Comparison of moraines formed by surging and normal glaciers

1969 ◽  
Vol 6 (4) ◽  
pp. 991-999 ◽  
Author(s):  
Nathaniel W. Rutter
Keyword(s):  
Flow Direction ◽  
Size Fraction ◽  
Preferred Orientation ◽  
Ground Moraine ◽  
Upper Limit ◽  
Glacier Flow ◽  
Surficial Deposits ◽  
Thick Mantle

A Neoglacial moraine of Bighorn Glacier, St. Elias Mountains, Yukon, probably formed by a surging glacier, and a Neoglacial normal moraine of nearby Grizzly Glacier were studied. Surficial deposits and erosional features were mapped, Fabric analyses were done in till at five sites in each moraine. Samples were subjected to laboratory lithologic and texture analyses.The Bighorn (surge) moraine is a thin, discontinuous, irregular mantle, mostly till, but including ice-contact stratified material. Lateral moraines show subdued ridges marking the upper limit of glaciation. Ground moraine of the Grizzly (normal) glacier is an irregular, continuous, thick mantle, mostly till and. ice-contact stratified material. Upper ice limits are marked by prominent ridges. Rocks of similar lithologies within the till are concentrated in bands parallel to glacier flow.Stones in till of the Grizzly moraine have strong preferred orientation roughly in the direction of glacier flow. In the Bighorn moraine, rocks in till are weakly oriented. Where orientation is apparent, it is not necessarily in the flow direction. For the size fraction finer than 2 mm, Bighorn till is coarser than Grizzly till although the bedrock terrain is similar.These differences are useful in distinguishing moraines of normal and surging glaciers.

scholarly journals Glacier disequilibrium in the Convoy Range, Transantarctic Mountains, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 269-276 ◽  
Author(s):  
T.J. Chinn
Keyword(s):  
Field Work ◽  
Snow Accumulation ◽  
Low Velocity ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Regime Changes ◽  
Positive Balance ◽  
Geological Map ◽  
Glacier Flow ◽  
Surficial Deposits

Field work for a geological map of the Convoy Range included mapping glaciers, moraines and surficial deposits. A range of glaciological indicators, including supraglacial and other moraines and margin morphology, has been used to assess the present equilibrium of the glaciers. Fields of rafted supraglacial moraine have accumulated over long periods of time at specific low-gradient, low-velocity locations. As the glacier regime changes, the shape of the moraine field distorts, signalling a change in flow pattern. By reversing the ice flow vectors directed at the moraine field, the directions from whence the debris came are shown. Unsorting the contortions of supraglacial moraine fields reveals the nature of the changes in glacier regime. Moraine-field configurations all suggest that local glaciers are expanding in response to higher local precipitation, estimated to have occurred between 2000 and 8000 year BP, most likely coincident with the world-wide “climatic optimum” of about 6000 year BP.Ice-cliff morphology, fresh terminal moraines and boulder trains indicate that larger local glaciers are currently receding from a Holocene maximum, while the margin of the large Mackay Ice Sheet outlet glacier shows no evidence of recent recession and is probably close to its Holocene maximum. In contrast, areas of present snow cover are expanding, superimposing a recent positive balance (decades to hundreds of years), which has yet to reverse a general recession of mid- to high-altitude glaciers. Local hollows in some névé areas imply that glacier flow is not in equilibrium with snow accumulation.

scholarly journals Clasts with Stoss-Lee Form in Lodgement Tills: A Discussion

1984 ◽  
Vol 30 (105) ◽  
pp. 241-243 ◽  
Author(s):  
Johannes Krüger
Keyword(s):  
Flow Direction ◽  
Ground Moraine ◽  
Opposite Orientation ◽  
Glacial Erosion ◽  
Ice Flow ◽  
Diagnostic Criterion ◽  
Lee Form

AbstractClasts modified by glacial erosion are described from lodgement tills in front of the glacier Mýrdalsjökull, south Iceland. Many clasts show modification of their lower surfaces in the same way as their upper ones. However, the lower surfaces have a smoothed down-glacier face and a truncated up-glacier face, which is the opposite orientation to that of the upper surfaces. This so-called double stoss-lee form is interpreted as a response to basal transport over abrading materials, following deposition of the clast and succeeded by glacial erosion. It is suggested that clasts with a double stoss-lee form are a diagnostic criterion for subglacial deposition by lodgement. Furthermore, the distribution and orientation of clasts with a stoss-lee form was investigated on a ground-moraine surface. 17.3% of 2199 clasts with an a-axis diameter > 30 cm had a stoss-lee form. The proportion of clasts with their smoothed ends facing up-glacier within ± 22.5° of the ice-flow direction was 72.7%. Thus, the preferred stoss-side orientation is closely related to the ice movement and indicates the direction from which the ice came. Only 11.7% of boulders with a divergent stoss-side orientation are located in connection with annual moraines. It is suggested that such boulders have mainly been re-deposited beneath the ice and not at the ice front by minor advances of the glacier.

