The Bottom Topography of Gulkana Glacier, Alaska Range, Alaska

1965 ◽  
Vol 5 (41) ◽  
pp. 651-660 ◽  
Author(s):  
N. A. Ostenso ◽  
P. V. Sellmann ◽  
T. L. Péwé
Keyword(s):  
Bottom Topography ◽  
Surface Flow ◽  
Ice Thickness ◽  
Intensive Study ◽  
Alaska Range ◽  
Glacier Terminus ◽  
Parallel Channels ◽  
Third Dimension ◽  
Eastern Channel ◽  
Insight Into

AbstractAs an extension of an intensive study of Gulkana Glacier a 42 station gravimeter survey was made to gain some insight into its third dimension. This survey showed that the glacier’s main tongue occupies a complex valley composed essentially of two parallel channels separated by a medial ridge which extends southward from rock bastions in the accumulation zone. At mid-glacier the ice thickness in the larger eastern channel is 225 m., in contrast to 130 m. in the western channel. The medial ridge degenerates down-glacier probably disappearing within 2 km. of the glacier terminus. The basic surface flow pattern of the glacier described by Moores can be adequately explained by this basal topography. Seasonal velocity variations are possibly caused by melt-water basal lubrication with one channel being favored over the other at different times of the year, in agreement with observations by Elliston on the Gorner-Gletscher, Switzerland, and with the glacier sliding theory of Weertman.

scholarly journals The Bottom Topography of Gulkana Glacier, Alaska Range, Alaska

1965 ◽  
Vol 5 (41) ◽  
pp. 651-660 ◽  
Author(s):  
N. A. Ostenso ◽  
P. V. Sellmann ◽  
T. L. Péwé
Keyword(s):  
Bottom Topography ◽  
Surface Flow ◽  
Ice Thickness ◽  
Intensive Study ◽  
Alaska Range ◽  
Glacier Terminus ◽  
Parallel Channels ◽  
Third Dimension ◽  
Eastern Channel ◽  
Insight Into

AbstractAs an extension of an intensive study of Gulkana Glacier a 42 station gravimeter survey was made to gain some insight into its third dimension. This survey showed that the glacier’s main tongue occupies a complex valley composed essentially of two parallel channels separated by a medial ridge which extends southward from rock bastions in the accumulation zone. At mid-glacier the ice thickness in the larger eastern channel is 225 m., in contrast to 130 m. in the western channel. The medial ridge degenerates down-glacier probably disappearing within 2 km. of the glacier terminus. The basic surface flow pattern of the glacier described by Moores can be adequately explained by this basal topography. Seasonal velocity variations are possibly caused by melt-water basal lubrication with one channel being favored over the other at different times of the year, in agreement with observations by Elliston on the Gorner-Gletscher, Switzerland, and with the glacier sliding theory of Weertman.

scholarly journals On the limit to resolution and information on basal properties obtainable from surface data on ice streams

2008 ◽  
Vol 2 (2) ◽  
pp. 167-178 ◽  
Author(s):  
G. H. Gudmundsson ◽  
M. Raymond
Keyword(s):  
Flow Line ◽  
Estimation Method ◽  
Optimal Estimation ◽  
Surface Flow ◽  
Ice Thickness ◽  
Ice Streams ◽  
Statistical Estimates ◽  
Surface Data ◽  
Highly Sensitive ◽  
Surface Measurements

Abstract. An optimal estimation method for simultaneously determining both basal slipperiness and basal topography from variations in surface flow velocity and topography along a flow line on ice streams and ice sheets is presented. We use Bayesian inference to update prior statistical estimates for basal topography and slipperiness using surface measurements along a flow line. Our main focus here is on how errors and spacing of surface data affect estimates of basal quantities and on possibly aliasing/mixing between basal slipperiness and basal topography. We find that the effects of spatial variations in basal topography and basal slipperiness on surface data can be accurately separated from each other, and mixing in retrieval does not pose a serious problem. For realistic surface data errors and density, small-amplitude perturbations in basal slipperiness can only be resolved for wavelengths larger than about 50 times the mean ice thickness. Bedrock topography is well resolved down to horizontal scale equal to about one ice thickness. Estimates of basal slipperiness are not significantly improved by accurate prior estimates of basal topography. However, retrieval of basal slipperiness is found to be highly sensitive to unmodelled errors in basal topography.

Comets: pre- and post-Halley

1991 ◽  
Vol 9 (2) ◽  
pp. 219-224
Author(s):  
K. S. Krishna Swamy
Keyword(s):  
Solar Wind ◽  
Intensive Study ◽  
Cometary Plasma ◽  
Comet Halley ◽  
Insight Into

AbstractThe recent intensive study of Comet Halley based on in situ measurements, observations carried out with rockets and satellites and supplemented with co-ordinated Earth based observations has not only confirmed pre-Halley results, but also has given new insight into the nature of the nucleus, dust, gas and the interaction of cometary plasma with the solar wind. These observations also have raised many new questions and problems. Several of these aspects will be discussed. For a better understanding of these problems, the planned future missions to comets will also be discussed.

scholarly journals Quiescent-phase evolution of a surge-type glacier: Black Rapids Glacier, Alaska, U.S.A.

