Roughness of a subglacial conduit under Hansbreen, Svalbard

Mankoff, Kenneth D.; Gulley, Jason; Tulaczyk, S. M.; Covington, M. D.; Liu, Xiaofeng; Chen, Yunxiang; Benn, Douglas I.; Głowacki, Piotr

doi:10.1017/jog.2016.134

Cited by 14 publications

(16 citation statements)

References 39 publications

(73 reference statements)

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“…6e), is most in agreement with field observations. In fact, it is the only scenario that represents the well-studied subglacial channels generated by Crystal Cave and Bird Brain Cave (Gulley et al, 2012;Murray et al, 2007;Schroeder, 1998;Turu, 2012), with a coherent orientation compared to existing maps Mankoff et al, 2017) and the authors' personal observations, along with the best location of outflows. In fact, the authors visited those two cave systems several times a year for a few years and repeated observations confirmed that the data cited above are still valid.…”

Section: Discussionmentioning

confidence: 78%

Role of discrete water recharge from supraglacial drainage systems in modeling patterns of subglacial conduits in Svalbard glaciers

et al. 2019

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Abstract. As the behavior of subglacial water plays a determining role in glacier dynamics, it requires particular attention, especially in the context of climate warming, which is increasing ablation and generating greater amounts of meltwater. On many glaciers, water flowing from the glacier's surface is the main source of supply to the subglacial drainage system. This system is largely influenced by the supraglacial drainage system, which collects meltwater and precipitation and rapidly delivers it to discrete points in the glacier bed via moulins and crevassed areas, called water input areas (WIAs). Models of patterns of subglacial conduits mainly based on the hydrological potential gradient are still regularly performed without taking into account the supraglacial drainage system. We modeled the pattern of subglacial channels in two glaciers located in Svalbard, the land-terminating Werenskioldbreen and the tidewater Hansbreen during the 2015 melt season. We modeled a spatial and a discrete water recharge in order to compare them. First, supraglacial catchments were determined for each WIA on a high-resolution digital elevation model using the standard watershed modeling tool in ArcGIS. Then, interpolated water runoff was calculated for all the main WIAs. Our model also accounts for several water pressure conditions. For our two studied glaciers, during the ablation season 2015, 72.5 % of total runoff was provided by meltwater and 27.5 % by precipitation. Changes in supraglacial drainage on a decadal timescale are observed in contrast to its nearly stable state on an annual timescale. Nevertheless, due to the specific nature of those changes, it seems to have a low impact on the subglacial system. Therefore, our models of subglacial channel are assumed to be valid for a minimum period of two decades and depend on changes in the supraglacial drainage system. Results showed that, for Svalbard tidewater glaciers with large crevassed areas, models of subglacial channels that assume spatial water recharge may be somewhat imprecise but are far from being completely incorrect, especially for the ablation zone. On the other hand, it is important to take discrete water recharge into account in the case of land-terminating Svalbard glaciers with limited crevassed areas. In all cases, considering a discrete water recharge when modeling patterns of theoretical subglacial channels seems to produce more realistic results according to current knowledge.

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Section: Discussionmentioning

confidence: 78%

Role of discrete water recharge from supraglacial drainage systems in modeling patterns of subglacial conduits in Svalbard glaciers

et al. 2019

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“…Bell 1975), glaciated bedrocks and sub-glacial surfaces (e.g. Hubbard, Siegert & McCarroll 2000;Mankoff et al 2017), the surfaces of other planets (e.g. Turcotte 1997;Nikora & Goring 2004) and a variety of machined surfaces (e.g.…”

Section: Roughness Characteristicsmentioning

confidence: 99%

Friction factor decomposition for rough-wall flows: theoretical background and application to open-channel flows

