bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistical characteristics for the type and length of deformation-induced cracks in columnar-grain ice
Authors: Gold Lorne W. 
Published: September 2017

AbstractObservations are reported on cracks formed during compressive, unidirectional, constant-strain-rate deformation of columnar-grain ice. The axis of hexagonal crystallographic symmetry of each grain tended to be in the plane perpendicular to the long direction of the grains and to have a random orientation in that plane. For stress applied perpendicular to the long direction of the grains, the deformation was practically two-dimensional. It was found that the relative proportion of grain-boundary cracks increased with increasing strain rate, decreasing temperature and, for strain rate greater than 7 × 10−5 s−1, with decreasing grain-size. Almost all the grain-boundary cracks had at least one edge at a triple point. For each test, the grain-boundary and transcrystalline crack lengths tended to have a log-normal distribution. The logarithmic mean crack length (LMCL) decreased with increasing strain rate, decreasing grain-size and decreasing temperature and tended to a constant value of 0.75 mm at 10°C. For grain-size of 3 mm or greater, the LMCL had a maximum at a strain rate of 10−5 to 10−6 S−1 at −10°C. The LMCLs and the relative proportion of grain-boundary cracks tended to be normally distributed for given load conditions.
Localized surface-ice weakness on a glacial ice runway
Authors: Lang R. M. , Blaisdell George L. 
Published: September 2017

AbstractFollowing construction of a glacial ice runway on the Ross Ice Shelf, Antarctica, and prior to flight operations, the runway was proof-rolled. The proof exercise was designed to simulate typical heavy aircraft. Initial testing produced numerous brittle surface failures in the runway ice. Thin sections of ice cores taken from the failed areas showed large crystals (с axis vertical) of clear, blue ice with long, vertical bubbles, indicative of ice formed directly from meltwater. Uniaxial unconfined compression tests on core samples were used to compare runway ice strength with published data for polycrystalline laboratory ice. Since the frequent failure of surface ice had not been expected, it was critical to understand the formation and mechanical properties of the weak ice to prevent its occurrence in the future and to strengthen the existing problem areas. We discuss the likely scenarios for development of weak ice on the airstrip and the physical properties of this type of ice. Also, the procedure used to repair successfully the runway surface is described, which culminated in test flights, followed by full flight operations.
Evidence from 40Ar/39Ar Ages for a Churchill province source of ice-rafted amphiboles in Heinrich layer 2
Authors: Gwiazda Roberto H. , Hemming Sidney R. , Broecker Wallace S. , Onsttot Tullis , Mueller Chris 
Published: September 2017

Abstract40Ar/39Ar ages of most single ice-ratted amphiboles from Heinrich layer 2 (H2) from a core in the Labrador Sea, a core in the eastern North Atlantic and a core in the western North Atlantic range from 1600 to 2000 Ma. This range is identical to that for K/Ar ages from the Churchill province of the Canadian Shield that outcrops at Hudson Strait and forms the basement of the northern part of Hudson Bay. The ambient glacial sediment includes some younger and older grains derived from Paleozoic, Mesoproterozoic and Archean sources, but still the majority of the amphiboles have ages in the 1600–2000 Ma interval. The Ca/K ratios of these 1600–2000 Ma old amphiboles, however, have a bimodal distribution in contrast with the uniformity of the Ca/K ratios of H2 amphiboles. This indicates that 1600–2000 Ma old amphiboles of the ambient sediment were derived from an additional Early Proterozoic source besides Churchill province. In H2, Churchill-derived grains constitute 20–40% of the ice-rafted debris (IRD). The fraction in the ambient glacial sediment is 65–80%. Results presented here are consistent with the hypothesis that Heinrich events were produced by a sudden intensification of the iceberg discharge through Hudson Strait that mixed, in the North Atlantic, with icebergs that continued to calve from other ice sheets. The shift from mixed sources in the background sediment to a large dominance of Churchill province grains in H2 indicates that, even if calving of other ice sheets intensified during the Heinrich episode, the increase in the iceberg discharge via Hudson Strait from the Hudson Bay drainage basin of the Laurentide ice sheet was by far the largest.
On Mertz and Ninnis Glaciers, East Antarctica
Authors: Wendler Gerd , Ahlnäs Kristina , Lingle Craig S. 
Published: September 2017

