scholarly journals Changes in the Behaviour of the Unteraargletscher in the Last 125 Years

1970 ◽  
Vol 9 (56) ◽  
pp. 195-212 ◽  
Author(s):  
R. Haefeli
Keyword(s):  
Marked Decrease ◽  
Decisive Role ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Surface Slope ◽  
Simple Method ◽  
Glacier Tongue ◽  
Slowing Down ◽  
Shear Component ◽  
Glacier Flow

All the measurements involved concern the glacier tongue between its end and 2 600 m a.s.l. The total loss of volume of the Unteraargletscher since its last maximum advance (1871) is estimated to be 2.4 km3, which corresponds to a mean surface lowering of 0.67 m/year (referred to a total glacierized area of c. 40 km2 on average). The considerable slowing down of the glacier flow velocity over the 125 years is primarily attributable to the marked decrease in the sliding component, whereas the shear component has only changed slightly. This behaviour is connected with the fact that the decrease in ice thickness has been accompanied by an increase in surface slope, so that the two effects on the shear component partially compensate each other. The seasonal variations in surface velocity were measured simultaneously at two profiles by Agassiz and his team in 1845/46. These variations are due to the variable amount of melt water and the resulting variations in hydrostatic pressure in the contact zone between ice and bedrock, in which the plastic contraction of the water channels plays a decisive role. This leads to the problem of water circulation in the interior of a glacier and its importance in the sliding process. Finally a simple method for the approximate calculation of the longitudinal profile of the surface of a glacier tongue in a steady state and with constant ablation is indicated.

scholarly journals Changes in the Behaviour of the Unteraargletscher in the Last 125 Years

1970 ◽  
Vol 9 (56) ◽  
pp. 195-212 ◽  
Author(s):  
R. Haefeli
Keyword(s):  
Marked Decrease ◽  
Decisive Role ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Surface Slope ◽  
Simple Method ◽  
Glacier Tongue ◽  
Slowing Down ◽  
Shear Component ◽  
Glacier Flow

All the measurements involved concern the glacier tongue between its end and 2 600 m a.s.l. The total loss of volume of the Unteraargletscher since its last maximum advance (1871) is estimated to be 2.4 km3, which corresponds to a mean surface lowering of 0.67 m/year (referred to a total glacierized area ofc. 40 km2on average). The considerable slowing down of the glacier flow velocity over the 125 years is primarily attributable to the marked decrease in the sliding component, whereas the shear component has only changed slightly. This behaviour is connected with the fact that the decrease in ice thickness has been accompanied by an increase in surface slope, so that the two effects on the shear component partially compensate each other. The seasonal variations in surface velocity were measured simultaneously at two profiles by Agassiz and his team in 1845/46. These variations are due to the variable amount of melt water and the resulting variations in hydrostatic pressure in the contact zone between ice and bedrock, in which the plastic contraction of the water channels plays a decisive role. This leads to the problem of water circulation in the interior of a glacier and its importance in the sliding process. Finally a simple method for the approximate calculation of the longitudinal profile of the surface of a glacier tongue in a steady state and with constant ablation is indicated.

scholarly journals Ice-Flow and Thickness Measurements in the Sør-Rondane, Dronning Maud Land, Antarctica

1966 ◽  
Vol 6 (43) ◽  
pp. 69-81
Author(s):  
T. Van Autenboer ◽  
K. V. Blaiklock
Keyword(s):  
Aerial Photographs ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Gravity Station ◽  
Close Relationship ◽  
Dronning Maud Land ◽  
Subglacial Topography ◽  
Glacier Flow ◽  
The Antarctic ◽  
Thickness Measurements

AbstractVelocity and ice-thickness profiles were measured un the western glaciers of the Sør-Rondane during the Expéditions Antarctiques Belges of 1959 and 1960 Some of the stations were re-occupied for velocity measurements during the Expédition Antarctique Belgo-Néerlandaise, Campagne d’Été 1964–65.The profiles, with stations at 1 mile. (1.6 km.) intervals, were generally east-west and at right-angles to the direction of flow of the plateau outlet glaciers. The movement was measured by resection of each station from the main triangulation points over periods ranging from 256 to 1,501 days. Double ties with a Worden geodetic-type gravity meter were measured between the stations. An additional gravity station was occupied on rock at each end of the profile. The ice thickness and the subglacial topography are calculated from the gravity profiles. Combined with the surface velocity, they allow an estimate of the discharge of the glacier. The results indicate a close relationship between the glacier flow and the supply from the Antarctic Ice Sheet, as demonstrated by a study of the aerial photographs.

