bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characteristics of tide-water calving at Glaciar San Rafael, Chile
Authors: Warren Charles R. , Glasser Neil F. , Harrison Stephan , Winchester Vanessa , Kerr Andrew R. , Rivera Andres 
Published: September 2017

AbstractGlacial calving is a poorly understood process. This study tests the influence of local environmental variables on the magnitude and frequency distributions of calving behaviour at Glaciar San Rafael, Chile. Near the terminus of the glacier, surface speeds average 17 m d−1in summer and calving is profuse and continual. The size, location and characteristics of over 7000 calving events were recorded during 32d in 1991 and 1992, together with meteorological, bathymetric and oceanographic data. Mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 Mm3d1. Mean annual calving speed and calving flux are about 4500 m a−1and 2.0 km3a−1, respectively. This calving speed is higher than that predicted by the established empirical relationship between tide-water calving speed and water depth. This is surprising, given the low salinity of Laguna San Rafael and that fresh-water calving speeds are commonly much lower than those in ride water. Daily patterns of calving frequency and flux correlate poorly or not at all with meteorological variables, but tidal stage may have some control over the timing of large submarine calving events. Submarine calving produced the largest bergs. However, the relatively small total flux recorded from the submerged pars of the ice cliff may imply unusually rapid melt rates.
Monthly balance and water discharge of an inter-tropical glacier: Zongo Glacier, Cordillera Real, Bolivia, 16° S
Authors: Francou Bernard , Ribstein Pierre , Saravia Ronald , Tiriau Eric 
Published: September 2017

AbstractMeasurements of mass balance were performed every month on Zongo Glacier. Bolivia. Simultaneously, water-discharge, temperature and precipitation data were obtained. The first year of the survey, 1991–92. was marked by an ENSO (El Niño-Southern Oscillation) event with high temperature and low precipitation, whilst the following year, 1992–93, was normal. Results point to the early and late wet season (October-December and March–May: as playing a critical role in the determination of the annual mass balance. The wet season is the warmest period of the year and consequently the duration of the wet season is a highly relevant variable in determining mass balance. Both glaciological and hydrological methods for the determination of the mass balance provide similar results. Our study confirms dial ENSO events have a major influence on the rapid glacier retreat currently affecting this part of the Andes.
Short-pulse radar wavelet recovery and resolution of dielectric contrasts within englacial and basal ice of Matanuska Glacier, Alaska, U.S.A.
Authors: Arcone Steven A. , Lawson Daniel E. , Delaney Allan J. 
Published: September 2017

AbstractWavelets transmitted by short-pulse radar are recovered from continuous profiles and used to determine interfacial dielectric contrasts within the englacial and basal ice at the terminus area of Matanuska Glacier, Alaska, U.S.A. The field studies were in the ablation region, where radar horizons could, at some point, be identified with interfaces between clear ice and air, water or basal ice, and were performed in early spring before drainage fully developed. The profiles used closely-spaced antennas with bandwidths centered near 50 and 400 MHz. Transmitted wavelets reflected from interfaces of known dielectric contrasts are used to establish a phase reference for other events from interfaces between unknown contrasts. Migration and Fourier-transform filtering are then applied to the profiles and shown to recover these wavelets from diffractions and reflections. Interfacial dielectric contrasts are determined from the relative phase of the wavelets. Near the terminus lake, some basal ice events above 8 m depth are interpreted as voids. Further up-glacier, most englacial events are interpreted as voids, but deeper localized reflectors and horizons to 90 m depth and within the basal zone are interpreted as voids, water or debris. Phase cannot be determined for the basal-substrate transition reflections. Recommendations are made for improving the wavelet recovery process and the quality of GPR migration.
Characterization and flexural strength of iceberg and glacier ice
Authors: Gagnon R.E. , Gammon P.H. 
Published: September 2017

