudes on Mars (Fig. 4A). Arcuate ridges,which are found at the bases of the crater walls, may beterminal moraines or protalus ramparts. They are postu-lated to have formed during periods of ice-rich depositionfrom the atmosphere, which may occur during changes inthe obliquity of Mars (Mustard et al., 2001; Laskar et al.,2004). Many of these features appear to be composites of

ain Model (DTM) map (Eliason et al., 1992) showing locations of MOC

features such as Hellas impact basin. (B) Similar to (A), but a 151� 151 tile

tions of MOC images m0000210 (Fig. 3C) and m0807937 (Fig. 3D) with

d valley fill that has been previously interpreted as extant or relict debris-

0210 showing lineated valley fill, including alignments of blocks. Also note

OC image m0807937 showing similar relationships observed in (C).

ARTICLE IN PRESS

Fig. 4. Environmental changes exemplified by: (A) (E09-02399, E10-04497, 43.51S, 161.91W) flow materials that partly infill an impact crater; two distinct

surfaces of varying relative age of formation, as indicated by the older surface that displays impact craters (1, arrows; also see (B) (E10-02945, 45.261S,

221.961W) and the relatively young surface with few if any impact craters and pristine flow structures (2); (C) (E10-03105, 41.571S, 234.991W) flows of

indeterminate age of formation, as the flows and possible impact craters appear to be mantled by materials (e.g., eolian, ice-enriched flows, etc.);

(D) (M18-01035, 31.851N, 338.331W) features with pristine flow structures and few if any impact craters, (E) high-resolution MOLA map showing

locations of Figs. 3 and 4.

W.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192186

ARTICLE IN PRESSW.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192 187

multiple cycles of deposition, as evidenced by the differentdegrees of degradation, the lack of craters on their surfaces,and recent gullies which overlie them. The formation of thegullies appears to be related to the arcuate ridges as theyare often found together and the shapes of the ridgesconform to the gully head alcove shapes. The presence ofremnant, less pronounced arcuate ridges beyond theprimary ridge crest suggests these features form from aseries of depositional cycles.

The presence of mantle-like material on the floor of acrater (Fig. 4B) exemplifies varying depositional cycles,including the possible emplacement of ice-rich materialsand/or deposition of eolian deposits. For some featuresresembling terrestrial rock glaciers, it is difficult toascertain their relative age of formation with respect topast environmental changes. Some features (Fig. 4B), forexample, indicate a more ancient environmental change (asevidenced from distinct impact craters), while othersappear to be indeterminate (more ancient cratered surfacescould be obscured through mantling processes; seeFig. 4C), while some appear to be pristine, with very littleevidence of mantling, and few, if any impact craters(Fig. 4D).

A relationship occurs among the latitude and orientationof arcuate ridges on crater walls (pole-facing orientationsare prevalent north of 441S, and equator facing orienta-tions are prevalent south of 441S), suggesting that theiremplacement is related to changes in obliquity, as differentregions would be subject to differing degrees of icedeposition and solar insolation during changes in obliquity(Berman et al., 2005). However, endogenic-induced envir-onmental responses and associated emplacement of flowfeatures such as rock glaciers cannot be ruled out (Baker,2001).

4. Rheology for both Earth and Mars

As discussed in Section 2, the formation of rock glaciersremains a topic for discussion (Berger et al., 2004). Incontrast to glaciers, where a continuous deformationprofile can be observed (Patterson, 1994), the processesthat govern the emplacement/deformation of rock glaciersare not fully understood. Nevertheless, flow-field measure-ments based on drilling, thermal datalogging, photogram-metry, borehole monitoring, and other modern geophysicalmethods provide important information regarding surfaceand subsurface emplacement/deformation-related phenom-ena, as well as the thermal structure of rock glaciers(Haeberli et al., 2000; Kaab and Vollmer, 2000; Arenson etal., 2002). These lead to general agreement that theirviscous appearance is due to the cumulative deformation ofthermally controlled ice/rock mixtures (Haeberli et al.,2000); this indicates that ice plays a major role in theemplacement of rock glaciers, including providing lubrica-tion to the unconsolidated clastic material, which forms thegreater length of a rock glacier.

Concerning the rheology of ice, the shear-stress depen-dency is pointed out through experimental work and isusually described using Glen’s law:

_� ¼ Asn, (1)

where _� is the effective strain rate, s is the effective shearstress, n is the stress exponent, and A is the material para-meter, which depends on ice temperature, crystal orien-tation, impurity content, among other factors (Patterson,1994; Azuma, 1994; Goldsby and Kohlstedt, 2001). Theexact value of the stress exponent for rock glaciers isdifficult to determine, but it is at least larger than the casewhere material moves as creep (i.e. Newtonian fluid). If themotion is dominated by dislocations, the stress exponent isoften assumed to be 3. We should note that the rheology ofa rock glacier is more complicated than that of a pure iceglacier because of non-viscous responses of the mixture ofrock and ice. Therefore, the best guess for the stressexponent for a rock glacier would be around 3, but it canbe a little larger or smaller, depending on many otherconditions such as rock content and amount of void space.The material parameter, A, is also difficult to deter-

mine. For pure ice, it is often described by the Arrheniusrelation as:

A ¼ A0 expð�Q=RTÞ, (2)

where A0 is a coefficient independent of temperature, Q isthe activation energy for creep, and R is the universal gasconstant (recent experiments of ice are given by Goldsbyand Kohlstedt, 2001).In fact, the rheology of rock glaciers would not be as

simple as that of pure ice because of the granulo-viscouseffects, including liquefaction, flocculation, slip, and stickdue to the presence of granular body (Hooke et al., 1972;Barcilon and MacAyeal, 1993). The overall rheologicaleffect may be modeled by a suspension-liquid model, asdiscussed in various research fields (Mangold et al., 2002;Ji, 2004; Miyamoto et al., 2004b). However, it becomesmathematically complex and can vary significantly fromthe extensively used, modified-versions of the Einsteinmodel (Kitanovski and Poredos, 2002). Furthermore, thereare other issues, such as soluble impurities, which canfurther complicate the problem.Here, we take an alternative approach: We do not

estimate exact rheological values, but rather use empiricalestimations of the material parameter, which ultimatelyleads to an improved estimate of the possible range of thisvalue. There are few long-term observations of current-daymovement of rock glaciers, but a summary given byGiardino et al. (1987) for terrestrial road glaciers showsthat a typical rate of rock glacier movement is �1m/yr(although this may be an over-estimation given data inFrauenfelder et al. (2005), which indicate mean velocitieso1.0m/yr). If we assume that the observed movement is adirect indication of the average velocity of the entire rockglacier, we can derive the following equation by assuming asimple shear throughout the flow and by vertically

ARTICLE IN PRESSW.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192188

integrating the Eq. (1) as (Patterson, 1994):

us � ub ¼2A

nþ 1ðrg sin aÞnhnþ1,

where us and ub are the surface and the bottom velocities ofthe flow, respectively, h is the thickness, r is the density, g isthe acceleration due to gravity, and a is the slope angle. Ifwe apply this equation to a typical flow with non-slipconditions at the bottom, with a thickness, density, andslope of �30m, 1500 kg/m3, and 301, respectively, we findthat A is 1.97� 10�25 (Pa�3 s�1). Note that this value iswithin the same order of those values for ice at �10 to�20 1C suggested and summarized by Patterson (1994).Therefore, for simplicity sake in order to attempt a firstorder approximation of the rheological behavior of a rockglacier, we use the flow law of an ice glacier, but vary theparameters as described below. Furthermore, we implicitlyassume high water-ice content for Mars, since recentpublished works suggest recent environmental change,which includes glacial activity (Baker, 2001).

With regard to glacial flow on Mars, the rheology of icehas been considered by investigators such as Lucchitta(1984) and by Colaprete and Jakosky (1998). These studiesnote extremely slow flow rates on Mars under the currentlow temperatures and extremely low accumulation rates.Nevertheless, Mangold and Allemand (2001) show that theconvex upward topographic profiles across martian lobatedebris aprons require solid-state deformation of icethicknesses up to a few hundred meters, which suggestsmartian rock glaciers may be much thicker than theirterrestrial counterparts. Higher flow rates during pastwarmer martian conditions may be implied by these results.

5. Rock glacier model

Ideally, we need to understand all of the effects describedabove and develop a full, coupled three-dimensional modelof the mass, temperature, and phase change. However, thisis, in our view, an enigmatic effort and is far beyond theintention of this paper. Instead, we prefer a more practicalway of discussing the overall movements of rock glacierson both Earth and Mars. The morphological appearance ofthe flow-like features on Mars more closely resemblesterrestrial lava flows than ice glaciers (Haeberli et al.,2000). As such, a numerical code, designed to betterunderstand the emplacement processes of lava flows(Miyamoto and Sasaki, 1997, 1998), may be useful forbetter assessing the bulk movement of rock glacier flows.Thus, here we slightly modify the code in order to estimatethe movements of martian rock glaciers. Note that, tomake the discussions simple, we adopt an iso-thermalmodel, which is in fact similar to the temperate glaciermodel (Miyamoto et al., 2005), and thus cannot be used toinvestigate the thermal effect of debris (Greve andMahajan, 2005) or lateral energy fluxes due to meltingand cold-air drainage.

