Englacial Debris Research Articles

Studies on the Basal-Ice Zone of Findelen Glacier, Switzerland

Basal and englacial debris layers have been observed to coincide distinctly with the location of glacier thrust planes or shear zones, e.g. at Shoestring Glacier (Brugman and Meier 1980) and Variegated Glacier (Kamb and others 1985). They are also evident at Findelen Glacier. Field observations strongly suggest that the mechanics of debris-laden ice can be important for understanding the flow response of certain glaciers. In this paper the material properties of basal ice at Findelen Glacier are examined, as studied with the aid of ice-core drilling techniques.Ice cores were taken from near the center line of Findelen Glacier during the summer of 1985, for the express purpose of characterizing the basal ice in terms of observed structures, composition and rheology. Related studies were simultaneously performed on bore-hole and surface strain-rate deformation (Iken and others, unpublished) and bore-hole resistivity (Schütz and Röthlisberger 1985). The ice core, retrieved from the deepest level possible (approximately 4 m above the bed), contained only a minor amount of fine rock debris. The presence of a debris-containing basal-ice zone is strongly suggested by the evidence that further hot-water drilling in the bore holes resulted in abraded drill stems and in the irregular progress of the drill for the few remaining meters to the glacier bed. Therefore, during 1986 samples of debris-laden basal ice were taken from several locations where the basal material was clearly exposed along lateral ice cliffs in the ablation area of the glacier.Three distinct types of ice at Findelen Glacier were compared: clean bubbly coarse-grained ice taken from above the glacier bed, clean clear coarse-grained ice taken from within a few meters of the glacier bed at center line (170 m depth), and debris-laden ice taken from the glacier bed at the lateral margin. Uniaxial compression experiments were conducted on the glacier-ice samples, using the triaxial testing apparatus of the 1GB at ETH-Höngerberg. Laboratory studies of ice deformation were carried out under the guidance of A. Hofer, P. Hertzog and Professor Huder of IGB. Sample temperature, volume and strain-rate were monitored throughout each experiment. The confining pressure of each experiment was set at 4 bars (1 bar = 100 kPa). The deviatoric stresses applied were 1, 2 and 4 bars, and testing temperatures were set at –1.5, -0.8 and –0.4°C for each type of ice sampled (clean bubbly, clean clear, and debris-laden).Preliminary results from experiments conducted on the clean bubbly and clean clear ice indicate that the mechanical behavior of the main bulk of the glacier is well represented by a power-law creep relationship with an exponent of about 4. This value is in close agreement with independent results obtained from bore-hole–tilt studies (Iken and others, unpublished) and within the range of values cited in the published literature (Paterson 1983). The pre-exponential factor is not well represented by an Arrhenius-type relationship, and enhanced deformation is indicated for samples tested nearest the melting point. Additional laboratory and field studies on the ice-crystal fabrics and the behavior of the debris-laden ice are still in progress. In this paper the results of these investigations are discussed, with special emphasis on information gained from the ice-core drilling studies.

Localised Enhanced Sedimentation from Icebergs in a Proglacial Lake in Briksdal, Norway

Studies of the ice-contact proglacial Briksdal Lake in Norway have demonstrated that drifting icebergs congregate in a well-defined zone near the outlet. Deposition of the englacial debris from decaying icebergs is concentrated within this area forming a shallow underwater shelf and associated beach. It is suggested that this process may have characterized former proglacial lakes.