Evidence of magmatic flow by 2-D image analysis of 3-D shape preferred orientation distributions

2004 ◽  
Vol 175 (4) ◽  
pp. 331-350 ◽  
Author(s):  
Patrick Launeau
Keyword(s):  
Image Analysis ◽  
Shear Flow ◽  
Simple Shear ◽  
Flow Direction ◽  
Preferred Orientation ◽  
Simple Shear Flow ◽  
Shear Direction ◽  
Thin Sections ◽  
Passive Deformation ◽  
Shape Ratio

Abstract The 3-D Shape Preferred Orientation (SPO) ellipsoid can be obtained by image analysis on a minimum of three perpendicular sections, when the 2-D measurements can be assimilated to ellipses. As numerous phenomenons can modify the SPO in magma (boundary condition effects, crystal interactions, joint migrations, etc.), the ellipsoid calculation is first tested on a set of digital models of simple shear flow. Those models, made of scattered shape ratio distribution, show that a suspension of crystals in a simple shear flow of the magma produces SPO parallel to the shear direction with an intensity given by the average shape ratio of the crystals, without any link with the amount of shear flow. This steady state SPO along the flow direction is particularly useful to study magma emplacement even if it is also shown that a critical shear rate γ between 4 and 8, for crystal shape ratio between 2 and 5 respectively, is sufficient to completely reorient a SPO. Therefore the SPO does not record magmatic strain as may do an enclave, which is an interface between two magmas with low viscosity contrast, that can record the whole strain of the magma by its passive deformation along the flow. An infinite strain is necessary here to parallelize the enclave on the shear flow direction. The application to a natural case (gabbronorite of the Bushveld, South Africa) shows that we must take care of the mineral chosen to describe a flow in a magma and that a careful classical study of the structures observed in thin sections is always required. To allow anyone to test the quality of the 2-D/3-D conversions, a web site is associated to this publication with a free access to all the image analysis and ellipsoid programs presented below.

Determining glacier flow direction from till fabrics

Geomorphology ◽  
2017 ◽  
Vol 299 ◽  
pp. 124-130 ◽  
Author(s):  
Neal R. Iverson
Keyword(s):  
Flow Direction ◽  
Glacier Flow

Ground-penetrating radar antenna orientation effects on temperate mountain glaciers

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. H15-H24 ◽  
Author(s):  
Lisbeth Langhammer ◽  
Lasse Rabenstein ◽  
Andreas Bauder ◽  
Hansruedi Maurer
Keyword(s):  
Ground Penetrating Radar ◽  
Flow Direction ◽  
Order Effect ◽  
Single Pair ◽  
Dipole Antennas ◽  
3D Numerical Modeling ◽  
Dipole Orientation ◽  
Bedrock Topography ◽  
Glacier Flow ◽  
Ground Penetrating

Ground-penetrating radar (GPR) surveys on glaciers are generally restricted to a single pair of bistatic dipole antennas orientated either parallel or perpendicular to the surveying direction. Extensive helicopter-borne and ground-based GPR investigations on the Glacier d’Otemma, Switzerland, demonstrated that the detectability of the ice-bedrock interface varies substantially with dipole orientation. We recorded several across and along profiles using two different commercial GPR systems operated with 15, 25, 50, and 70 MHz antennas. Dipole alignments parallel to the glacier flow generated considerably stronger and more coherent bedrock reflections compared with a perpendicular dipole setup. We observed the behavior for all the systems and antenna frequencies that we used. To help explain these findings, we performed 3D numerical modeling using the open source software gprMax. Simulations with 20 MHz transmitting and receiving dipoles indicated that the changes of the bedrock reflection amplitude are primarily governed by the bedrock topography. Scattering and intrinsic attenuation may also influence the amplitudes of the bedrock reflections, but these effects seem to be much less pronounced. Evidently, to increase the GPR bedrock reflection quality, dipole antennas should be orientated parallel to the glacier flow direction on a glacier confined to a valley. Because the directional dependence is a first-order effect, it is advisable to perform multicomponent surveys when the general shape of the bedrock topography is unknown. The multicomponent setup preferably consists of two sets of dipole antennas, each in broadside configuration and the sets being orthogonal to each other.

scholarly journals Glacier disequilibrium in the Convoy Range, Transantarctic Mountains, Antarctica

1994 ◽  
Vol 20 ◽  
pp. 269-276 ◽  
Author(s):  
T.J. Chinn
Keyword(s):  
Field Work ◽  
Snow Accumulation ◽  
Low Velocity ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Regime Changes ◽  
Positive Balance ◽  
Geological Map ◽  
Glacier Flow ◽  
Surficial Deposits