AbstractFlexural strength of iceberg and glacier ice was determined from Four-point beam-bending experiments. A large quantity of glacial ice was collected from four icebergs and one glacier, and a detailed ice-characterization program was performed on samples from the five sources. Beam-bending experiments were conducted at four temperatures in the range −1 ° to-16 °C and at strain rates of 10 −3 and 10−5 s−1. The flexural strength was found to increase with increasing strain rate (based on extreme fibre strain and decreasing temperature. The data suggest than air-bubble inclusions play an important role in determining the flexural strength of glacial ice and this can explain the significant differences in mean strength of the ice from the five sources. At a strain rate of 10−3 s−1 and temperature of —11 °C, the flexural strength was found to increase as the number of bubbles per unit volume increased. Reduction of crack-initiating stresses at grain boundaries by “softening” of grains due to intragranular air-bubble inclusions is thought to be the mechanism.
Response of valley glaciers to climate change and kinematic waves: a study with a numerical ice-flow model
Authors: van de Wal R. S. W. , Oerlemans J. 
Published: September 2017

AbstractA simple numerical flow model that couples mass divergence directly to basal shear stress as the only driving force is used to study kinematic waves. Kinematic waves that result from a perturbation of the ice thickness or mass balance are compared with the linear kinematic-wave theory of Nye/Weertman. The wave velocity is calculated as a function of the wavelength and amplitude of a perturbation. The modelled wave velocity is typically 6–8 times the vertically averaged velocity in the flow direction whereas linear theory predicts a factor of only 5.An experiment with the geometry of Hintereisferner, Austria, shows that the increase in the local ice velocity during a kinematic wave is about 10% but varies slightly depending on the position along the glacier and the amplitude of the kinematic wave. Kinematic waves are thus hard to detect from velocity measurements.The dynamics of simple continuity models are rich enough to support a variety of kinematic-wave phenomena. Such models are a useful tool to study the response of valley glaciers to climate change.
Variations of ablation, albedo and energy balance at the margin of the Greenland ice sheet, Kronprins Christian Land, eastern north Greenland
Authors: Konzelmann Thomas , Braithwaite Roger J. 
Published: September 2017

AbstractA meteorological and glaciological experiment was carried out in July 1993 at the margin of the Greenland ice sheet in Kronprins Christian Land, eastern north Greenland. Within a small area (about 100 m2) daily measurements were made on ten ablation stakes fixed in “light” and “dark” ice and were compared to each other. Simultaneously, the components of the energy balance, including net radiation, sensible-heat flux, latent-heat flux and conductive-heat flux in the ice were determined. Global radiation, longwave incoming radiation and albedo were measured, and longwave outgoing radiation was calculated by assuming that the glacier surface was melting. Sensible-and latent-heat fluxes were calculated from air temperature, humidity and wind speed. Conductive-heat flux in the ice was estimated by temperature-profile measurements in the uppermost ice layer. Net radiation is the major source of ablation energy, and turbulent fluxes are smaller energy sources by about three times, while heat flux into the ice is a substantial heat sink, reducing energy available for ice melt. Albedo varies from 0.42 to 0.56 within the experimental site and causes relatively large differences in ablation at stakes close to each other. Small-scale albedo variations should therefore be carefully sampled for large-scale energy-balance calculations.
Mapping c-axis fabrics to study physical processes in ice
Authors: Alley R. B. , Gow A.J. , Meese D.A. 
Published: September 2017

AbstractMapping the spatial distribution of c-axis orientations in ice thin sections is not much more difficult than preparing c-axis scatter plots but can reveal additional information about processes responsible for the observed fabric and texture of the ice. Distributions of angles between c axes of neighboring grains from the Byrd Station (West Antarctica) ice core suggest that polygonization causes average grain-size to stabilize below 400 m depth.
Ice–Brine Dendritic Aggregate formed on Freezing of Aqueous Solutions
Authors: Rohatgi P. K. , Adams C. M. 
Published: September 2017