Studies on the Basal-Ice Zone of Findelen Glacier, Switzerland

Basal and englacial debris layers have been observed to coincide distinctly with the location of glacier thrust planes or shear zones, e.g. at Shoestring Glacier (Brugman and Meier 1980) and Variegated Glacier (Kamb and others 1985). They are also evident at Findelen Glacier. Field observations strongly suggest that the mechanics of debris-laden ice can be important for understanding the flow response of certain glaciers. In this paper the material properties of basal ice at Findelen Glacier are examined, as studied with the aid of ice-core drilling techniques. Ice cores were taken from near the center line of Findelen Glacier during the summer of 1985, for the express purpose of characterizing the basal ice in terms of observed structures, composition and rheology. Related studies were simultaneously performed on bore-hole and surface strain-rate deformation (Iken and others, unpublished) and bore-hole resistivity (Schütz and Rõthlisberger 1985). The ice core, retrieved from the deepest level possible (approximately 4 m above the bed), contained only a minor amount of fine rock debris. The presence of a debris-containing basal-ice zone is strongly suggested by the evidence that further hot-water drilling in the bore holes resulted in abraded drill stems and in the irregular progress of the drill for the few remaining meters to the glacier bed. Therefore, during 1986 samples of debris-laden basal ice were taken from several locations where the basal material was clearly exposed along lateral ice cliffs in the ablation area of the glacier. Three distinct types of ice at Findelen Glacier were compared: clean bubbly coarse-grained ice taken from above the glacier bed, clean clear coarse-grained ice taken from within a few meters of the glacier bed at center line (170 m depth), and debris-laden ice taken from the glacier bed at the lateral margin. Uniaxial compression experiments were conducted on the glacier-ice samples, using the triaxial testing apparatus of the 1GB at ETH-Höngerberg. Laboratory studies of ice deformation were carried out under the guidance of A. Hofer, P. Hertzog and Professor Huder of IGB. Sample temperature, volume and strain-rate were monitored throughout each experiment. The confining pressure of each experiment was set at 4 bars (1 bar = 100 kPa). The deviatone stresses applied were 1, 2 and 4 bars, and testing temperatures were set at –1.5, -0.8 and –0.4°C for each type of ice sampled (clean bubbly, clean clear, and debris-laden). Preliminary results from experiments conducted on the clean bubbly and clean clear ice indicate that the mechanical behavior of the main bulk of the glacier is well represented by a power-law creep relationship with an exponent of about 4. This value is in close agreement with independent results obtained from bore-hole–tilt studies (Iken and others, unpublished) and within the range of values cited in the published literature (Paterson 1983). The pre-exponential factor is not well represented by an Arrhenius-type relationship, and enhanced deformation is indicated for samples tested nearest the melting point. Additional laboratory and field studies on the ice-crystal fabrics and the behavior of the debris-laden ice are still in progress. In this paper the results of these investigations are discussed, with special emphasis on information gained from the ice-core drilling studies.

Mapping Recent Fluctuations of Shoestring Glacier, Mount St. Helens (Abstract)

Mapping Recent Fluctuations of Shoestring Glacier, Mount St. Helens (Abstract)

Mapping Recent Fluctuations of Shoestring Glacier, Mount St. Helens (Abstract)

Mapping Recent Fluctuations of Shoestring Glacier, Mount St. Helens (Abstract)

Compositional variability of Saalian till in The Netherlands and its origin

Variations in composition between and within Saalian till types of The Netherlands are demonstrated with reference to grain‐size distribution, fine‐gravel petrography and heavy‐mineral composition. Several factors explain different aspects of the compositional variations. Firstly, a compositional layering results from differences in the amount of local material that has been assimilated in successive till hands. Secondly, a petrographic stratification is present in the erratic components, which is most strikingly expressed by the occurrence of flint‐poor till overlying till rich in flints. This feature is interpreted to have been inherited from an englacial debris stratification which is related to the distribution of source rock types in the up‐glacier area. Finally, a predominantly lateral variation in till composition is present, reflected best in the assemblages of the indicator pebbles, resulting from deposition by ice streams of different source and direction of flow.

Medial Moraines of the Haut Glacier D’arolla, Valais, Switzerland: Debris Supply and Implications For Moraine Formation

AbstractThe Haut Glacier d’Arolla displays three medial moraines: anablation-dominant moraineeast of the glacier centre line, anice-stream interaction morainewest of the glacier centre line, and amedial-lateral supraglacial moraine complexalong the western margin of the glacier. The eastern moraine is formed by the emergence of coarse angular clasts from a series of short longitudinal debris bands 1 km from the glacier terminus; this debris is derived from rock falls at the glacier head-wall, and follows a low-level transport path through the glacier. The western moraine is formed partly by the direct fall of weathered debris on to the ice surface at a point 2.6 km from the snout, but it receives further increments of sediment from extensive longitudinal englacial debris bands developed from the convergence of two ice streams with lateral englacial debris septa. The medial-lateral moraine complex is formed largely by rock falls from the western valley wall, but is also nourished by a debris layer developed at the base of the small tributary Glacier de la Mitre. This layer crops out at the eastern margin of the re- sultant inset ice stream, and releases more rounded, abraded and comminuted rock fragments to supplement the surface debris cover of supraglacial origin.

