Glacial hydrology and erosion patterns: A mechanism for carving glacial valleys

Herman, Frédéric; Beaud, Flavien; Champagnac, Jean‐Daniel; Lemieux, Jean‐Michel; Sternai, Pietro

doi:10.1016/j.epsl.2011.08.022

Cited by 165 publications

(199 citation statements)

References 69 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%

“…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. 4); however, a full understanding of the physics of ice sheet decay, especially regarding subglacial hydrology, is some way off [1][2][3]40 . What we can say with confidence is that the regional pattern of eskers in northern Sweden is evidence for an energetic and channelized subglacial meltwater system (see Supplementary Fig.…”

Section: Discussionmentioning

confidence: 99%

“…At Leverett Glacier (67.06°N, 50.17°W) satellite imaging of lake drainage events suggests that the seasonal increase in the hydraulic efficiency of subglacial drainage (that is, the capacity to erode the substrate via channelized flow) extends tens of kilometres inboard from the terminus, and surface meltwater is accessing the base of the ice sheet and evacuating debris at rapid rates 1,2,39 . In addition to the effects of subglacial hydrology on sliding velocity 2,40 , the expansion inboard of zones of subglacial erosion 1 is probably characteristic of decaying ice sheets 2,10 . Figure 4 illustrates how inner gorges may be generated as a function of channelized meltwater flux at the margin of a retreating ice sheet.…”

Section: Discussionmentioning

confidence: 99%

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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%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay

et al. 2014

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“…(iv) Basin uplift between phases of glaciation can act to counter glacial erosional feedback. (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).…”

Section: Confounding Factorsmentioning

confidence: 99%

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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“…As a result, there is a total geoid shift of around 13 cm over the glaciation, which causes a loading effect that is small compared to sediment thickness changes. To obtain a time series of sediment thickness, it is assumed that the temporal variation in sediment transport follows that of total ice mass change, based on the common assumption that the erosion rate is proportional to sliding velocity (see Herman et al, 2011). Recently, erosion has been found to be proportional to sliding velocity squared (Herman et al, 2015), which would enhance the erosion rate during periods of the largest ice change compared to our erosion history.…”

Section: B2 Creation Of a Spatial Pattern From Reported Sediment Dispmentioning

confidence: 99%

The effect of sediment loading in Fennoscandia and the Barents Sea during the last glacial cycle on glacial isostatic adjustment observations

Wal

IJpelaar²

2017

Solid Earth

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Abstract. Models for glacial isostatic adjustment (GIA) routinely include the effects of meltwater redistribution and changes in topography and coastlines. Since the sediment transport related to the dynamics of ice sheets may be comparable to that of sea level rise in terms of surface pressure, the loading effect of sediment deposition could cause measurable ongoing viscous readjustment. Here, we study the loading effect of glacially induced sediment redistribution (GISR) related to the Weichselian ice sheet in Fennoscandia and the Barents Sea. The surface loading effect and its effect on the gravitational potential is modeled by including changes in sediment thickness in the sea level equation following the method of Dalca et al. (2013). Sediment displacement estimates are estimated in two different ways: (i) from a compilation of studies on local features (trough mouth fans, large-scale failures, and basin flux) and (ii) from output of a coupled ice-sediment model. To account for uncertainty in Earth's rheology, three viscosity profiles are used.It is found that sediment transport can lead to changes in relative sea level of up to 2 m in the last 6000 years and larger effects occurring earlier in the deglaciation. This magnitude is below the error level of most of the relative sea level data because those data are sparse and errors increase with length of time before present. The effect on present-day uplift rates reaches a few tenths of millimeters per year in large parts of Norway and Sweden, which is around the measurement error of long-term GNSS (global navigation satellite system) monitoring networks. The maximum effect on present-day gravity rates as measured by the GRACE (Gravity Recovery and Climate Experiment) satellite mission is up to tenths of microgal per year, which is larger than the measurement error but below other error sources. Since GISR causes systematic uplift in most of mainland Scandinavia, including GISR in GIA models would improve the interpretation of GNSS and GRACE observations there.

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Glacial hydrology and erosion patterns: A mechanism for carving glacial valleys

Cited by 165 publications

References 69 publications

Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay

Inner gorges cut by subglacial meltwater during Fennoscandian ice sheet decay

A review of topographic controls on moraine distribution

The effect of sediment loading in Fennoscandia and the Barents Sea during the last glacial cycle on glacial isostatic adjustment observations

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