1996 ◽  
Vol 42 (140) ◽  
pp. 110-122 ◽  
Author(s):  
T.A. Heinrichs ◽  
L.R. Mayo ◽  
K.A. Echelmeyer ◽  
W.D. Harrison
Keyword(s):  
Phase Evolution ◽  
Ice Thickness ◽  
Alaska Range ◽  
Thickness Change ◽  
Quiescent Phase ◽  
Cyclical Fluctuations ◽  
Ice Velocity ◽  
The Mean ◽  
Black Rapids Glacier ◽  
Speed Fluctuations

AbstractBlack Rapids Glacier, a surge-type glacier in the Alaska Range, most recently surged in 1936–37 and is currently in its quiescent phase. Mass balance, ice velocity and thickness change have been measured at three to ten sites from 1972 to 1994. The annual speed has undergone cyclical fluctuations of as much as 45% about the mean speed. Ice thickness and surface slope did not change enough to cause the speed fluctuations through changes in ice deformation, which indicates that they are being drinven by changes in basal motion. The behavior of Black Rapids Glacier during this quiescent phase is significantly different from that of Variegated Glacier, another well-studied surge-type glacier in Alaska. The present medial-moraine configuration of Black Rapids Glacier indicates that a surge could occur at any time. However, ice velocity data indicate that the next surge may not be imminent. We belive that there is little chance that the next surge will cross and dam the Delta River.

Generalized vortex methods for free-surface flow problems

1982 ◽  
Vol 123 ◽  
pp. 477-501 ◽  
Author(s):  
Gregory R. Baker ◽  
Daniel I. Meiron ◽  
Steven A. Orszag
Keyword(s):  
Water Waves ◽  
Evolution Equations ◽  
Bottom Topography ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Three Dimensions ◽  
Fredholm Integral Equations ◽  
Free Surfaces ◽  
Flow Problems ◽  
Dipole Vortex

The motion of free surfaces in incompressible, irrotational, inviscid layered flows is studied by evolution equations for the position of the free surfaces and appropriate dipole (vortex) and source strengths. The resulting Fredholm integral equations of the second kind may be solved efficiently in both storage and work by iteration in both two and three dimensions. Applications to breaking water waves over finite-bottom topography and interacting triads of surface and interfacial waves are given.

scholarly journals A minimal model of a tidewater glacier

2005 ◽  
Vol 42 ◽  
pp. 1-6 ◽  
Author(s):  
J. Oerlemans ◽  
F.M. Nick
Keyword(s):  
Velocity Field ◽  
Water Depth ◽  
Ice Thickness ◽  
Global Dynamics ◽  
Equilibrium Line Altitude ◽  
Glacier Terminus ◽  
Tidewater Glacier ◽  
Glacier Length ◽  
Parameterized Model ◽  
Calving Rate

AbstractWe propose a simple, highly parameterized model of a tidewater glacier. The mean ice thickness and the ice thickness at the glacier front are parameterized in terms of glacier length and, when the glacier is calving, water depth. We use a linear relation between calving rate and water depth. The change in glacier length is determined by the total change in the mass budget (surface balance and calving flux), but not by the details of the glacier profile and the related velocity field. We show that this may still yield relatively rapid rates of retreat for an idealized bed geometry with a smooth overdeepening. The model is able to simulate the full cycle of ice-free conditions, glacier terminus on land, tidewater glaciers terminus, and backwards. We study two cases: (i) a glacier with a specific balance (accumulation) that is spatially uniform, and (ii) a glacier in a warmer climate with the specific balance being a linear function of altitude. Equilibrium states exhibit a double branching with respect to the climatic forcing (equilibrium-line altitude). One bifurcation is related to the dependence of the calving process on the bed profile; the other bifurcation is due to the height–mass-balance feedback. We discuss the structure of the solution diagram for different values of the calving-rate parameter. The model results are similar to those of Vieli and others (2001), who combined a fairly sophisticated two-dimensional (vertical plane) numerical ice-flow model with the modified flotation criterion suggested by Van der Veen (1996). With regard to the global dynamics of a tidewater glacier, we conclude that the details of the glacier profile or velocity field are less significant than the bed profile and the relation between the water depth and the calving rate.

scholarly journals Field Studies of Bottom Crevasses in the Ross Ice Shelf, Antarctica (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 341 ◽  
Author(s):  
Kenneth C. Jezek ◽  
Charles R. Bentley
Keyword(s):  
Bottom Topography ◽  
Field Studies ◽  
Airborne Radar ◽  
Ice Thickness ◽  
Ice Shelf ◽  
The West ◽  
West Antarctic Ice Sheet ◽  
Ross Ice Shelf ◽  
West Antarctic ◽  
Grounding Line