Medial Moraines of the Haut Glacier D’arolla, Valais, Switzerland: Debris Supply and Implications For Moraine Formation

AbstractThe Haut Glacier d’Arolla displays three medial moraines: an ablation-dominant moraine east of the glacier centre line, an ice-stream interaction moraine west of the glacier centre line, and a medial-lateral supraglacial moraine complex along the western margin of the glacier. The eastern moraine is formed by the emergence of coarse angular clasts from a series of short longitudinal debris bands 1 km from the glacier terminus; this debris is derived from rock falls at the glacier head-wall, and follows a low-level transport path through the glacier. The western moraine is formed partly by the direct fall of weathered debris on to the ice surface at a point 2.6 km from the snout, but it receives further increments of sediment from extensive longitudinal englacial debris bands developed from the convergence of two ice streams with lateral englacial debris septa. The medial-lateral moraine complex is formed largely by rock falls from the western valley wall, but is also nourished by a debris layer developed at the base of the small tributary Glacier de la Mitre. This layer crops out at the eastern margin of the re- sultant inset ice stream, and releases more rounded, abraded and comminuted rock fragments to supplement the surface debris cover of supraglacial origin.

Glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on Quaternary examples

Three variables control the type of glacial debris source and where and when debris is introduced to an ocean: (1) type of glacial ice source (ice sheet or valley glacier); (2) condition of a grounded glacier (melting/freezing or frozen base and cold or warm internal ice); and (3) type of glacier front (ice shelf or tidewater). Using these variables in different combinations eight glacimarine regimes are postulated to exist. By integrating information from Holocene sediment and Pleistocene glacimarine sequences with the eight inductive regimes, lithofacies relationships are predicted and modelled. The models show a complexity of glacimarine lithofacies. The importance of recognizing this complexity lies in realistic interpretations of ancient sequences. Ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation. Alternatively, in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes. Ice-proximal sediment is distinctive, especially near subglacial meltwater stream effluxes. Ice shelves and tidewater glaciers may produce similar ice-proximal lithofacies (e.g. morainal bank associations and laminites) in certain regimes. However, details of lithofacies may aid in distinguishing ice shelf from tidewater regimes. Ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high-level englacial debris can be distinguished. Ice shelf zone sediment out from the grounding line has a basal debris source. High-level englacial debris is deposited in more distal ice shelf zones resulting in sediment by-pass. In corresponding positions of a tidewater glacier regime, iceberg rafted debris comprises mixed basal and high-level englacial debris. Deeper water zones receive large volumes of sediment when a melting/freezing-base grounding line is at the edge of a continental shelf. When the grounding line retreats sediment supply may be drastically reduced because of a back-sloping continental shelf and trapping by morainal banks. Cool water bioclastic carbonates may accumulate once a grounding line has retreated. Although ice shelf iceberg zones are more extensive than those in tidewater regimes, ice shelf icebergs have low debris content and resulting ice-rafted debris may be scarce. The smallest volume of sediment is produced by a frozen-base ice sheet ending as a tidewater front, and the largest volume by a melting/freezing-base valley, tidewater glacier. Glacimarine sediment has a relatively high preservation potential near continental interiors or margins. However, at continental margins mass flow (olistostrome) and tectonic (melange) deposits may be preserved with glacimarine diamictites. These deposits may be difficult to distinguish from each other, especially if metamorphosed such as at a convergent margin. The models presented do not fully represent the glacimarine environment, because many other variables are omitted. However, the principal concepts of generating glacimarine lithofacies associations are considered. Continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models.

