Control of glacial quarrying by bedrock joints

Hooyer, Thomas S.; Cohen, Denis; Iverson, Neal R.

doi:10.1016/j.geomorph.2012.02.012

Cited by 60 publications

(79 citation statements)

References 50 publications

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“…The distinct offset between plucked-face orientation and palaeo-ice flow direction (which was 487 observed in KA2i, KA2ii, IN1, and IN2) has also been reported by other studies (Gordon, 1981; Rea 488 23 and Whalley, 1996;Krabbendam and Bradwell, 2011;Hooyer et al, 2012). Plucking is facilitated by 489 pre-glacial bedding planes and joints and by bedrock rock bridges (Hooyer et al, 2012) (Fig.…”

supporting

confidence: 73%

“…High bedrock hardness increases abrasion resistance 118 (Krabbendam and Glasser, 2011), while joint spacing can control bedform type by facilitating or 119 resisting quarrying (Dühnforth et al, 2010;Iverson, 2012). Joint orientation can control lee side 120 plucking, irrespective of palaeo-ice flow direction (Gordon, 1981;Rea and Whalley, 1996; 121 Krabbendam and Bradwell, 2011;Hooyer et al, 2012). …”

Section: Glacial Erosion and Bedrock Bedforms 87mentioning

confidence: 99%

“…Plucking is facilitated by 489 pre-glacial bedding planes and joints and by bedrock rock bridges (Hooyer et al, 2012) (Fig. 10).…”

mentioning

confidence: 99%

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Controls on bedrock bedform development beneath the Uummannaq Ice Stream onset zone, West Greenland

et al. 2015

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Citation for published item:vneD FF nd oertsD hFrF nd eD fFF nd ¡ y gofighD gF nd ieliD eF @PHISA 9gontrols on suglil edrok edform development t the se of the ummnnq se tremD est qreenlndF9D qeomorphologyFD PQI F ppF QHIEQIQF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. This paper investigates the controls on the formation of subglacially eroded bedrock bedforms 17 beneath the topographically confined region upstream of the Uummannaq Ice Stream (UIS). During 18 the last glacial cycle, palaeoglaciological conditions are believed to have been similar for all sites in 19 the study, characterised by thick, fast-flowing ice moving over a rigid bedrock bed. Classic bedrock 20 bedforms indicative of glacially eroded terrain were mapped, including p-forms, roches moutonnées, 21 and whalebacks. Bedform long axes and plucked face orientations display close correlation (parallel 22 and perpendicular) to palaeo-ice flow directions inferred from striae measurements. Across all sites, 23 elongation ratios (length to width) varied by an order of magnitude between 0.8:1 and 8.4:1. 24Bedform properties (length, height, width, and long axis orientation) from four subsample areas, 25 *Revised manuscript with no changes marked Click here to view linked References 2 form morphometrically distinct populations, despite their close proximity and hypothesised 26 similarity in palaeoglaciological conditions. 27 28Variations in lithology and geological structures (e.g., joint frequency; joint dip; joint orientation; 29 bedding plane thickness; and bedding plane dip) provide lines of geological weakness, which focus 30 the glacial erosion, in turn controlling bedform geometries. Determining the relationship(s) between 31 bedding plane dip relative to palaeo-ice flow and bedform shape, relative length, amplitude, and 32 wavelength has important ramifications for understanding subglacial bed roughness, cavity 33 formation, and likely erosion style (quarrying and/or abrasion) at the ice-bed interface. This paper 34 demonstrates a direct link between bedrock bedform geometries and geological structure and 35 emphasises the need to understand bedrock bedform characteristics when reconstructing 36 palaeoglaciological conditions. 37 38Keywords: ice stream; glacial erosion; bedrock bedform; abrasion; quarrying; Greenland ice sheet 39 3 Introduction 40 41 Importance of glacial bedforms 42An understanding of past ice sheet dynamics can significantly improve our understanding of current 43 and potential future ...

