bluuebunny/crossref_metadata_2025_split huggingface dataset:
Primary Transverse Crevasses
Authors: Holdsworth G. 
Published: September 2017

Measurements of strain-rates on a temperate glacier in a region of initial transverse fracturing indicate a critical strain-rate of 3.5±0.5 × 10−5 d−1, associated with a regional strain-rate gradient of 5 × 10−8 d−1 m−1. At only one section of the glacier is the theoretical longitudinal strain-rate (Nye, 1959[c]) in approximate agreement with the value measured at the surface at that point. Corresponding measurements on a polar glacier (temperature −27.9°C at 10 m depth during the summer) indicate that the critical strain-rate is about 0.6±0.05 × 10−5 d−1, which is associated with a gradient of strain rate of about 3 × 10−9 d−1 m−1. At one section there is close agreement between the theoretical and measured longitudinal strain-rate. For the temperate glacier crevasse depths ranged from 23.5 to 28 m; in the polar glacier one crevasse was 23.9±0.5 m deep, assuming a wedge form. Only an approximate agreement with the measured values of depth is obtained by using the regional strain-rate values in Nye’s crevasse-depth formula.Over a distance of 1.2 km the temperate glacier transverse crevasse spacings are very variable, ranging from 30 m to 96 m, but initially the spacings range from 55 m to 96 m, and for the first four cases the spacing s varies from 2.7 d to 3.3 d, where d is the crevasse depth. In the cold ice, crevasse spacings are far more uniform, ranging from 57 m to 66 m. A value of s ≈ 2.5 d is obtained in only one case. This greater uniformity of spacing may be explained in terms of the dynamics of flow. Despite large differences in thermal, dimensional and strain-rate parameters between the two glaciers, (1) the crevasse depths are closely similar, and (2) the spacings of crevasses are similar. It has been demonstrated from two lines of evidence that the assumption that the strain on an intercrevasse block is negligible is not correct. The direction of the principal extending strain-rate is, in the most reliable cases, perpendicular to the crevasse traces within 2° to 7°.
Basal Sliding and Conditions at the Glacier Bed as Revealed by Bore-hole Photography
Authors: Engelhardt H. F. , Harrison W. D. , Kamb Barclay 
Published: September 2017

AbstractBore-hole photography demonstrates that the glacier bed was reached by cable-tool drilling in five bore holes in Blue Glacier, Washington. Basal sliding velocities measured by bore-hole photography, and confirmed by inclinometry, range from 0.3 to 3.0 cm/d and average 1.0 cm/d, much less than half the surface velocity of 15 cm/d. Sliding directions deviate up to 30° from the surface flow direction. Marked lateral and time variations in sliding velocity occur. The glacier bed consists of bedrock overlain by a ≈ 10 cm layer of active subsole drift, which intervenes between bedrock and ice sole and is actively involved in the sliding process. It forms a mechanically and visibly distinct layer, partially to completely ice-free, beneath the zone of debris-laden ice at the base of the glacier. Internal motions in the subsole drift include rolling of clasts caught between bedrock and moving ice. The largest sliding velocities occur in places where a basal gap, of width up to a few centimeters, intervenes between ice sole and subsole drift. The gap may result from ice—bed separation due to pressurization of the bed by bore-hole water. Water levels in bore holes reaching the bed drop to the bottom when good hydraulic connection is established with sub-glacial conduits; the water pressure in the conduits is essentially atmospheric. Factors responsible for the generally low sliding velocities are high bed roughness due to subsole drift, partial support of basal shear stress by rock friction, and minimal basal cavitation because of low water pressure in subglacial conduits. The observed basal conditions do not closely correspond to those assumed in existing theories of sliding.
A Study of Several Pressure Ridges and Ice Islands in the Canadian Beaufort Sea
Authors: Hnatiuk J. , Kovacs A. , Mellor M. 
Published: September 2017

