scholarly journals Localized basal motion of a polythermal Arctic glacier:McCall Glacier, Alaska, USA

2005 ◽  
Vol 40 ◽  
pp. 47-51 ◽  
Author(s):  
Frank Pattyn ◽  
Matt Nolan ◽  
Bernhard Rabus ◽  
Shuhei Takahashi
Keyword(s):  
Flow Model ◽  
Central Frequency ◽  
Ice Flow ◽  
Model Experiments ◽  
Ablation Area ◽  
Basal Ice ◽  
Basal Sliding ◽  
Radio Echo Sounding ◽  
Glacier Modeling ◽  
Enhanced Surface

AbstractWe analyzed the ice flow of McCall Glacier, Alaska, USA, by numerical glacier modeling and radio-echo sounding (RES). Model experiments were carried out with a higher-order numerical ice-flow model, and results were validated with measurements of annual ice velocities and compared with previous estimates of ice-flow dynamics. During the 2003 summer campaign, detailed RES measurements were carried out along the central flowline of the ablation area with a 5 MHz (central frequency) ice-penetrating radar, where 10m ice temperatures are approximately –7.5˚C. The bed reflection power (BRP) beneath this central flowline abruptly increases at one location area, followed by a slow decrease down-glacier. The model experiments show that basal sliding (<50%) is necessary to match the observed annual mean surface velocities in the area that is characterized by high BRP values. However, when thermomechanical effects are taken into account, a temperate basal ice layer is apparent in the ablation area, which locally softens the ice and can explain to a certain extent the anomalous flow field. The model results confirm that the present temperature field is a remnant of a larger glacier geometry that was near steady state before the onset of enhanced surface thinning in the 1970s.

scholarly journals A search in north Greenland for a new ice-core drill site

1997 ◽  
Vol 43 (144) ◽  
pp. 300-306 ◽  
Author(s):  
D. Dahl-Jensen ◽  
N.S. Gundestrup ◽  
K. Keller ◽  
S.J. Johnsen ◽  
S.P. Gogineni ◽  
...  
Keyword(s):  
Melting Point ◽  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Flow ◽  
Basal Ice ◽  
Drill Site ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
North Greenland

AbstractA new deep ice-core drilling site has been identified in north Greenland at 75.12° N, 42.30° W, 316 km north-northwest (NNW) of the GRIР drill site on the summit of the ice sheet. The ice thickness here is 3085 m; the surface elevation is 2919 m.The North GRIP (NGRIP) site is identified so that ice of Eemian age (115–130 ka BP,calendar years before present) is located as far above bedrock as possible and so the thickness of the Eemian layer is as great as possible. An ice-flow model, similar to the one used to date the GRIP ice core, is used to simulate the flow along the NNW-trending ice ridge. Surface and bedrock elevations, surface accumulation-rate distribution and radio-echo sounding along the ridge have been used as model input.The surface accumulation rate drops from 0.23 m fee equivalent year−1 at GRIP to 0.19 m ice equivalent year−1 50 km from GRIP. Over the following 300km the accumulation is relatively constant, before it starts decreasing again further north. Ice thicknesses up to 3250 m bring the temperature of the basal ice up to the pressure-melting point 100–250 km from GRIP. The NGRIP site islocated 316 km from GRIP in a region where the bedrock is smooth and the accumulation rate is 0.19 m ice equivalent year−1. The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traced between the GRIP and NGRIP sites, allowing us to date the ice down to 2300 m depth (52 ka BP). An ice-flow model predicts that the Eemian-age ice will be located in the depth range 2710–2800 m, which is 285 m above the bedrock. This is 120 m further above the bedrock, and the thickness of the Eemian layer of ice is 20 m thicker, than at the GRIP ice-core site.

scholarly journals A search in north Greenland for a new ice-core drill site

1997 ◽  
Vol 43 (144) ◽  
pp. 300-306 ◽  
Author(s):  
D. Dahl-Jensen ◽  
N.S. Gundestrup ◽  
K. Keller ◽  
S.J. Johnsen ◽  
S.P. Gogineni ◽  
...  
Keyword(s):  
Melting Point ◽  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Ice Flow ◽  
Basal Ice ◽  
Drill Site ◽  
Radio Echo Sounding ◽  
Pressure Melting ◽  
North Greenland

