Subglacial basins: Their origin and importance in glacial systems and landscapes

Cook, Simon J.; Swift, Darrel A.

doi:10.1016/j.earscirev.2012.09.009

Cited by 156 publications

(181 citation statements)

References 282 publications

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“…Specifically, a contrast is often made between glacially modified basins, which are deep -wide and punctuated by topographic steps and overdeepenings (see Harbor, 1992;MacGregor et al, 2000;Montgomery, 2002;Cook and Swift, 2012) -and nonglacial basins -which have comparatively smooth longitudinal profiles that gradually decrease in slope downvalley (MacGregor et al, 2000). These topographic characteristics have important implications for the extent of the ice masses that come to occupy such basins (see Oerlemans, 1984;MacGregor et al, 2000).…”

Section: Evolving Basin Topography As a Control On Moraine Formationmentioning

confidence: 99%

“…(v) As a landscape becomes tuned to glacial occupation, the extent to which glaciers deepen/erode their basins is likely to diminish (e.g., Charreau et al, 2011;Herman et al, 2011). This is likely to be reinforced in regions where overdeepened basins prevent the efficient removal of subglacial debris (Cook and Swift, 2012). In this instance, the intensity of erosion (and sediment production) is likely to peak during the initial transition from a largely fluvial to glacial landscape (Charreau et al, 2011) and diminish with time thereafter.…”

Section: Confounding Factorsmentioning

confidence: 99%

“…For example, reverse bed slopes, such as the downvalley sides of overdeepenings (Fig. 11C), require glaciers to advance uphill (see Cook and Swift, 2012). These topographic steps therefore act as obstacles to flow and are likely to encourage ice margin stability, leading to moraine deposition (Kerr, 1993).…”

Section: Physical Restrictions To Glacier Advancementioning

confidence: 99%

“…In particular, topographic pinning points represent potentially stable locations where moraine formation can occur (Warren, 1991;O'Neel et al, 2005;Jamieson et al, 2012Jamieson et al, , 2014Carr et al, 2013). These pinning points often consist of laterally confined shallow basins, subaerial topographic obstructions (i.e., islands) or bathymetric highs (such as the adverse slopes of overdeepenings) (Warren and Hulton, 1990;Warren, 1991Warren, , 1992Cook and Swift, 2012). During retreat from stable locations into wider/deeper sections of troughs and/or away from islands or bathymetric highs, ablation will increase significantly (perhaps enhanced by the incursion of warm water into previously enclosed basins -see Jenkins et al, 2010), and glaciers will undergo rapid retreat until the next topographic pinning point is reached (Warren and Hulton, 1990;Boyce et al, 2007;Nick et al, 2009;Jamieson et al, 2012;Carr et al, 2013).…”

Section: Fjord Topographymentioning

confidence: 99%

“…It is suggested that the entrainment of subglacial debris is particularly efficient on the adverse slopes of overdeepenings, where supercooling processes result in the formation of debris-rich basal ice (Cook et al, 2010) and debris is entrained and elevated via shear planes (Swift et al, 2002). As a consequence, some of the largest moraines may well form in front of temperate glaciers with terminal overdeepenings (see Swift et al, 2002;Cook and Swift, 2012). This assertion is often difficult to test, as terminal overdeepenings can be infilled and are sometimes difficult to identify in the modern landscape (Cook and Swift, 2012).…”

Section: Supply Of Debris To Glacier Marginsmentioning

confidence: 99%

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A review of topographic controls on moraine distribution