AbstractThe environmental conditions in the southern Beaufort Sea are described with special emphasis on pressure ridges and ice islands. Techniques for determining the geometric configurations and the physical and mechanical properties of sea-ice structures and ice islands are described. Profiles of pressure ridges were determined by surface surveys, drill-hole probes and side-looking sonar scanning. Multi-year pressure ridges with thicknesses up to 20 m and widths up to 120 m were examined in detail. The first-year ridge of 22 m thickness and 100 m width was studied. Results are given for several multi-year and the first-year ridges. Information obtained from dives under the ice is also given. Corresponding data are given for grounded ice islands with particular attention being given to contact between the ice and sea bed. A 20 m thick ice-island fragment grounded in 15 m of water was one of several investigated. Measurements of temperature, salinity, tensile strength, and compressive strength are given for ice taken from old pressure ridges and factors influencing the interpretation of test data were discussed. The data obtained in this study will be used in engineering design studies for offshore structures for drilling and production of hydrocarbons from the Beaufort Sea area. Exploratory drilling in shallow water has already been carried out and offshore drilling from drillships is scheduled to commence in the study area during the open water season of 1976.
Determination of the Water Content of Snow from the Study of Electromagnetic Wave Propagation in the Snow Cover
Authors: Tobarias J. , Saguet P. , Chilo J. 
Published: September 2017

AbstractWe propose a method for measuring in situ and continuously, the water content of a sample of snow in the snow cover. This method is based on the measurement of the attenuation of an electromagnetic wave propagating in a sample of snow situated between two antennae, an emitter and a receiver. The working frequency is 9.4 GHz.
Glaciological Problems Set by the Control of Dangerous Lakes in Cordillera Blanca, Peru. II. Movement of a Covered Glacier Embedded within a Rock Glacier
Authors: Lliboutry Louis 
Published: September 2017

AbstractIn front of Laguna Parón there is a huge moraine which turns through 90° in the middle of the valley and with a narrow covered glacier on the top. It has been studied by electrical exploration, and using the displacements of 43 marked boulders on the glacier. Assuming a uniform balance on the glacier tongue and semi-elliptical cross-sections, it has been possible to estimate this balance and the glacier thickness. A great amount of the measured velocity comes from the creep of the moraine itself, which seems 10 be a kind of rock glacier, probably without interstitial ire. It must have taken all the Holocene to be formed. During its complex history a proglacial lake must have formed at some time, the rupture of which explains the crooked form.
Southward Displacement of the Distribution of Glaciation During the Three Maxima of the Last Ice Age
Authors: Mörner Nils-Axel 
Published: September 2017

AbstractThe Laurentide and Fennoscandian ice sheets had three major glaciation maxima during the Last Ice Age. All data from the southern margins of the ice sheets indicate that these maxima, as well as minor fluctuations, were synchronous. The same synchroneity is supposed to apply also for correlations between fluctuations on the north and south margins, which reveal a continuously southward displacement of the distribution of glaciation during the Last Ice Age. This southward displacement explains the saw-tooth pattern of 18O records from deep-sea cores in which the first glaciation maximum is under-represented due to its distribution more towards the north. The synchroneity is consistent with a global climatic control of the stadial/interstadial changes and with the recorded global eustatic changes. The southward displacement of glaciation seems to be a general rule also applicable to earlier Pleistocene glaciations.
Energy Exchange at a Glacier Surface: An Alternative to Aerodynamic Methods of Measurement
Authors: Wager A.C. , Jamieson A. W. 
Published: September 2017