Nikora

Stoesser

Cameron³

et al. 2019

J. Fluid Mech.

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A theoretically based relationship for the Darcy–Weisbach friction factor $f$ for rough-bed open-channel flows is derived and discussed. The derivation procedure is based on the double averaging (in time and space) of the Navier–Stokes equation followed by repeated integration across the flow. The obtained relationship explicitly shows that the friction factor can be split into at least five additive components, due to: (i) viscous stress; (ii) turbulent stress; (iii) dispersive stress (which in turn can be subdivided into two parts, due to bed roughness and secondary currents); (iv) flow unsteadiness and non-uniformity; and (v) spatial heterogeneity of fluid stresses in a bed-parallel plane. These constitutive components account for the roughness geometry effect and highlight the significance of the turbulent and dispersive stresses in the near-bed region where their values are largest. To explore the potential of the proposed relationship, an extensive data set has been assembled by employing specially designed large-eddy simulations and laboratory experiments for a wide range of Reynolds numbers. Flows over self-affine rough boundaries, which are representative of natural and man-made surfaces, are considered. The data analysis focuses on the effects of roughness geometry (i.e. spectral slope in the bed elevation spectra), relative submergence of roughness elements and flow and roughness Reynolds numbers, all of which are found to be substantial. It is revealed that at sufficiently high Reynolds numbers the roughness-induced and secondary-currents-induced dispersive stresses may play significant roles in generating bed friction, complementing the dominant turbulent stress contribution.

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“…Second, more data on the geometry of conduits in the snout marginal zone would be valuable. It is now possible to acquire such data, at a coarse resolution using GPR (Rüttimann et al, n.d.) and at a very fine resolution by caving (Mankoff et al, ), albeit under conditions that allow safe access. With further developments in GPR technology, it may become possible to monitor subglacial conduit dynamics at the within‐daily scale to assess the extent to which conduit geometry evolves in response to end of day sediment deposition.…”

Section: Discussionmentioning

confidence: 99%

Subglacial sediment production and snout marginal ice uplift during the late ablation season of a temperate valley glacier

Perolo

Bakker

Gabbud

et al. 2019

Earth Surf Processes Landf

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Sediment export from glaciated basins involves complex interactions between ice flow, basal erosion and sediment transfer in subglacial and proglacial streams. In particular, we know very little about the processes associated with sediment transfer by subglacial streams. The Haut Glacier d'Arolla (VS, Switzerland) was investigated during the summer melt season of 2015. LiDAR survey revealed positive surface changes in the ablation zone, indicating glacier uplift, at the end of the morning during the period of peak ablation. Instream measures of sediment transport showed that suspended load and bedload responded differently to diurnal flow variability. Suspended load depended on the availability of fine material whereas bedload depended mainly on the competence of the flow. Interpretation of these results allowed development of a conceptual model of subglacial sediment transport dynamics. It is based upon the mechanisms of clogging (deposition) and flushing (transport/erosion) in sub‐glacial channels as forced by diurnal flow variability. Through the melt season, the glacier hydrological response evolves from being buffered by glacier snow cover with a poorly developed subglacial drainage system to being dominated by more rapid ice melt with a more hydraulically efficient subglacial channel system. The resultant changes in the shape of diurnal discharge hydrographs, and notably higher peak flows and lower base flows, causes sediment transport to become discontinuous, with overnight clogging and late morning flushing of subglacial channels. Overnight clogging may be sufficient to reduce subglacial channel size, creating temporarily pressurized flow and lateral transfer of water away from the subglacial channels, leading to the late morning glacier surface uplift. However, without further data, we cannot exclude other hypotheses for the uplift. © 2018 John Wiley & Sons, Ltd.

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Roughness of a subglacial conduit under Hansbreen, Svalbard

Cited by 14 publications

References 39 publications

Role of discrete water recharge from supraglacial drainage systems in modeling patterns of subglacial conduits in Svalbard glaciers

Role of discrete water recharge from supraglacial drainage systems in modeling patterns of subglacial conduits in Svalbard glaciers

Friction factor decomposition for rough-wall flows: theoretical background and application to open-channel flows

Subglacial sediment production and snout marginal ice uplift during the late ablation season of a temperate valley glacier

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