Simple calculations show the qualitative effects ofvarying gravity and temperature on the morphology ofrock glaciers. The temperature dependency of A isdescribed in the following, assuming that the overallrheological behavior is similar to that of an ice glacier:

A ¼ expðaT � bÞ, (3)

where a ¼ 0:138 and b ¼ 91:7. We calculate the verticallyintegrated mass flux, U, through the vertical integration ofEq. (1) by

U ¼2A

nþ 2rg sin a�

dh

dx

� �� �nþ1

hnþ2. (4)

We incorporate the above equation into the masscontinuity equation to calculate the time-dependent move-ment of a flow (Miyamoto and Sasaki, 1998; Miyamotoet al., 2004a). Fig. 5 shows profiles, which exemplify themodeled results using varying gravitational and tempera-ture conditions. Though the modeling is useful for under-standing the general behavior of terrestrial and martianrock glaciers, it should not be considered absolute (notethat the rheology plays a more critical role than density: forexample, the density of talus comprised of volcanic rockmaterials without water/ice is only about 2–3 times largerthan that of pure ice, while the A value can vary as much asa couple of orders of magnitude). Generally speaking, boththe lower gravity and atmospheric temperature on Marsresults in thicker and more immobile flows (as suggested byColaprete and Jakosky, 1998), which may explain the lackof cross-valley lobate ridges in some rock glaciers. In otherwords, if the rheological properties and accumulation ratesare the same, flows on Earth become longer and thinnerthan those observed on Mars. Fig. 6 shows that theaccumulation rate can significantly alter the geometry ofthe rock glacier (e.g., length and thickness). In this case,rapid accumulation results in a thicker flow in a relativelyshort period of time, and ultimately leads to a fastermoving flow. Therefore, climatic conditions have at leasttwo important effects on the movement of a rock glacier:(1) rapid accumulation results in more rapid thickening ofthe flow, which in turn enhances the gravitational drivingforce that results in more rapid deformation, and (2) anaverage surface temperature ultimately controls the rheol-ogy of the rock glacier, and thus significantly changes itsmorphology—in some cases allowing the development of aconvex surface profile. This effect would be much largerthan implied by our simple model because liquid watermight exist inside the rock glacier under warmer condi-tions. Liquid water at grain boundaries contributes tocreep in higher temperature ranges and facilitates theadjustment between neighboring grains with differentorientations. Therefore, a flow with liquid water wouldbe expected to have more rapid deformation than a dryflow. In addition, warmer climatic conditions may allow iceto have soluble impurities, which is usually known toincrease the creep rate (Jones and Glen, 1969).

ARTICLE IN PRESS

Fig. 5. Snap shot at t ¼ 2� 104 yr from simple simulations of rock glaciers on Mars (solid lines) and Earth (dotted line). Slope angle, density,

accumulation rate, and accumulation area are 51, 1500 kg/m3, 0.1m/yr, 100m, respectively. Due to larger gravity, longer and thinner flow will appear on

Earth if the temperature of ice is the same. Lower temperature (i.e. harder rheology) makes the flow thicker and shorter.

Fig. 6. Snap shots at t ¼ 104 yr for Mars (solid lines) and Earth (dotted line) showing that the accumulation rates can significantly change the cross-

sectional profile. Parameters used in the calculation other than accumulation rate are: slope angle ¼ 51, density ¼ 1500kg/m3, accumulated

volume ¼ 105m2, and accumulation area ¼ 100m.

W.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192 189

6. Age, paleoclimate and implications

Rock glaciers on Earth record both soil and rock rindhistories (Mahaney et al., 1984; Mahaney, 1990b), whilesome young systems may also carry a lichen record(Benedict, 1968; Birkeland, 1973; Mahaney et al., 1984)that provides information on age of various lobes (Figs. 1and 2) and paleoclimate (Mahaney et al., 1984). If weassume that the lobes of rock glaciers originate fromincreased frost riving of rock under colder climaticconditions and that lobe emplacement occurs during glacialstages/advances, then rock glaciers provide proxy recordsof colder climates. A discontinuous soil cover, for example,often provides soil morphological data (Mahaney et al.,1984) that can be correlated to soil stratigraphic transectsin local areas providing relative age data and allowingcorrelation to the glacial stratigraphy. On Mt. Kenya, forexample, correlation of rock glaciers of Late Glacial age tothe Liki II stade (10–12 ka) of the last glaciation wasprovided principally by comparing significant aspects ofweathering/soil morphology (Mahaney, 1990b) betweenrock glacier lobes and moraines. In the Wind RiverMountain Range of western Wyoming, US, the lobe-shaped rock glaciers that predominate there (Mahaneyet al., 1984) have been assigned various Neoglacial agesbased on the morphology of a discontinuous soil cover andon rock rinds, which show a progressive thickening from

the source area to the toe of the rock glacier (Mahaney andSpence, 1984; Mahaney et al., 1984).Recent investigations of the age and velocity of rock

