Buried and open tunnel valleys in Denmark—erosion beneath multiple ice sheets

Jørgensen, Flemming; Sandersen, Peter B.E.

doi:10.1016/j.quascirev.2005.11.006

Cited by 218 publications

(254 citation statements)

References 93 publications

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“…However, unlike elsewhere in the world few buried tunnel valleys have been reported along the southern margin of the Laurentide Ice Sheet, and most of the completely buried tunnel valley networks in Europe relate to pre-Weichselian ice advances (e.g. Jørgensen and Sandersen, 2006;Kristensen et al, 2007Kristensen et al, , 2008Stewart and Lonergan, 2011), so we suppose this problem to be minimal. Moreover, unless there is a systematic bias predisposing burial in some locations over others then the mapped pattern and distribution of tunnel valleys is likely to be informative.…”

Section: Limitationsmentioning

confidence: 96%

“…They are observed in many formerly glaciated landscapes around the world, and tend to be orientated parallel to the direction of former ice flow (e.g. Ussing, 1903;Wright, 1973;Attig et al, 1989;Wingfield, 1990;Piotrowski, 1994;Patterson, 1997;Huuse and LykkeAnderson, 2000;Jørgensen and Sandersen, 2006). Features with similar dimensions have also been described beneath current ice masses (e.g.…”

Section: Introductionmentioning

confidence: 92%

“…Genesis is typically thought to occur via repeated low to moderate magnitude floods that may be at or below bankfull flow (e.g. Wright, 1973;Boyd et al, 1988;Wingfield, 1990;Piotrowski, 1994;Cutler et al, 2002;Hooke and Jennings, 2006;Jørgensen and Sandersen, 2006). Catastrophic erosion of entire tunnel valley networks by massive sheet floods has also been proposed (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Morphological properties of tunnel valleys of the southern sector of the Laurentide Ice Sheet and implications for their formation

Livingstone

Clark

2016

Earth Surf. Dynam.

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Abstract. Tunnel valleys have been widely reported on the bed of former ice sheets and are considered an important expression of subglacial meltwater drainage. Although known to have been cut by erosive meltwater flow, the water source and development of channels has been widely debated; ranging between outburst flood events through to gradually occurring channel propagation. We have mapped and analysed the spatial pattern and morphometry of tunnel valleys and associated glacial landforms along the southern sector of the former Laurentide Ice Sheet from high-resolution digital elevation models. Around 2000 tunnel valleys have been mapped, revealing an organised pattern of sub-parallel, semi-regularly spaced valleys that form in distinctive clusters. The tunnel valleys are typically < 20 km long, and 0.5-3 km wide, although their width varies considerably down-valley. They preferentially terminate at moraines, which suggests that formation is time dependent; while we also observe some tunnel valleys that have grown headwards out of hill-hole pairs. Analysis of cross-cutting relationships between tunnel valleys, moraines and outwash fans permits reconstruction of channel development in relation to the retreating ice margin. This palaeo-drainage reconstruction demonstrates incremental growth of most valleys, with some used repeatedly or for long periods, during deglaciation, while others were abandoned shortly after their formation. Our data and interpretation support gradual (rather than a single-event) formation of most tunnel valleys with secondary contributions from flood drainage of subglacial and or supraglacially stored water down individual tunnel valleys. The distribution and morphology of tunnel valleys is shown to be sensitive to regional factors such as basal thermal regime, ice and bed topography, timing and climate.

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Section: Limitationsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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Morphological properties of tunnel valleys of the southern sector of the Laurentide Ice Sheet and implications for their formation

Livingstone

Clark

2016

Earth Surf. Dynam.

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“…The synthetic demonstration model used here is, to a large degree, inspired by the model of Doherty and Christensen (2011). The hydrogeological setting of the model domain is typical for large areas of northern Europe and North America: a glacially formed landscape with a buried tunnel valley eroded into impermeable bedrock (fat clay) with very low electrical resistivity (Wright, 1973;Piotrowski, 1994;Clayton et al, 1999;Jørgensen and Sandersen, 2006). The case is designed to have a perfect relationship between hydraulic conductivity and electrical resistivity.…”

Section: Demonstration Modelmentioning

confidence: 99%

Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models

Christensen¹,

Christensen²,

Ferré³

2016

Hydrol. Earth Syst. Sci.