AbstractTwo large glacier tongues, which extend substantially across the coastline of King George V Land in East Antarctica, have been studied by remote sensing (synthetic aperture radar, JERS-1). The tongue of Mertz Glacier is in a state of advance, while the Ninnis Glacier tongue is retreating. Some more specific points are:
The distinctive surface structure and the form of the glacier tongues indicates that they are floating.While the tongue of Ninnis Glacier has lost about two-thirds of its area since 1913, the Mertz Glacier tongue has advanced substantially and has about doubled its areal extent over the same time period.The annual movement of the tongue of Mertz Glacier was determined as about 1.2 km. This is close to the value of the advance of the tip of the tongue since 1963, which was determined as 0.9 km year−1.
Superimposed ice in glacier mass balance on the Tibetan Plateau
Authors: Fujita Koji , Seko Katsumoto , Ageta Yutaka , Jianchen Pu , Tandong Yao 
Published: September 2017

AbstractThe relations between mass balance and meltwater refreezing were examined on the basis of glaciological observations carried out in summer 1993 on Xiao Dongkemadi Glacier, Tanggula Mountains, central Tibetan Plateau. On this glacier, a part of meltwaler refreezes at the snow/ice interface as superimposed ice. The amount of superimposed ice formation was determined by both meltwater supply and temperature condition of the glacier. Snow-layer thickness on the glacier ice body is less than 2 m, even in the higher accumulation zone. About 60% of meltwaler generated in the accumulation zone for the period May–September was trapped at the snow/ice interface by refreezing, and was not discharged out of the glacier. About 26% of accumulated snow to the glacier surface was replaced on the snow/ice interface by refreezing in the accumulation zone. These facts indicate that superimposed ice formation is quite significant for water retention in glaciers under low-precipitation conditions.
On the effect of phase transformations on saline ice compliance
Authors: McKittrick L. R. , Brown R. L. 
Published: September 2017

AbstractTo obtain a better understanding of the compliance of saline ice, we developed a simple conceptual model of a process that presumably takes place in saline ice. Using elastic models, we assessed the role that phase transformations might play when brine is sealed into small cells during crystal growth. Cooling of a sealed brine cell, leading to the precipitation of ice, provides a mechanism for the accumulation of “large” localized stresses. Based on our analysis, this mechanism has the potential to be a significant source for the nucleation of dislocations, and can conceivably make a significant contribution to the greater compliance (softness) of saline ice relative to non-saline ice.The results of this model are consistent with the observation that laboratory-grown saline crystals sometimes display extensive differences in mechanical behavior that appear to be due to variations in the growth and storage conditions experienced by the crystals.
Estimation of relative water content in a sub-polar glacier using surface-penetration radar
Authors: Hamran Sveinerik , Aarholt Eldar , Hagen Jon Ove , Mo Per 
Published: September 2017

AbstractRadar-sounding data taken at Uvérsbreen glacier, Svalbard, are used to estimate the relative water content of the temperate part of the glacier. The relative change in water content of the temperate part of the glacier. The relative change in water content is estimated from the strength of the backscttered radar energy without knowing the size of the scatterers. The main findings are that the water content is on average changing by a factor of five in the ice, with the exception of some bright spots believed to stem fro larger water moulins. The general trend is also that the water content is increasing with lower altitude. The applied technique may be a useful method for large-scale mapping of the relative water-content variation in temperate and polythermal glaciers.
Mass balance of White Glacier, Axel Heiberg Island, N.W.T., Canada, 1960–91
Authors: Cogley J.Graham , Adams W. P. , Ecclestone M. A. , Jung-Rothenhäusler F. , Ommanney C. S. L. 
Published: September 2017