scholarly journals Stress-Gradient Coupling in Glacier Flow: II. Longitudinal Averaging in the Flow Response to Small Perturbations in Ice Thickness and Surface Slope

1986 ◽  
Vol 32 (111) ◽  
pp. 285-298 ◽  
Author(s):  
Keith A. Echelmeyer ◽  
Barclay Kamb ◽  
Barclay Kamb
Keyword(s):  
Coupling Length ◽  
Ice Thickness ◽  
Simple Shear Flow ◽  
Finite Width ◽  
Longitudinal Stress ◽  
Surface Slope ◽  
Data Set ◽  
Flow Response ◽  
Influence Coefficients ◽  
Glacier Flow

AbstractAs a result of the coupling effects of longitudinal stress gradients, the perturbations ∆u in glacier-flow velocity that result from longitudinally varying perturbations in ice thickness ∆h and surface slope ∆α are determined by a weighted longitudinal average of ϕh∆h and ϕα∆α, where ϕh and ϕα are “influence coefficients” that control the size of the contributions made by local ∆h and ∆α to the flow increment in the longitudinal average. The values of ϕh and ϕα depend on effects of longitudinal stress and velocity gradients in the unperturbed datum state. If the datum state is an inclined slab in simple-shear flow, the longitudinal averaging solution for the flow perturbation is essentially that obtained previously (Kamb and Echelmeyer, 1985) with equivalent values for the longitudinal coupling length l and with ϕh = n + 1 and ϕα + n, where n is the flow-law exponent. Calculation of the influence coefficients from flow data for Blue Glacier, Washington, indicates that in practice ϕα differs little from n, whereas ϕh can differ considerably from n + 1. The weighting function in the longitudinal averaging integral, which is the Green’s function for the longitudinal coupling equation for flow perturbations, can be approximated by an asymmetric exponential, whose asymmetry depends on two “asymmetry parameters” μ and σ, where μ is the longitudinal gradient of ℓ(= dℓ/dx). The asymmetric exponential has different coupling lengths ℓ+ and ℓ− for the influences from up-stream and from down-stream on a given point of observation. If σ/μ is in the range 1.5–2.2, as expected for flow perturbations in glaciers or ice sheets in which the ice flux is not a strongly varying function of the longitudinal coordinate x, then, when dℓ/dx > 0, the down-stream coupling length ℓ+ is longer than the up-stream coupling length ℓ−, and vice versa when dℓ/dx < 0. Flow-, thickness- and slope-perturbation data for Blue Glacier, obtained by comparing the glacier in 1957–58 and 1977–78, require longitudinal averaging for reasonable interpretation. Analyzed on the basis of the longitudinal coupling theory, with 4ℓ + 1.6 km up-stream, decreasing toward the terminus, the data indicate n to be about 2.5, if interpreted on the basis of a response factor Ѱ + 0.85 derived theoretically by Echelmeyer (unpublished) for the flow response to thickness perturbations in a channel of finite width. The data contain an apparent indication that the flow response to slope perturbations is distinctly smaller, in relation to the response to thickness perturbations, than is expected on a theoretical basis (i.e. ϕα/ ϕh + (n/n + 1) for a slab). This probably indicates that the effective ℓ is longer than can be tested directly with the available data set owing to its limited range in x.

scholarly journals Ice Flow Leading to the Deep Core Hole at Dye 3, Greenland

1984 ◽  
Vol 5 ◽  
pp. 185-190 ◽  
Author(s):  
I. M. Whillans ◽  
K. C. Jezek ◽  
A. R. Drew ◽  
N. Gundestrup
Keyword(s):  
Flow Line ◽  
Surface Velocity ◽  
Surface Pattern ◽  
Ice Thickness ◽  
Surface Slope ◽  
Core Hole ◽  
Lateral Velocity ◽  
Ice Flow ◽  
The Core ◽  
Surface Ice