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supporting

confidence: 73%

Section: Glacial Erosion and Bedrock Bedforms 87mentioning

confidence: 99%

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Controls on bedrock bedform development beneath the Uummannaq Ice Stream onset zone, West Greenland

et al. 2015

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“…Roche moutonnées show the classic distinct asymmetry -a smooth rounded stoss-side and a jagged plucked lee-side. Plucking generally exploits preexisting joints in the gneiss in the manner described by Rea (1994), Glasser (2011) andHooyer et al (2012). In most of the area, roche moutonnées are more common than whalebacks, but this is reversed in the Laxford area.…”

Section: Roche Moutonnées Whalebacks P-formsmentioning

confidence: 99%

“…This 'background' jointing is represented in Fig 8A by the Loch na Facial and Ceannabeinne Beach localities, which joint spacing of 0.33 m and 0.74 m respectively (Table 1), although joint spacing and orientation varies greatly throughout the study area (Pless, 2011). Joints play a major role in glacial plucking (Rea, 1994;Krabbendam and Glasser, 2011;Hooyer et al, 2012) and many plucked faces coincide with joints (e.g. Fig 6A, D).…”

Section: Jointingmentioning

confidence: 99%

Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion

Krabbendam

Bradwell

2014

Quaternary Science Reviews

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Vast areas previously covered by Pleistocene ice sheets consist of rugged bedrock-dominated terrain of innumerable knolls and lake-filled rock basins -the 'cnoc-and-lochan' landscape or 'landscape of areal scour'. These landscapes typically form on gneissose or granitic lithologies and are interpreted (1) either to be the result of strong and widespread glacial erosion over numerous glacial cycles; or (2) formed by stripping of a saprolitic weathering mantle from an older, deeply weathered landscape.We analyse bedrock structure, erosional landforms and weathering remnants and within the 'cnoc-andlochan' gneiss terrain of a rough peneplain in NW Scotland and compare this with a geomorphologically similar gneiss terrain in a non-glacial, arid setting (Namaqualand, South Africa). We find that the topography of the gneiss landscapes in NW Scotland and Namaqualand closely follows the old bedrock-saprolite contact (weathering front). The roughness of the weathering front is caused by deep fracture zones providing a highly irregular surface area for weathering to proceed. The weathering front represents a significant change in bedrock physical properties. Glacial erosion (and aeolian erosion in Namaqualand) is an efficient way of stripping saprolite, but is far less effective in eroding hard, unweathered bedrock. Significant glacial erosion of hard gneiss probably only occurs beneath palaeo-ice streams.We conclude that the rough topography of glaciated 'cnoc-and-lochan' gneiss terrains is formed by a multistage process: 1) Long-term, pre-glacial chemical weathering, forming deep saprolite with an irregular weathering front;2) Stripping of weak saprolite by glacial erosion during the first glaciation(s), resulting in a rough land surface, broadly conforming to the pre-existing weathering front ('etch surface');3) Further modification of exposed hard bedrock by glacial erosion. In most areas, glacial erosion is limited, but can be significant beneath palaeo-ice stream. The roughness of glaciated gneiss terrains is crucial for modelling of the glacial dynamics of present-day ice sheets. This roughness is shown here to depend on the intensity of pre-glacial weathering as well as glacial erosion during successive glaciations.

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Subglacial extensional fracture development and implications for Alpine Valley evolution

Leith

Moore

Amann³

et al. 2014

JGR Earth Surface

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[1] Bedrock stresses induced through exhumation and tectonic processes play a key role in the topographic evolution of alpine valleys. Using a finite difference model combining the effects of tectonics, erosion, and long-term bedrock strength, we assess the development of near-surface in situ stresses and predict bedrock behavior in response to glacial erosion in an Alpine Valley (the Matter Valley, southern Switzerland). Initial stresses are derived from the regional tectonic history, which is characterized by ongoing transtensional or extensional strain throughout exhumation of the brittle crust. We find that bedrock stresses beneath glacial ice in an initial V-shaped topography are sufficient to induce localized extensional fracturing in a zone extending laterally 600 m from the valley axis. The limit of this zone is reflected in the landscape today by a valley "shoulder," separating linear upper mountain slopes from the deep U-shaped inner valley. We propose that this extensional fracture development enhanced glacial quarrying between the valley shoulder and axis and identify a positive feedback where enhanced quarrying promoted valley incision, which in turn increased in situ stress concentrations near the valley floor, assisting erosion and further driving rapid U-shaped valley development. During interglacial periods, these stresses were relieved through brittle strain or topographic modification, and without significant erosion to reach more highly stressed bedrock, subsequent glaciation caused a reduction in differential stress and suppressed extensional fracturing. A combination of stress relief during interglacial periods, and increased ice accumulation rates in highly incised valleys, will reduce the likelihood of repeat enhanced erosion events.

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Control of glacial quarrying by bedrock joints

Cited by 60 publications

References 50 publications

Controls on bedrock bedform development beneath the Uummannaq Ice Stream onset zone, West Greenland

Controls on bedrock bedform development beneath the Uummannaq Ice Stream onset zone, West Greenland

Quaternary evolution of glaciated gneiss terrains: pre-glacial weathering vs. glacial erosion

Subglacial extensional fracture development and implications for Alpine Valley evolution

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