AbstractWhite Glacier is a valley glacier at 79.5°N with an area of 38.7 km2. Its mass balance has been measured, over 32 years with a 3 year gap, by standard techniques using the stratigraphic system with a stake density of the order of one stake per km2. Errors in stake mass balance are about ±(200–250) mm, due largely to the local unrepresentativeness of measurements. Errors in the whole-glacier mass balance B are of the same order as single-slake errors. However, the lag-1 autocorrelation in the time series of B is effectively zero, so it consists of independent random samples, and the error in the long-term “balance normal” 〈B〉 is noticeably less. 〈B〉 is −100 ± 48 mm. The equilibrium-line altitude (ELA) averages 970 m. with a range of 470–1400 m. Mass balance is well correlated with ELA, but detailed modelling shows that the equilibrium line is undetectable on visible-band satellite images. A reduced network of a few stakes could give acceptable but less accurate estimates of the mass balance, as could estimates based on data from a weather station 120 km away. There is no evidence of a trend in the mass balance of White Glacier. To detect a climatologically plausible trend will require a ten-fold reduction of measurement error, a conclusion which may well apply to most estimates of mass balance based on similar stake densities.
A simple technique for growing large, optically “perfect” ice crystals
Authors: Knight Charles A. 
Published: September 2017

AbstractLarge, single ice crystals containing nо air bubbles and free of both small-angle grain boundaries and visible stress birefringence can be grown using a very simple growth chamber within a temperature-controlled, outer enclosure. The method relies upon the spontaneous formation of an ice crystal with its с axis accurately normal to a free, slightly supercooled, water surface.
Seismic-reflection evidence for a deep subglacial trough beneath Jakobshavns Isbræ, West Greenland
Authors: Clarke Ted S. , Echelmeyer Keiih 
Published: September 2017

AbstractSeismic-reflection methods were used to determine the ice thickness and basal topography of Jakobshavns Isbræ, a large, fast-moving ice stream/outlet glacier in West Greenland. A method of data analysis was developed which involves the pointwise migration of data from a linear seismic array and a single explosive source; the method yields the depth, horizontal position and slope of the basal reflector. A deep U-shaped subglacial trough was found beneath the entire length of the well-defined ice stream. The trough is incised up to 1500 m into bedrock, and its base lies 1200–1500 m below sea level for at least 70 km inland. Center-line ice thickness along most of the channel is about 2500 m, or about 2.5 times that of the surrounding ice sheet. This prominent bedrock trough was not apparent in existing radio-echo-sounding data. Reflection coefficients indicate that much of the basal interface is probably underlain by compacted, non-deforming sediment. The large ice thickness, coupled with relatively steep surface slopes, leads to high basal shear stresses (200–300 k Pa) along the ice stream. The large shear stresses and lack of a deformable bed imply that internal deformation plays a dominant role in the dynamics of Jakobshavns Isbræ.
Glacier change in northern Sweden from AD 500: a simple geometric model of Storglaciären
Authors: Raper S. C. В. , Briffa K. R. , Wigley Т. M. L. 
Published: September 2017

AbstractA simple geometric model of glacier volume is derived. The model is based on the assumption that the net mass balance averaged over the glacier surface is related to the summer temperature and winter accumulation at a representative height on the glacier. This height varies with time as climate changes, in ways that are determined by the geometry of the glacier surface. Expressions are derived for the equilibrium glacier volume (Veq) as a function of summer temperature and winter accumulation and for the glacier-response time (τ) as a function of volume.The model is used to reconstruct the volume of Storglaciären over the period AD 500–1992. Measured net mass-balance data for Storglaciren (1946–92) are used to estimate the model parameters. For the summer temperature forcing, the long tree-ring-based temperature reconstruction for northern Fennoscandia is used to extend a temperature record near the glacier back to AD 500. For the past accumulation forcing, a range of assumptions is tested.The results show that the prime cause of the decrease in volume of Storglaciären between 1946 and 1992 was relatively low accumulation over 1946–89 as opposed to warm temperatures as previously supposed. Reconstructed volume changes agree well with geomorphological evidence. Where differences occur, deductions can be made about past accumulation. For example, the maximum reconstructed glacier volume is associated with the cold period from 1580 to 1740 but relatively low accumulation probably limited the volume to values not much larger than that achieved around 1916.
Thermal Convection in Ice Sheets: We look but do not see
Authors: Hughes T. 
Published: September 2017