2014

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Ice-marginal moraines are often used to reconstruct the dimensions of former ice masses, which are then used as proxies for palaeoclimate. This approach relies on the assumption that the distribution of moraines in the modern landscape is an accurate reflection of former ice margin positions during climatically controlled periods of ice margin stability. However, the validity of this assumption is open to question, as a number of additional, nonclimatic factors are known to influence moraine distribution. This review considers the role played by topography in this process, with specific focus on moraine formation, preservation, and ease of identification (topoclimatic controls are not considered). Published literature indicates that the importance of topography in regulating moraine distribution varies spatially, temporally, and as a function of the ice mass type responsible for moraine deposition. In particular, in the case of ice sheets and ice caps ( > 1000 km 2 ), one potentially important topographic control on where in a landscape moraines are deposited is erosional feedback, whereby subglacial erosion causes ice masses to become less extensive over successive glacial cycles. For the marine-terminating outlets of such ice masses, fjord geometry also exerts a strong control on where moraines are deposited, promoting their deposition in proximity to valley narrowings, bends, bifurcations, where basins are shallow, and/or in the vicinity of topographic bumps. Moraines formed at the margins of ice sheets and ice caps are likely to be large and readily identifiable in the modern landscape. In the case of icefields and valley glaciers (10-1000 km 2 ), erosional feedback may well play some role in regulating where moraines are deposited, but other factors, including variations in accumulation area topography and the propensity for moraines to form at topographic pinning points, are also likely to be important. This is particularly relevant where land-terminating glaciers extend into piedmont zones (unconfined plains, adjacent to mountain ranges) where large and readily identifiable moraines can be deposited. In the case of cirque glaciers (< 10 km 2 ), erosional feedback is less important, but factors such as topographic controls on the accumulation of redistributed snow and ice and the availability of surface debris, regulate glacier dimensions and thereby determine where moraines are deposited. In such cases, moraines are likely to be small and particularly susceptible to post-depositional modification, sometimes making them difficult to identify in the modern landscape. Based on this review, we suggest that, despite often being difficult to identify, quantify, and mitigate, topographic controls on moraine distribution should be explicitly considered when reconstructing the dimensions of palaeoglaciers and that moraines should be judiciously chosen before being used as indirect proxies for palaeoclimate (i.e., palaeoclimatic inferences should only be drawn from moraines when topographic controls on mora...

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Section: Evolving Basin Topography As a Control On Moraine Formationmentioning

confidence: 99%

Section: Confounding Factorsmentioning

confidence: 99%

Section: Physical Restrictions To Glacier Advancementioning

confidence: 99%

Section: Fjord Topographymentioning

confidence: 99%

Section: Supply Of Debris To Glacier Marginsmentioning

confidence: 99%

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A review of topographic controls on moraine distribution

2014

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The hydrology of subglacial overdeepenings: A new supercooling threshold formula

Werder

2016

Geophysical Research Letters

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Overdeepenings are a hallmark glacial landform of broad geomorphologlogical and glaciological interest. Their formation mechanism has not yet been fully uncovered, but subglacial drainage is likely a key factor. One prominent hypothesis states that the depth of an overdeepening stabilizes at the supercooling threshold. This threshold is reached when the adverse bed slope terminating an overdeepening is sufficiently large to shut down the efficient, channelized drainage system. Classic theory puts this threshold at a ratio of bed to surface slope of −1.6. Here I extend that theory by taking into account that downstream water pressure can be below overburden pressure. The new formula agrees well with results from one‐ and two‐dimensional subglacial drainage models. Applying it to observations of 147 overdeepenings from alpine glaciers and ice sheets shows that the depth of overdeepenings rarely exceeds the new supercooling threshold. Thus, this work supports the stabilizing hypothesis.

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Rerouting of subglacial water flow between neighboring glaciers in West Greenland

2016

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Investigations of the Greenland ice sheet's subglacial hydrological system show that the connectivity of different regions of the system influences how the glacier velocity responds to variations in surface melting. Here we examine whether subglacial water flow paths can be rerouted beneath three outlet glaciers in the ablation zone of western Greenland. We use Lamont‐Doherty and Center for Remote Sensing of Ice Sheets of University of Kansas (CReSIS) ice‐penetrating radar data to create a new ice thickness map. We then use a simple subglacial water flow model to examine whether flow paths can be rerouted and identify the topographic conditions that are sensitive to subglacial rerouting. By varying water pressures within an observationally constrained range, we show that moderate changes in pressure can cause flow paths to reroute and exchange water from one subglacial catchment to another. Flow across subglacial overdeepenings is particularly sensitive to rerouting. These areas have low hydraulic gradients driving flow, so subtle water pressure variations have a strong influence on water flow direction. Based on correlations between water flow paths and ice velocity changes, we infer that water piracy between neighboring catchments can result in a different spatial pattern of hydrologically induced ice velocity speedup depending on the amount and timing of surface melt. The potential for subglacial water to reroute across different catchments suggests that multiple hydrographs from neighboring glaciers are likely necessary to accurately ascertain melt budgets from proglacial point measurements. The relationship between surface runoff, ice dynamics, and proglacial discharge can be altered by rerouting of subglacial water flow within and across outlet glaciers.

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Subglacial basins: Their origin and importance in glacial systems and landscapes

Cited by 156 publications

References 282 publications

A review of topographic controls on moraine distribution

A review of topographic controls on moraine distribution

The hydrology of subglacial overdeepenings: A new supercooling threshold formula

Rerouting of subglacial water flow between neighboring glaciers in West Greenland

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