Field work for a geological map of the Convoy Range included mapping glaciers, moraines and surficial deposits. A range of glaciological indicators, including supraglacial and other moraines and margin morphology, has been used to assess the present equilibrium of the glaciers. Fields of rafted supraglacial moraine have accumulated over long periods of time at specific low-gradient, low-velocity locations. As the glacier regime changes, the shape of the moraine field distorts, signalling a change in flow pattern. By reversing the ice flow vectors directed at the moraine field, the directions from whence the debris came are shown. Unsorting the contortions of supraglacial moraine fields reveals the nature of the changes in glacier regime. Moraine-field configurations all suggest that local glaciers are expanding in response to higher local precipitation, estimated to have occurred between 2000 and 8000 year BP, most likely coincident with the world-wide “climatic optimum” of about 6000 year BP.Ice-cliff morphology, fresh terminal moraines and boulder trains indicate that larger local glaciers are currently receding from a Holocene maximum, while the margin of the large Mackay Ice Sheet outlet glacier shows no evidence of recent recession and is probably close to its Holocene maximum. In contrast, areas of present snow cover are expanding, superimposing a recent positive balance (decades to hundreds of years), which has yet to reverse a general recession of mid- to high-altitude glaciers. Local hollows in some névé areas imply that glacier flow is not in equilibrium with snow accumulation.

scholarly journals Supraglacial ice cliffs and ponds on debris-covered glaciers: spatio-temporal distribution and characteristics

2019 ◽  
Vol 65 (252) ◽  
pp. 617-632 ◽  
Author(s):  
JAKOB F. STEINER ◽  
PASCAL BURI ◽  
EVAN S. MILES ◽  
SILVAN RAGETTLI ◽  
FRANCESCA PELLICCIOTTI
Keyword(s):  
High Resolution ◽  
Flow Direction ◽  
Temporal Distribution ◽  
Central Himalaya ◽  
Catchment Scale ◽  
Monsoon Period ◽  
Glacier Tongue ◽  
Space And Time ◽  
Spatio Temporal ◽  
Glacier Flow

ABSTRACTIce cliffs and ponds on debris-covered glaciers have received increased attention due to their role in amplifying local melt. However, very few studies have looked at these features on the catchment scale to determine their patterns and changes in space and time. We have compiled a detailed inventory of cliffs and ponds in the Langtang catchment, central Himalaya, from six high-resolution satellite orthoimages and DEMs between 2006 and 2015, and a historic orthophoto from 1974. Cliffs cover between 1.4% (± 0.4%) in the dry and 3.4% (± 0.9%) in the wet seasons and ponds between 0.6% (± 0.1%) and 1.6% (± 0.3%) of the total debris-covered tongues. We find large variations between seasons, as cliffs and ponds tend to grow in the wetter monsoon period, but there is no obvious trend in total area over the study period. The inventory further shows that cliffs are predominately north-facing irrespective of the glacier flow direction. Both cliffs and ponds appear in higher densities several hundred metres from the terminus in areas where tributaries reach the main glacier tongue. On the largest glacier in the catchment ~10% of all cliffs and ponds persisted over nearly a decade.

scholarly journals Clasts with Stoss-Lee Form in Lodgement Tills: A Discussion

1984 ◽  
Vol 30 (105) ◽  
pp. 241-243 ◽  
Author(s):  
Johannes Krüger
Keyword(s):  
Flow Direction ◽  
Ground Moraine ◽  
Opposite Orientation ◽  
Glacial Erosion ◽  
Ice Flow ◽  
Diagnostic Criterion ◽  
Lee Form

AbstractClasts modified by glacial erosion are described from lodgement tills in front of the glacier Mýrdalsjökull, south Iceland. Many clasts show modification of their lower surfaces in the same way as their upper ones. However, the lower surfaces have a smoothed down-glacier face and a truncated up-glacier face, which is the opposite orientation to that of the upper surfaces. This so-called double stoss-lee form is interpreted as a response to basal transport over abrading materials, following deposition of the clast and succeeded by glacial erosion. It is suggested that clasts with a double stoss-lee form are a diagnostic criterion for subglacial deposition by lodgement. Furthermore, the distribution and orientation of clasts with a stoss-lee form was investigated on a ground-moraine surface. 17.3% of 2199 clasts with ana-axis diameter > 30 cm had a stoss-lee form. The proportion of clasts with their smoothed ends facing up-glacier within ± 22.5° of the ice-flow direction was 72.7%. Thus, the preferred stoss-side orientation is closely related to the ice movement and indicates the direction from which the ice came. Only 11.7% of boulders with a divergent stoss-side orientation are located in connection with annual moraines. It is suggested that such boulders have mainly been re-deposited beneath the ice and not at the ice front by minor advances of the glacier.

