doi:10.1144/SP320.5 2009; v. 320; p. 57-69 Geological Society, London, Special Publications

 Richard I. Waller, Julian B. Murton and Peter G. Knight  

same science?Basal glacier ice and massive ground ice: different scientists, 

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Basal glacier ice and massive ground ice: different scientists,

same science?

RICHARD I. WALLER1*, JULIAN B. MURTON2 & PETER G. KNIGHT1

1Research Institute for the Environment, Physical Sciences & Applied Mathematics,

Keele University, Keele, Staffordshire ST5 5BG, UK2Department of Geography, University of Sussex, Brighton, BN1 9QJ, UK

*Corresponding author (e-mail: r.i.waller@esci.keele.ac.uk)

Abstract: Whilst glaciologists and permafrost researchers investigate ice bodies using similartechniques, there has been surprisingly little collaboration between the two communities. Thispaper examines the potential benefits of interdisciplinary research into the formation of basal icebeneath glaciers and the origin of massive ice in glaciated permafrost regions. Active collaborationin these areas has already improved our understanding of the formation of basal ice beneath cold-based glaciers, the critical role played by basal freezing in controlling the dynamic behaviour ofstagnating ice streams and the significance of glacier–permafrost interactions at the margins ofPleistocene ice sheets. However, in order to promote future collaboration certain obstacles needto be overcome. The contrasting ice-classification schemes employed by glaciologists and perma-frost scientists, for example, need to be unified in order to allow detailed comparisons of ice-richsequences in both environments. This could, in turn, enable exciting research advances, mostnotably by facilitating the identification of preserved remnants of Pleistocene ice sheets within per-mafrost regions that provide a potentially invaluable and currently largely untapped source ofpalaeoglaciological information.

The study of ice, liquid water and sediment mixturesis a major research focus within both glaciology andpermafrost science (e.g. Christoffersen et al. 2006;Rempel 2007). Glaciologists have long recognizedthe importance of debris-rich ice at the base of gla-ciers and ice sheets, and have made rapid progressover the last 50 years in identifying its key charac-teristics, processes of formation and glaciologicalsignificance (for relevant reviews see Hubbard &Sharp 1989; Knight 1997; Cook et al. 2006). Simi-larly, permafrost scientists have elucidated thenature, origin and palaeoenvironmental significanceof massive bodies of ground ice (e.g. Mackay 1971,1989; Mackay & Dallimore 1992; Murton 2005).Not surprisingly, researchers in both fields usesimilar techniques, ranging from the simple descrip-tion and characterization of ice–sediment facies(e.g. Lawson 1979; Murton & French 1994;Hubbard & Sharp 1995), to the application of stable-isotope analyses (e.g. Lorrain & Demeur 1985;Knight 1989; Cardyn et al. 2007), geophysics(e.g. Dallimore & Davis 1992; Arcone et al.1995; Kneisel et al. 2008) and drilling (Mackay1971; Murray & Porter 2001). Nonetheless, interdis-ciplinary collaboration remains limited (Harris &Murton 2005).

This paper argues that greater collaborationbetween glaciology and permafrost science is essen-tial to elucidate the processes of ice formation

and the palaeoenvironmental significance of debris-bearing ice. It reviews recent research about theformation of basal ice, and the origin and palaeoen-vironmental significance of massive ice. Three casestudies are presented to illustrate the ways in whichprogress in these related fields can be facilitated bythe combined knowledge and efforts of glaciologistsand permafrost scientists. Finally, we identifyobstacles to collaboration and highlight futureresearch possibilities.

The origin and glaciological significance

of basal ice

Many glaciers have a distinctive basal horizon thatdiffers markedly from the overlying firnifiedglacier ice due to its interaction with the glacierbed (Fig. 1). Such basal-ice layers can reach tensof metres in thickness, and are usually distinguishedfrom the overlying glacier ice by an abrupt increasein debris content and an anisotropic physical struc-ture (Hubbard & Sharp 1989). Basal ice is alsocharacterized by a distinctive isotopic signatureowing to the fractionation that occurs on freezing.This results in basal ice being enriched in theheavier isotopes of oxygen (less negative d18Oratios) relative to the water from which it isderived. In a closed-system setting, basal ice also

From: KNIGHT, J. & HARRISON, S. (eds) Periglacial and Paraglacial Processes and Environments.The Geological Society, London, Special Publications, 320, 57–69.DOI: 10.1144/SP320.5 0305-8719/09/$15.00 # The Geological Society Publishing House 2009.

displays a co-isotopic relationship that differs fromthat associated with firnified ice (Knight 1997).Basal-ice layers have been described at temperateglaciers in Alaska and the Alps (e.g. Hubbard &Sharp 1995), subpolar glaciers in Greenland andSvalbard (e.g. Boulton 1970), polar glaciers in thehigh Arctic and Antarctica (e.g. Tison et al. 1993),and glaciers descending from tropical ice caps(Knight 1988). The presence of basal ice can influ-ence the behaviour of glaciers or ice sheets with,for example, its enhanced debris content affectingits crystal size and fabric, rheology and, conse-quently, the dynamic response of the entire icebody (e.g. Lawson 1996; Fitzsimons 2006). Inaddition, the presence of debris-rich basal ice caninfluence rates of glacier erosion, transport anddeposition, and, therefore, sediment budgets (e.g.Rea & Whalley 1994). Finally, recent work hassuggested that basal freeze-on associated with thedevelopment of thick sequences of basal ice cancause ice-stream stagnation by increasing tillconsolidation and shear strength (Christoffersen &Tulaczyk 2003a, b).

Most research on basal ice has focused on itsmechanisms of formation. Work on this subject

has continued for almost five decades and a broadrange of mechanisms have now been advocated(for lengthier reviews see Hubbard & Sharp 1989;Knight 1997). A large motivation behind thisresearch is the belief that subglacial processes andconditions can be reconstructed from examiningthe distinctive characteristics of basal ice, and,therefore, that the conditions beneath inaccessibleice-sheet interiors can be determined via obser-vations at easily accessible ice margins (e.g.Sugden et al. 1987). Consequently, basal-iceresearchers have attempted to develop geneticclassification schemes in which the appearance ofdistinctive basal-ice facies can be related to theoccurrence of specific basal processes and con-ditions (e.g. Sharp et al. 1994; Hubbard &Sharp 1995).

Whilst initial research on the origin of basal iceadvocated debris entrainment via shearing (e.g.Goldthwait 1951), this hypothesis was soon criti-cized by both Weertman (1961) and Boulton(1970), who argued that shearing alone was incap-able of entraining debris. They suggested that ther-mally controlled processes involving the freeze-onof water onto the glacier sole provide the dominantmechanism of debris entrainment and basal-ice for-mation. Subsequent research has identified twomain thermally controlled processes responsiblefor basal-ice formation: regelation and basaladfreezing.

Regelation, as originally described by Weertman(1957), involves the melting of basal ice on theup-glacier side of an obstacle due to the develop-ment of excess pressure and an accompanyingreduction in the pressure melting point. The result-ing meltwater then flows to the low-pressure areaon the lee side of the obstacle, where it refreezes,releasing latent heat of fusion. This heat is then con-ducted back to the stoss face where it contributes tofurther melting. As a result the mechanism involvesthe mass transport of water in a thin basal layer andthe bulk transport of the whole ice mass above.Kamb & La Chappelle (1964) subsequentlyobserved a layer of ice heavily laden with debrisconsisting of both mud and rock fragments1–2 mm in diameter beneath the Blue Glacier inWashington, USA. They related this debris-richlayer to Weertman’s process of regelation, andsuggested that debris accumulates on the stoss sideof obstacles and is then entrained into the regelationice when the meltwater refreezes, producingbanners of sediment that extend from the crests ofthe bedrock obstacles. The operation of thisprocess has subsequently been advocated by manyworkers in the field, notably Lawson (1979) andSugden et al. (1987).