AbstractA new deep ice-core drilling site has been identified in north Greenland at 75.12° N, 42.30° W, 316 km north-northwest (NNW) of the GRIР drill site on the summit of the ice sheet. The ice thickness here is 3085 m; the surface elevation is 2919 m.The North GRIP (NGRIP) site is identified so that ice of Eemian age (115–130 ka BP,calendar years before present) is located as far above bedrock as possible and so the thickness of the Eemian layer is as great as possible. An ice-flow model, similar to the one used to date the GRIP ice core, is used to simulate the flow along the NNW-trending ice ridge. Surface and bedrock elevations, surface accumulation-rate distribution and radio-echo sounding along the ridge have been used as model input.The surface accumulation rate drops from 0.23 m fee equivalent year−1at GRIP to 0.19 m ice equivalent year−150 km from GRIP. Over the following 300km the accumulation is relatively constant, before it starts decreasing again further north. Ice thicknesses up to 3250 m bring the temperature of the basal ice up to the pressure-melting point 100–250 km from GRIP. The NGRIP site islocated 316 km from GRIP in a region where the bedrock is smooth and the accumulation rate is 0.19 m ice equivalent year−1. The modeled basal ice here has always been a few degrees below the pressure-melting point. Internal radio-echo sounding horizons can be traced between the GRIP and NGRIP sites, allowing us to date the ice down to 2300 m depth (52 ka BP). An ice-flow model predicts that the Eemian-age ice will be located in the depth range 2710–2800 m, which is 285 m above the bedrock. This is 120 m further above the bedrock, and the thickness of the Eemian layer of ice is 20 m thicker, than at the GRIP ice-core site.

scholarly journals At what depth is the Eemian layer expected to be found at NEEM?

2008 ◽  
Vol 48 ◽  
pp. 100-102 ◽  
Author(s):  
Susanne L. Buchardt ◽  
Dorthe Dahl-Jensen
Keyword(s):  
Flow Model ◽  
Accumulation Rate ◽  
Ice Core ◽  
Monte Carlo Analysis ◽  
Interglacial Period ◽  
Ice Flow ◽  
North West ◽  
Flow Parameters ◽  
Drill Site ◽  
Radio Echo Sounding

AbstractNo continuous record from Greenland of the Eemian interglacial period (130–115 ka BP) currently exists. However, a new ice-core drill site has been suggested at 77.449˚ N, 51.056˚Win north-west Greenland (North Eemian or NEEM). Radio-echo sounding images and flow model investigations indicate that an undisturbed Eemian record may be obtained at NEEM. In this work, a two-dimensional ice flow model with time-dependent accumulation rate and ice thickness is used to estimate the location of the Eemian layer at the new drill site. The model is used to simulate the ice flow along the ice ridge leading to the drill site. Unknown flow parameters are found through a Monte Carlo analysis of the flow model constrained by observed isochrones in the ice. The results indicate that the Eemian layer is approximately 60m thick and that its base is located approximately 100m above bedrock.

scholarly journals The Variation in the Ice Sheet of Mizuho Plateau, East Antarctica (Abstract)

1988 ◽  
Vol 11 ◽  
pp. 219
Author(s):  
Shinji Mae
Keyword(s):  
Accumulation Rate ◽  
Ice Sheet ◽  
Ice Cores ◽  
Simple Calculation ◽  
Ice Surface ◽  
Basal Ice ◽  
Basal Sliding ◽  
Radio Echo Sounding ◽  
Antarctic Research ◽  
Basal Shear

The Japanese Antarctic Research Expedition (JARE) has conducted glaciological studies on Mizuho Plateau since 1981. We have already reported that the ice sheet flowing from Mizuho Plateau into Shirase Glacier is thinning at a rate of about 70 cm/year and that the profile of the distribution of basal shear stress is similar to that of surging glaciers. A 5 year glaciological programme on Mizuho Plateau and in east Queen Maud Land is now being carried out and we have obtained the following new results: (1) The ice sheet in the down-stream region (where ice elevation is lower than about 2400 m) is thinning, based on measurements of horizontal and vertical flow velocity, strain-rate, the slope of the ice surface, the accumulation rate and densification of snow. (2) δ18O analysis of deep ice cores obtained at Mizuho Station (2240 m a.s.l.) and point G2 (1730 m a.s.l.) shows that δ18O increased about 200 years ago at Mizuho Station and about 400 years ago at point G2. If we can assume that the increase in δ18O is caused by the thinning of the ice sheet, then this result means that this thinning propagates to up-stream areas. (3) Radio-echo-sounding measurements on Mizuho Plateau show that the ice base in the down-stream region is wet. This supports the result described in (1), since the basal sliding due to a wet base causes ice-sheet thinning, as proposed in our previous studies. In summary, a possible explanation of ice-sheet variation on Mizuho Plateau is as follows: the thinning of the ice sheet, caused by the basal sliding due to basal ice melting, started at Shirase Glacier and has been propagating up-stream to reach its present position. A simple calculation, using flow velocities, shows that the thinning started at Shirase Glacier about 1500–2000 years ago.