glacier lobes in the Swiss Alps (Frauenfelder et al., 2005)showed a close correlation between Schmidt-hammerrebound values and weathering rind thickness on sixdifferent rock glacier systems. This work assumed thecontinuous deformation of ice-rich debris mantle, wherebythe age of the surface increases from the sources to the toesof the rock glaciers. Age is demonstrated by decreasingrebound of the Schmidt-Hammer due to weathering ofsurface clasts and an increase in the thickness of weatheringrinds on surface clasts. Unlike similar investigations(Mahaney, 1978) in the Wind River Mountains of thewestern US, only the maximum thickness of oxidation wasmeasured and no mention is made of the variability of therinds (in practical terms, rinds are rarely uniform inthickness around the entire clast; see Mahaney (1990b), fordiscussion of rind variability). While the authors of theSwiss study claim that the analytical methods using theSchmidt-hammer and weathering rind measurements cor-relate closely with age estimates made by photogrammetricstreamline interpretations, it is difficult to imaginehow lobe position may be used to infer age ranges ofseveral millennia. Nevertheless, the weathering rindvalues for these Neoglacial lobes, composed mainly ofgranite, diorite, and unspecified gneiss yield median rind

ARTICLE IN PRESSW.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192190

thicknesses similar to weathering rind values on rockglacier lobes in the Wind River Mountains (Mahaney et al.,1984; Mahaney, unpublished data). These data andinterpretations, both in Switzerland and the RockyMountains, clearly show examples of a continuum: firstglaciation c glacial decay c mass wasting from adjoiningslopes.

Similar to the terrestrial examples, mass flows on Marsthat simulate rock glaciers on Earth indicate a response toclimatological activity and the presence of water. Further-more, Earth counterparts are produced by processesoperating in a relatively dense atmosphere along withrelated gravitational transport and precipitation of water.All of these assumptions suggest climatic variations (someperhaps very recent) from the current cold and dry desertconditions on Mars. Furthermore, many of these featurescould be frozen archives of a past environmental changewhen conditions were optimal for enhanced surfaceprocess, which includes the growth of ice-enriched flows.

7. Conclusions

Recent identification of terrestrial-type rock glaciers onMars, including both lobate and tongue-shaped forms,reveal a martian periglacial landscape that has closesimilarities to that of Earth. The presence of coarse-textured flows with well-defined pressure ridges and over-steepened fronts suggests both active and inactive typeswith climatic implications similar to terrestrial rockglaciers. These feature types, which occur mostly in asouthern latitudinal band, display similar morphologiccharacteristics of terrestrial rock glaciers. Their existence isnot without tremendous implications, as they are markersof environmental change and water-related resurfacingprocesses. While it is not possible at present to determinethe extent to which interstitial ice exists in martian rockglaciers, it is probable that permafrost (either frozen porewater or glacial ice) contributed to the flow characteristicsobserved in MOC imagery.

Based on published geologic and geomorphic informa-tion, the prospect of finding rock glaciers on Mars wellbeyond an age of 105 or even 106 yr is probable. A millionyear old rock glacier on Mars would be several orders ofmagnitude older than its terrestrial counterparts on Earth,and thus affording the opportunity to investigate thephysical properties of a glacial/periglacial surficial environ-mental system operating over long time periods, under ararefied atmosphere and low gravity, and during tempera-ture perturbations from present-day conditions, whichresult from a combination of obliquity variations and/orgeothermal heat release from volcanic activity. It is evenpossible that some martian rock glacier systems may recordboth active and inactive phases, perhaps in step withvarious climatic changes. Finally, since water probablyplays an important role in their formation, these featuresrepresent prime candidate sites for future astrobiologicalmissions to Mars.

Acknowledgements

This work was partially funded by grants fromQuaternary Surveys, Toronto to WCM and from NASAto the University of Arizona and SETI Institute/NASAAmes Research Center. John Dawson prepared some ofthe illustrations.

References

Ackert Jr., R.P., 1998. A rock glacier/debris-covered glacier system at

Galena Creek, Absaroka Mountains, Wyoming. Geog. Ann. 80A

(3&4), 267–276.

Arenson, L., Hoelzle, M., Springman, S., 2002. Borehole deformation

measurements and internal structure of some rock glaciers in Switzer-

land. Permafrost and Periglacial Processes 13, 117–135.

Azuma, N., 1994. A flow law for anisotropic ice and its application to ice

sheets. Earth Planet Sci. Lett. 128, 601–614.

Baker, V.R., 2001. Water and the martian landscape. Nature 412,

228–236.

Baker, V.R., Strom, R.G., Gulick, V.C., Kargel, J.S., Komatsu, G., Kale,

V.S., 1991. Ancient oceans, ice sheets and the hydrological cycle on

Mars. Nature 352, 589–594.

Baker, V.R., Strom, R.G., Dohm, J.M., Gulick, V.C., Kargel, J.S.,

Komatsu, G., Ori, G.G., Rice Jr., J.W., 2000. Mars’ Oceanus Borealis,

ancient glaciers, and the MEGAOUTFLO hypothesis. In: Thirty-first

Lunar Planetary Science Conference, Houston, [CD-ROM], abstract

1863.

Barcilon, V., MacAyeal, D.R., 1993. Steady flow of a viscous ice stream

across a no slip/free transition at the bed. J. Glaciol. 39, 167–185.

