Analysis of flute forming conditions using ice sheet reconstructions and field techniques

Hubbard, Trent D.; Reid, John R.

doi:10.1016/j.geomorph.2005.07.013

Cited by 5 publications

(10 citation statements)

References 38 publications

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“…Observing the frequent occurrence of flutes that do not initiate at a boulder, Rose [1989] alludes to transverse ''flow cells'' in basal ice that could explain the formation of flutes, and speculates that boulders could be natural starting points for such flow cells without being necessary for their formation.We suggest that our theory indicates a possible origin of precisely such flow cells. Transverse flow cells of this kind are also compatible with the general observation of till fabrics indicating the flow of till from interflute trough toward the flute crest noted by Shaw and Freschauf [1973] for megaflutes and by Boulton [1976] for smaller flutes and reproduced by other researchers since [Benn, 1994;Rose, 1989], though not universally [Eklund and Hart, 1996;Hubbard and Reid, 2006]. The absence of a herringbone-type pattern could, of course simply indicate a weak transverse flow component.…”

supporting

confidence: 87%

A model for spiral flows in basal ice and the formation of subglacial flutes based on a Reiner‐Rivlin rheology for glacial ice

Schoof

Clarke

2008

J. Geophys. Res.

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[1] Flutes are elongated sediment ridges formed at the base of glaciers and ice sheets. In this paper, we show that flutes can be the product of a corkscrew-like spiral flow in basal ice that removes sediment from troughs between flutes and deposits it at their crests, as first suggested by Shaw and Freschauf. In order to generate the type of basal ice flow required for this mechanism, the viscous rheology of ice must allow for the generation of deviatoric normal stresses transverse to the main flow direction. This type of behavior, which is commonly observed in real nonlinearly viscous and viscoelastic fluids, can be described by a Reiner-Rivlin rheology. Here, we develop a mathematical model that describes the role of these transverse stresses in generating spiral flows in basal ice and investigate how these flows lead to the amplification of initially small basal topography and the eventual formation of assemblies of evenly spaced subglacial flutes.

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supporting

confidence: 87%

A model for spiral flows in basal ice and the formation of subglacial flutes based on a Reiner‐Rivlin rheology for glacial ice

Schoof

Clarke

2008

J. Geophys. Res.

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“…Some ridges have lengths of up to 450 m and lateral spacings on the order of ca 5 m (Figs and to ). Preliminary geomorphological observations were made of these flutes by McPherson & Gardner () and in more detail by Boyce () and, more recently, by Hubbard & Reid (); these workers all agree that some form of bed deformation was involved, although their detailed interpretations differ.…”

Section: Study Areamentioning

confidence: 96%

Neoglacial (<3000 years) till and flutes at Saskatchewan Glacier, Canadian Rocky Mountains, formed by subglacial deformation of a soft bed

2014

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Understanding the processes that deposit till below modern glaciers provides fundamental information for interpreting ancient subglacial deposits. A process-deposit-landform model is developed for the till bed of Saskatchewan Glacier in the Canadian Rocky Mountains. The glacier is predominantly hard bedded in its upper reaches and flows through a deep valley carved into resistant Palaeozoic carbonates but the ice margin rests on a thick (<6 m) soft bed of silt-rich deformation till that has been exposed as the glacier retreats from its Little Ice Age limit reached in 1854. In situ tree stumps rooted in a palaeosol under the till are dated between ca 2900 and 2700 yr BP and record initial glacier expansion during the Neoglacial. Sedimentological and stratigraphic observations underscore the importance of subglacial deformation of glaciofluvial outwash deposited in front of the advancing glacier and mixing with glaciolacustrine carbonate-rich silt to form a soft bed. The exposed till plain has a rolling drumlinoid topography inherited from overridden end moraines and is corrugated by more than 400 longitudinal flute ridges which record deformation of the soft bed and fall into three genetically related types: those developed in propagating incipient cavities in the lee of large subglacial boulders embedded in deformation till, and those lacking any originating boulder and formed by pressing of wet till up into radial crevasses under stagnant ice. A third type consists of U-shaped flutes akin to barchan dunes; these wrap around large boulders at the downglacier ends of longitudinal scours formed by the bulldozing of boulders by the ice front during brief winter readvances across soft till. Pervasive subglacial deformation during glacier expansion was probably facilitated by large boulders rotating within the soft bed ('glacioturbation').

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“…Coarser-grained and more permeable tills are, therefore, likely to strengthen more quickly in response to loading by the glacier and are more likely to propagate cavities than finer-grained and less permeable tills. However, the claim cannot be made that coarse tills are more likely to form flutes because they are also less likely to deform into a cavity and initiate flute formation (Hubbard and Reid, 2006).…”

Section: Discussionmentioning

confidence: 99%

“…Parallel-flute fabrics are oriented parallel to the flute's central axis everywhere (Fig. 1-3B) (Gordon et al, 1992;Hubbard and Reid, 2006). No matter the trend of the pebble fabrics measured in flutes, the plunge of the fabric is usually near zero.…”

Section: A B Cmentioning

confidence: 98%

“…Pebble fabric data were imported only from papers that included the orientations of all clasts measured either as lines on equal-area, lower hemisphere stereonets or as supplementary data. Clast fabric data from articles that included only the resulting eigenvectors (Benn, 1995), contour density plots (Boulton, 1976;Hubbard and Reid, 2006), or rose diagrams (Glasser and Hambrey, 2001) were not used. Locations where clast fabrics were measured in the flute also needed to be reported for them to be usable.…”

Section: Importing Data From Literaturementioning

confidence: 99%

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Magnetic mineralogy and fabrics of small-scale glacial flutes, Múlajökull and Breiðamerkurjökull, Iceland

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Analysis of flute forming conditions using ice sheet reconstructions and field techniques

Cited by 5 publications

References 38 publications

A model for spiral flows in basal ice and the formation of subglacial flutes based on a Reiner‐Rivlin rheology for glacial ice

A model for spiral flows in basal ice and the formation of subglacial flutes based on a Reiner‐Rivlin rheology for glacial ice

Neoglacial (<3000 years) till and flutes at Saskatchewan Glacier, Canadian Rocky Mountains, formed by subglacial deformation of a soft bed

Magnetic mineralogy and fabrics of small-scale glacial flutes, Múlajökull and Breiðamerkurjökull, Iceland

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