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Abstract. In spite of geophysics being used increasingly, it is often unclear how and when the integration of geophysical data and models can best improve the construction and predictive capability of groundwater models. This paper uses a newly developed HYdrogeophysical TEst-Bench (HYTEB) that is a collection of geological, groundwater and geophysical modeling and inversion software to demonstrate alternative uses of electromagnetic (EM) data for groundwater modeling in a hydrogeological environment consisting of various types of glacial deposits with typical hydraulic conductivities and electrical resistivities covering impermeable bedrock with low resistivity (clay). The synthetic 3-D reference system is designed so that there is a perfect relationship between hydraulic conductivity and electrical resistivity. For this system it is investigated to what extent groundwater model calibration and, often more importantly, model predictions can be improved by including in the calibration process electrical resistivity estimates obtained from TEM data. In all calibration cases, the hydraulic conductivity field is highly parameterized and the estimation is stabilized by (in most cases) geophysics-based regularization.For the studied system and inversion approaches it is found that resistivities estimated by sequential hydrogeophysical inversion (SHI) or joint hydrogeophysical inversion (JHI) should be used with caution as estimators of hydraulic conductivity or as regularization means for subsequent hydrological inversion. The limited groundwater model improvement obtained by using the geophysical data probably mainly arises from the way these data are used here: the alternative inversion approaches propagate geophysical estimation errors into the hydrologic model parameters. It was expected that JHI would compensate for this, but the hydrologic data were apparently insufficient to secure such compensation. With respect to reducing model prediction error, it depends on the type of prediction whether it has value to include geophysics in a joint or sequential hydrogeophysical model calibration. It is found that all calibrated models are good predictors of hydraulic head. When the stress situation is changed from that of the hydrologic calibration data, then all models make biased predictions of head change. All calibrated models turn out to be very poor predictors of the pumping well's recharge area and groundwater age. The reason for this is that distributed recharge is parameterized as depending on estimated hydraulic conductivity of the upper model layer, which tends to be underestimated. Another important insight from our analysis is thus that either recharge should be parameterized and estimated in a different way, or other types of data should be added to better constrain the recharge estimates.

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“…The studied aquifer is located within a buried valley structure (Figure 1c), which is a part of a regional system of buried valleys found within the area outlined in Figure 1b (Jørgensen and Sandersen, 2006;Møller et al, 2009). The valleys are incised into Paleogene clay, which acts as an impermeable bed of the deepest aquifer.…”

Section: Field Casementioning

confidence: 99%

On determining uncertainties of magnetic resonance sounding estimated transmissivities for groundwater modeling

2016

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The nuclear magnetic resonance sounding (MRS) method is used increasingly as a tool for hydrological investigations. Compared to other geophysical methods, the advantage of MRS is that it is directly sensitive to the presence of water in the subsurface. Data interpretations can also be used to get information about the subsurface pore structures, which under special conditions can be related to hydraulic properties such as aquifer transmissivity. However, to broaden the usage of this information in hydrological modeling, the uncertainties related to these transmissivity estimates must be determined. Otherwise, properly balanced weights cannot be given to the prior information obtained from MRS transmissivity estimates as compared to the hydrological data sets when used for groundwater model calibration. We have developed a methodology to estimate the uncertainties of MRS-based transmissivity estimates. Compared to previous studies, the methodology is well defined, and it takes into account important factors such as the uncertainties of the hydraulically estimated transmissivities, the uncertainty of the correlation factor in the petrophysical relation, and the uncertainties and correlations of the geophysically estimated parameters. We have determined the correlations and uncertainties of the geophysical parameters using a linear and a nonlinear method, and we find that the results are comparable.

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Buried and open tunnel valleys in Denmark—erosion beneath multiple ice sheets

Cited by 218 publications

References 93 publications

Morphological properties of tunnel valleys of the southern sector of the Laurentide Ice Sheet and implications for their formation

Morphological properties of tunnel valleys of the southern sector of the Laurentide Ice Sheet and implications for their formation

Testing alternative uses of electromagnetic data to reduce the prediction error of groundwater models

On determining uncertainties of magnetic resonance sounding estimated transmissivities for groundwater modeling

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