Mechanical and hydrologic basis for the rapid motion of a large tidewater glacier: 1. Observations

Meier, Mark F.; Lundstrom, Scott C.; Stone, Dan B.; Kamb, Barclay; Engelhardt, Hermann; Humphrey, N. F.; Dunlap, William W.; Fahnestock, M. A.; Krimmel, Robert M.; Walters, Roy A.

doi:10.1029/94jb00237

Cited by 132 publications

(103 citation statements)

References 23 publications

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“…Basal water pressure was consistently high and the effective pressure varied within a range of −100 and 300 kPa (ref. 19). These figures are similar to those we observed at GPM, but ice speed at Columbia Glacier was not well correlated with water pressure nor with air temperature.…”

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confidence: 80%

Ice speed of a calving glacier modulated by small fluctuations in basal water pressure

et al. 2011

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Ice flow acceleration has played a crucial role in the recent rapid retreat of calving glaciers in Alaska 1,2 , as well as in Greenland and Antarctica 3,4 . Fast flow of such glaciers is due primarily to basal ice motion 5 , but its mechanism is poorly understood because subglacial observations are scarce in calving glaciers. Here we show high-frequency ice speed and basal water pressure measurements performed in Glaciar Perito Moreno, a fast-flowing calving glacier in Patagonia. The water pressure was measured in a borehole drilled through the 515±5 m thick glacier at a site where more than 60% of ice is below the proglacial lake level. We found that mean basal water pressure reached 94-96% of the ice overburden pressure, and that a few percent of pressure changes were driving nearly 40% of ice speed variations. The ice speed was strongly correlated to air temperature, suggesting the glacier motion was modulated by water pressure 1 under the influence of changing meltwater input. Our observations demonstrate the great importance of basal water pressure in the calving glacier dynamics and its close connection to climate conditions. It is thus crucial to take into account the elevated basal water pressure for predicting future evolution of calving glaciers.Acceleration of fast-flowing calving glaciers is the focus of attention as it is responsible for the rapid retreat of large tidewater glaciers in Alaska 1,2 as well as the recent wastage of Greenland and the Antarctic ice sheets 3,4 . Calving glaciers flow much faster than those terminating on land as a result of basal ice motion enhanced by high basal water pressure 5 . A commonly used basal flow law stateswhere u b is the basal ice speed, τ b is the basal shear stress, P i and P w are ice overburden and basal water pressures, and k, p and q are empirical parameters 6,7 . Because τ b is primarily controlled by ice thickness and surface slope, changes in basal water pressure play a critical role in short-term ice speed variations. Observations in mountain glaciers have shown rapid acceleration as basal water pressure approaches ice overburden pressure 8−10 , which confirms the non-linear dependence of the basal ice speed on the effective pressure defined by P e = P i − P w .The hydraulic head within a calving glacier is expected to be higher than the surface level of the proglacial water body, which maintains basal water pressure closer to ice overburden.According to the inverse proportionality of u b to P e , small perturbations in P w near P i result in large ice speed variations. Moreover, changes in P i due to glacier thinning or thickening have a great impact on the ice speed as well. These characteristics make calving glacier dynamics more susceptible to external forcing than land terminating glaciers. Studying the response of ice speed to the changes in P e is thus crucial for predicting the future evolution of calving glaciers. In the austral summer 2008/09 and 2010, we operated three GPS (Global Positioning System) receivers on GPM at hourly intervals ...

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confidence: 80%

Ice speed of a calving glacier modulated by small fluctuations in basal water pressure

et al. 2011

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“…The loop closed when the drainage system started to develop again in the consecutive spring. Previous studies at Columbia Glacier [33,35,36] [33,36] observed ice velocity, basal water pressure and rainfall data at Columbia Glacier on a diurnal scale between 07/05/1987 and 08/31/1987. Similarly, Sugiyama et al (2011) [9] observed the coupling of ice dynamics to basal water pressure on Perito Moreno Glacier in Patagonia.…”

Section: Variations In Ice Dynamics During 2011-2016mentioning

confidence: 99%

Seasonal and Interannual Variability of Columbia Glacier, Alaska (2011–2016): Ice Velocity, Mass Flux, Surface Elevation and Front Position