Micromechanical Model for the Orthotropic Elastic Constants of Polyetheretherketone Composites Considering the Orientation Distribution of the Hydroxyapatite Whisker Reinforcements

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Justin M. Deuerling ◽  
J. Scott Vitter ◽  
Gabriel L. Converse ◽  
Ryan K. Roeder
Keyword(s):  
Elastic Constants ◽  
Volume Fraction ◽  
Flow Direction ◽  
Micromechanical Model ◽  
Orientation Distribution ◽  
Short Fiber ◽  
Preferred Orientation ◽  
Experimental Measurements ◽  
Fiber Reinforced ◽  
Model Predictions

Hydroxyapatite (HA) whisker reinforced polyetheretherketone (PEEK) composites have been investigated as bioactive materials for load-bearing orthopedic implants with tailored mechanical properties governed by the volume fraction, morphology, and preferred orientation of the HA whisker reinforcements. Therefore, the objective of this study was to establish key structure-property relationships and predictive capabilities for the design of HA whisker reinforced PEEK composites and, more generally, discontinuous short fiber-reinforced composite materials. HA whisker reinforced PEEK composites exhibited anisotropic elastic constants due to a preferred orientation of the HA whiskers induced during compression molding. Experimental measurements for both the preferred orientation of HA whiskers and composite elastic constants were greatest in the flow direction during molding (3-axis, C33), followed by the transverse (2-axis, C22) and pressing (1-axis, C11) directions. Moreover, experimental measurements for the elastic anisotropy and degree of preferred orientation in the same specimen plane were correlated. A micromechanical model accounted for the preferred orientation of HA whiskers using two-dimensional implementations of the measured orientation distribution function (ODF) and was able to more accurately predict the orthotropic elastic constants compared to common, idealized assumptions of randomly oriented or perfectly aligned reinforcements. Model predictions using the 3-2 plane ODF, and the average of the 3-1 and 3-2 plane ODFs, were in close agreement with the corresponding measured elastic constants, exhibiting less than 5% average absolute error. Model predictions for C11 using the 3-1 plane ODF were less accurate, with greater than 10% error. This study demonstrated the ability to accurately predict differences in orthotropic elastic constants due to changes in the reinforcement orientation distribution, which will aid in the design of HA whisker reinforced PEEK composites and, more generally, discontinuous short fiber-reinforced composites.

scholarly journals Crystallographic analysis of temperate ice on Rhonegletscher, Swiss Alps

2021 ◽  
Vol 15 (2) ◽  
pp. 677-694
Author(s):  
Sebastian Hellmann ◽  
Johanna Kerch ◽  
Ilka Weikusat ◽  
Andreas Bauder ◽  
Melchior Grab ◽  
...  
Keyword(s):  
Numerical Modelling ◽  
Compressive Stress ◽  
Flow Direction ◽  
Swiss Alps ◽  
Integrated Analysis ◽  
Polar Regions ◽  
Large Area ◽  
Axis Orientation ◽  
Glacier Flow ◽  
The Individual

Abstract. Crystal orientation fabric (COF) analysis provides information about the c-axis orientation of ice grains and the associated anisotropy and microstructural information about deformation and recrystallisation processes within the glacier. This information can be used to introduce modules that fully describe the microstructural anisotropy or at least direction-dependent enhancement factors for glacier modelling. The COF was studied at an ice core that was obtained from the temperate Rhonegletscher, located in the central Swiss Alps. Seven samples, extracted at depths between 2 and 79 m, were analysed with an automatic fabric analyser. The COF analysis revealed conspicuous four-maxima patterns of the c-axis orientations at all depths. Additional data, such as microstructural images, produced during the ice sample preparation process, were considered to interpret these patterns. Furthermore, repeated high-precision global navigation satellite system (GNSS) surveying allowed the local glacier flow direction to be determined. The relative movements of the individual surveying points indicated longitudinal compressive stresses parallel to the glacier flow. Finally, numerical modelling of the ice flow permitted estimation of the local stress distribution. An integrated analysis of all the data sets provided indications and suggestions for the development of the four-maxima patterns. The centroid of the four-maxima patterns of the individual core samples and the coinciding maximum eigenvector approximately align with the compressive stress directions obtained from numerical modelling with an exception for the deepest sample. The clustering of the c axes in four maxima surrounding the predominant compressive stress direction is most likely the result of a fast migration recrystallisation. This interpretation is supported by air bubble analysis of large-area scanning macroscope (LASM) images. Our results indicate that COF studies, which have so far predominantly been performed on cold ice samples from the polar regions, can also provide valuable insights into the stress and strain rate distribution within temperate glaciers.

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