Tunnel valleys: Concepts and controversies — A review

Kehew, Alan E.; Piotrowski, Jan A.; Jørgensen, Flemming

doi:10.1016/j.earscirev.2012.02.002

Cited by 163 publications

(185 citation statements)

References 133 publications

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“…A point at the base of the Fennoscandian ice sheet B100 km inboard from the margin would have been icefree after B100-170 y, assuming a retreat rate of 0.6-1.0 km y -1 (Figs 1a and 4). Thus, development of subglacial inner gorges that are tens of metres deep implies extreme, though not implausible, erosion rates that we speculate signify intense meltwater activity 2,17,20,40 perhaps involving abrupt drainage of supraglacial lakes into the base of the ice sheet 24,39 . We strongly suspect that the transition in ice margin retreat from marine to terrestrial mode is somehow critical to the formation of gorges near the grounding line (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…The notion of channelized subglacial meltwater acting as the primary erosional agent is rooted in early Scandinavian studies 15,21,22 , and continues to receive strong support among those concerned with tunnel valley genesis 23,24 . Typical field evidence for subglacial meltwater erosion includes anastomosing channels, irregular valley long profiles and topography that amplifies hydraulic potential 2,9,18,20 .…”

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Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay

et al. 2014

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The century-long debate over the origins of inner gorges that were repeatedly covered by Quaternary glaciers hinges upon whether the gorges are fluvial forms eroded by subaerial rivers, or subglacial forms cut beneath ice. Here we apply cosmogenic nuclide exposure dating to seven inner gorges along B500 km of the former Fennoscandian ice sheet margin in combination with a new deglaciation map. We show that the timing of exposure matches the advent of ice-free conditions, strongly suggesting that gorges were cut by channelized subglacial meltwater while simultaneously being shielded from cosmic rays by overlying ice. Given the exceptional hydraulic efficiency required for meltwater channels to erode bedrock and evacuate debris, we deduce that inner gorges are the product of ice sheets undergoing intense surface melting. The lack of postglacial river erosion in our seven gorges implicates subglacial meltwater as a key driver of valley deepening on the Baltic Shield over multiple glacial cycles.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay

et al. 2014

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“…The channels are up to 1.5 km wide and extend for long distances (up to 100 km), consistent with the dimensions of tunnel valleys (e.g. Kehew, Piotrowski, & Jørgensen, 2012;Livingstone & Clark, 2016;Ó Cofaigh, 1996;Wright, 1973). Many appear to initiate on the northern edge of Aberdeen Lake, whilst a smaller number originate further south and trend through it.…”

Section: Mapped Landformsmentioning

confidence: 66%

Glacial geomorphology of the northern Kivalliq region, Nunavut, Canada, with an emphasis on meltwater drainage systems

Storrar

Livingstone

2017

Journal of Maps

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This paper presents a glacial geomorphological map of glacial lineations, ribbed terrain, moraines, meltwater channels (subglacial and ice-marginal/proglacial), eskers, glaciofluvial deposits, ice-contact outwash fans and deltas and abandoned shorelines on the bed of the former Laurentide Ice Sheet in northern Canada. Mapping was compiled from satellite imagery and digital elevation data and landforms were digitised directly into a Geographical Information System. The map reveals a complex glacial history characterised by multiple iceflow events, including fast-flowing ice streams. Moraines record a series of pauses or readvances during overall SE retreat towards the Keewatin Ice Divide. The distribution of subglacial meltwater landforms indicates that several distinctive scales and modes of drainage system operated beneath the retreating ice sheet. This includes a large (>100 km) integrated network of meltwater channels, eskers, ice-contact outwash fans and deltas and glaciofluvial deposits that originates at the northern edge of Aberdeen Lake. The map comprises zone 66 of the Canadian National Topographic System, which encompasses an area of 160,000 km 2 . It is presented at a scale of 1:500,000 and is designed to be printed at A0 size. ARTICLE HISTORY

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“…Section 3 includes the results from field observations regarding channel longitudinal profiles, the Digital Surface Models produced with photogrammetric and KLS datasets, and a comparison of rivers and tunnel valleys within the same geological units. The compiled data allows us to discuss and revisit the guidelines 10 reviewed by Kehew et al (2012) in the context of remote sensing of previously glaciated areas.…”

mentioning

confidence: 99%

“…These guidelines are qualitative, and a topographic and imagery based approach to tunnel valley identification is yet to be developed. (e.g., Kehew et al, 2012).…”

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Subglacial drainage patterns of Devon Island, Canada: Detailed comparison of river and tunnel valleys

Galofre

Jellinek

Osinski

et al. 2017

Preprint

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Abstract. Tunnel valleys are bedrock incised channels (N-channels) attributed to erosion by meltwater in subglacial conduits.They exert a major control on meltwater accumulation at the base of ice sheets, serving as drainage pathways and modifying ice flow rates. Exposed relict tunnel valleys offer a unique opportunity to study the geomorphologic fingerprint of subglacial erosion and characterize the geometry of individual channels. In this study we present field and remote sensing observations of exposed tunnel valleys on Devon Island (Canadian Arctic Archipelago), including descriptions of tunnel valley cross sec-5 tions and longitudinal profiles, as well as network morphology, to describe the spatial extend and distinctive characteristics of subglacial drainage systems. We use field-based GPS measurements of tunnel valley longitudinal profiles, along with stereo imagery derived Digital Surface Models (DSM), and novel kinematic mobile LiDAR data to establish a quantitative comparison of tunnel and river valleys in our field study area. Tunnel valleys typically cluster in groups of 5-10 channels throughout the island, oriented radially with respect to active or former ice margins. We identify departures in tunnel valley direction from 10 local topographic gradients and undulations in the longitudinal profiles. We also observe that the width of first order tributaries is one to two orders of magnitude larger than in river systems, and remarkably constant downstream. These distinctive aspects of tunnel valley morphology are similar among the different locations characterized in the study. Furthermore, our findings are consistent with expectations of flow driven by gradients in effective water pressure related to variations in ice thickness.Our field and remote sensing observations provide a rigorous way to distinguish tunnel and river valleys in local and regional 15 topography data that revisits well-established field identification guidelines. Distinguishing river and tunnel valleys in topographic data is critical for understanding the emergence, geometry and extent of channelized subglacial drainage systems. The final aim of this study is to facilitate the identification of tunnel valley networks throughout the globe by using remote sensing techniques, which will improve the detection of these systems and help to build understanding of the mechanics of subglacial channelized drainage. 201 The Cryosphere Discuss., https://doi

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Tunnel valleys: Concepts and controversies — A review

Cited by 163 publications

References 133 publications

Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay

Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay

Glacial geomorphology of the northern Kivalliq region, Nunavut, Canada, with an emphasis on meltwater drainage systems

Subglacial drainage patterns of Devon Island, Canada: Detailed comparison of river and tunnel valleys

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