Bed properties and hydrological conditions underneath McCall Glacier, Alaska, USA

Pattyn, Frank; Delcourt, Charlotte; Samyn, Denis; Smedt, Bert De; Nolan, M.

doi:10.3189/172756409789097559

Cited by 18 publications

(20 citation statements)

References 16 publications

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“…Nonetheless, certainly in polythermal glaciers, subglacial drainage structures do exist and observations of nontemperate glacier dynamics showed seasonal and subseasonal variations in ice velocities not dissimilar to those recorded at temperate glaciers [ Andreason , 1985; Blatter and Kappenberger , 1988; Iken , 1972; Müller and Iken , 1973; Rabus and Echelmeyer , 1997]; such velocities necessitate the presence of subglacial water and suggest that it is incorrect to assume a reduced surface‐subsurface hydraulic coupling in polythermal glaciers. Moreover, it is likely that at the macroscale, subglacial drainage at polythermal glaciers, particularly those with extensive temperate ice areas, may exhibit similarities with the long‐standing Shrevian model, perhaps forgiving modeling based upon glacier‐scale hydraulic potential [e.g., Copland and Sharp , 2001; Flowers and Clarke , 1999; Hagen et al , 2000; Pälli et al , 2003; Pattyn et al , 2009; Rippin et al , 2003]. However, water delivery to the glacier bed in nontemperate examples may be more spatially discrete than at temperate counterparts, and the controls imposed by spatial variability in mesoscale and microscale thermal regime and water content should not be underestimated.…”

Section: Summary and Implicationsmentioning

confidence: 99%

Polythermal Glacier Hydrology: A Review

Irvine‐Fynn¹,

Hodson²,

Moorman³

et al. 2011

Reviews of Geophysics

177

225

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[1] The manner by which meltwater drains through a glacier is critical to ice dynamics, runoff characteristics, and water quality. However, much of the contemporary knowledge relating to glacier hydrology has been based upon, and conditioned by, understanding gleaned from temperate valley glaciers. Globally, a significant proportion of glaciers and ice sheets exhibit nontemperate thermal regimes. The recent, growing concern over the future response of polar glaciers and ice sheets to forecasts of a warming climate and lengthening summer melt season necessitates recognition of the hydrological processes in these nontemperate ice masses. It is therefore timely to present an accessible review of the scientific progress in glacial hydrology where nontemperate conditions are dominant. This review provides an appraisal of the glaciological literature from nontemperate glaciers, examining supraglacial, englacial, and subglacial environments in sequence and their role in hydrological processes within glacierized catchments. In particular, the variability and complexity in glacier thermal regimes are discussed, illustrating how a unified model of drainage architecture is likely to remain elusive due to structural controls on the presence of water. Cold ice near glacier surfaces may reduce meltwater flux into the glacier interior, but observations suggest that the transient thermal layer of near surface ice holds a hydrological role as a depth-limited aquifer. Englacial flowpaths may arise from the deep incision of supraglacial streams or the propagation of hydrofractures, forms which are readily able to handle varied meltwater discharge or act as locations for water storage, and result in spatially discrete delivery of water to the subglacial environment. The influence of such drainage routes on seasonal meltwater release is explored, with reference to summer season upwellings and winter icing formation. Moreover, clear analogies emerge between nontemperate valley glacier and ice sheet hydrology, the discussion of which indicates how persistent reassessment of our conceptualization of glacier drainage systems is required. There is a clear emphasis that continued, integrated endeavors focused on process glaciology at nontemperate glaciers are a scientific imperative to augmenting the existing body of research centered on ice mass hydrology.

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Section: Summary and Implicationsmentioning

confidence: 99%

Polythermal Glacier Hydrology: A Review

Irvine‐Fynn¹,

Hodson²,

Moorman³

et al. 2011

Reviews of Geophysics

177

225

View full text Add to dashboard Cite

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“…BRP R is the residual BRP, the variations of which are not related to changes in the amount of energy transmitted into the ice (Gades, 1998). In order to obtain BRP est , some authors have used empirical methods, where the measured BRP values from a given area are plotted against ice thickness and a best-fit curve is used as a representative model (usually an exponential fit) (Gades, 1998; Gades and others, 2000; Copland and Sharp, 2001; Pattyn and others, 2009). In contrast, other authors have estimated BRP est theoretically by using the radar equation for which parameters are known (Bentley and others, 1998; Peters and others, 2005).…”