AbstractThermal convection in the Antarctic and Greenland ice sheets has been dismissed on the grounds that radio-echo stratigraphy is undisturbed for long distances. However, the undisturbed stratigraphy lies, for the most part, above the density inversion in polar ice sheets and therefore does not disprove convection. An echo-free zone is widespread below the density inversion, yet nobody has cited this as a strong indication that convection is indeed present at depth. A generalized Rayleigh criterion for thermal convection in elastic-viscoplastic polycrystalline solids heated from below is developed and applied to ice-sheet convection. An infinite Rayleigh number at the onset of primary creep decreases with time and becomes constant when secondary creep dominates, suggesting that any thermal buoyancy stress can initiate convection but convection cannot be sustained below a buoyancy stress of about 3 kPa. An analysis of the temperature profile down the Byrd Station core hole suggests that about 1000 m of ice below the density inversion will sustain convection. Creep along the Byrd Station strain network, radar sounding in East Antarctica, and seismic sounding in West Antarctica are examined for evidence of convective creep superimposed on advective creep. It is concluded that the evidence for convection is there, if we look for it with the intention of finding it.
Strength of Bonds between Ice Grains after Short Contact Times
Authors: Gubler H. 
Published: September 2017

AbstractThe tensile force required to break bonds between ice grains after short contact times (1–500 s) is measured as a function of temperature and contact pressure. The results indicate a sharp increase of the tensile load capacity of bonds alter short contact times near the melting point and a maximum rate of increase of the load capacity at −5 °C. The initial state or sintering is modelled, assuming viscous surface flow and plastic deformation as the main mechanisms.
Unweathered, Glaciated Bedrock on an Exposed Lake Bed in Wales
Authors: Gray J. M. 
Published: September 2017

AbstractIn Snowdonia, norh-west Wales, the construction of a hydro-electric scheme involved the exposure of a lake bed. Despite the fact that it is over 13 000 years since the bed was glaciated, erosional features on the slate and grit bedrock have been preserved from weathering below the lake waters. Examples of abrasion, bedrock fracture, plucking, and melt-water erosion are described. The formation of transverse friction cracks is briefly discussed and it is suggested that not all crescentic gouges are associated with rolling blocks as recently proposed. The relationship of small-scale erosional forms to the direction of ice movement is briefly reviewed.
Basal Water Film, Basal Water Pressure, and Velocity of Traveling Waves on Glaciers
Authors: Weertman J. , Birchfield G. E. 
Published: September 2017

AbstractThe theory of Nye and of Weertman of traveling waves on glaciers is extended to cover the situation where the presence of abundant basal water or increased basal water pressure produces increased sliding of a glacier over its bed. It is found that the ratio of traveling-wave velocity to surface velocity is independent of the amount of water or the basal water pressure. The theoretical value of this ratio, about 4 to 5, agrees with that found in field measurements (the most recent data are from Mer de Glace). It is concluded that field observations of traveling-wave velocities lend strong support to any glacier sliding theory in which the sliding velocity is proportional to the basal shear stress raised to about a second to fifth power and in which the sliding velocity is a function of either or both the amount of water at the bed of a glacier and the pressure within this water.
A Coupled Marine Ice-Stream – Ice-Shelf Model
Authors: Muszynski Isabelle , Birchfield G. E. 
Published: September 2017

AbstractEvidence as to the potential roles of marine ice flows in the dramatic climatological changes which have occurred from the late Pleistocene to the present is reviewed, indicating the need for careful modeling studies to evaluate several crucial hypotheses. A scale analysis of the flow of a marine ice stream coupled to a freely floating ice shelf is presented, in two dimensions and ignoring thermodynamic effects. With these limitations, the most important control of the dynamics of the ice stream is associated with first-order buoyancy effects related to the density contrast ∆ρ/ρw between ice and sea-water. It is shown that longitudinal stretching, arising from large gradients in basal sliding velocity, dominates shearing deformation provided the aspect ratio ω2 « ∆ρ/ρw. The buoyancy control is established through the necessity of having continuously varying longitudinal strain-rates in the neighborhood of the grounding line.The scale analysis is the basis for derivation of a simplified model of a fast-flowing ice stream coupled to a freely floating ice shelf. The distance in the ice stream up-stream from the grounding line over which the above dynamic regime extends is estimated and found to be relatively insensitive to the basal sliding velocity and to the rheological constant of ice. A further potentially important feed-back mechanism between ice stream and ice shelf is associated with buoyancy corrections to the longitudinal deviatoric stress field.
The Surface Topography of Large Ice Masses from Landsat Imagery
Authors: Dowdeswell Julian A. , McIntyre Neil F. 
Published: September 2017