Detailed studies of the last 20 km of the flow-line leading to the core hole at Dye 3 Greenland, provide a description of ice flow over and around basal hills. The surface pattern is very simple. Velocity vectors are nearly parallel to one another and the largest variations in velocity are speed changes along the direction of flow. The surface elevation is stepped and the speed is faster than average where the surface slope is steepest. These positions correspond to basal highs, and the surface velocity increases as expected, based on the decrease in ice thickness, which indicates that most of the ice thickness must vary in velocity as does surface ice. Further support for this comes from the form of an internal radio-reflecting layer, which, in general, has the same shape as the bed but with much reduced relief. The damping of the relief is the same both along and across the flowline, suggesting that lateral velocity fluctuations are not important and that flow around and between obstacles is not well developed at the surface or at depth. At two sites, however, the internal layer does not match the bed and at one of these there must be important third-dimensional flow at depth.

scholarly journals Ice Flow Leading to the Deep Core Hole at Dye 3, Greenland

1984 ◽  
Vol 5 ◽  
pp. 185-190 ◽  
Author(s):  
I. M. Whillans ◽  
K. C. Jezek ◽  
A. R. Drew ◽  
N. Gundestrup
Keyword(s):  
Flow Line ◽  
Surface Velocity ◽  
Surface Pattern ◽  
Ice Thickness ◽  
Surface Slope ◽  
Core Hole ◽  
Lateral Velocity ◽  
Ice Flow ◽  
The Core ◽  
Surface Ice

Detailed studies of the last 20 km of the flow-line leading to the core hole at Dye 3 Greenland, provide a description of ice flow over and around basal hills. The surface pattern is very simple. Velocity vectors are nearly parallel to one another and the largest variations in velocity are speed changes along the direction of flow. The surface elevation is stepped and the speed is faster than average where the surface slope is steepest. These positions correspond to basal highs, and the surface velocity increases as expected, based on the decrease in ice thickness, which indicates that most of the ice thickness must vary in velocity as does surface ice. Further support for this comes from the form of an internal radio-reflecting layer, which, in general, has the same shape as the bed but with much reduced relief. The damping of the relief is the same both along and across the flowline, suggesting that lateral velocity fluctuations are not important and that flow around and between obstacles is not well developed at the surface or at depth. At two sites, however, the internal layer does not match the bed and at one of these there must be important third-dimensional flow at depth.

scholarly journals The flow of a polythermal glacier: McCall Glacier, Alaska, U.S.A.

1997 ◽  
Vol 43 (145) ◽  
pp. 522-536 ◽  
Author(s):  
B.T. Rabus ◽  
K. A. Echelmeyer
Keyword(s):  
Surface Profile ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Longitudinal Stress ◽  
Surface Slope ◽  
Basal Sliding ◽  
Speed Up ◽  
Polythermal Glacier ◽  
Long Term Variations

AbstractWe have analyzed the flow of polythermal McCall Glacier in Arctic Alaska. Using measurements of surface velocity from the 1970s and 1990s, together with measurements of ice thickness and surface slope, we have investigated both the present flow and seasonal and long-term flow variations. Our analysis of the present flow reveals that (i) longitudinal stress coupling is important along the entire length of the glacier, and (ii) there is significant basal sliding beneath a 2 km long section of the lower glacier. This sliding exists year-round and it accounts for more than 70% of the total motion there. We have developed a numerical model which shows that such a sliding anomaly causes an asymmetric decrease in ice thickness. Accompanying this decrease in thickness is a decrease in surface slope at the center of the anomaly and an increase in slope up-glacier from it. Both effects are reflected in the observed surface profile of McCall Glacier.The longitudinal stress-coupling length of McCall Glacier is three times the ice thickness, almost twice that typical of temperate glaciers. This is a direct effect of lower strain rates, which themselves are associated with the smaller mass-balance gradients of Arctic and continental glaciers. Long-term variations in surface velocity between the 1970s and 1990s are explained solely by the effects of changes in glacier geometry on the deformational flow contribution. This means that long-term variations in the spatial patterns of longitudinal stresses and basal sliding must have been small. Seasonally, Velocities reach their annual minimum in spring and increase during the short summer nick season by up to 75% above mean winter values. However, the extra motion associated with the period of elevated velocities is only about 5% of the total annual motion. The speed-up is due to an increase in basal sliding. This implies that most of the glacier bed is at the melting point. The zone a affected by the melt-season speed-up extends well up-glacier of any moulins or other obvious sources for melt water at the bed.

scholarly journals Numerical Modelling of Glacier Response to a Perturbation in Thickness (Abstract only)