Vijay

Braun

2017

Remote Sensing

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Alaskan glaciers are among the largest contributors to sea-level rise outside the polar ice sheets. The contributions include dynamic discharge from marine-terminating glaciers which depends on the seasonally variable ice velocity. Columbia Glacier is a large marine-terminating glacier located in Southcentral Alaska that has been exhibiting pronounced retreat since the early 1980s. Since 2010, the glacier has split into two branches, the main branch and the west branch. We derived a 5-year record of surface velocity, mass flux (ice discharge), surface elevation and changes in front position using a dense time series of TanDEM-X synthetic aperture radar data (2011)(2012)(2013)(2014)(2015)(2016). We observed distinct seasonal velocity patterns at both branches. At the main branch, the surface velocity peaked during late winter to midsummer but reached a minimum between late summer and fall. Its near-front velocity reached up to 14 m day −1 in May 2015 and was at its lowest speed of~1 m day −1 in October 2012. Mass flux via the main branch was strongly controlled by the seasonal and interannual fluctuations of its velocity. The west branch also exhibited seasonal velocity variations with comparably lower magnitudes. The role of subglacial hydrology on the ice velocities of Columbia Glacier is already known from the published field measurements during summers of 1987. Our observed variability in its ice velocities on a seasonal basis also suggest that they are primarily controlled by the seasonal transition of the subglacial drainage system from an inefficient to an efficient and channelized drainage networks. However, abrupt velocity increase events for short periods (2014-2015 and 2015-2016 at the main branch, and 2013-2014 at the west branch) appear to be associated with strong near-front thinning and frontal retreat. This needs further investigation on the role of other potential controlling mechanisms. On the technological side, this study demonstrates the potential of high-resolution X-band SAR missions with a short revisit interval to examine glaciological variables and controlling processes.

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“…These usually exhibit a diurnal signal, which reflects changes in delivery of meltwater to the bed and creates transverse hydraulic gradients that make meltwater pathways highly changeable (e.g. Meier et al, 1994;Hubbard et al, 1995). Consistently high basal water pressures have been associated with glaciers where the evacuation of meltwater from the subglacial environment is inefficient or where the drainage system is unstable (e.g.…”

Section: Subglacial Drainage Of Kronebreenmentioning

confidence: 99%

Rapidly changing subglacial hydrological pathways at a tidewater glacier revealed through simultaneous observations of water pressure, supraglacial lakes, meltwater plumes and surface velocities

et al. 2017

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Abstract. Subglacial hydrological processes at tidewater glaciers remain poorly understood due to the difficulty in obtaining direct measurements and lack of empirical verification for modelling approaches. Here, we investigate the subglacial hydrology of Kronebreen, a fast-flowing tidewater glacier in Svalbard during the 2014 melt season. We combine observations of borehole water pressure, supraglacial lake drainage, surface velocities and plume activity with modelled run-off and water routing to develop a conceptual model that thoroughly encapsulates subglacial drainage at a tidewater glacier. Simultaneous measurements suggest that an earlyseason episode of subglacial flushing took place during our observation period, and a stable efficient drainage system effectively transported subglacial water through the northern region of the glacier tongue. Drainage pathways through the central and southern regions of the glacier tongue were disrupted throughout the following melt season. Periodic plume activity at the terminus appears to be a signal for modulated subglacial pulsing, i.e. an internally driven storage and release of subglacial meltwater that operates independently of marine influences. This storage is a key control on ice flow in the 2014 melt season. Evidence from this work and previous studies strongly suggests that long-term changes in ice flow at Kronebreen are controlled by the location of efficient/inefficient drainage and the position of regions where water is stored and released.

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Mechanical and hydrologic basis for the rapid motion of a large tidewater glacier: 1. Observations

Cited by 132 publications

References 23 publications

Ice speed of a calving glacier modulated by small fluctuations in basal water pressure

Ice speed of a calving glacier modulated by small fluctuations in basal water pressure

Seasonal and Interannual Variability of Columbia Glacier, Alaska (2011–2016): Ice Velocity, Mass Flux, Surface Elevation and Front Position

Rapidly changing subglacial hydrological pathways at a tidewater glacier revealed through simultaneous observations of water pressure, supraglacial lakes, meltwater plumes and surface velocities

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