Whilst regelation was originally conceived of asoperating beneath rigid-bed glaciers, the process has

Fig. 1 Debris-rich basal ice exposed at the base of theMatanuska Glacier, Alaska (6184603100N, 14784503300W).The ice axe is given for scale.

R. I. WALLER ET AL.58

now been extended to soft-bed glaciers. Iverson &Semmens (1995) have suggested that regelationmay occur downwards into porous sediments as aresult of regelation past individual grains. Theyargued that this mechanism may represent the domi-nant process of entrainment in soft-bedded environ-ments, particularly where effective pressures arehigh. This process has subsequently been used byChristoffersen et al. (2006) in combination withcongelation to explain the development of avariety of basal-ice facies (see later). Iverson et al.(2007) have recently provided the first fieldmeasurements of the process of ‘regelation infiltra-tion’ by installing a prism of simulated till withina bedrock trough in an artificial cavity beneathEngabreen, a temperate glacier in Norway. Duringa 12-day experiment in 2001, when the cavity wasallowed to close, the glacier bed was subsequentlyfound to have infiltrated 50–80 mm into the upperpart of the till prism at a rate close to that predictedby theoretical models (Philip 1980).

Boulton (1970), amongst others, pointed out thatwhilst regelation may explain the presence of debriswithin basal-ice, as it merely redistributes existingice it is unable to explain the observed thicknessof some basal-ice layers in subpolar regions,which can reach tens of metres in thickness (e.g.Knight et al. 1994). The process of basal adfreezingprovides an alternative mechanism of basal-ice for-mation capable of generating thicker basal-icesequences as it involves the net addition of ice.

Basal adfreezing was initially proposed byWeertman (1961), and has been widely advocatedas the principal cause of thick and laterally exten-sive basal-ice sequences beneath polythermalglaciers (e.g. Knight et al. 1994; Zdanowicz et al.1996). Weertman (1961) proposed his ‘freezingmodel’ after concluding that the shearing hypothesisof Goldthwait (1951) failed to provide a tenableexplanation for a series of ice-cored morainesobserved near Thule, Greenland. Weertman arguedthat under the thick ice of the ice-sheet interior,the temperature gradient would be insufficient todrain away the heat generated at the bed. Thisexcess heat would lead to basal melting, producingwater that flows along the local pressure gradienttowards the margin. As the ice thins nearer themargin, the temperature gradient steepens, remov-ing all heat generated at the bed and returning thebase to freezing conditions, where the waterrefreezes. As a result, there is a net transport ofmass from the ice-sheet interior to a locationcloser to the margin, allowing the accretion ofthick basal-ice sequences.

Glaciohydraulic supercooling provides analternative mechanism of basal adfreezing andbasal-ice formation that has recently been describedto explain the formation of thick basal-ice beneath

temperate glaciers (Alley et al. 1998; Lawsonet al. 1998, see Cook et al. 2006 for a detailedreview). The process is associated with the pressure-dependence of the melting point of ice and the flowof subglacial water through topographic basins or‘overdeepenings’. At the base of the overdeepening,the melting temperature is depressed because of theoverburden pressure, and water can remain liquid attemperatures below the pressure melting point. Aswater is forced by the pressure gradient to ascendthe adverse slope out of the overdeepening, thepressure-dependent melting temperature graduallyrises towards 0 8C as the overburden pressuredecreases. If the adverse bed slope is sufficientlysteep (.1.2–1.7 times the gradient of the ice-surface slope) the heat generated and the rate ofincrease in water temperature will be insufficientto match the changing pressure melting pointand the water will become supercooled (Alleyet al. 2003).

Whilst the theoretical basis for glaciohydraulicsupercooling has been established for some time(e.g. Rothlisberger 1968), field evidence of theprocess has not been identified until recently.Work at the Matanuska Glacier, Alaska, reportedby Lawson et al. (1998) has provided evidence forthe supercooling of subglacial discharge via directtemperature measurements and the observation offeatures such as anchor ice terraces around super-cooled outlets. Owing principally to physical, sedi-mentological and isotopic similarities between thebasal ice and ice accreting around vents dischargingsupercooled water, the authors have also related theprocess to the formation of a thick basal-ice layerexposed at the glacier margin (Fig. 1). Subsequentwork in Iceland by Roberts et al. (2002) hassuggested that the process comprises the dominantmechanism of basal-ice formation under normalflow conditions and that it is also capable of entrain-ing large quantities of sediment during extreme flowconditions (i.e. jokulhlaups). However, additionalresearch has either failed to find evidence for theoperation of glaciohydraulic supercooling wherelarge overdeepenings occur (e.g. Swift et al.2006), or has concluded that the process cannotexplain the observed variability in basal-ice facies(Cook et al. 2007). Consequently, the relativeimportance of the process versus other establishedmechanisms of basal-ice formation remains thesubject of ongoing research.

Substantial progress has clearly been made inidentifying the processes and products of basal-iceformation. However, the focus on thermally cont-rolled processes that involve melting and refreezinghas led to the question of how basal ice can beformed beneath cold-based glaciers on permafrostwhere temperatures remain below freezing. Thisissue is explored further in a later section.

PERMAFROST AND BASAL ICE 59

The origin and palaeoenvironmental

significance of massive ice

Many permafrost regions contain ground ice, a termused to refer to any type of ice formed in freezing orfrozen ground (French 2007). Large bodies ofmassive ice constitute one of the most spectacularforms of ground ice, and have been widely docu-mented in both the western Canadian Arctic (e.g.French & Harry 1990; Mackay & Dallimore 1992)and western Siberia (e.g. Vtyurin & Glazsovskiy1986; Astakhov & Isayeva 1988; Astakhov et al.1996). Massive ice is defined by an ice content inexcess of 250% by weight (Harris et al. 1988) andordinarily occurs as large, tabular bodies that canreach over 10 m in thickness. Whilst the distri-bution, stratigraphic setting, and physical andchemical characteristics of massive ice have beenincreasingly well constrained, its mode of originand palaeoenvironmental significance is subjectto debate.

There are two principal theories for the origin ofmassive ice. First, massive ice represents exception-ally large bodies of segregated intrusive ice createdby subaerial permafrost aggradation and high sub-permafrost porewater pressures (e.g. Mackay1971, 1989; Mackay & Dallimore 1992). Onceaggrading permafrost reaches or generates a press-urized aquifer, a sustained water flow to the freezingfront allows the development of a thick, tabularbody of ‘intrasedimental ice’. Supporting evidencehas come from the analysis of borehole logs in the

western Canadian Arctic which indicates thatmassive ice frequently occurs at the boundarybetween clay-rich materials and underlying sandsand gravels, i.e. at the boundary between materialsof high and low frost-susceptibility (Mackay1971). In addition, coastal exposures at sites likePeninsula Point near Tuktoyaktuk indicate a promi-nent subhorizontal layering and a conformablecontact with the overlying sediments (Fig. 2).Finally, ice dykes extending upwards from the topof massive ice into the overburden demonstratethe existence – during massive ice formation – ofporewater pressures sufficiently high to hydrofrac-ture the overlying frozen sediments (Mackay &Dallimore 1992). Rampton (1988a, 1991) hasargued that high porewater pressures and massive-ice formation relate to a glacially imposed hydraulicgradient driving subglacial meltwater to an aggrad-ing proglacial permafrost table during deglaciation(see also Lacelle et al. 2004).

