Subsurface hydrology of an overdeepened cirque glacier

Dow, Christine F.; Kavanaugh, Jeffrey L.; Sanders, J. W.; Cuffey, Kurt M.; MacGregor, K. R.

doi:10.3189/002214311798843412

Cited by 15 publications

(28 citation statements)

References 58 publications

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“…The water pressure has to rise to overcome the closure of the conduits and escape down−glacier (Röthlisberger 1972). That also stimulates the formation of subglacial channels around the overdeepening (Dow et al 2011), the development of englacial drainage above an overdeepening (Hooke and Pohjola 1994) and/or a distributed drainage system (Röthlisberger 1968;Paterson 1994). In consequence, the pressure of water filling the basin increases up to the threshold value that al− lows the water to escape downglacier through, above or around the riegel.…”

Section: Discussionmentioning

confidence: 99%

Surface and bed morphology of Hansbreen, a tidewater glacier in Spitsbergen

Grabiec¹,

Jania²,

Puczko³

et al. 2012

Polish Polar Research

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Hansbreen, a medium size tidewater glacier in Southern Spitsbergen (Svalbard) is one of the most intensively studied glaciers in the Arctic. This work presents new digital elevation models of its surface and basal topography based on data collected during GPS/GPR campaigns conducted in the spring seasons of 2005 and 2008, as well as on other recent topographic/bathymetric sources. The mean thickness of the glacier is calculated as 171 m and its volume is estimated to be 9.6 (±0.1) km 3 . The main feature of the bedrock morphology is a vast depression that is overdeepened below sea level and extends as far as 11 km upstream from the glacier front. This depression is divided into four individual bas− ins by distinct sills that are related to the main geological/tectonic features of the area. The bedrock morphology affects considerably the glacier's surface topography. The influence of bedrock and surface relief on the subglacial drainage system geometry is discussed. Vast depressions on the glacier surface favor concentration of meltwater and development of moulin systems.

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Section: Discussionmentioning

confidence: 99%

Surface and bed morphology of Hansbreen, a tidewater glacier in Spitsbergen

Grabiec¹,

Jania²,

Puczko³

et al. 2012

Polish Polar Research

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“…Reflection R280 most likely marks the transition from isotropic to a (almost) VTI structure with a cone opening angle up to 45 ∘ . This anisotropic ice is vertically less compressible but horizontally twice more easily deformable, having an enhancement factor of ∼2 for simple shear (Cuffey & Paterson, 2010;Thorsteinsson, 2000). The value of the enhancement factor may be affected by the assumption of overlying isotropic ice.…”

Section: Interpretation Of the Four Media At The Interfaces Of R280 mentioning

confidence: 99%

Physical Conditions of Fast Glacier Flow: 2. Variable Extent of Anisotropic Ice and Soft Basal Sediment From Seismic Reflection Data Acquired on Store Glacier, West Greenland

et al. 2018

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Outlet glaciers of the Greenland Ice Sheet transport ice from the interior to the ocean and contribute directly to sea level rise because discharge and ablation often exceed the accumulation. To develop a better understanding of these fast‐flowing glaciers, we investigate the basal conditions of Store Glacier, a large outlet glacier flowing into Uummannaq Fjord in west Greenland. We use two crossing seismic profiles acquired near the centerline, 30 km upstream of the calving front, to interpret the physical nature of the ice and bed. We identify one notably englacial and two notably subglacial seismic reflections on both profiles. The englacial reflection represents a change in crystal orientation fabric, interpreted to be the Holocene‐Wisconsin transition. From Amplitude‐Versus‐Angle (AVA) analysis we infer that the deepest ∼80 m of ice of the parallel‐flow profile below this reflection is anisotropic with an enhancement of simple shear of ∼2. The ice is underlain by ∼45 m of unconsolidated sediments, below which there is a strong reflection caused by the transition to consolidated sediments. In the across‐flow profile subglacial properties vary over small scale and the polarity of the ice‐bed reflection switches from positive to negative. We interpret these as patches of different basal slipperiness associated with variable amounts of water. Our results illustrate variability in basal properties, and hence ice‐bed coupling, at a spatial scale of ∼100 m, highlighting the need for direct observations of the bed to improve the basal boundary conditions in ice‐dynamic models.