Section: Introductionmentioning

confidence: 99%

50 MHz helicopter-borne radar data for determination of glacier thermal regime in the central Chilean Andes

et al. 2015

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ABSTRACT. Despite their importance as freshwater reservoirs for downstream river systems, few glaciers in central Chile have been comprehensively surveyed. This study presents ground-penetrating radar (GPR) and field-based observations for characterizing the englacial and basal conditions of Glaciar Olivares Alfa (33°11 0 S, 70°13 0 W), central Chilean Andes. Using a 50 MHz radar mounted onto a helicopter platform, data were collected covering large portions of the glacier accumulation and ablation zones. The radar data revealed boundaries of a temperate-ice layer at the base of the eastern body of Glaciar Olivares Alfa which appears to be covered by colder ice that extends throughout large parts of the glacier. The thickness of the temperate ice layer is highly variable across the glacier, being on average 40% of the total ice thickness. Radar data analyses reveal regions of cold ice at the bottom/ base of the glacier and also patterns of highly saturated sediments beneath the glacier. Using GPR data, this study represents the most exhaustive analysis of glacier ice structure performed in the central Chilean Andes. The results will enable improved estimations of the glacier's mass balance and ice dynamics, helping us to understand its further development and its impact on water availability.

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“…Depth‐averaged attenuation rates to the bed of polar ice sheets can vary across more than two orders of magnitude (<10 to ∼30 dB km −1 one way) [e.g., Jacobel et al , 2009, 2010; Matsuoka et al , 2010a, 2012], yet the reflectivity difference between dry and wet beds is only 10–15 dB [e.g., Peters et al , 2005]. Furthermore, many studies have assumed a uniform depth‐averaged attenuation rate [e.g., Bentley et al , 1998; Copland and Sharp , 2001; Rippin et al , 2004; Peters et al , 2005; Pattyn et al , 2009; MacGregor et al , 2011; Pettersson et al , 2011]. Although in many cases their inferences regarding basal conditions from radar data are qualitatively consistent with glaciological expectations, this assumption limits both the quality of those inferences and the straightforward detection of regions with basal conditions that do not conform with predictions.…”

Section: Introductionmentioning

confidence: 99%

Spatial variation of englacial radar attenuation: Modeling approach and application to the Vostok flowline

MacGregor¹,

Matsuoka²,

Waddington³

et al. 2012

J. Geophys. Res.

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[1] Constraining the spatial variation of englacial radar attenuation is critical for accurate inference of the spatial variation of the englacial and basal properties of ice sheets from radar returned power. Here we evaluate attenuation models that account for spatial variations in ice temperature and chemistry and test them along the flowline that passes through the Vostok ice core site, Antarctica. The simplest model, often used but rarely valid, assumes a uniform attenuation rate everywhere along the flowline, so that total attenuation is proportional to ice thickness. The next simplest model uses spatially varying temperatures predicted by an ice-flow model and assumes uniform chemistry. Additional models account for spatially varying chemistry using englacial stratigraphy. We find that the roundtrip attenuation to the bed can easily differ by 10 dB or more between the uniform attenuation-rate model and models that account for variable ice temperature. Such differences are sufficient to confound the delineation of dry and wet beds. Also including spatial variations in chemistry produces smaller differences (<10 dB), but the magnitude of these differences depends on the relative importance of dry and wet deposition of impurities in the past. Accounting for dry-deposited impurities requires ice-flow modeling and results in larger differences from all other models, which assume uniform chemistry or wet deposition only. These results indicate that modeling the spatial variation of attenuation requires a spatially varying temperature model in order to infer bed conditions from bed returned power accurately, and that both ice core data and radar stratigraphy are also strongly desirable.

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Bed properties and hydrological conditions underneath McCall Glacier, Alaska, USA

Cited by 18 publications

References 16 publications

Polythermal Glacier Hydrology: A Review

Polythermal Glacier Hydrology: A Review

50 MHz helicopter-borne radar data for determination of glacier thermal regime in the central Chilean Andes

Spatial variation of englacial radar attenuation: Modeling approach and application to the Vostok flowline

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