An alternative explanation for the origin ofmassive ice is that it represents buried glacier icethat has been preserved within permafrost followingice retreat. The preservation of glacier ice for centu-ries within ice-marginal sediments under non-permafrost conditions is well established (e.g.Everest & Bradwell 2002), whilst Sugden et al.(1995) have suggested that under permafrost con-ditions glacier ice can be preserved for millions ofyears. This hypothesis is the preferred explanationfor massive ice in western Siberia by manyRussian scientists, who suggest that the widespread,

Fig. 2 Massive intrasedimental ice with prominent sub horizontal stratification exposed at Peninsula Point, westernCanadian Arctic (6982403400N, 13380704600W). The ice face is approximately 5 m high.

R. I. WALLER ET AL.60

prolonged preservation of glacier ice within the per-mafrost indicates ‘incomplete’ or ‘retarded’ degla-ciation (e.g. Astakhov & Isayeva 1988; Grosvaldet al. 1986; Kaplyanskaya & Tarnogradskiy 1986;Astakhov et al. 1996). Key lines of evidence forthis mode of origin include the stratigraphicsetting and structural characteristics of the massiveice. In contrast to intrasedimental ice, massive iceof glacial origin has an unconformable uppercontact and is often entirely surrounded by diamic-ton, whose low permeability precludes an open-system water supply to an aggrading freezingfront. Consequently, such ice is frequently describedwithin moraine complexes (e.g. French & Harry1988; Dyke & Savelle 2000; Lacelle et al. 2007).In addition, the ice frequently contains both large-and small-scale tectonic structures such as thrustfaults and recumbent folds (e.g. French & Harry1990; Astakhov et al. 1996) (Fig. 3). Such featuresare widely considered indicative of shear defor-mation within the basal layers of an ice sheet andto be inconsistent with an origin through segregationfollowing deglaciation, although Rampton (1988a,1991) has argued that such features might beimparted on intrasedimental ice by glacierre-advance. Finally, some workers have suggestedthat buried glacier ice displays a distinctive isotopicsignature (e.g. Lorrain & Demeur 1985; Lacelleet al. 2007).

Distinguishing between these modes of origin iscrucial to our understanding of their significance. Ifthey represent intrasedimental ice then they provide

important information on the climatic regime at thetime of their formation. Alternatively, if they rep-resent buried glacier ice then they provide an unpar-alleled source of palaeoglaciological information.As the latter hypothesis involves a glacial origin, itis clear that its rigorous appraisal requires athorough knowledge and understanding of the phys-ical, chemical and isotopic characteristics of the fullrange of glacial-ice facies. An example of how thiscan assist in the interpretation of massive ice isprovided in the following sections.

Interdisciplinary research

Given that basal-ice and permafrost researchersexamine fundamentally identical materials usingsimilar techniques, it is unsurprising that thereare significant overlapping areas of research thatwould benefit from more collaboration. The follow-ing section examines three such examples beforeconsidering the current barriers to and futurepossibilities afforded by a more interdisciplinaryapproach.

Examples

Basal-ice formation in permafrost

environments

With the majority of proposed mechanisms ofbasal-ice formation involving melting and

Fig. 3 Debris-rich massive ice with folded clear ice layers exposed at Mason Bay, western Canadian Arctic (6983203100N,13480205600W). The ice face is approximately 3 m high.

PERMAFROST AND BASAL ICE 61

refreezing over a variety of spatial scales, thedevelopment of basal-ice sequences beneath cold-based glaciers resting on permafrost where there isnegligible meltwater available for refreezing hasprovided an ongoing glaciological problem. Thisis symptomatic of a broader issue within glaciologyconcerning the plausibility of the assumption thatbasal processes cease at temperatures below thepressure melting point (e.g. Waller 2001).

Shaw (1977) suggested that cold-based glaciersentrain debris when they override frontal aprons ofice and sediment. Many polar and subpolar glaciersterminate in a vertical cliff, the foot of which ismasked by an apron of ice blocks, refrozen melt-water, supraglacial and englacial debris, and wind-blown sediment. This apron may be entrained byglacier advance, and subsequently folded, attenu-ated and foliated by flow metamorphism. Thismodel has subsequently been applied by Evans(1989), who described the dominance of apronentrainment in the formation of basal-ice layers inglaciers in the Canadian High Arctic. The shearinghypothesis originally proposed by Goldthwait(1951) has also experienced a renaissance as apotential explanation for basal-ice formationbeneath cold-based glaciers, with Tison et al.(1993) concluding that the overriding of active iceover stagnant ice and subsequent shearing was theonly tenable hypothesis of debris entrainment at asite at the margin of the Antarctic ice sheet.

Continued research on basal-ice formationbeneath cold-based glaciers has emphasized theimportance of glacier–permafrost interactions.The excavation of a 26 m-long tunnel beneath the

Suess Glacier in the Dry Valleys of Antarctica(e.g. Fitzsimons 2006) has revealed the presenceof a heterogeneous basal-ice layer up to 3.8 mthick containing large blocks of sediment with well-preserved sedimentary structures thought to reflectthe erosion and entrainment of subglacialpermafrost.

Observations by the authors at the margin of theRussell Glacier in western Greenland suggest thatglacier–permafrost interactions play a significantrole in the development of the basal-ice layer atthis site. This outlet glacier discharges ice fromthe southwestern sector of the Greenland ice sheet,approximately 15 km east of Kangerlussuaq(678060N, 508090W), and terminates in a region ofcontinuous permafrost where permafrost thick-nesses are estimated at 127 + 31 m (van Tatenhove1995). The Russell Glacier has experienced signifi-cant oscillations during the last century, with aretreat phase between 1943 and 1968, and a sub-sequent re-advance between the early 1970s and1999 of more than 200 m in places (Knight et al.2000). The basal-ice layer at this site has been exten-sively studied (e.g. Knight 1989; Knight et al. 1994;Waller et al. 2000) and comprises two main facies: aconspicuously debris-rich stratified facies and anoverlying dispersed facies.

Knight et al. (1994) suggested that the stratifiedfacies is formed by the entrainment and deformationof blocks of old snow, frozen till and laminatedice–debris layers. Observations associated withthe recent re-advance of the glacier marginsuggest that glacier–permafrost interactions playan important role in the formation of the stratified

Fig. 4 Frozen moraine sediment adhering to the base of the Russell Glacier, western Greenland (6780601200N,5081303000W) and being ripped-up by continued ice motion. The metre rule is given for scale.

R. I. WALLER ET AL.62

facies basal ice with frozen moraine sedimentsbeing ripped up by the advancing ice margin(Fig. 4), with the result that the entrained basal iceand moraine sediments display very similar particle-size distributions.

It is suggested that in the absence of freezing orregelation, entrainment occurs in response to thetransmission of basal shear stress from the glacierbed into the frozen subglacial sediment, resultingin the traction of a layer of subglacial sedimentand its entrainment as a layer of stratified faciesice. In other words, the glacier couples with theunderlying permafrost and the effective bed of theglacier (the plane beneath which glacier-inducedmotion ceases) shifts from the ice–bed interface toa plane of weakness within the underlying substrate.In permafrost environments the base of the perma-frost layer may be characterized by high porewaterpressures and, therefore, provides a potential planeof weakness that can allow the entrainment and sub-sequent deformation of the overlying frozenmaterial (Mathews & Mackay 1960; Astakhovet al. 1996). Alternatively, planes of localized weak-ness may occur within the permafrost in the form ofice-rich or clay-rich layers (Astakhov et al. 1996;Fitzsimons et al. 1999). Whilst this provides aviable hypothesis of basal-ice entrainment in theabsence of freezing and thawing, it does generatean additional set of uncertainties. Fitzsimons(2006) has pointed out that in such situations itcan be difficult, if not impossible, to identify theexact location of the glacier bed. Whilst this is tra-ditionally viewed as being texturally defined by aclear ice rock or ice sediment interface, in circum-stances where a glacier with basal ice overridesice-rich sediment then no such boundary isevident. Fitzsimons (2006) argues that the glacierbed is more accurately viewed as a heterogeneouszone in which the lower boundary of glacier-induced flow is dependent on thermal and mecha-nical processes, and likely, therefore, to varyspatially and temporally.