scholarly journals Dynamic behavior of Glaciar Perito Moreno, southern Patagonia

1997 ◽  
Vol 24 ◽  
pp. 268-271 ◽  
Author(s):  
Pedro Skvarca ◽  
Renji Naruse
Keyword(s):  
Stable Condition ◽  
Early Summer ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Ablation Area ◽  
Short Period ◽  
Southern Patagonia ◽  
Large Fluctuations ◽  
Basal Sliding ◽  
Ice Field

Frontal oscillations since the beginning of the 20th century are known at Glaciar Perito Moreno, an eastward outlet glacier of Hielo Patagónico Sur (southern Patagonia ice field). In 1900, the calving front was located about 1 km from the opposite bank. From 1935 to 1988, ruptures of ice-dams occurred at intervals of 1–5 years. Although this glacier has thus oscillated, it can be regarded as having been in a rather stable condition during the last half-century. Ice thickness in the ablation area has also remained unchanged from 1990 to 1996. The near-steady behavior of Glaciar Perito Moreno may be attributed to a regulating effect of the calving rate, namely, a decrease in the ablation amount due to calving with a retreat of the glacier. Using 12 m long ablation poles, ice-flow velocities at the ablation area were measured several times in 1993 and 1994. The velocity in the early summer (November) was found to be slightly larger than the annual mean. It is concluded that basal sliding is significant throughout the year at this temperate glacier, with large fluctuations within a short period.

scholarly journals Dynamic behavior of Glaciar Perito Moreno, southern Patagonia

1997 ◽  
Vol 24 ◽  
pp. 268-271 ◽  
Author(s):  
Pedro Skvarca ◽  
Renji Naruse
Keyword(s):  
Stable Condition ◽  
Early Summer ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Ablation Area ◽  
Short Period ◽  
Southern Patagonia ◽  
Large Fluctuations ◽  
Basal Sliding ◽  
Ice Field

Frontal oscillations since the beginning of the 20th century are known at Glaciar Perito Moreno, an eastward outlet glacier of Hielo Patagónico Sur (southern Patagonia ice field). In 1900, the calving front was located about 1 km from the opposite bank. From 1935 to 1988, ruptures of ice-dams occurred at intervals of 1–5 years. Although this glacier has thus oscillated, it can be regarded as having been in a rather stable condition during the last half-century. Ice thickness in the ablation area has also remained unchanged from 1990 to 1996. The near-steady behavior of Glaciar Perito Moreno may be attributed to a regulating effect of the calving rate, namely, a decrease in the ablation amount due to calving with a retreat of the glacier.Using 12 m long ablation poles, ice-flow velocities at the ablation area were measured several times in 1993 and 1994. The velocity in the early summer (November) was found to be slightly larger than the annual mean. It is concluded that basal sliding is significant throughout the year at this temperate glacier, with large fluctuations within a short period.

scholarly journals Influence of increasing surface melt over decadal timescales on land-terminating Greenland-type outlet glaciers

2018 ◽  
Vol 64 (247) ◽  
pp. 700-710 ◽  
Author(s):  
OLIVIER GAGLIARDINI ◽  
MAURO A. WERDER
Keyword(s):  
Mass Loss ◽  
Flow Model ◽  
Greenland Ice Sheet ◽  
Spatial Extent ◽  
Flow Conditions ◽  
Ice Flow ◽  
Ablation Area ◽  
Sheet Surface ◽  
Warming Climate ◽  
Surface Melt

ABSTRACTOver recent decades, Greenland ice sheet surface melt has shown an increase both in intensity and spatial extent. Part of this water probably reaches the bed and can enhance glacier speed, advecting a larger volume of ice into the ablation area. In the context of a warming climate, this mechanism could contribute to the future rate of thinning and retreat of land-terminating glaciers of Greenland. These changes in ice flow conditions will in turn influence surface crevassing and thus the ability of water to reach the bed at higher elevations. Here, using a coupled basal hydrology and prognostic ice flow model, the evolution of a Greenland-type glacier subject to increasing surface melt is studied over a few decades. For different scenarios of surface melt increase over the next decades, the evolution of crevassed areas and the ability of water to reach the bed is inferred. Our results indicate that the currently observed crevasse distribution is likely to extend further upstream which will allow water to reach the bed at higher elevations. This will lead to an increase in ice flux into the ablation area which, in turn, accelerates the mass loss of land-terminating glaciers.