1983 ◽  
Vol 4 ◽  
pp. 298 ◽  
Author(s):  
Keith Echelmeyer
Keyword(s):  
High Stress ◽  
Three Dimensional ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Surface Slope ◽  
Three Dimensional Modeling ◽  
Flow Response ◽  
Non Linear ◽  
Flow Law ◽  
Three Dimensional Models

Blue Glacier was subject to 5 to 10% increase in thickness during the period 1958 to 1978. A surface velocity increase of 15 to 50% has accompanied this change in ice thickness. A non-uniform distribution of thickening over the glacier produced a general decrease in surface slope. The flow law parameters in a power-law relation for ice can be obtained from the resulting increase in velocity. In 1957–58 the surface velocities and surface elevation along several transverse profiles were determined by others. During the period 1977 to 1980 similar measurements were made of surface velocity, elevation, and ice thickness along profiles spatially equivalent to those of the 1957–58 survey. Using these results a detailed study of the flow response has been made. Preliminary results indicate that the controlling surface slope a is one that is averaged over approximately ten times the glacier thickness and also indicate a relatively high stress exponent n = 4 to 5. Blue Glacier flows in a complex channel and any detailed interpretation of the flow response requires the inclusion of this geometry in a model. For this reason multi-dimensional finite-element methods using a non-linear constitutive relation were employed. Various degrees of model sophistication allowed for the specification of different parameters governing the flow of the glacier. Variations in the flow law parameters and the curvature of the channel were found to have significant effects on the velocity and stress fields, as well as on the characteristics of the flow response to the thickness perturbation. Fully three-dimensional models of the flow of Blue Glacier and its response to the thickness increase were developed. Important effects such as those arising from longitudinal thickness and surface slope variations were included in three-dimensional modeling. The three-dimensional effects were seen to play an important role in flow of a rheologically non-linear fluid such as ice.

scholarly journals The flow of a polythermal glacier: McCall Glacier, Alaska, U.S.A.

1997 ◽  
Vol 43 (145) ◽  
pp. 522-536 ◽  
Author(s):  
B.T. Rabus ◽  
K. A. Echelmeyer
Keyword(s):  
Surface Profile ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Longitudinal Stress ◽  
Surface Slope ◽  
Basal Sliding ◽  
Speed Up ◽  
Polythermal Glacier ◽  
Long Term Variations

AbstractWe have analyzed the flow of polythermal McCall Glacier in Arctic Alaska. Using measurements of surface velocity from the 1970s and 1990s, together with measurements of ice thickness and surface slope, we have investigated both the present flow and seasonal and long-term flow variations. Our analysis of the present flow reveals that (i) longitudinal stress coupling is important along the entire length of the glacier, and (ii) there is significant basal sliding beneath a 2 km long section of the lower glacier. This sliding exists year-round and it accounts for more than 70% of the total motion there. We have developed a numerical model which shows that such a sliding anomaly causes an asymmetric decrease in ice thickness. Accompanying this decrease in thickness is a decrease in surface slope at the center of the anomaly and an increase in slope up-glacier from it. Both effects are reflected in the observed surface profile of McCall Glacier.The longitudinal stress-coupling length of McCall Glacier is three times the ice thickness, almost twice that typical of temperate glaciers. This is a direct effect of lower strain rates, which themselves are associated with the smaller mass-balance gradients of Arctic and continental glaciers. Long-term variations in surface velocity between the 1970s and 1990s are explained solely by the effects of changes in glacier geometry on the deformational flow contribution. This means that long-term variations in the spatial patterns of longitudinal stresses and basal sliding must have been small. Seasonally, Velocities reach their annual minimum in spring and increase during the short summer nick season by up to 75% above mean winter values. However, the extra motion associated with the period of elevated velocities is only about 5% of the total annual motion. The speed-up is due to an increase in basal sliding. This implies that most of the glacier bed is at the melting point. The zone a affected by the melt-season speed-up extends well up-glacier of any moulins or other obvious sources for melt water at the bed.

scholarly journals Stress-Gradient Coupling in Glacier Flow: II. Longitudinal Averaging in the Flow Response to Small Perturbations in Ice Thickness and Surface Slope

1986 ◽  
Vol 32 (111) ◽  
pp. 285-298 ◽  
Author(s):  
Keith A. Echelmeyer ◽  
Barclay Kamb
Keyword(s):  
Coupling Length ◽  
Ice Thickness ◽  
Simple Shear Flow ◽  
Finite Width ◽  
Longitudinal Stress ◽  
Surface Slope ◽  
Data Set ◽  
Flow Response ◽  
Influence Coefficients ◽  
Glacier Flow