AbstractAnalysis of wind-speed measurements made over a six-month period on an Antarctic glacier showed that conditions near the surface were dominated by gravity winds flowing downhill. In such conditions there is no satisfactory method of calculating the amount of energy exchanged between the glacier and the atmosphere. It is also difficult to extrapolate satisfactorily energy changes measured at a single point to the whole glacier. Moreover the loss of five days’ meteorological records may cause an error as large as the total change in energy content of the glacier during a year. In view of these difficulties it is more fruitful to measure the changes in energy content of the glacier directly. This can be done by accurate measurements of ice temperature and density near the surface. By defining the total energy content of a glacier as the heat required to melt it, fractional changes in the energy content and mass occurring over a year are equal and indicate the probable lifetime of the glacier. Estimates based on data from an Antarctic glacier suggest that the long-term change of energy of the glacier (≈ 1.5 W/m2) could be measured with an accuracy of 10% within a year.
A New Climatic Model for Glacier Behavior of the Austrian Alps
Authors: Posamentier Henry W. 
Published: September 2017

AbstractTwo climatic models are proposed for the fluctuation of Austrian Alpine glacier termini. The glacier record, based on annual observations by the Österreichische Alpenverein. is related to climatological data from the high-elevation Sonnblick-Observatorium. Monthly mean temperature and total precipitation during the ablation season for the concurrent plus preceding eleven years are the variables used in this analysis. The preferred model, mean temperature for June, July and August for the concurrent plus preceding seven years, is inversely related to glacier advance. This model was derived by combining those variables with the highest correlation coefficient relative to the glacier record. Mean lag time between climate and glacier termini response seems to be seven years. The second and less preferred model is derived by multiple regression analysis and includes seven variables temperature and precipitation. Variation in the glacier behavior record accounted for by the two models is 71% and 67% respectively.
Short Notes: On Depth Hoar and the Strength of Snow
Authors: Bradley C.C. , Brown R.L , Williams T. 
Published: September 2017

AbstractIt has long been known that a temperature gradient in the snowpack, when temperatures are less than 0°C, can metamorphose the snow to produce a fragile euhedral crystalline end product called “depth hoar" which is considered to be responsible for snowpack collapse and climax avalanches. The wave of metamorphism advancing through anhedral snow converts it, first to subhedral, and finally to euhedral depth hoar. Our field observations, which are at the moment supported by laboratory evidence, reveal that the zone of minimum snow strength in the gradient metamorphic layer is associated with the intermediate subhedral phase rather than with the euhedral end product.
Internal Reflections in Polar Ice Sheets
Authors: Paren J. G. , Robin G. de. Q. 
Published: September 2017

AbstractInternal reflections are due to changes in electrical admittance between adjacent depositional layers. Reflection coefficients are given for discontinuous changes in either the permittivity or loss tangent. The observed strengths of internal echoes rule out the possibility that they are caused by isolated layers containing “foreign” material, but suggest instead that they are due to systematic fluctuations of density, anisotropy, or loss tangent. The electrical behaviour of ice from polar ice sheets is reviewed and compared with that of ice grown in controlled laboratory conditions. We suggest that the impurity distribution in polycrystalline ice is dependent on the impurity content and the temperature of freezing, and the conductivity is essentially determined by the intrinsic and impurity defects within the crystal lattice. In a polar ice sheet, density fluctuations decrease with depth, whereas loss tangents (and hence their fluctuations) increase since the ice becomes warmer towards bedrock. Echo strengths in central Antarctica are compared with those calculated for a boundary where either all bubbles disappear or the loss tangent changes by 50%. Assuming a constant layering geometry to 2 700 m depth, density fluctuations account for echoes above 1 500 m, but deeper echoes are best explained by variations in the ice conductivity.
Sublimation or Melting: Observations from the White Mountains, California and Nevada,U.S.A.
Authors: Beaty Chester B. 
Published: September 2017

AbstractStudy of the waning snow-pack along the crest of the White Mountains of California and Nevada in 1970 and 1974 indicates that a significant proportion of the high-altitude snow in the range sublimates and/or evaporates shortly after melting. Qualitative and limited quantitative evidence suggest that the amount of snow thus disposed of may be as much as 50-80% of the total springtime pack. Meteorological observations in the White Mountains demonstrate that atmospheric conditions particularly favorable for effective sublimation/evaporation are common in May and June, the main ablation period in the mountains. The general lack of evidence of surficial erosion on slopes above 3 500 m, often supposed to be wide-spread and caused by so-called "snow-melt" runoff, is therefore readily explained-there is little "snow-melt" erosion simply because there is only limited snow-melt.
Measurement of Small Strain-Rates over Short Time Periods
Authors: Holdsworth G. 
Published: September 2017