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“…We used 10 boreholes (Dow et al, 2011) and two englacial fl ux profi les (EFP1 and EFP2 in Fig. 4) to estimate the rock concentration inside the glacier.…”

Section: Englacial Diffusementioning

confidence: 99%

The sediment budget of an alpine cirque

Sanders

Cuffey

MacGregor

et al. 2012

Geological Society of America Bulletin

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Cirques form and evolve as glaciers attack the bed and subaerial processes dismantle the surrounding walls. Collectively, these processes-which can make a cirque longer, or deeper, or both-profoundly infl uence near-divide regions of glaciated mountains and yet are rarely studied in a systematic way. Toward this end, we developed a theoretical framework for the sediment budget of a cirque that includes sediment sources, transport pathways, and storage elements. We quantifi ed each component of the sediment budget using fi eld measurements and remote-sensing data of a glaciated alpine cirque in British Columbia, Canada. The cirque has a plan-view area of 1.64 km 2 and relief of ~780 m. Our budget values, which correspond to a period of substantial glacier retreat, are based on measurements refl ecting time intervals ranging from 1 yr to 80 yr. We report errors as a range (enclosed in parentheses), analogous to 95% confi dence bounds.On average, 1640 (250-7950) metric tons of rock are released by the headwall each year; nearly 90% of this debris leaves the wall as small rockfalls or in snow avalanches. Our fi eld observations indicated that snow avalanches originating as cornice failures are currently the most important transport process on the headwall. We estimated the mass of debris transported annually by the glacier to the foreland using (1) the volume and age of the foreland ground moraine and (2) the product of rock mass per unit volume of ice and glacier velocity. Over the past several decades, the glacier delivered 6440 (1180-14930) tons/yr to the foreland via forward ice motion and margin retreat (mostly in subglacial till or sediment-rich basal layers). Less than 3% of the glacier-borne sediment fl ux traveled as supra glacial debris (170 [50-320] tons/yr). At present, sediment evacuation from the cirque occurs in a single meltwater stream. We monitored water discharge and suspended sediment concentration in this stream between 29 June and 28 August 2007. By season's end, 650 (80-1860) tons of sediment had passed our gauging station (equivalent to an erosion rate of 0.2 [0.03-0.70] mm/yr, when averaged over the glacier bed). Approximately one third of the total annual streamborne sediment transport occurred over a 2 d period during the fi rst major melt event of the year.Using our budget relations and fl ux magnitudes, we estimate the glacier is removing between 1240 and 2470 tons of rock from its bed per year, a rate equivalent to 0.5-0.9 mm/yr of erosion glacierwide. The headwall, by comparison, is being worn away horizontally at ~1.2 (0.2-5.9) mm/yr. Thus, our results suggest that the headwall is retreating at rates roughly equivalent to vertical incision by the glacier. Our sediment budget results demonstrate that the wide variety of sediment sources and transport processes active in cirques necessitates a holistic view of cirque formation, one that most morphometric, range-scale, and glacial erosion analyses ignore.

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Subsurface hydrology of an overdeepened cirque glacier

Cited by 15 publications

References 58 publications

Surface and bed morphology of Hansbreen, a tidewater glacier in Spitsbergen

Surface and bed morphology of Hansbreen, a tidewater glacier in Spitsbergen

Physical Conditions of Fast Glacier Flow: 2. Variable Extent of Anisotropic Ice and Soft Basal Sediment From Seismic Reflection Data Acquired on Store Glacier, West Greenland

The sediment budget of an alpine cirque

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