Barsch, D., 1996. Rock Glaciers: indicators for the Present and Former

Geoecology in High Mountain Environments. Springer, Berlin, 331pp.

Barsch, D., Fierz, H., Haeberli, W., 1979. Shallow core drilling and bore-

hole measurements in permafrost of an active rock glacier near the

Grubengletscher, Wallis, Swiss Alps. Arctic Alpine Res. 11, 215–228.

Behre, C.H., 1933. Talus behavior above timber in the Rocky Mountains.

J. Geol. 41, 622–635.

Benedict, J.B., 1968. Recent glacial history of an alpine area in the

Colorado Front Range, USA II, Dating the glacial deposits. J. Glaciol.

7, 77–88.

Berger, J., Krainer, K., Mostler, W., 2004. Dynamics of an active rock

glacier (Otztal Alps, Austria). Q. Res. 62, 233–242.

Berman, D.C., Hartmann, W.K., Crown, D.A., Baker, V.R., 2005. The

role of arcuate ridges and gullies in the degradation of craters in the

Newton Basin region of Mars. Icarus 178, 465–486.

Birkeland, P.W., 1973. Use of relative age-dating methods in a

stratigraphic study of rock glacier deposits, Mt. Sopris, Colorado.

Arctic Alpine Res. 5, 401–416.

Boynton, W.V., Feldman, W.C., Squyres, S.W., Prettyman, T., Bruckner,

J., Evans, L.G., Reedy, R.C., Starr, R., Arnold, J.R., Drake, D.M.,

Englert, P.A.J., Metzger, A.E., Mitrofanov, I., Trombka, J.I., d’Uston,

C., Wanke, H., Gasnault, O., Hamara, D.K., Janes, D.M., Marcialis,

R.L., Maurice, S., Mikheeva, I., Taylor, G.J., Tokar, R., Shinohara,

C., 2002. Distribution of hydrogen in the near-surface of Mars:

evidence for subsurface ice deposits. Science 297, 81–85.

Brown, H., 1925. A probable fossil glacier. J. Geol. 33, 464–466.

Cabrol, N.A., Grin, E.A., 2002a. The Recent Mars Global Warming

(MGW) and/or South Pole Advance (SPA) hypothesis: global

geological evidence and reasons why gullies might still be forming

today. In: Thirty-third Lunar Planetary Science Conference, Houston,

[CD-ROM], abstract 1058.

Cabrol, N. A., Grin, E.A., 2002b. Astrobiological implications of modern

glaciers and surface ice on Mars. In: Second Astrobiology Conference,

NASA Ames Research Center, 2002.

Cabrol, N.A., Grin, E.A., Dohm, J.M., 2001a. From Gullies to Glaciers:

a morphological continuum supporting a Recent Climate Change on

ARTICLE IN PRESSW.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192 191

Mars. In: American Geophysical Union Abstracts with Programs,

vol. 82(47), San Francisco, p. F694.

Cabrol, N.A., Wynn-Williams, D.D., Crawford, D.A., Grin, E.A., 2001b.

Recent aqueous environments in Martian impact craters: an astro-

biological perspective. Icarus 154, 98–112.

Cabrol, N. A., Wynn-Williams, D.D., Crawford, D.A., Grin, E.A., 2001c.

Recent aqueous environments in impact craters and the astrobiological

exploration of Mars. In: Thirty-second Lunar Planatery Science

Conference, Houston, [CD-ROM], 32, abstract 1251.

Capps, S.R., 1910. Rock glaciers in Alaska. J. Geol. 18, 359–375.

Carr, M.H., Clow, G.D., 1981. Martian channels and valleys: their

characteristics, distribution and age. Icarus 48, 901–917.

Carr, M.H., Schaber, G.G., 1977. Martian permafrost features.

J. Geophys. Res. 28, 4039–4054.

Clark, D.H., Steig, E.J., Potter Jr., N.J., Gillespie, A.R., 1998. Genetic

variability of rock glaciers. Geog. Ann. 80A (3&4), 175–182.

Colaprete, A., Jakosky, B.M., 1998. Ice flow and rock glaciers on Mars.

J. Geophys. Res. 103, 5897–5909.

Corte, A., 1976. Rock glaciers. Biul Peryglacjalny 26, 175–197.

Cross, C. W., Whitman, E., Howe, E., 1905. Geography and general

geology of the quadrangle. In: Silverton Folio. USG.S. Folio no. 120,

pp. 1–25.

Cui, Z., 1983. An investigation of rock glaciers in the Kunlun Shan,

China. In: Proceedings of Fourth International Conference on

Permafrost, Fairbanks, AL. Academic Press, Washington,

pp. 208–211.

Dohm, J.M., Anderson, R.C., Baker, V.R., Ferris, J.C., Rudd, L.P., Hare,

T.M., Rice Jr., J.W., Casavant, R.R., Strom, R.G., Zimbelman,

J.R., Scott, D.H., 2001a. Latent outflow activity for western Tharsis,

Mars: significant flood record exposed. J. Geophys. Res. 106,

12,301–12,314.