AbstractA laser interferometer has been used to measure small relative displacements between two reference points spaced up to 99.76 m apart and fixed in an ice surface. Strain-rates of order 10−11 s−1 can be detected easily within a 24 h period and possibly within an 8 h period.
Source, Transportation and Deposition of Debris on Arapaho Glacier, Front Range, Colorado, U.S.A.
Authors: Reheis Marith Jean 
Published: September 2017

This study was undertaken to determine the sources of debris and methods of transportation and deposition in and on a small cirque glacier. Data were collected on the amount of debris, stone roundness, the presence of striations and polish, and till fabric. Lichenometry gave relative ages of the tills, and suggests that the Gannett Peak till is of at least three ages and probably overlies Audubon till.Debris originating from subglacial erosion can be differentiated from that from rockfall or avalanches on stone roundness, polish and striations. A maximum of 70% of the present glacial load derives from subglacial erosion, as compared to 88% during the Gannett Peak stade. Rockfall rates are 35-50 m3/year at present and were 290–485 m3/year during the Gannett Peak stade. Data on present-day processes and on the volume and age of Gannett Peak moraines can be used to make comparisons on present and past rates of denudation. The denudation rate in the cirque at present is 95–165 mm/1 000 year; in the past it was 4 920-8 160 mm/ 1 000 year. The denudation rate and the glacial effects on debris are comparable to rates from other glacial areas and effects on debris carried by valley glaciers and continental ice sheets.
The Study of Fresh-Water Lake Ice Using Multiplexed Imaging Radar
Authors: Bryan M. Leonard , Larson R. W. 
Published: September 2017

The study of ice in the upper Great Lakes, both from the operational and the scientific points of view, is receiving continued attention. Quantitative and qualitative field work is being conducted to provide the needed background for accurate interpretation of remotely sensed data. The data under discussion in this paper were obtained by a side-looking multiplexed airborne radar (SLAR) supplemented with ground-truth data.Because of its ability to penetrate adverse weather, radar is an especially important instrument for monitoring ice in the upper Great Lakes. It has previously been shown that imaging radars can provide maps of ice cover in these areas. However, questions concerning both the nature of the surfaces reflecting radar energy and the interpretation of the radar imagery continually arise.Our analysis of ice in Whitefish Bay (Lake Superior) indicates that the combination of the ice/water interlace and the ice/air interface is the major contributor to the radar backscatter as seen on the imagery. At these frequencies the ice has a very low relative dielectric permittivity (< 3.0) and a low loss tangent. Thus, this ice is somewhat transparent to the energy used by the imaging SLAR system. The ice types studied include newly formed black ice, pancake ice, and frozen and consolidated pack and brash ice.Although ice thickness cannot be measured directly from the received signals, it is suspected that by combining the information pertaining to radar backscatter with data on the meteorological and sea-state history of the area, together with some basic ground truth, better estimates of the ice thickness may be provided. In addition, certain ice features (e.g. ridges, ice-foot formation, areas of brash ice) may be identified with reasonable confidence. There is a continued need for additional ground work to verify the validity of imaging radars for these types of interpretations.
The Pleistocene Moraine Stages of West-Central Peru
Authors: Clapperton Chalmers M. 
Published: September 2017

AbstractDetailed field mapping in three massifs of the central Andes of Peru indicates that there are four glacial moraine stages. Historical evidence and correlation with Patagonia and South Georgia suggest that the three youngest stages relate to Neoglacial re-advances which culminated before 4000 b.p., between a.d. 1750 and 1800 and during the late nineteenth century. The oldest moraine stage may be of late Wisconsin/Weichselian age. The absence of older moraines suggests that the Peruvian Andes were not high enough earlier in the Pleistocene to support larger glaciers.
Grain-Boundary Energy and Grain-Boundary Groove Angles in Ice
Authors: Suzuki Shigenao , Kuroiwa Daisuke 
Published: September 2017