Glaciologists have started to acknowledge thatcold-based glaciers can couple with frozen sub-strates (e.g. Echelmayer & Zhongxiang 1987;Cuffey et al. 2000). In addition, permafrostresearchers have identified evidence for the wide-spread and deep-seated deformation of permafrostin response to it being overridden by Pleistoceneice sheets (e.g. Astakhov et al. 1996; Murton et al.2004). Therefore, in the same way in whichglacial geologists have worked in close collabor-ation with glaciologists to constrain the mechanismsand glaciological significance of subglacial sedi-ment deformation beneath warm-based ice, closercollaboration between glaciologists working onmodern-day cold-based glaciers, and perma-frost researchers examining glacier–permafrost

interactions beneath former ice sheets, is requiredto fully understand the mechanisms of sedimententrainment and mobilization beneath cold-basedglaciers.

Frost heave, basal-ice formation and

ice-stream dynamics

Recent work on basal freezing and ice accretionbeneath ice streams (Christoffersen & Tulaczyk2003a, b) has already benefitted from the use ofexisting models of frost heave originally devisedby permafrost engineers. Their findings havemajor implications both for our understanding ofthe dynamic behaviour of ice streams (Bougamontet al. 2003) and the glaciological significance of dis-tinctive basal-ice facies (Christoffersen et al. 2006).

In comparing borehole observations from twoice streams of the West Antarctic Ice Sheet, theactive Whillans Ice Stream (formerly called IceStream B) and the slow-moving Kamb Ice Stream(formerly called Ice Stream C), Christoffersen &Tulaczyk (2003a) observed that the latter wascharacterized by: (1) comparatively steep basaltemperature gradients; (2) comparatively thicklayers of debris-rich basal ice approximately 12–25 m thick; (3) unfrozen till displaying supercooledtemperatures (up to 20.35 8C); and (4) a decrease intill porosity close to the ice–sediment interface.They hypothesized that whilst the rapid motion ofthe Whillans Ice Stream is promoted by activebasal melting and a reduction in effective pressureand shear strength within the subjacent till, the stag-nation of the Kamb Ice Stream was caused by basalfreeze-on and an associated consolidation andstrengthening of the subglacial till.

In attempting to develop a numerical, vertical-column model of the freezing process in such a situ-ation, Christoffersen & Tulaczyk (2003b, p. 2) notedthat ‘there is a paucity of theoretical and empiricalinvestigations of heat, water, and solute flowduring basal freeze-on’. As a result, recognizingthe general similarity of ice formed by basal freez-ing and by near-surface frost heave, the authors uti-lized theoretical treatments of frost heave originallydeveloped by permafrost engineers. In particular,they used the Clapeyron equation that provides ameans for coupling pressure and temperature in afreezing porous medium, and which provides thefundamental basis for frost-heave models (e.g.Fowler & Krantz 1994). In addition, whilst ice–water phase changes are often considered solely theresult of temperature and pressure, Christoffersen &Tulaczyk (2003b) also considered the roles playedby both solute concentration and interfacial effects.The latter are particularly important in fine-grainedporous media such as the clay-rich till sampled

PERMAFROST AND BASAL ICE 63

beneath the nearby Whillans Ice Stream (Tulaczyket al. 1998), in which the curvature of ice–waterinterfaces can lead to high interfacial pressures, asubstantial reduction in the freezing point and thepresence of supercooled water (e.g. Willliams &Smith 1989).

Christoffersen & Tulaczyk (2003b) providedmodel results for both high interfacial pressures(i.e. fine-grained till) and low interfacial pressures(i.e. coarse-grained till) under two hydrogeologicalsettings (closed- and open-water systems). In thecase of a closed-water system, freeze-on extractsporewater resulting in till consolidation, an increasein shear strength and a reduction in ice velocity. Forboth high and low interfacial pressures, till strengthmatches the driving stress after 65 years and the icestream shuts down. Subsequently, the freezing frontmigrates into the subglacial till causing further tillconsolidation and the development of segregatedice lenses, whose thickness and spacing are deter-mined by depth and by surface tension (i.e. particlesize). In the case of an open-water system, thetiming of ice-stream shutdown and the spacing ofice lenses are similar, although the individual icelenses are thicker and the degree of till consolidationis more limited.

The model’s prediction of the development ofintercalated layers of debris-rich ice (frozen till)and debris-poor ice (segregation ice) is consistentwith borehole observations of a debris-rich basalice layer 10–14 m thick described by Vogel et al.(2005). They described a basal-ice layer comprisingalternating layers of clear ice and debris-rich icelayers, with the thickness and sediment content ofdebris-rich layers generally increasing towards theice–sediment interface. A rapid transition fromrelatively clean ice to sediment-rich ice is arguedto reflect a change from abundant water availabilityto limited water availability, in turn associated witha shutdown of the Kamb Ice Stream approximately300 years ago. In addition, the presence ofdecimetre-thick layers of clear ice close to theice–sediment interface and a basal water layer isthought to suggest imminent ice-stream reactiva-tion, with a water supply in excess of that consumedby basal freeze-on leading to a relubrication ofthe bed.

Christoffersen et al. (2006) have subsequentlyused the same model to quantitatively define thedevelopment of four types of basal ice beneath soft-bedded glaciers whose formation is associated withsubglacial frost-heave processes and controlled bythe delivery of water to the freezing front. Clearice (type I) forms when the influx of watermatches or exceeds the freezing rate, such that theheat budget is satisfied with no extraction of waterfrom the underlying till. In the other three icetypes, a progressive reduction in the water supply

results in enhanced ice–bed coupling and debrisentrainment through regelation. Laminated ice(type II) is produced by periodic regelation eventsassociated with an influx of groundwater slightlylower than the freezing rate. Brief periods ofsoft-bed regelation entrain thin layers of debris-richice, whilst intervening longer periods of congelationentrain thicker layers of clear ice. Massive regela-tion ice (type III) is created when the influx ofwater is roughly half that required to satisfy thefreezing rate. Regelation events are still episodic,but the increase in effective pressure results in anincrease in the regelation rate and the thickness ofthe regelation ice layers, ultimately generating afacies of approximately 50% debris by volume.Finally, solid dirty regelation ice (type IV) isassociated with a closed system whereby all thewater is drawn from the till pore spaces. In thiscase, very little congelation ice is generated andthe effective stress increases rapidly, producing arapidly thickening regelation layer with a sedimentcontent of more than 60% by volume (i.e. lackingexcess ice). Rempel et al. (2007) identified someproblems with the modelling framework used byChristoffersen et al. (2006), notably concerningthe spatial distribution of ice saturation. Further dis-cussion on this topic is given by Christoffersenet al. (2007).

The origin of massive ice in glaciated

permafrost terrains

Massive ice within glaciated permafrost terrains hasusually been interpreted either as buried glacier iceor as intrasedimental ice formed in subaerial perma-frost regions. Distinguishing between them is funda-mental to understanding the interactions betweenglaciers and permafrost, and the characteristicsand behaviour of former ice sheets. However,interpretation of massive ice has often been proble-matic (Vtyurin & Glazovskiy 1986; French & Harry1990) because intrasedimental ice is difficult to dis-tinguish from basal glacier ice, since both ice typesform by the same freezing processes operating inporous media (cf. Mackay 1989; Rempel 2008)and, therefore, display similar physical and chemi-cal properties. Indeed, it seems increasingly likelythat the only real distinction between them isspatial, rather than genetic, because massive icecan form within sedimentary sequences (i.e. intrase-dimentally) beneath, at the margin or in front of gla-ciers, or in permafrost regions unrelated to glacialactivity. Thus, the more useful distinctionsamongst massive-ice occurrences in permafrostregions are between: (1) subglacial or submarginalice (e.g. Murton et al. 2005); (2) proglacial ice(e.g. Lacelle et al. 2004); and (3) non-glacial ice

R. I. WALLER ET AL.64

(e.g. Lawson 1983). The lack of a clear genetic dis-tinction between basal glacier ice and massive intra-sedimental ice may also explain why rigoroushypothesis testing to discriminate them has proveddifficult. Instead, the genetic discrimination isclearer between firnified glacier ice and other icetypes (Cardyn et al. 2007; Lacelle et al. 2007).