Dohm, J.M., Ferris, J.C., Baker, V.R., Anderson, R.C., Hare,

T.M., Strom, R.G., Barlow, N.G., Tanaka, K.L., Klemaszewski,

J.E., Scott, D.H., 2001b. Ancient drainage basin of the Tharsis region,

Mars: potential source for outflow channel systems and putative

oceans or paleolakes. J. Geophys. Res. 106, 32,943–32,958.

Eliason, E., Batson, R., Wu, S., 1992. Mars Mosaicked Digital Image

Model (MDIM) and Digital Terrain Model (DTM). Mission to

Mars: PDS volumes USA_NASA_PDS_VO_2001 through VO_2014.

Distributed on CD-ROMmedia by the NASA Planetary Data System.

Evin, M., Assier, A., 1983. Mesures d’orientation de blocs sur quelques

accumulations des Alpes du Sud (Brianconnais, Queyras, Embrunais,

Ubaye, Argentera-Mercantour. France et Italie): Etablissement de

coefficients permettant l’etude des glaciers rocheux. Z. Gletscherkd

Glazialgeol. 19, 107–126.

Fabre, D., Ribolini, A., Federici, P.R., Pappalardo, M., 2003. The lower

discontinuous permafrost boundary in the Argentera Massif (Maritime

Alps, Italy): insight from rock glacier geo-electrical soundings. In:

Haeberli, W., Brandova, D. (Eds.), Eighth International Conference

on Permafrost, Zurich, Switzerland, 20–25 July 2003, Extended

Abstracts, pp. 33–34.

Fairen, A.G., Dohm, J.M., Baker, V.R., de Pablo, M.A., Ruiz, J., Ferris,

J.C., Anderson, R.C., 2003. Episodic flood inundations of the northern

plains of Mars. Icarus 165, 53–67.

Feldman, W.C., Boynton, W.V., Tokar, R.L., Prettyman, T.H., Gasnault,

O., Squyres, S.W., Elphic, R.C., Lawrence, D.J., Lawson,

S.L., Maurice, S., McKinney, G.W., Moore, K.R., Reedy, R.C.,

2002. Global distribution of neutrons from Mars: results from Mars

Odyssey. Science 297, 75–78.

Ferris, J.C., Dohm, J.M., Baker, V.R., Maddock III, T., 2002. Dark slope

streaks on Mars. Geophys. Res. Lett. 29 (10), 128-1–128-4.

Foster, H.L., Holmes, G.W., 1965. A large transitional rock glacier in the

Johnson River Area, Alaska Range. USG.S. Professional Paper 525B,

112–116.

Frauenfelder, R., Laustela, M., Kaab, A., 2005. Relative age dating of

Alpine Rockglacier surfaces. Zeitsch. Geomorphol. 49, 145–166.

Giardino, J.R., Vitek, J.D., Shroder, J.F. (Eds.), 1987. Rock Glaciers.

Unwin Hyman, UK, 355pp.

Goldsby, D.L., Kohlstedt, D.L., 2001. Superplastic deformation of ice:

experimental observations. J. Geophys. Res. 106 (B6), 11,017–11,030.

Gorbunov, A.P., 1983. Rock glaciers of the mountains of middle Asia. In:

Proceedings of the Fourth International Conference on Permafrost,

Fairbanks, AL. National Academic Press, Washington, pp. 359–362.

Greve, R., Mahajan, R.A., 2005. Influence of ice rheology and dust

content on the dynamics of the north-polar cap of Mars. Icarus 174,

475–485.

Gulick, V.C., Baker, V.R., 1989. Fluvial valleys and Martian paleocli-

mates. Nature 341, 514–516.

Haberle R. M., McKa,y, C.P., Schaeffer, J., Joshi, M., Cabrol,

N.A., Grin, E.A., 2000. Meteorological control on the formation of

paleolakes on Mars. In: Thirty-first Lunar Planetary Science Con-

ference, Houston, [CD-ROM], abstract 1509.

Haeberli, W., 1983. Permafrost-glacier relationships in the Swiss Alps–to-

day and in the past. In: Proceedings of the Fourth International

Conference on Permafrost, Fairbanks, AL. National Academic Press,

Washington, pp. 415–420.

Haeberli, W., Huder, J., Keusen, H.R., Pika, J., Rothlisberger, H., 1988.

Core drilling through rock glacier permafrost. In: Proceedings of the

Fifth International Conference Permafrost in Trondheim, Norway,

vol. 2, pp. 937–942.

Hole, A.D., 1912. Glaciation in the Telluride Quadrangle, Colorado.