Dendritic aggregates of ice and brine formed upon freezing of aqueous solutions have been studied. Chlorides of sodium, potassium, lithium and hydrogen were used as solutes; structures produced on freezing of binary, ternary and quaternary solutions were examined. Effects of freezing rate, solute concentration, solute diffusivity, mixing of solutions and magnetic fields are reported.The spacing between ice platelets or dendrites was found experimentally to be proportional to the square root of the freezing time when the freezing rate was constant from beginning to end of solidification. During unidirectional freezing from a constant temperature chill, the solution at each location is subjected to a spectrum of freezing rates; dendrite spacing increases linearly with distance from the chill surface and it is inversely proportional to the square root of the maximum freezing rate.In binary solutions dendrite spacing increases linearly with solute concentration; above a critical solute concentration ice platelets develop side branches. Application of an external magnetic field has an effect similar to increasing concentration. At a given solute concentration, spacing between ice dendrites increases linearly with solute diffusivity.In ternary and quaternary solutions dendrite spacing is a function of the concentrations and diffusivities of each of the constituent solutes.
Mass-Balance Studies of Gara Glacier
Authors: Raina V. K. , Kaul M. K. , Singh Surinder 
Published: September 2017

AbstractThe Gara Glacier, a north-facing valley glacier situated in the western Himalaya, was selected to be part of the study undertaken by India in connection with the International Hydrological Decade. This paper deals with the procedure adopted and the results obtained for mass-balance assessment over a period of one year between September 1974 and September 1975. The glacier has recorded a positive net balance of the order of 2.48 X 106 m3 in terms of water equivalent.
An experimental study of the glacier boundary layer over melting ice
Authors: Munro D. S. , Davies J. A. 
Published: September 2017

AbstractThe results of an experiment to examine the glacier boundary layer over melting ice are described. They show that the boundary layer, as defined by the applicability of the log—linear profile, is approximately 1 m thick. The boundary layer is a frequent, but not a dominant feature of the air close to the ice. The frequency of occurrence is relatively high in cases where wind speeds are mainly controlled by katabatic forces.
Deuterium, Tritium, andβactivity in a snow core taken on the summit of mont blanc (french alps). Determination of the accumulation rate
Authors: Jouzel J. , Merlivat L. , Pourchet M. 
Published: September 2017

AbstractDeuterium, tritium, and grossβactivity measurements have been performed to a depth of 16 m on a snow core taken on Mont Blanc (French Alps) to establish a chronology of its formation and then deduce the annual accumulation. These three independent methods show that the core was formed over a three-year period. This corresponds to a mean annual accumulation of 2.8 m water equivalent In addition, the isotopic measurements indicate the existence of an altitude effect in the distribution of deuterium and tritium in the precipitation in the Mont Blanc area.
Local Friction Laws for Glaciers: A Critical Review and New Openings
Authors: Lliboutry L. 
Published: September 2017

Abstract“Sliding velocity” and “friction law” are precisely defined. Different scales for tackling glacier dynamics are introduced. The energy balance in the melting-refreezing process is clarified. The validity of a Glen body as a model for ice rheology is discussed. The assumed model for subglacial water is a very slightly pervious ice, and a not absolutely watertight ice-bedrock interface, owing to glacial striae and rock joints. Then autonomous hydraulic regimes and cavities at water vapour pressure have a negligible influence on the drag, and only the interconnected regime has to be considered.A more rigorous treatment of Weertman’s model (independent knobs) gives quite different numerical factors. In general a term increasing with Terzaghi’s effective pressure N has to be added to the drag. The double-valued friction law found by Weertman is shown to have been an error.Kamb’s relations for the model with a vanishing microrelief are considerably simplified. His conjectural solution cannot be extended to slopes actually found in the microrelief.The author’s (Lliboutry, 1968) treatment is unsatisfactory and includes an error. With a model consisting of irregular bumps of similar length, a new friction law is given. The pertinent measure of the bedrock roughness is then the shadowing function, not the spectral power density.
The Unsolved General Glacier Sliding Problem
Authors: Weertman J. 
Published: September 2017