An example of a collaborative research pro-gramme bringing together glaciologists and perma-frost scientists in order to interpret the origin andspatial significance of massive ice has been carriedout in the Tuktoyaktuk Coastlands of westernArctic Canada (Murton et al. 2004, 2005). Heremany exposures of massive ice and icy sedimentsat former ice-marginal sites of the Laurentide IceSheet (LIS) contain features characteristic of bothso-called basal and intrasedimental ice. Basal-icefeatures comprise: (1) ice facies and facies group-ings similar to those from the basal-ice layers ofcontemporary glaciers and ice sheets in Alaska,Greenland and Iceland (Fig. 3); (2) ice-crystalfabrics similar to those from basal ice in Antarcticaand ice-cored moraines on Axel Heiberg Island,Canada; and (3) a thaw or erosional unconformityalong the top of the massive ice and icy sediments,buried by glacigenic or aeolian sediments. Intrasedi-mental ice consists of pore ice and segregated iceformed within Pleistocene sands deposited beforeglacial overriding.

The co-existence of basal and intrasedimentalice within massive ice and icy sediments suggeststhat they formed within the basal ice layer of theLIS. This layer is thought to have developed byaccretion of both new and existing ice, its formativemechanisms including: (a) large-scale freeze-on ofmeltwater and sediment at the transition fromwarm- to cold-based ice; (b) permafrost aggradationbeneath thinning, stagnant basal ice; and (c) pore-water expulsion in ice-free areas prior to glacialoverriding. Stagnation of the ice sheet andmelt-out of till from the ice surface allowed burialand preservation of the basal-ice layer on a regionalscale in the Tuktoyaktuk Coastlands. At other sitesclose to but within the Laurentide ice limit, buriedglacier ice beneath frozen glacitectonite that con-tains subglacially eroded clasts of ground ice indi-cates that near-surface permafrost did not degradebeneath some parts of the ice margin (cf. Mackayet al. 1972; Mackay & Matthews 1983; Rampton1988b). Interestingly, permafrost has also beeninferred beneath the margin of Pleistocene icesheets in Europe (Haeberli 1981).

To integrate all of the studies of massive icein the Tuktoyaktuk Coastlands, a two-stage modelof ground-ice development has been proposedbased on the cryostratigraphic distinction of twogenerations of ground ice: pre- and post-deformation ice (Murton 2005). Pre-deformation

ice was glacially deformed or eroded beneath thecold-based margin of the LIS during MarineIsotope Stage 2 (Murton et al. 2007), and comprises:(1) buried basal ice; (2) massive segregated ice; and(3) ice clasts subglacially eroded from pre-existingground ice. In contrast, post-deformation ice hasnot been glacially disturbed because it formedduring or after deglaciation, and includes; (4)dykes and sills of intrusive ice; (5) massive segre-gated intrusive ice; (6) ice wedges and compositewedges; (7) segregated ice; and (8) pool ice. Thesuperimposition of post-deformation ice into perma-frost containing older, pre-deformation ice indicatesthat substantial quantities of overpressurized waterwere injected into ice-marginal permafrost duringor after deglaciation. The required external watersource for the post-deformation intrusive ice wasprobably overpressurized subpermafrost ground-water in front of the retreating margin of the LIS.Injection of this water into proglacial permafrosthydraulically fractured the permafrost and formedice dykes, ice sills and massive segregated intrusiveice. This model may have wider application to thedevelopment of massive ice wherever ice sheetsadvanced and retreated across lowland regions ofcontinuous permafrost.

Current problems

A number of problems currently act as barriers tomore effective collaboration between the glaciolo-gical and permafrost research communities. Oneof the most fundamental problems involves the con-trasting nature of the schemes employed to describeand classify ice–sediment mixtures. With the classi-fication schemes used within basal ice (e.g. Lawson1979; Sharp et al. 1994) and permafrost research(e.g. Murton & French 1994; Shur & Jorgenson1998) involving different parameters (e.g. volu-metric ice content, particle size, ice-crystal size,bubble content, distribution of ice and sediment,etc.), it is currently difficult to translate betweenthe resulting classifications. The resolution of thisproblem through the development of a more com-parable classification scheme appears straightfor-ward in theory but may prove harder to achieve inpractice. Within the field of basal-ice research, forexample, despite concerns that ‘any attempt tocompare field descriptions from different publi-cations is hampered by a babel of classifications asdiverse as the number of workers in the field’(Knight 1993, p. 352), there is still no universallyaccepted classification scheme (see howeverHubbard et al. in press). Until this situation isresolved through deliberate and determined collab-oration between the two communities, any attemptto compare massive-ice facies with basal-ice

PERMAFROST AND BASAL ICE 65

facies as a starting point when determining theorigin of massive ice will continue to proveproblematic.

An additional concern involves the contrastingfoci of researchers within the two communities.Whilst glaciologists are principally concerned withprocesses and their products, permafrost scientistsare often required to carefully examine the lithostra-tigraphic and cryostratigraphic context of the ice–sediment mixture being studied. Identification ofthe origin of massive ice, for example, ofteninvolves the resolution of problematic stratigraphicissues such as dating and facies correlation (e.g.Harry et al. 1988). The requirement to engagewith such issues may deter the active involvementof some glaciologists.

Future research possibilities

Powerful incentives to overcome these problems arethe future research possibilities offered by the rem-nants of ice sheets buried in Arctic and Antarcticpermafrost. Such remnants are thought to be wide-spread in, for example, western Siberia (e.g.Kaplyanskaya & Tarnogradskiy 1986), northernEuropean Russia (Henriksen et al. 2003), thewestern Canadian Arctic (Dyke & Savelle 2000;Dyke & Evans 2003) and East Antarctica (Sugdenet al. 1995). If these ice masses can be reliably dis-tinguished from non-glacial ice types, then theseproducts of ‘incomplete’ or ‘retarded’ deglaciationprovide a palaeoglaciological archive of immensevalue. For example, Grosvald et al. (1986) estimatedthat approximately 10 000 km3 of relict glacier iceremains preserved within western Siberia alone.Whilst this is likely to represent an overestimate,even if only a fraction of this is related to Pleisto-cene ice sheets then its detailed investigation stillhas the potential to revolutionize our knowledgeand understanding of the stratigraphy, physicalproperties and dynamic behaviour of continentalice sheets within high-latitude regions. Grosvaldet al. (1986) consequently argued that this iceshould be the subject of special glaciologicalstudies. Such an invitation is particularly pressingin the twenty first century as the dramatic rise intemperatures within the Arctic threatens the lossof this archive before its importance was everappreciated.

Conclusions

It is clear that there are a variety of interdisciplinaryresearch problems within glacial and permafrostenvironments, whose resolution requires greatercollaboration between glaciologists and permafrostresearchers. Whilst such interdisciplinary research

has to date been rather limited, the examples dis-cussed earlier illustrate the benefits that such anapproach could bring to both disciplines. In particu-lar, the application of frost-heave models to subgla-cial settings in order to elucidate the influence of iceaccretion on till properties and the flow of icestreams has potentially major implications for ourunderstanding of the dynamic behaviour of icesheets.