Ice-Cored Lateral Moraines in Tarfala Valley, Swedish Lapland

A morphological study which included detailed mapping and ice fabric studies was conducted on the ice-cored lateral moraines in the Tarfala valley, Lapland, Sweden. This study reveals a close association between the lateral moraines and the adjacent talus tongues. The talus tongues are deflected in their lower portions in the direction of glacier flow. Ridges of talus debris continue down-glacier as distinct features which are here termed talus trails. The talus trails coalesce to form the lateral moraines. These relationships suggest the ice-cored moraines are composed primarily of previously englacial debris and glacier ice. The deflected talus tongues and talus trails represent fossil ice flowlines. The geometry of these flowlines reflects conditions characteristic of an accumulation zone and are thus believed to be a unique class of glacial deposits. These deposits are responsible for the bulk and geometry of the lateral moraines and are also the oldest parts of the moraines. The deflected talus tongues and talus trails are estimated to have been formed between 2400 and 2700 BP. These deposits are used to tentatively infer some aspects of the climatic regime during this period. Reconstruction of local accumulation zones and associated equilibrium lines indicates a mean summer temperature decrease of at least 0.9°C. Morphological considerations indicate an unusually large input of talus debris during this period.

Genesis of Englacial Debris within the Lower Glacier De Tsidjiore Nouve, Valais, Switzerland, as Revealed by Scanning Electron Microscopy

Previous analysis has failed to establish unequivocally the genesis of englacial debris bands within the Glacier de Tsidjiore Nouve. Although extraglacial sources were presumed to be dominant, some of the debris appeared to be derived either from a subglacial source or had not been passively transported. Evidence obtained through the application of scanning electron microscopy reinforces the view that the englacial debris was incorporated within the glacier via crevasses in the firn basin, and indicates that it is derived from (1) supraglacial debris, resulting from subaerial weathering of rock-faces above the ice in the firn basin, and (2) subglacial debris derived from the base of ice standing above these rock faces. The results of this investigation demonstrate the value of scanning electron microscopy in the study and interpretation of complex sediment assemblages on and within glaciers.

Submarine flow tills at Victoria, British Columbia: Reply

during winter to maintain the same average position over a year. Perhaps these cones originated by slumps on the foreslope of subaquatic outwash fans similar to those postulated by Aario (1972) and Rust and Romanelli (1975) for a glacimarine setting. The small proportion of traction current deposits may be due to subglacial streams not having a sufficiently high sediment concentration to maintain an underflow away from the efflux. Occasionally the streams were sufficiently dense to deposit outwash sand and gravel in the foreslope area. The gravity flows may have incorporated the stream gravel, sand, and mud as well as melt-out debris from englacial and basal debris layers. Mixing of these sources during liquefaction perhaps induced by iceberg calving (Powell 1980; p. 70) may produce poorly sorted sediment flows. Thick accumulation by supraglacial melt out from debris layers in a tidewater glacier may best occur where the glacier has almost retreated from the sea and ablation occurs primarily by surface melting rather than iceberg calving (the situation in facies association 111 of Powell 1981). A similar situation of ice in shallow water under mid-latitude temperature conditions was envisaged by Evenson et al. (1977) to explain stratified Quaternary tills, although their interpretation has been questioned (Gibbard 1980). Here the glacial regime and processes are similar to those of the terrestrial environment. Mudflows and debris flows may occur from the ice surface and retain their integrity whilst flowing down a shallower (though still relatively steep) slope into shallow water. If such deposits are not modified by wave action and remain preserved, then they may indicate proximity to sea level in a similar way to deltaic plains.

Submarine flow tills at Victoria, British Columbia: Discussion

Hicock et al. describe complex submarine outwash cones from Quarternary glacimarine exposures. I do not question their interpretation of the diamicton sediments in the cones as being submarine flows or slumps from glacial debris; indeed, their descriptions are invaluable for tidewater glacier facies modelling. However, I have some comments on the suggested origin of the flows. Several different configurations of tidewater ice fronts may exist, but few allow the formation and preservation of sediment gravity flow deposits that originate subaerially and flow into the sea. Under polar conditions where glaciers cannot maintain themselves as floating ice tongues or ice shelves, they end in very shallow water and a beach is constructed at the base of their cliffs (e.g., Sugden and John 1976, Fig. 11.94. Most debris is slowly melted out, but rarely flowage may occur. However, such material is highly likely to be reworked by waves and, further, the ice margin in Puget Sound that Hicock et al. describe was probably not under polar-type conditions. In my experience of modem temperate tidewater glaciers in Glacier Bay, Alaska, only restricted conditions allow thick accumulation of supraglacial melt-out tills from englacial debris layers. Ablation of tidewater glaciers occurs more by berg calving rather than upper-surface melting, and ice fronts (at least above tide level) are nearly vertical cliffs. Ice is very crevassed back from the face, and the free face with consequent extensive flow commonly creates large transverse crevasses. Englacial debris layers are exposed across an ice face rather than transversely across the upper surface. However, the sides of each layer may intersect the upper surface of a glacier snout to form supraglacial melt-out debris parallel to the valley walls. Other supraglacial debris is primarily from rockfalls off valley walls and is rubble rather than diamicton. Rarely, some debris flows down the face from the upper edge, but the steepness of slope ensures sorting and separation of particles as the flow proceeds. The larger mass of pebbles and coarse-grained sand particles causes them to fall faster