AbstractThe status of the theory of glacier sliding is reviewed in this paper. The theory of Nye and Kamb essentially solves the problem of glacier sliding when the basal ice is in intimate contact with a non-deformable bed. But experimental work is needed on cyclic creep and the regelation process in order to put better numbers into the theory. The outstanding problem that remains to be solved, called in this paper the general glacier sliding problem, is the case of sliding when basal ice is not in intimate contact with a non-deformable bed because of the presence of cavities and a water film of finite thickness. This problem involves solving an intricately coupled basal water-flow problem. A new field of research is the study of the motion of glaciers over deformable beds.
Empirical Studies of Ice Sliding
Authors: Budd W. F. , Keage P. L. , Blundy N. A. 
Published: September 2017

AbstractAn experimental programme has been carried out for studying temperate-ice sliding over rock surfaces with a wide range of roughnesses, for normal and shear stresses comparable to those expected under real ice masses. The limiting static shear stress for acceleration has been found to be directly proportional to the normal load giving a constant limiting coefficient of static friction characteristic of the surface. For a constant applied normal stress N and shear stress τb, well below the limiting static shear, a steady velocity Vb results which increases approximately proportionally to τb and decreases with increasing N and the roughness of the surface. For high normal stress the velocity becomes approximately proportional to the shear stress cubed and inversely proportional to the normal stress. As the shear stress increases acceleration sets in, which, for different roughness and normal loads, tends to occur for a constant value of the product τbVb. For some surfaces at high normal loads this acceleration was retarded by erosion. For constant-applied-velocity tests a steady shear stress resulted, which tended to become constant with high velocities, and which increased with increasing normal stress but with a reduced coefficient of sliding friction. The relevance of the results to the sliding of real ice masses is discussed with particular reference to the importance of the effect of the relative normal stress, above basal water pressure, to the sliding rate.
Seismic Evidence for Discrete Glacier Motion at the Rock–Ice Interface
Authors: Weaver Craig S. , Malone Stephen D. 
Published: September 2017

AbstractSeismic monitoring on three Cascade volcanoes in Washington State, U.S.A., has shown that small seismic events are generated by the active glaciers found on each mountain. Detailed seismic experiments have been conducted to investigate the sources for these icequakes. Considerable evidence indicates that the events are the result of a stick–slip type of motion taking place at the bed of the glaciers. The few events we have been able to locate had depths comparable with the glaciers’ thickness. The similarity of wave form from an explosion at the bottom of a glacier and natural icequakes suggests that the complexity of the seismic wave form is due to the path and not the source. The events exhibit an annual trend with more events being recorded in the summer than during the winter. A ten-fold increase in the number of events preceded a large ice avalanche that involved the entire glacier thickness, suggesting that seismic monitoring may be useful in predicting catastrophic ice movements.
Giant Grooves Made by Concentrated Basal Ice Streams
Authors: Goldthwait R. P. 
Published: September 2017

AbstractGlacial grooves are known on all the flat-lying limestone islands in western Lake Erie. The largest megagroove complexes are on Kelleys Island, each 2–6 m deep, 5–20 m wide, and 100–400 m long before quarrying. Each megagroove floor is rolling with second-order rounded ridges and “sine-shaped” grooves 10–90 cm deep, and 5–40 m long. Furthermore, these are gouged laterally by sharply curving and nesting gouges up to 10 cm deep. All grooves exhibit third-order striation up to 1–2 mm deep and 5–200 cm long made by individual tools of debris traveling mostly 240–260°.Ice of the Erie lobe was under compressive flow as it rose from 9 m below present lake level to 12 m above. Some sort of ice vortices (fixed eddies in the basal ice stream) are postulated to make the scoop marks and ridge ends. Fast-moving ice rather than water or a slurry is favored because there are no percussion marks. Very likely, a till mat of interfering engraving points is required. A strong convergence (2× to 10×) of striae into the deepest grooves indicates squeezing together of the debris tools and increase in local ice velocity. Interglacial subareal streams may well have shaped the initial trough up which these ice streams concentrated, because dendritic tributary grooves intersect, and main groove sets curve as much as 10° or 20°. Furthermore, sharp 100–180° meander curves are preserved at the bottom of the deepest grooves. Hiram-age clay-till with rare erratics half fills the original grooves; it shows that this groove cutting was completed before 15 500 14C years ago.
Direct Measurement of Basal Water Pressures: Progress and Problemss
Authors: Hodge Steven M. 
Published: September 2017