Greater co-operation is also required to examinethe nature of glacier–permafrost interactionsbeneath cold-based, soft-bedded glaciers. Whilstglaciologists working on modern-day glaciers havetraditionally assumed that basal processes cease tooperate at temperatures below the pressure meltingpoint, permafrost researchers have long recognizedthe ability of both sediments to retain liquid waterat subfreezing temperatures and of glaciers toactively couple with permafrost. Further examin-ation of the operation of these processes in bothpast and present subglacial environments is requiredto evaluate their potential influence on glacier flowand sediment transport.

There are some obstacles to effective collabor-ation that need to be targeted and resolved beforereal progress can be made. The resolution of suchproblems, however, has the potential to generate awide range of new research possibilities. The mostobvious includes the development of an ice–sediment-classification scheme that will allowdetailed comparisons to be made between the icefacies observed at modern-day glaciers with thoseobserved in exposures of massive ice. This wouldgreatly assist in the accurate identification of buriedglacier ice with permafrost environments which, byunlocking a new palaeoglaciological archive, couldrevolutionize our understanding of past ice sheets.

The authors gratefully acknowledge the financial andlogistical support that enabled a series of field expeditionsto the western Canadian Arctic and Greenland where theseideas were developed. Financial support was provided bythe University of Greenwich (RW), the LeverhulmeTrust (PGK & JM), the Tyrell Fund of the GeologicalSociety (JM) and the Royal Society (RW & PGK). Theauthors would also like to thank the referees (S. Harrisonand one anonymous) for helpful comments that led to sub-stantial improvements to this review.

References

ALLEY, R. B., LAWSON, D. E., EVENSON, E. B.,STRASSER, J. C. & LARSON, G. J. 1998. Glacio-hydraulic supercooling: a freeze-on mechanism tocreate stratified, debris-rich basal ice. II. Theory.Journal of Glaciology, 44, 563–569.

ALLEY, R. B., LAWSON, D. E., LARSON, G. J., EVENSON,E. B. & BAKER, G. S. 2003. Stabilizing feedbacks inglacier-bed erosion. Nature, 424, 758–760.

R. I. WALLER ET AL.66

ARCONE, S. A., LAWSON, D. E. & DELANEY, A. J. 1995.Short-pulse wavelet recovery and resolution ofdielectric constants within englacial and basal ice ofMatanuska Glacier, Alaska, U.S.A. Journal of Glaciol-ogy, 41, 68–86.

ASTAKHOV, V. I. & ISAYEVA, L. L. 1988. The ‘Ice Hill’:an example of ‘retarded deglaciation’ in Siberia.Quaternary Science Reviews, 7, 29–40.

ASTAKHOV, V. I., KAPLYANSKAYA, F. A. & TARNO-

GRADSKIY, V. D. 1996. Pleistocene permafrost ofWest Siberia as a deformable glacier bed. Permafrostand Periglacial Processes, 7, 165–191.

BOUGAMONT, M., TULACZYK, S. & JOUGHIN, I. 2003.Response of subglacial sediments to basal freeze-on2. Application in numerical modeling of the recentstoppage of Ice Stream C, West Antarctica. Journal ofGeophysical Research, 108(B4), 2223, doi: 10.1029/2002JB001936.

BOULTON, G. S. 1970. On the origin and transport of eng-lacial debris in Svalbard glaciers. Journal of Glacio-logy, 9, 213–229.

CARDYN, R., CLARK, I. D., LACELLE, D., LAURIOL, B.,ZDANOWICZ, C. M. & CALMELS, F. 2007. Molar gasratios of air entrapped in ice: a new tool to determinethe nature and origin of relict massive ground-icebodies in permafrost. Quaternary Research, 68,239–248.

CHRISTOFFERSEN, P. & TULACZYK, S. 2003a. Thermo-dynamics of basal freeze-on: predicting basal andsubglacial signatures of stopped ice streams and inter-stream ridges. Annals of Glaciology, 36, 233–243.

CHRISTOFFERSEN, P. & TULACZYK, S. 2003b. Responseof subglacial sediments to basal freeze-on. 1. Theoryand comparison to observations from beneath the WestAntarctic Ice Sheet. Journal of Geophysical Research,108(B4), 2222, doi: 10.1029/2002JB001935.

CHRISTOFFERSEN, P., TULACZYK, S., CARSEY, F. D. &BEHAR, A. E. 2006. A quantitative framework forinterpretation of basal ice facies formed by ice accre-tion over subglacial sediment. Journal of GeophysicalResearch, 111, F01017, doi: 10.1029/2005JF000363.

CHRISTOFFERSEN, P., TULACZYK, S., BEHAR, A. &CARSEY, F. 2007. Reply to comment byA. W. Rempel et al. on ‘A quantitative frameworkfor interpretation of basal ice facies formed by iceaccretion over subglacial sediment’. Journal ofGeophysical Research, 112, F02037, doi: 10.1029/2006JF000732.

COOK, S. J., KNIGHT, P. G., WALLER, R. I., ROBINSON,Z. P. & ADAM, W. G. 2007. The geography of basal iceand its relationship to glaciohydraulic supercooling:Svınafellsjokull, southeast Iceland. QuaternaryScience Reviews, 26, 2309–2315.

COOK, S. J., WALLER, R. I. & KNIGHT, P. G. 2006. Gla-ciohydraulic supercooling: the process and itssignificance. Progress in Physical Geography, 30,577–588.

CUFFEY, K. M., CONWAY, H. ET AL. 2000. Entrainment atcold glacier beds. Geology, 28, 351–354.

DALLIMORE, S. R. & DAVIS, J. L. 1992. Ground Pene-trating Radar Investigations of Massive Ice. Geologi-cal Survey of Canada, Paper, 90-4, 41–48.

DYKE, A. S. & EVANS, D. J. A. 2003. Ice-marginal terres-trial landsystems: northern Laurentide and Innuitian

ice sheet margins. In: EVANS, D. J. A. (ed.) GlacialLandsystems. Arnold, London, 143–165.

DYKE, A. S. & SAVELLE, J. M. 2000. Major end morainesof Younger Dryas age on Wollaston Peninsula, Vic-toria Island, Canadian Arctic: implications for paleo-climate and for formation of hummocky moraine.Canadian Journal of Earth Sciences, 37, 601–619.

ECHELMEYER, K. & ZHONGXIANG, W. 1987. Directobservation of basal sliding and deformation of basaldrift at subfreezing temperatures. Journal of Glacio-logy, 33, 83–98.

EVANS, D. J. A. 1989. Apron entrainment at the marginsof sub-polar glaciers, North-west Ellesmere Island,Canadian High Arctic. Journal of Glaciology, 35,317–324.

EVEREST, J. & BRADWELL, T. 2002. Buried glacier ice insouthern Iceland and its wider significance. Geomor-phology, 52, 347–358.

FITZSIMONS, S. J. 2006. Mechanical behaviour and struc-ture of the debris-rich basal ice layer. In: KNIGHT,P. G. (ed.) Glacier Science & EnvironmentalChange. Blackwell, Oxford, 329–335.

FITZSIMONS, S. J., MCMANUS, K. J. & LORRAIN, R. D.1999. Structure and strength of basal ice and substrateof a dry-based glacier: evidence for substrate defor-mation at sub-freezing temperatures. Annals of Gla-ciology, 28, 236–240.

FOWLER, A. C. & KRANTZ, W. B. 1994. A generalizedsecondary frost heave model SIAM. Journal ofApplied Mathematics, 54, 1650–1675.

FRENCH, H. M. 2007. The Periglacial Environment, 3rdedn. Wiley, Chichester.