AbstractAs a result of the coupling effects of longitudinal stress gradients, the perturbations ∆uin glacier-flow velocity that result from longitudinally varying perturbations in ice thickness ∆hand surface slope ∆α are determined by a weighted longitudinal average ofϕh∆handϕα∆α, whereϕhandϕαare “influence coefficients” that control the size of the contributions made by local ∆hand ∆α to the flow increment in the longitudinal average. The values ofϕhandϕα depend on effects of longitudinal stress and velocity gradients in the unperturbed datum state. If the datum state is an inclined slab in simple-shear flow, the longitudinal averaging solution for the flow perturbation is essentially that obtained previously (Kamb and Echelmeyer, 1985) with equivalent values for the longitudinal coupling lengthland withϕh=n+ 1 andϕα+n, wherenis the flow-law exponent. Calculation of the influence coefficients from flow data for Blue Glacier, Washington, indicates that in practiceϕα differs little fromn, whereasϕhcan differ considerably fromn+ 1. The weighting function in the longitudinal averaging integral, which is the Green’s function for the longitudinal coupling equation for flow perturbations, can be approximated by an asymmetric exponential, whose asymmetry depends on two “asymmetry parameters”μand σ, whereμis the longitudinal gradient of ℓ(= dℓ/dx). The asymmetric exponential has different coupling lengths ℓ+and ℓ−for the influences from up-stream and from down-stream on a given point of observation. If σ/μis in the range 1.5–2.2, as expected for flow perturbations in glaciers or ice sheets in which the ice flux is not a strongly varying function of the longitudinal coordinatex, then, when dℓ/dx&gt; 0, the down-stream coupling length ℓ+is longer than the up-stream coupling length ℓ−, and vice versa when dℓ/dx&lt; 0. Flow-, thickness- and slope-perturbation data for Blue Glacier, obtained by comparing the glacier in 1957–58 and 1977–78, require longitudinal averaging for reasonable interpretation. Analyzed on the basis of the longitudinal coupling theory, with 4ℓ + 1.6 km up-stream, decreasing toward the terminus, the data indicatento be about 2.5, if interpreted on the basis of aresponse factor Ѱ+ 0.85 derived theoretically by Echelmeyer (unpublished) for the flow response to thickness perturbations in a channel of finite width. The data contain an apparent indication that the flow response to slope perturbations is distinctly smaller, in relation to the response to thickness perturbations, than is expected on a theoretical basis (i.e.ϕα/ ϕh+ (n/n+ 1) for a slab). This probably indicates that the effective ℓ is longer than can be tested directly with the available data set owing to its limited range inx.

scholarly journals Ice-Flow and Thickness Measurements in the Sør-Rondane, Dronning Maud Land, Antarctica

1966 ◽  
Vol 6 (43) ◽  
pp. 69-81 ◽  
Author(s):  
T. Van Autenboer ◽  
K. V. Blaiklock
Keyword(s):  
Aerial Photographs ◽  
Surface Velocity ◽  
Ice Thickness ◽  
Gravity Station ◽  
Close Relationship ◽  
Dronning Maud Land ◽  
Subglacial Topography ◽  
Glacier Flow ◽  
The Antarctic ◽  
Thickness Measurements

AbstractVelocity and ice-thickness profiles were measured un the western glaciers of the Sør-Rondane during the Expéditions Antarctiques Belges of 1959 and 1960 Some of the stations were re-occupied for velocity measurements during the Expédition Antarctique Belgo-Néerlandaise, Campagne d’Été 1964–65.The profiles, with stations at 1 mile. (1.6 km.) intervals, were generally east-west and at right-angles to the direction of flow of the plateau outlet glaciers. The movement was measured by resection of each station from the main triangulation points over periods ranging from 256 to 1,501 days. Double ties with a Worden geodetic-type gravity meter were measured between the stations. An additional gravity station was occupied on rock at each end of the profile. The ice thickness and the subglacial topography are calculated from the gravity profiles. Combined with the surface velocity, they allow an estimate of the discharge of the glacier. The results indicate a close relationship between the glacier flow and the supply from the Antarctic Ice Sheet, as demonstrated by a study of the aerial photographs.

Sign in / Sign up

Export Citation Format

Share Document