Giant glacial grooves in northwest Canada

Smith, H. T. U.

doi:10.2475/ajs.246.8.503

Cited by 49 publications

(61 citation statements)

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“…5b) would be 4 times slower, even though this obstacle is more streamlined (having a longer aspect ratio). This result contradicts most observed geomorphology (Stokes and Clark, 1999;Bradwell et al, 2008) and supports the notion that pressure melting is not dominant for large obstacles.…”

Section: The Pressure-melting Componentcontrasting

confidence: 56%

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Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

Krabbendam

2016

The Cryosphere

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Abstract. Basal ice motion is crucial to ice dynamics of ice sheets. The classic Weertman model for basal sliding over bedrock obstacles proposes that sliding velocity is controlled by pressure melting and/or ductile flow, whichever is the fastest; it further assumes that pressure melting is limited by heat flow through the obstacle and ductile flow is controlled by standard power-law creep. These last two assumptions, however, are not applicable if a substantial basal layer of temperate (T ∼ T melt ) ice is present. In that case, frictional melting can produce excess basal meltwater and efficient water flow, leading to near-thermal equilibrium. High-temperature ice creep experiments have shown a sharp weakening of a factor 5-10 close to T melt , suggesting standard power-law creep does not operate due to a switch to melt-assisted creep with a possible component of grain boundary melting. Pressure melting is controlled by meltwater production, heat advection by flowing meltwater to the next obstacle and heat conduction through ice/rock over half the obstacle height. No heat flow through the obstacle is required. Ice streaming over a rough, hard bed, as possibly in the Northeast Greenland Ice Stream, may be explained by enhanced basal motion in a thick temperate ice layer.

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Section: The Pressure-melting Componentcontrasting

confidence: 56%

“…(Smith, 1948;Stokes and Clark, 2003;Roberts and Long, 2005;Bradwell et al, 2008;Eyles, 2012;Bradwell, 2013;Eyles and Putkinen, 2014;Krabbendam et al, 2016). In these areas, the deforming-bed models cannot apply because little or no soft sediment is present.…”

Section: Introductionmentioning

confidence: 99%

Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

Krabbendam

2016

The Cryosphere

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“…However, the exact formation mechanism of MSGL in bedrock remains elusive. Focused glacial abrasion and high-energy subglacial meltwater are both likely to play key roles in megagroove formation (Smith, 1948;Boulton, 1979;Bradwell, 2005). Other localities with less pronounced streamlined bedforms (elongation ratios <6:1) indicate the onset of ice streaming -in NE Lewis, on Raasay, in Loch Ewe, around Loch Snizort (Skye), and around Loch Laxford (Josenhans, 1997), offshore Norway Stalsberg et al, 2003;Ottesen et al, 2005) and Antarctica (Pudsey et al, 1994;Ó Cofaigh et al, 2002;Dowdeswell et al, 2004).…”

Section: Methods and Resultsmentioning

confidence: 99%

Geomorphological signature and flow dynamics of The Minch palaeo‐ice stream, northwest Scotland

Bradwell

Stoker

Larter

2007

J Quaternary Science

115

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“…Large-scale bedrock grooves have been reported in other previously glaciated areas (Carney, 1910;Smith, 1948;Witkind, 1978). These workers concluded that the grooves formed as a result of mechanical abrasion under localized, particularly favourable, conditions at the base of the ice sheet.…”

Section: Accepted M Manuscriptmentioning

confidence: 94%

“…Megagrooves are linear features with negative topographic expression, >100 m long and >1 m deep, cut in bedrock (Bradwell, 2005). 10-km long, 20-m deep examples have been reported from North America (Smith, 1948;Witkind, 1978).…”

Section: (I) Megagroovesmentioning

confidence: 99%

Megagrooves and streamlined bedrock in NW Scotland: The role of ice streams in landscape evolution

2008

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New multibeam bathymetry data, onshore high-resolution elevation data (NEXTMap) and fieldwork in the Ullapool area of NW Scotland reveal large-scale megagrooves and streamlined bedrock forms in a well-defined ~20-km wide zone. The landsystem is typical of a coherent flow corridor within a grounded ice sheet on bedrockdominated terrain. We describe the morphology of the large-scale features, discuss their likely formation, and consider the wider implications for ice-sheet dynamics. Based on the strongly convergent bedform distribution, the presence of megagrooves and highly elongate bedrock forms, we interpret the erosional landscape to be the signature of a fast-flowing tributary that once fed the The Minch palaeo-ice stream -a major artery of the last British-Irish ice sheet. The exact genesis of bedrock megagrooves remains uncertain, although focused subglacial abrasion is likely to have carved most of the shallow, strongly parallel, features; whilst glacial meltwater may have carved or modified others. Bedform morphometry is used to discriminate zones reflecting the degree of glacial streamlining (elongation ratios <5:1 or >5:1). We interpret these zones to represent the transition from potentially cold-based slow ice-sheet flow to warm-based fast flow. Based on these results, and the presence of ribbed moraines, we suggest a bedform continuum model for onset zones of palaeoice streams on rigid beds. Rapid spatial bedform evolution is suggested to reflect an increase in subglacial erosive power that may be diagnostic of palaeo-ice-sheet thermal boundaries (i.e. from cold-to warm-based), and is also consistent with the expected downstream increase in ice velocity within an ice-stream onset zone. Finally, this study speculates on the role played by basal meltwater in ice-stream initiation and the role of ice streams and their tributaries in landscape evolution.

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Giant glacial grooves in northwest Canada

Cited by 49 publications

References 0 publications

Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming

Geomorphological signature and flow dynamics of The Minch palaeo‐ice stream, northwest Scotland

Megagrooves and streamlined bedrock in NW Scotland: The role of ice streams in landscape evolution

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