J. Geol. 20, 502–529 and 605–639.

Hollermann, P., 1983. Probleme der Blockgletscherforschung, Referat des

Diskussionsbeitrages. In: Poser, H., Schunke, E. (Eds.), Abhandlungen

der Akademie der Wissenschaften Gottingen. Math Phys Kl Folge,

vol. 3, pp. 116–119

Hooke, R.L., Dahlin, B.H., Kauper, M.T., 1972. Creep of ice containing

dispersed fine sand. J. Glaciol. 11, 327–336.

Howe, E., 1909. Landslides in the San Juan Mountains, Colorado. USG.S.

Professional Paper 67, 58pp.

Humlum, O., 1996. Origin of rock glaciers: observations from Mellemf-

jord, Disko Island, Central WestGreenland. Perm. Perig. Proc. 7,

361–380.

Ives, R.L., 1940. Rock glaciers in the Colorado front range. Geol. Soc.

Am. Bull. 50, 1271–1294.

Jakob, M., 1992. Active rock glaciers and the lower limit of discontinuous

alpine permafrost, Khumbu Himalaya, Nepal. Permafrost Periglacial

Process. 3, 253–256.

Jeanneret, F., 1975. Blockgletscher in den Sudalpen Neuseelands.

Z. Geomorphol. NF 19, 83–94.

Ji, S., 2004. A generalized mixture rule for estimating the viscosity of solid-

liquid suspensions and mechanical properties of polyphase rocks and

composite materials. J. Geophys. Res. 109, B10207.

Jones, S.J., Glen, J.W., 1969. The mechanical properties of single crystals

of pure ice. J. Glaciol. 8, 463–473.

Kaab, A., Vollmer, M., 2000. Surface geometry, thickness changes

and flow fields on creeping mountain permafrost: automatic extrac-

tion by digital image analysis. Permafrost Periglacial Process. 11,

315–326.

Kargel, J.S., Strom, R.G., 1992. Ancient glaciation on Mars. Geology 20,

3–7.

Kesseli, J.E., 1941. Rock streams in the Sierra Nevada. Geogr. Rev. 31,

203–227.

Kitanovski, A., Poredos, A., 2002. Concentration distribution and

viscosity of ice-slurry in heterogeneous flow. Int. J. Refrig. 25,

827–835.

Laskar, J., Correia, A.C.M., Gastineau, M., Joutel, F., Levrard, B.,

Robutel, P., 2004. Long term evolution and chaotic diffusion of the

insolation quantities of Mars. Icarus 170, 343–364.

Lucchitta, B.K., 1984. Ice and debris in the fretted terrain, Mars.

J. Geophys. Res. 89, B409–B418.

Mahaney, W.C., 1987. Late Quaternary soil stratigraphy in the Wind

River Mountains, Western Wyoming. In: Mahaney, W.C. (Ed.),

Quaternary Soils, Geo Abstracts. Norwich, UK, pp. 223–264.

Mahaney, W.C., 1980. Late quaternary rock glaciers, Mount Kenya, East

Africa. J. Glaciol. 25, 492–497.

ARTICLE IN PRESSW.C. Mahaney et al. / Planetary and Space Science 55 (2007) 181–192192

Mahaney, W.C., 1981. Paleoclimate reconstructed from paleosols:

evidence from the Rocky Mountains and East Africa. In: Mahaney,

W.C. (Ed.), Quaternary paleoclimate, GeoAbstracts, Norwich, UK,

pp. 227–247.

Mahaney, W.C., 1990a. Macrofabrics and quartz microstructures confirm

glacial origin of Sunnybrook Drift in the Lake Ontario Basin. Geology

18, 145–148.

Mahaney, W.C., 1990b. Ice on the Equator. Wm Caxton Ltd., Ellison

Bay, WI, 386pp.

Mahaney, W.C., 1995. Pleistocene and Holocene glacier thicknesses and/

or transport histories inferred from microtextures on quartz particles.

Boreas 24, 293–304.

Mahaney, W.C., Spence, J.R., 1984. Late Quaternary deposits, soils,

chronology and floristics, Jaw Cirque area, Central Teton Range,

Western Wyoming. Am. J. Sci. 284, 1056–1081.

Mahaney, W.C., Piegat, J., Halvorson, D.L., Sanmugadas, K., 1984.

Evaluation of dating methods used to assign ages in the Wind River

and Teton Ranges, western Wyoming. In: Mahaney, W.C. (Ed.),

Q. Dating Meth. Elsevier, Amsterdam, pp. 355–374.

Malin, M.C., Edgett, K.S., 2000. Evidence for recent groundwater seepage

and surface runoff on Mars. Science 288, 2330–2335.

Mangold, N., Allemand, P., 2001. Topographic analysis of features related

to ice on mars. Geophys. Res. Lett. 28, 407–410.

Mangold, N., Allemand, P., Duval, P., Geraud, Y., Thomas, P., 2002.

Experimental and theoretical deformation of ice-rock mixtures:

implications on rheology and ice content of Martian permafrost,

Planet. Space Sci. 50, 385–401.

Masursky, H., 1973. An overview of geologic results from Mariner 9.