Surface and airborne radar sounding data were used to identify and map fields of bottom crevasses on the Ross Ice Shelf. Two major concentrations of crevasses were found, one along the grid-eastern grounding line and another, made up of eight smaller sites, grid-west of Crary Ice Rise. Based upon an analysis of bottom crevasse heights and locations, and of the strength of radar waves diffracted from the apex and bottom corners of the gridcrevasses, we conclude that the crevasses are formed at discrete locations on the ice shelf. By comparing the locations of crevasse formation with ice thickness and bottom topography, we conclude that most of the crevasse sites are associated with grounding. Hence we have postulated that six grounded areas, in addition to Crary Ice Rise and Roosevelt Island, exist in the grid-western sector of the ice shelf. These pinning points may be important for interpreting the dynamics of the West Antarctic ice sheet.

scholarly journals Subcritical, transcritical and supercritical flows over a step

1997 ◽  
Vol 333 ◽  
pp. 257-271 ◽  
Author(s):  
YINGLONG ZHANG ◽  
SONGPING ZHU
Keyword(s):  
Steady State ◽  
Froude Number ◽  
Bottom Topography ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Transient Waves ◽  
Subcritical Case ◽  
Transcritical Flows ◽  
Supercritical Flows ◽  
Fkdv Equation

Free-surface flow over a bottom topography with an asymptotic depth change (a ‘step’) is considered for different ranges of Froude numbers varying from subcritical, transcritical, to supercritical. For the subcritical case, a linear model indicates that a train of transient waves propagates upstream and eventually alters the conditions there. This leading-order upstream influence is shown to have profound effects on higher-order perturbation models as well as on the Froude number which has been conventionally defined in terms of the steady-state upstream depth. For the transcritical case, a forced Korteweg–de Vries (fKdV) equation is derived, and the numerical solution of this equation reveals a surprisingly conspicuous distinction between positive and negative forcings. It is shown that for a negative forcing, there exists a physically realistic nonlinear steady state and our preliminary results indicate that this steady state is very likely to be stable. Clearly in contrast to previous findings associated with other types of forcings, such a steady state in the transcritical regime has never been reported before. For transcritical flows with Froude number less than one, the upstream influence discovered for the subcritical case reappears.

scholarly journals Scouring due to submerged sills

2018 ◽  
Vol 40 ◽  
pp. 03021
Author(s):  
Ashley Dudill ◽  
Jose Vasquez ◽  
Dave Mclean
Keyword(s):  
Surface Flow ◽  
Water Levels ◽  
Bridge Piers ◽  
Walnut Shell ◽  
Flume Experiments ◽  
Mixing Dynamics ◽  
Flow And Sediment Transport ◽  
Bed Stability ◽  
Insight Into

As the construction of infrastructure in and around a river channel modifies the flow and sediment transport characteristics, prediction of scour depths is an integral part of engineering design. Whilst there are a substantial number of predictive equations available to estimate the scour resulting from bridge piers, other types of structures have been less examined. This paper reports on flume experiments and numerical modelling to examine the role of submerged sills in the development of scour. Sills can be utilised in a channel to control bed stability, influence mixing dynamics or dictate water levels. Additionally, sills can occur due to infrastructure including riprap-covered pipeline crossings. The majority of previous work on sills has been undertaken on unsubmerged or partially submerged sills. The only experimental work on submerged sills is restricted to a range of conditions not applicable to pipeline crossings in large sand-bed rivers. This paper presents experiments, using artificial light-weight sediment (crushed walnut shell), undertaken with a fixed flow depth but a range of velocities and sill heights, all of which are in the surface flow regime. Hydrodynamic numerical simulations were run for the same conditions to gain insight into the corresponding flow structure.

scholarly journals Quiescent-phase evolution of a surge-type glacier: Black Rapids Glacier, Alaska, U.S.A.

1996 ◽  
Vol 42 (140) ◽  
pp. 110-122 ◽  
Author(s):  
T.A. Heinrichs ◽  
L.R. Mayo ◽  
K.A. Echelmeyer ◽  
W.D. Harrison
Keyword(s):  
Phase Evolution ◽  
Ice Thickness ◽  
Alaska Range ◽  
Thickness Change ◽  
Quiescent Phase ◽  
Cyclical Fluctuations ◽  
Ice Velocity ◽  
The Mean ◽  
Black Rapids Glacier ◽  
Speed Fluctuations

AbstractBlack Rapids Glacier, a surge-type glacier in the Alaska Range, most recently surged in 1936–37 and is currently in its quiescent phase. Mass balance, ice velocity and thickness change have been measured at three to ten sites from 1972 to 1994. The annual speed has undergone cyclical fluctuations of as much as 45% about the mean speed. Ice thickness and surface slope did not change enough to cause the speed fluctuations through changes in ice deformation, which indicates that they are being drinven by changes in basal motion. The behavior of Black Rapids Glacier during this quiescent phase is significantly different from that of Variegated Glacier, another well-studied surge-type glacier in Alaska. The present medial-moraine configuration of Black Rapids Glacier indicates that a surge could occur at any time. However, ice velocity data indicate that the next surge may not be imminent. We belive that there is little chance that the next surge will cross and dam the Delta River.

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