AbstractIn 1975 and 1977, 24 bore holes were drilled to the bed of South Cascade Glacier, Washington, U.S.A., using both electrothermal and hot-water drills. Only two holes connected directly with the basal water system, a significant decrease from the four to five such connections in 13 holes drilled in 1973 and 1974 (Hodge, 1976). Most of the bed, possibly as much as 90%, appears to be hydraulically inactive and isolated from a few active subglacial conduits. Bore holes which penetrate these inactive areas initially should connect eventually with the active basal water system due to bed pressurization by the water standing in the bore hole, provided there is a sufficient supply of water available to form and maintain the connection passageway. These sealed-off areas probably consist of the sub-sole drift and permeability barriers found recently at the bed of Blue Glacier by Engelhardt and others (1978); an increase in the area of bed covered by these features probably caused the decrease in chance of bore-hole connection. This apparently was not due to any external cause but rather was the result of a real internal change in the subglacial hydraulic system which occurred between 1974 and 1975.If most of the area of a glacier bed is hydraulically isolated sub-sole drift, or something similar, such features may well control large-scale glacier sliding changes, since changes in the amount of water having access to the glacier bed will take considerable time to affect the interstitial water pressure in the more widespread sub-sole drift.Water pressures in the active part of the basal water system of South Cascade Glacier are generally in the range of 50–75% of the ice overburden pressure. Water levels in a connected bore hole are probably representative over an area of the bed 100 m or more in extent. A correlation of bore-hole water levels with changes in surface motion supports the idea that the sliding of a temperate glacier is controlled largely by the basal water pressure.
Quantitative Determination of the Subglacial Hydrology of Two Alpine Glaciers
Authors: Collins David N. 
Published: September 2017

AbstractTwo components of discharge through the internal hydrological systems of Alpine glaciers were separated on the basis of chemical composition of water. Some surface melt waters retain low solute contents after flowing without delay through conduits in which no chemical enrichment occurs, whereas those flowing slowly at the glacier bed have increased ionic concentrations. A simple mixing model was used to investigate temporal variations in the quantities of water routed through each of the two sub-systems. Electrical conductivity was taken as an indicator of melt-water composition and was monitored for periods during the summer ablation season of 1975 at Gornergletscher and of 1977 at Findelengletscher. At both glaciers, conductivity of melt waters varied diurnally inversely with discharge fluctuations, depending on the proportion of total discharge routed through the two sub-systems. Total discharge and the flow component routed rapidly through conduits within the glacier, a large proportion (50–80%) of total discharge, exhibited in-phase rhythmic diurnal hydrographs at the two glaciers. Distinctive subglacial hydrological regimes are contrasted. At Findelengletscher, the hydrographs of total discharge and of subglacial chemically enriched flow were in phase. At Gornergletscher, the subglacial hydrograph occurred with reverse asymmetry and out of phase. A possible interpretation is that water was temporarily stored in basal cavities during high total discharge. During the night, stored water was released, contributing much of the total discharge at times of low flow.
Characterizing the Glacier Bed Using a Radio-Echo Technique
Authors: Doake C. S. M. 
Published: September 2017

AbstractIf glacier ice is assumed to be a uniaxial birefringent material then two parameters are needed for describing the orientation behaviour of the polarization ellipse of a radio signal returned from the glacier bed. These are δ, the relative phase between the ordinary and extraordinary wave, and r, the ratio of their attenuation coefficients (Woodruff and Doake, 1979). If it is assumed that the attenuation in ice is isotropic, then a value of r other than unity will be due to anisotropic reflection coefficients at the glacier bed. A simple way of measuring r separately from δ could then be used to characterize the reflecting surface.