J. Geophys. Res. 78, 4037–4047.

Miyamoto, H., Sasaki, S., 1997. Simulating lava flows by an improved

cellular automata method. Comput. Geosci. 23, 283–292.

Miyamoto, H., Sasaki, S., 1998. Numerical simulations of flood basalt

lava flows: roles of some parameters on flow morphologies.

J. Geophys. Res. 103, 27,489–27,502.

Miyamoto, H., Dohm, J.M., Beyer, R.A., Baker, V.R., 2004a. Fluid

dynamical implications of anastomosing slope streaks on Mars.

J. Geophys. Res. 109, E06008.

Miyamoto, H., Dohm, J.M., Baker, V.R., Beyer, R.A., Bourke,

M., 2004b. Dynamics of unusual debris flows on Martian sand dunes.

Geophys. Res. Lett. 31, L13701.

Miyamoto, H., Mitri, G., Showman, A.P., Dohm, J.M., 2005. Putative ice

flows on Europa: Geometric patterns and relation to topography

collectively constrain material properties and effusion rates. Icarus

177, 413–424.

Mustard, J.F., Cooper, C.D., Rifkin, M.K., 2001. Evidence for recent

climate change on Mars from the identification of youthful near-

surface ground ice. Nature 412, 411–414.

Nicholas, J.W., 1994. Fabric analysis of rock glacier debris mantles, La Sal

Mountains, UT. Permafrost Periglacial Process. 5, 53–66.

Østrem, G., Arnold, K., 1970. Ice-cored moraines in southern British

Columbia and AB, Canada. Geogr. Ann. 52A, 120–128.

Outcault, S.I., Benedict, J.B., 1965. Photo-interpretation of two types of

rock glacier in the Colorado Front Range, USA. J. Glaciol. 5,

849–856.

Patterson, W.S.B., 1994. The Physics of Glaciers, third ed. Elsevier,

Amsterdam, 480pp.

Patton, H.B., 1910. Rock streams of Veta Peak, Colorado. Geol. Soc. Am.

Bull. 21, 663–676.

Pollack, J.B., et al., 1987. The case for a warm, wet climate on early Mars.

Icarus 71, 203–224.

Potter, N., 1968. Galena Creek rock glacier, northern Absaroka

Mountains, Wyoming. Geol. Soc. Am. Spec. Paper 115, 438.

Potter, N., 1972. Ice-cored rock glacier, Galena Creek, northern Absaroka

Mountains, Wyoming. Geol. Soc. Am. Bull. 83, 3025–3058.

Scott, D. H., Dohm, J.M., Rice Jr., J.W., 1995. Map of Mars showing

channels and possible paleolake basins, USGS Misc. Inv. Ser. Map

I-2461 (1:30,000,000).

Seppi, R., Baroni, C., Carton, A., 2003. Rock glacier inventory of the

Adamello Presanella massif (Central Alps, Italy). In: Haeberli, W.,

Brandova, D. (Eds.), Eighth International Conference on Permafrost,

Zurich, Switzerland, 20–25 July 2003, Extended Abstracts,

pp. 145–146.

Squyres, S.W., 1978. Martian fretted terrain: Flow of erosional debris.

Icarus 34, 600–613.

Squyres, S.W., 1989. Urey prize lecture: water on Mars. Icarus 79,

229–288.

Squyres, S.W., Carr, M.H., 1986. Geomorphic evidence for the distribu-

tion of ground ice on Mars. Science 231, 249–252.

Steenstrup, K.J.V., 1883. Bidrage til Kjendskab til Braeerne og Brae-Isen i

Nor-Gronland. Medd Gronl 4, 69–112.

Tanaka, K.L., 1986. The stratigraphy of Mars. In: Proceedings of 17th

Lunar and Planetary Science Conference, Houston, March 17–21,

1986, pt. 1. J. Geophys. Res. 91(B13), E139–E158.

Tyrrell, J.B., 1910. Rock glaciers or chrystocrenes. J. Geol. 28,

549–553.

Vietoris, L., 1972. Uber die Blockgletscher des AuXeren Hochegbenkars.

Z. Gletscherk Glazialgeol. 8, 169–188.

Vonder Muhll, D., Haeberli, W., 1990. Thermal characteristics of the

permafrost within an active rock glacier (Murtel/Corvatsch, Grisons,

Swiss Alps). J. Glaciol. 36, 151–158.

Wahrhaftig, C., Cox, A., 1959. Rock glaciers in the Alaska Range. Geol.

Soc. Am. Bull. 70, 383–436.

Whalley, B., 1974. Rock glaciers and their formation as part of a glacier

debris-transport system. Geographical Report 24. Reading Geogra-

phical Papers, Reading, UK, 60pp.

Whalley, W.B., Azizi, F., 2003. Rock glaciers and protalus landforms:

analogous forms and ice sources on Earth and Mars. J. Geophys. Res.

108 (E4), 8032.