Properties of Debris-Laden Ice: Application to the Flow Response of the Glaciers on Mount St Helens

Intense deformation within an extensive englacial debris layer appears to be a dominant flow mechanism for glaciers on Mount St Helens, Washington. Observations of this phenomenon have been made on Shoestring Glacier and more recently on other glaciers on the volcano. Transverse velocity profiles on Shoestring Glacier have shown a marked plug flow behavior occurring between narrow marginal zones of crevassing. Both longitudinal and transverse velocity profiles on Shoestring Glacier were measured during the year before and the two years after the cataclysmic eruption of the volcano on 18 May 1980.The geometry and regime of every glacier on Mount St Helens dramatically changed during the eruption. The entire accumulation area of Shoestring Glacier was removed by a volcanic landslide and blast, and the glacier surface was deeply incised through the action of pyroclastic flows and mudflows. Surface velocity measurements were supplemented by vertical profiles taken along the newly exposed ice cliffs. Large velocity gradients seen in the transverse, longitudinal and vertical profiles coincided with the mapped location of a recently exposed englacial debris layer. Further detailed measurements on the vertical profiles show that the intense shear occurs by deformation internal to the debris layer, A study of the properties of debris-laden ice was undertaken to determine the mechanism for localization of deformation to the debris layer and for the associated response of the glacier to a sudden change in stress.

Properties of Debris-Laden Ice: Application to the Flow Response of the Glaciers on Mount St Helens

Intense deformation within an extensive englacial debris layer appears to be a dominant flow mechanism for glaciers on Mount St Helens, Washington. Observations of this phenomenon have been made on Shoestring Glacier and more recently on other glaciers on the volcano. Transverse velocity profiles on Shoestring Glacier have shown a marked plug flow behavior occurring between narrow marginal zones of crevassing. Both longitudinal and transverse velocity profiles on Shoestring Glacier were measured during the year before and the two years after the cataclysmic eruption of the volcano on 18 May 1980. The geometry and regime of every glacier on Mount St Helens dramatically changed during the eruption. The entire accumulation area of Shoestring Glacier was removed by a volcanic landslide and blast, and the glacier surface was deeply incised through the action of pyroclastic flows and mudflows. Surface velocity measurements were supplemented by vertical profiles taken along the newly exposed ice cliffs. Large velocity gradients seen in the transverse, longitudinal and vertical profiles coincided with the mapped location of a recently exposed englacial debris layer. Further detailed measurements on the vertical profiles show that the intense shear occurs by deformation internal to the debris layer, A study of the properties of debris-laden ice was undertaken to determine the mechanism for localization of deformation to the debris layer and for the associated response of the glacier to a sudden change in stress.

Genesis of Englacial Debris within the Lower Glacier de Tsidjiore Nouve, Valais, Switzerland, as Revealed by Scanning Electron Microscopy

Genesis of Englacial Debris within the Lower Glacier de Tsidjiore Nouve, Valais, Switzerland, as Revealed by Scanning Electron Microscopy

The problem of recognizing melt‐out till

Deposition of till by melt‐out was described as early as a hundred years ago, and today the criteria which provide evidence to support an interpretation of melt‐out till are available. The most important criteria are (P1) the presence of unlithified, sorted and stratified sediments within or interstratified with the till(s). (P2) the presence of a statistically preferred orientation of stone axes closely related to ice‐flow condition, and (P3) a configuration of till with a recognizable textural or lithological property closely related to the configruation of englacial debris with regard to P1. Based on P1 and P2 and on regional aspects, tills composing ridges transverse to the dircetion of ice flow are interpreted as mult‐out till and flow till. The interpretation of till genesis must be based on the balnce of probability, as absolute proof is unrealistic in most cases.