AbstractApparent ice-surface topography is observed at several scales on Landsat multi-spectral scanner (MSS) imagery. Digitally enhanced MSS scenes from Antarctica and Nordaustlandet, Svalbard, are compared with ice-surface elevations from aircraft altimetry (relative accuracy 2–3 m) to show that this apparent topography is real. Apparent ice divides on Landsat images fit closely with divides on altimetric records. Ice-surface irregularities within drainage basins are also shown to be real. On Byrd Glacier, Antarctica, apparent “flow lines” coincide with ridges on altimetric records. Synoptic Landsat data, calibrated by information from aircraft altimetric flight lines, are used to classify the surface roughness of the ice caps on Nordaustlandet and 40% of the Antarctic ice sheet. On Nordaustlandet, the roughest ice is of amplitude 15–25 m and wavelength 3–4.5 km. Drainage basins with such rough surface characteristics may be associated with ice streams or possibly past surge activity. The most rough Antarctic terrain is up to 60 m in amplitude, with wavelengths of <10 km. The roughness of the Antarctic ice sheet increases with distance from ice divides, reflecting changes in the parameters affecting the transfer of basal stresses to the ice surface.
Development of Collapsed Glacial Topography in the Adams Inlet Area, Alaska, U.S.A.
Authors: McKenzie Garry. D , Goodwin Robert G 
Published: September 2017

AbstractModes of formation and rates of collapse have been determined for kame terraces and a fan delta in the Adams Inlet area, Alaska. The hummocky and trenched surface of the kame terrace develops by mass-wasting processes caused by differential melting of buried ice. The dry channels in the collapsed part of the terrace are formed by melt water during stagnant-ice bursts. Measurements over a period of 17 years indicate that terrace back-wasting averages 4.3 m a−1. The fan delta is forming near sea-level by streams that derive part of their load from the kame terrace. The fan delta seaward of the retreating kame terrace is undergoing partial collapse to produce kettles ringed by concentric fractures. Vegetation, now as much as 5 m below high tide, suggests a fan-delta collapse rate of about 0.5 m a−1.
Continued Decrease of Ice-Flow Velocity at Lewis Glacier, Mount Kenya, East Africa
Authors: Hastenrath Stefan 
Published: September 2017

AbstractOur earlier monitoring program on Lewis Glacier, Mount Kenya, indicated a slow-down of the ice flow to January 1982, while based on the numerical modeling of the ice dynamics a further drastic decrease of the ice flow was predicted from the 1978 to the 1985 datum. This paper presents velocity measurements over the years 1982–83, 1984, and 1985. Changes of ice-flow conditions from 1978 to the mid 1980s are characterized by a velocity decrease by nearly half; a decrease of the maximum mass flux by more than half; a flattening and up-glacier shift of the velocity and mass-flux maxima; an up-glacier displacement of the transition between prevailingly longitudinal crevasses in the lower glacier and transverse crevasses in the upper glacier; and a terminus retreat by about 50 m. In consequence of the very weak ice flow remaining in Lewis Glacier, thinning and terminus retreat of the glacier are now primarily controlled by the in-situ net balance.
Observations on Speke Glacier, Ruwenzori Range, Uganda
Authors: Kaser Georg , Noggler Bernd 
Published: September 2017

AbstractSpeke Glacier, the best studied and largest single glacier in the Ruwenzori Range (Uganda, East Africa), was revisited in January 1990. A comparison of its present state with former observations reveals that its terminus receded 35–45 m between 1958 and 1977; since 1977 it has retreated more than 150 m. Nearly half the width of the snout has been lost, mainly on its western side, and the entire western section of the south-facing glacier has shrunk substantially. The observed fluctuation conforms with changes occurring on other tropical glaciers. Explanations concerning the reasons for the glacier recession are presented.