FRENCH, H. M. & HARRY, D. G. 1988. Nature and originof ground ice, Sandhills Moraine, southwest BanksIsland, Western Canadian Arctic. Journal of Quatern-ary Science, 3, 19–30.

FRENCH, H. M. & HARRY, D. G. 1990. Observations onburied glacier ice and massive segregated ice,Western Arctic Coast, Canada. Permafrost and Peri-glacial Processes, 1, 31–44.

GOLDTHWAIT, R. P. 1951. Development of end morainesin east-central Baffin Island. Journal of Geology, 59,567–577.

GROSVALD, M. G., VTYURIN, B. I., SUKHODROVSKIY,V. L. & SHISHORINA, Z. G. 1986. Undergroundice in western Siberia: origin and geologicalsignificance. Polar Geography and Geology, 10,173–183.

HAEBERLI, W. 1981. Ice motion on deformable sedi-ments. Journal of Glaciology, 27, 365–366.

HARRIS, C. & MURTON, J. B. (eds). 2005. CryosphericSystems: Glaciers and Permafrost. GeologicalSociety, London, Special Publications, 242.

HARRIS, S. A., FRENCH, H. M., HEGINBOTTOM, J. A.,JOHNSTON, G. H., LADANYI, B., SEGO, D. A. &VAN EVERDINGEN, R. O. 1988. Glossary of Perma-frost and Related Ground-ice Terms. PermafrostSubcomittee on Geotechnical Research, NationalResearch Council of Canada, Ottawa, TechnicalMemorandum, 142.

HARRY, D. G., FRENCH, H. M. & POLLARD, W. H. 1988.Massive ground ice and ice-cored terrain near SabinePoint, Yukon Coastal Plain. Canadian Journal ofEarth Sciences, 25, 1846–1856.

PERMAFROST AND BASAL ICE 67

HENRIKSEN, M., MANGERUD, J., MATIOUCHKOV, A.,PAUS, A. & SVENDSEN, J. I. 2003. Lake stratigraphyimplies an 80 000 yr delayed melting of buried deadice in northern Russia. Journal of QuaternaryScience, 18, 663–679.

HUBBARD, B. & SHARP, M. J. 1989. Basal ice formationand deformation: a review. Progress in PhysicalGeography, 13, 529–558.

HUBBARD, B. & SHARP, M. J. 1995. Basal ice facies andtheir formation in the Western Alps. Arctic and AlpineResearch, 27, 301–310.

HUBBARD, B., COOK, S. & COULSON, H. in press.Basal ice facies: a review and unifying approach. Qua-ternary Science Reviews, doi: 10.1016/j.quascirev.2009.03.005.

IVERSON, N. R. & SEMMENS, D. J. 1995. Intrusion of iceinto porous media by regelation: mechanism of sedi-ment entrainment by glaciers. Journal of GeophysicalResearch, 100(B7), 10,219–10,230.

IVERSON, N. R., HOOYER, T. S. ET AL. 2007. Soft-bedexperiments beneath Engabreen, Norway: regelationinfiltration, basal slip and bed deformation. Journalof Glaciology, 53, 323–340.

KAMB, B. & LA CHAPPELLE, E. 1964. Direct obser-vations of the mechanism of glacier sliding overbedrock. Journal of Glaciology, 5, 159–172.

KAPLYANSKAYA, F. A. & TARNOGRADSKIY, V. D.1986. Remnants of the Pleistocene ice sheets in thepermafrost zone as an object for paleoglaciologicalresearch. Polar Geography and Geology, 10, 257–266.

KNEISEL, C., HAUCK, C., FORTIER, R. & MOORMAN, B.2008. Advances in geophysical methods for permafrostinvestigations. Permafrost and Periglacial Processes,19, 157–178.

KNIGHT, P. G. 1988. The basal ice and debris sequence atthe margin of an equatorial ice-cap; El Cotopaxi,Ecuador. Geografiska Annaler, 70A, 9–13.

KNIGHT, P. G. 1989. Stacking of basal debris layerswithout bulk freezing-on: isotopic evidence fromWest Greenland. Journal of Glaciology, 35, 214–216.

KNIGHT, P. G. 1993. Glaciers (progress report). Progressin Physical Geography, 17, 349–353.

KNIGHT, P. G. 1997. The basal ice layer of glaciers and icesheets. Quaternary Science Reviews, 16, 975–993.

KNIGHT, P. G., SUGDEN, D. E. & MINTY, C. D. 1994. Iceflow around large obstacles as indicated by basal iceexposed at the margin of the Greenland ice sheet.Journal of Glaciology, 40, 359–367.

KNIGHT, P. G., WALLER, R. I., PATTERSON, C. J.,JONES, A. P. & ROBINSON, Z. P. 2000. Glacieradvance, ice-marginal lakes and routing of meltwaterand sediment: Russell Glacier, Greenland. Journal ofGlaciology, 46, 423–426.

LACELLE, D., BOJORNSON, J., LAURIOL, B., CLARK,I.D. & TROUTET, Y. 2004. Segregated-intrusive iceof subglacial meltwater origin in retrogressive thawflow headwalls, Richardson Mountains, NWT,Canada. Quaternary Science Reviews, 23, 681–696.

LACELLE, D., LAURIOL, B., CLARK, I. D., CARDYN, R.& ZDANOWICZ, C. 2007. Nature and origin of aPleistocene-age massive ground-ice body exposed inthe Chapman Lake moraine complex, central YukonTerritory, Canada. Quaternary Research, 68,249–260.

LAWSON, D. E. 1979. Sedimentological Analysis of theWestern Terminus Region of the Matanuska Glacier,Alaska. US Army, Cold Regions Research and Engin-eering Laboratory, Report, 79-9.

LAWSON, D. E. 1983. Ground ice in perennially frozensediments, Northern Alaska. In: Permafrost: FourthInternational Conference, Proceedings, Fairbanks,Alaska. National Academy Press, Washington, DC,695–700.

LAWSON, D. E., STRASSER, J. C., EVENSON, E. B.,ALLEY, R. B., LARSON, G. J. & ARCONE, S. A.1998. Glaciohydraulic supercooling:a freeze-on mech-anism to create stratified, debris-rich basal ice: I. Fieldevidence. Journal of Glaciology, 44, 547–562.

LAWSON, W. 1996. The relative strengths of debris-ladenbasal ice and clean glacier ice: some evidence fromTaylor Glacier, Antarctica. Annals of Glaciology, 23,270–276.

LORRAIN, R. D. & DEMEUR, P. 1985. Isotopic evidencefor relic Pleistocene glacier ice on Victoria Island,Canadian Arctic archipelago. Arctic & AlpineResearch, 17, 89–98.

MACKAY, J. R. 1971. The origin of massive icy beds inpermafrost, western Arctic Coast, Canada. CanadianJournal of Earth Sciences, 8, 397–422.

MACKAY, J. R. 1989. Massive ice: some field criteria forthe identification of ice types. Current Research,Part G, Geological Survey of Canada, Paper, 89-1G,5–11.

MACKAY, J. R. & DALLIMORE, S. R. 1992. Massive ice ofthe Tuktoyaktuk area, western Arctic coast, Canada.Canadian Journal of Earth Science, 29, 1235–1249.

MACKAY, J. R. & MATTHEWS, J. V. 1983. Pleistocene iceand sand wedges, Hooper Island, Northwest Terri-tories. Canadian Journal of Earth Sciences, 20,1087–1097.

MACKAY, J. R., RAMPTON, V. N. & FYLES, J. G. 1972.Relic Pleistocene permafrost, Western Arctic,Canada. Science, 176, 1321–1323.

MATHEWS, W. H. & MACKAY, J. R. 1960. Deformationof soils by glacier ice and the influence of pore press-ures and permafrost. Transactions of the RoyalSociety of Canada, 54, 27–36.