AbstractRelative grain-boundary energies in ice were measured as a function of mismatch angles made by the c-axes or a-axes in grains, using ice specimens having triple grain boundaries. It was found that the Read–Shockley equation for grain-boundary energy was valid for grain boundaries tilted between 0° and 15°. Angles of the solid–vapour grain-boundary groove in ice were measured by the use of micro-interferometry at grain-boundary grooves covered with extremely thin metalic foil. The data were compared with those measured by a silvered replica of grain-boundary grooves.
Generalization of Haefeli’s Creep-Angle Analysis
Authors: Perla R. I. 
Published: September 2017

AbstractUsing geometrical arguments, Haefeli developed a stress analysis for slabs of compressible viscous materials. His analysis was based on a key parameter called the creep angle. A generalization of the creep angle, called the deformation-rate coefficient, is derived by replacing geometrical arguments with continuum mechanics. Once the deformation-rate coefficient is found from in situ measurements, the stress field of the slab can be determined from a set of hyperboic partial differential equations.
The Creep of Ice Shelves Theory
Authors: Thomas R. H. 
Published: September 2017

AbstractBudd’s expressions for strain-rate gradient along the centre line of a bounded ice shelf are shown to be applicable only to ice shelves with almost constant thickness and very small longitudinal strain-rates. A general expression is derived for creep in an ice shelf where the sole restriction is that of zero shear stresses in vertical planes. This is applied to the two special cases:
(1)movement of an ice shelf restricted in at least one direction by sea-water pressure only;(2)movement of an ice shelf flowing between roughly parallel sides.
The Creep of Ice Shelves: Interpretation of Observed Behaviour
Authors: Thomas R. H. 
Published: September 2017

AbstractAvailable measurements of creep rates and dimensions of ice shelves are used, in conjunction with equations derived in a companion paper (Thomas, 1973), to evaluate the flow law parameters B and n for stresses down to 104 N m−2. The results show good agreement with laboratory work at higher stresses. Adoption of these values of B and n enables us to examine the restraining effects on an ice shelf of obstructions such as areas of grounding.
A Flow Law for Temperate Glacier Ice
Authors: Colbeck S. C. , Evans R. J. 
Published: September 2017

AbstractUniaxial compressive creep tests were performed on polycrystalline samples of glacier ice at stresses ranging from 0.06 bar to 1.0 bar under conditions similar to those actually occurring in a temperate glacier. Tests were conducted in an ice tunnel on the Blue Glacier, Mt Olympus, Washington, U.S.A., thus ensuring that the temperature remained at the pressure melting point.The flow law proposed as an appropriate one-dimensional flow law for temperate glacier ice is a polynomial expression containing linear, cubic and fifth-order terms. This law provides a good fit to the data and is also consistent with the quasi-viscous creep data of Glen (1955).
Radio Echo Sounding on a Valley Glacier in East Greenland
Authors: Davis J. L. , Halliday J. S. , Miller K. J. 
Published: September 2017

AbstractAlthough radio echo sounding equipment has been used with success for measuring the thickness of ice sheets in the Arctic and Antarctic, a valley glacier poses the additional problems of echoes from the valley walls, which may obscure the bottom echoes, and a high attenuation of radio waves in the ice. During July and August 1970, a study was carried out on Roslin Gletscher in Stauning Alper, East Greenland, to investigate the problems of radio echo sounding on a valley glacier. Results show that reflections from the valley walls are minimized by using sufficiently directional antennae, but attenuation of the signal in the ice is higher than that in polar ice at the same temperature. Water in and on the ice probably accounts for much of the attenuation, and the use of a lower frequency or measurements before the melt commences should give improved performance.