Temperate Ice Beneath the “Polar” Taylor Glacier, Victoria Land, Antarctica (Abstract only)

Two interdependent lines of evidence contribute to an understanding of basal ice conditions within Taylor Glacier, from the thermal regime and from features of the englacial and basal debris. The thermal regime of the basal ice in Taylor Glacier suggests mechanisms for the entrainment and transportation of debris near the glacier sole.Assuming steady-state conditions, basal temperatures over the ablation area of Taylor Glacier were calculated from the geothermal heat in flux, the nearsurface ice temperatures, ice velocities, and the ice thickness. In over 50% of the lower ablation area the basal ice may be melting.The englacial and basal debris is incorporated by processes operating at the glacier sole. Englacial debris is incorporated by particle regelation; basal debris is incorporated by freezing block regelation. Both processes occur close to the glacier margin, where inner warm basal ice is in contact with marginal cold ice. The debris frozen to the sole here remains relatively unmodified during transport to the margin.Both lines of evidence indicate that Taylor Glacier is, and has been, capable of erosion and entrainment of debris by temperate ice at the glacier sole. Debris deposited along the margin i s similar to drift deposited beyond the glacier, implying that any recent climatic changes have had little effect on basal ice conditions within Taylor Glacier.

Temperate Ice Beneath the “Polar” Taylor Glacier, Victoria Land, Antarctica (Abstract only)

Two interdependent lines of evidence contribute to an understanding of basal ice conditions within Taylor Glacier, from the thermal regime and from features of the englacial and basal debris. The thermal regime of the basal ice in Taylor Glacier suggests mechanisms for the entrainment and transportation of debris near the glacier sole. Assuming steady-state conditions, basal temperatures over the ablation area of Taylor Glacier were calculated from the geothermal heat in flux, the nearsurface ice temperatures, ice velocities, and the ice thickness. In over 50% of the lower ablation area the basal ice may be melting. The englacial and basal debris is incorporated by processes operating at the glacier sole. Englacial debris is incorporated by particle regelation; basal debris is incorporated by freezing block regelation. Both processes occur close to the glacier margin, where inner warm basal ice is in contact with marginal cold ice. The debris frozen to the sole here remains relatively unmodified during transport to the margin. Both lines of evidence indicate that Taylor Glacier is, and has been, capable of erosion and entrainment of debris by temperate ice at the glacier sole. Debris deposited along the margin i s similar to drift deposited beyond the glacier, implying that any recent climatic changes have had little effect on basal ice conditions within Taylor Glacier.

Depositional Landforming Processes at the Snouts of Five Surging Glaciers in Vestspitsbergen (Abstract only)

Recent work by Clapperton (1975) proposes that the rapid rates of advance experienced by glaciers which surge may lead to enhanced debris incorporation, increased compressive flow near the glacier snout at the point of maximum extension, and to the upward translation and vertical stacking of debris near the glacier snout and margin. Five glaciers in Spitsbergen (Battyebreen, Holmströmbreen, Lisbetbreen, Vonbreen, Elnabreen) display morphological features which are widely accepted as being diagnostic of surging glaciers.Results of detailed observations regarding the nature, distribution, melt-out, and reworking of englacial debris at Battyebreen are presented. Basally derived till is brought to the surface of the glacier in narrow lateral and terminal belts, no more than 100 m wide. Within this zone, (i.e. up-valley from the snout and towards the valley centre) the ice is debris-free with the exception of small amounts of en-glacial debris which form the core of lobate medial moraines. Differential ablation of debris-free and debris-rich ice leads to the production of a topographic basin within which melt-out and reworking processes occupy restricted locations, as follows. Immediately inside the encircling melt-out till, a zone of flow tills is found. Melt streams are located at the foot of, the flow till-mantled slope, producing narrow (150 m wide) outwash trains, which merge into deltas. The central area of the topographic basin is occupied by a supraglacial lake.Observations of the remaining four locations confirm that other glaciers in the vicinity, which display similar characteristics associated with surging, are developing a stagnant-ice zone of identical appearance. The pattern of processes observed at Battyebreen is thus repeated at each site.A simple model of depositional landscape development is proposed for surging valley glaciers in a sub-polar environment.