scholarly journals A Mathematical Approach to the Theory of Glacier Sliding

1979 ◽  
Vol 23 (89) ◽  
pp. 131-141 ◽  
Author(s):  
A. C. Fowler
Keyword(s):  
Variational Principles ◽  
Water Film ◽  
Continuous Functions ◽  
Leading Order ◽  
Complete Model ◽  
Ice Flow ◽  
Major Consequence ◽  
Basal Ice ◽  
Basal Sliding ◽  
Ice Water

AbstractPrevious theories of glacier sliding are subject to the criticism that they are not properly formulated. Here we describe how the basal ice flow may be related to the bulk ice flow by means of the formal mathematical method of matched asymptotic expansions. A complete model of the basal sliding (involving coupled problems in ice, water film, and bedrock) may be rationally reduced by a dimensional analysis to a consideration of the ice flow only, and regelation may be neglected provided roughness is absent on the finest scales (<c. 1 mm). If the viscosity is supposed to be independent of the moisture content, then complementary variational principles exist which allow bounds on the drag to be obtained. In particular, these determine the magnitude of the basal velocity in terms of two crucial dimensionless parameters. Arguments are presented as to why realistic sliding laws should be taken as continuous functions of the temperature, and a (major) consequence of this assumption is mentioned. Finally the effect of cavitation is discussed, via an (exact) leading-order solution of the ice flow in the particular case of a Newtonian fluid and a “small” bedrock slope.

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

2009 ◽  
Vol 50 (51) ◽  
pp. 80-84 ◽  
Author(s):  
Frank Pattyn ◽  
Charlotte Delcourt ◽  
Denis Samyn ◽  
Bert de Smedt ◽  
Matt Nolan
Keyword(s):  
Potential Gradient ◽  
Ice Thickness ◽  
Central Frequency ◽  
Bed Topography ◽  
Ice Volume ◽  
Arctic Alaska ◽  
Digital Elevation ◽  
Basal Sliding ◽  
Radio Echo Sounding ◽  
Elevation Model

AbstractDuring three summer field seasons (2003, 2005 and 2006) we carried out radio-echo sounding measurements with a 5MHz (central frequency) ice-penetrating radar on McCall Glacier, Arctic Alaska, USA, along the central flowline and 17 cross-profiles. Two-way travel time was, after migration, converted to ice thickness, which, in combination with a recent digital elevation model of the surface of the glaciated area, resulted in a detailed map of the bed topography. This reveals a complex basal topography in the confluence area of the different glacial cirques. The pattern of subglacial water flow following the hydraulic potential gradient was calculated for the whole glacier area and shows a confluence of subglacial water downstream from the confluence of the glacier cirques. From the ice-thickness map the total ice volume was estimated as slightly less than 0.5 km3. Bed reflection power (BRP) was determined for the glacier after correction for ice-thickness dependence. Results reveal a clear relationship between the BRP pattern and basal sliding anomalies along the central flowline.

scholarly journals Modelling glacier response to measured mass-balance forcing

2000 ◽  
Vol 31 ◽  
pp. 91-96 ◽  
Author(s):  
Olaf Albrecht ◽  
Peter Jansson ◽  
Heinz Blatter
Keyword(s):  
Mass Balance ◽  
Flow Model ◽  
Ice Flow ◽  
Surface Evolution ◽  
Bed Topography ◽  
The Past ◽  
Basal Sliding ◽  
Measured Change ◽  
Measured Mass ◽  
Limited Accuracy

AbstractMeasurements of summer and winter mass balances have been carried out over the past 53 years on Storglaciären, northern Sweden. Repeated surveys of the glacier have resulted in several maps of surface topography as well as a map of the bed topography A new time-dependent ice flow model allows us to compare the observed surface evolution of the glacier with that computed by the model using measured mass-balance maps as input. The computed volume change compares well with the measured change: the model replicates the distribution of surface elevation to within ±10 m over 30 years of integration. On the model side, these deviations can be attributed to the low-resolution discretization of the model domain as well as to the limited accuracy of the ice rheology and omitted basal sliding. On the other hand, the uncertainties of the topography and mass-balance maps match the model uncertainties. In this sense, the experiments are a validation of both model and observations.

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