MURRAY, T. & PORTER, P. R. 2001. Basal conditionsbeneath a soft-bedded polythermal surge-type glacier:Bakaninbreen, Svalbard. Quaternary International,86, 103–116.

MURTON, J. B. 2005. Ground-ice stratigraphy and for-mation at North Head, Tuktoyaktuk Coastlands,western Arctic Canada: a product of glacier–permafrost interactions. Permafrost and PeriglacialProcesses, 16, 31–50.

MURTON, J. B. & FRENCH, H. M. 1994. Cryostructures inpermafrost, Tuktoyaktuk Coastlands, Western ArcticCanada. Canadian Journal of Earth Sciences, 31,737–747.

MURTON, J. B., FRECHEN, M. & MADDY, D. 2007. Lumi-nescence dating of Mid to Late Wisconsinan aeoliansand as a constraint on the last advance of the Lauren-tide Ice Sheet across the Tuktoyaktuk Coastlands,western Arctic Canada. Canadian Journal of EarthSciences, 44, 857–869.

MURTON, J. B., WALLER, R. I., HART, J. K., WHITEMAN,C. A., POLLARD, W. & DALLIMORE, S. R. 2004.

R. I. WALLER ET AL.68

Stratigraphy and glaciotectonic structures of perma-frost deformed beneath the northwest margin of theLaurentide ice sheet, Tuktoyaktuk Coastlands,Canada. Journal of Glaciology, 50, 399–412.

MURTON, J. B., WHITEMAN, C. A., WALLER, R. l.,POLLARD, W. & DALLIMORE, S. R. 2005. Basal icefacies and supraglacial melt-out till of the LaurentideIce Sheet, Tuktoyaktuk Coastlands, western CanadianArctic. Quaternary Science Reviews, 24, 681–708.

PHILIP, J. R. 1980. Thermal fields during regelation. ColdRegions Science & Technology, 3, 193–203.

RAMPTON, V. N. 1988a. Origin of massive ground ice onTuktoyaktuk Peninsula, Northwest Territories,Canada: a review of stratigraphic and geomorphic evi-dence. In: SENNESET, K. (ed.) Proceedings of the 5thInternational Conference on Permafrost, 2–5 August1988, Trondheim, Norway, Volume 1. Tapir, Trond-heim, 850–855.

RAMPTON, V. N. 1988b. Quaternary Geology of theTuktoyaktuk Coastlands, Northwest Territories. Geo-logical Survey of Canada.

RAMPTON, V. N. 1991. Observations on buried glacier iceand massive segregated ice, Western Arctic Coast:Discussion (Short Communication). Permafrost andPeriglacial Processes, 2, 163–165.

REA, B. R. & WHALLEY, W. B. 1994. Subglacial obser-vations from Oksfjordjokelen. Earth Surface Pro-cesses and Landforms, 19, 659–673.

REMPEL, A. W. 2007. Formation of ice lenses and frostheave. Journal of Geophysical Research, 112,pF02S21, doi: 10.1029/2006JF000525.

REMPEL, A. W. 2008. A theory for ice-till interactions andsediment entrainment beneath glaciers. Journal ofGeophysical Research, 113, F01013, doi: 10.1029/2007JF000870.

REMPEL, A. W., WETTLAUFER, J. S. & WORSTER, M. G.2007. Comment on ‘A quantitative framework forinterpretation of basal ice facies formed by ice accre-tion over subglacial sediment’ by Poul Christoffersenet al. Journal of Geophysical Research, 112, F02036,doi: 10.1029/2006JF000701.

ROBERTS, M. J., TWEED, F. S. ET AL. 2002. Glaciohydrau-lic supercooling in Iceland. Geology, 30, 439–442.

ROTHLISBERGER, H. 1968. Erosive processes which arelikely to accentuate or reduce the bottom relief ofvalley glaciers. International Association of Hydrolo-gical Sciences Publication, 79, 87–97.

SHARP, M. J., JOUZEL, J., HUBBARD, B. & LAWSON, W.1994. The character, structure and origin of the basalice layer of a surge-type glacier. Journal of Glaciology,40, 327–340.

SHAW, J. 1977. Till body morphology and structure relatedto glacier flow. Boreas, 6, 189–201.

SHUR, Y. L. & JORGENSON, M. T. 1998. Cryostructuredevelopment on the floodplain of the Colville Riverdelta, northern Alaska. In: LEWKOWICZ, A. G. &ALLARD, M. (eds) Proceedings of the 7th InternationalPermafrost Conference, Yellowknife, Canada, 23–27

June 1998. Collection Nordicana, Centre d’etudesnordiques, Universite Laval, 993–999.

SUGDEN, D. E., KNIGHT, P. G., LIVESEY, N., LORRAIN,R. D., SOUCHEZ, R. A., TISON, J. L. & JOUZEL, J.1987. Evidence for two zones of debris entrainmentbeneath the Greenland ice sheet. Nature, 328,238–241.

SUGDEN, D. E., MARCHANT, D. R., POTTER, N., JR,SOUCHEZ, R. A., DENTON, G. H., SWISHER, C. C.III, & TISON, J. L. 1995. Preservation of Mioceneglacier ice in East Antarctica. Nature, 376, 412–414.

SWIFT, D. A., EVANS, D. J. A. & FALLICK, A. E. 2006.Tranverse englacial debris-rich ice bands at Kvıarjo-kull, southeast Iceland. Quaternary Science Reviews,25, 1708–1718.

TISON, J. L., PETIT, J. R., BARNOLA, J. M. & MAHANEY,W. C. 1993. Debris entrainment at the ice–bedrockinterface in sub-freezing temperature conditions(Terre Adelie, Antarctica). Journal of Glaciology, 39,303–315.

TULACZYK, S., KAMB, B., SCHERER, R. P. & ENGEL-

HARDT, H. F. 1998. Sedimentary processes at thebase of a West Antarctic ice stream: constraints fromtextural and compositional properties of subglacialdebris. Journal of Sedimentary Research, 68,487–496.

VAN TATENHOVE, F. G. M. 1995. The Dynamics of Holo-cene Deglaciation in West Greenland with Emphasison Recent Ice-marginal Processes. PhD thesis, Univer-siteit van Amsterdam.

VOGEL, S. W., TULACZYK, S. ET AL. 2005. Subglacialconditions during and after stoppage of an AntarcticIce Stream: Is reactivation imminent? GeophysicalResearch Letters, 32, L14502, doi: 10.1029/2005GL022563.

VTYURIN, B. I. & GLAZOVSKIY, A. F. 1986. Compositionand structure of the Ledyanaya Gora tabular ground icebody on the Yenisey. Polar Geography and Geology,10, 273–285.

WALLER, R. I. 2001. The influence of basal processes onthe dynamic behaviour of cold-based glaciers. Qua-ternary International, 86, 117–128.

WALLER, R. I., HART, J. K. & KNIGHT, P. G. 2000. Theinfluence of tectonic deformation on facies variabilityin stratified debris-rich basal ice. Quaternary ScienceReviews, 19, 775–786.

WEERTMAN, J. 1957. On the sliding of glaciers. Journal ofGlaciology, 3, 33–38.

WEERTMAN, J. 1961. Mechanism for the formation ofinner moraines found near the edge of cold ice capsand ice sheets. Journal of Glaciology, 3, 965–978.

WILLIAMS, P. J. & SMITH, M. V. 1989. The FrozenEarth: Fundamentals of Geocryology. CambridgeUniversity Press, Cambridge.

ZDANOWICZ, C. M., MICHEL, F. A. & SHILTS, W. W.1996. Basal debris entrainment and transport in gla-ciers of southwestern Bylot Island, Canadian Arctic.Annals of Glaciology, 22, 107–113.

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