bluuebunny/crossref_metadata_2025_split huggingface dataset:
Glacier-Bed Landforms of The Prairie Region of North America
Authors: Moran S. R. , Clayton Lee , Hooke R. Leb , Fenton M.M , Andriashek L.D. 
Published: September 2017

AbstractTwo major types of terrain that formed at or near the bed of Pleistocene continental ice sheets are widespread throughout the prairie region of Canada and the United States. These are (1) glacial-thrust blocks and source depressions, and (2) streamlined terrain.Glacial-thrust terrain formed where the glacier was frozen to the substrate and where elevated pore-pressure decreased the shear strength of the substrate to a value less than that applied by the glacier. The marginal zone of ice sheets consisted of a frozen-bed zone, no more than 2–3 km wide in places, within which glacial-thrust blocks are large and angular. Up-glacier from this zone, the thrust blocks are generally smaller and smoothed. Streamlined terrain begins 2–3 km behind known ice-margin positions and extends tens of kilometres up-glacier Streamlined terrain formed in two ways: (1) erosion of the substrate as a consequence of basal sliding in the sub-marginal thawed-bed zone, and (2) erosional smoothing accompanied by emplacement of till in the lee of thrust blocks where they were deposited and subsequently exposed to thawed-bed conditions as a result of further advance of the glacier.
Short–Lived Damming of a High–Arctic Ice–Marginal Stream, Ellesmere Island, N.W.T., Canada
Authors: Ballantyne C.K. , McGann S.B 
Published: September 2017

AbstractThe discharge pattern of the “Schei River”, which drains a 91.2 km2 partly glacierized catchment on Ellesmere Island, is dominated by diurnal oscillations reflecting variations in the melt rate of snow and ice in the basin. Superimposed on this diurnal pattern are numerous short–lived discharge fluctuations of irregular periodicity and magnitude. The characteristics of such irregular fluctuations are described and attributed to periodic collapse of the glacier margin and concomitant damming of the main tributary of the “Schei River”. Collapse is initiated by the river undercutting the ice margin, and tends to be most frequent in the latter part of the flow season during periods of high discharge. Release of ponded water following the collapse of such ice dams may engender significant flood events.
A Field and Laboratory Study of Wave Damping by Grease Ice
Authors: Martin Seelye , Kauffman Peter 
Published: September 2017

AbstractIn a field and laboratory study we discuss the formation, growth, and wave-absorption properties of grease ice. Our field observations show that grease-ice formation occurs under cold windy conditions in both leads and polynyas. In leads grease ice forms in the open water, then is herded to the down-wind edge of the lead; in polynyas a Langmuir circulation herds the grease ice into long plumes parallel to the wind. In the laboratory we grow grease ice in a wave tank and measure its wave absorption properties for single-frequency, two-dimensional waves. On a large scale we find that the thickness of the grease ice, which increases away from the paddle, is determined by a balance between the wave-momentum flux and the free-surface tilt. On a small scale our photographs show that the crystals which make up the grease ice consist of discs measuring about 1 mm in diameter and 1–10 µm thick, which at low rates of shear sinter together into larger clumps yielding a viscosity increase. To measure this non-linear viscosity, we study the decay of wave amplitude between two critical distances measured inwards from the leading edge. The first occurs when the depth of grease ice exceeds k−1 where k is the wave number; the second further distance is a line of transition from liquid to solid behavior which we call the dead zone. Between these two distances the wave amplitude decays with a linear slope α, which increases as (a0k)2 where a0 is the wave amplitude in open water. Concurrent measurements of ice concentration show that it increases from values of 18–22% at the leading edge to a local maximum of 32–44% at the dead zone, while the values at the dead zone increase non-linearly with a0k. Finally, comparison of the observed α to that calculated from a yield-stress viscosity model shows if the yield-stress coefficient is proportional to the incident wave-momentum flux, the model predicts the observed α.
Estimating Ratios of Snow Accumulation in Antarctica by Chemical Methods
Authors: Warburton J. A , Young L. G. 
Published: September 2017

AbstractSnow and firn samples from 2 and 5 m deep pits were analyzed for seven sites on the Ross Ice Shelf, Antarctica. Na, Mg, Ca, and K concentrations change with depth, the range of concentrations being approximately 10 : 1 for all four elements. The changes in concentrations for the four elements at any one site are highly correlated, suggesting that the impurities are introduced into the snow-pack simultaneously by the same mechanisms.Pronounced periodic structure of the vertical chemical profiles leads to strong correlations (γ> 0.9) of the chemical features from site to site separated by distances up to 440 km.Assuming that the observed chemical features are periodic as a function of depth due to temporal variations caused by large-scale phenomena, then the wavelength (in depth) of these features should be proportional to the accumulation. Under the assumptions, the linear regression ratio of one site to another will give the relative accumulations at these sites. The ratios of snow accumulation estimated by these chemical methods agree, within a few per cent, with the ratios for the same sites estimated by total β-activity or stratigraphic methods.It is suggested that the chemical variations with depth are caused by meteorological events which may have seasonal changes in frequency and intensity. It is also suggested that the most-favored season for the production of chemical-concentration maxima is autumn because of the documented higher frequency of precipitating storms on the Ross Ice Shelf and the minimum in sea-ice extent at that time of year.
Propagating Strain Anomalies during Mini-Surges of Variegated Glacier, Alaska, U.S.A.
Authors: Raymond Charles F. , Malone Stephen 
Published: September 2017

AbstractWire strain meters and seismometers spaced longitudinally along the upper part of Variegated Glacier, Alaska, showed quasi-periodic episodes of increased velocity (mini-surges), which lasted about 1 day and recurred at intervals of a few days to 2 weeks during the early part of the melt seasons of 1979, 1980, and 1981. The zone affected by these mini-surges corresponds to the zone of highest velocity and basal stress increase over the previous decade, and the initiation of the most recent surge in 1982. Mini-surges initiate locally; as a single melt season progresses, the later mini-surges start at higher locations and show a distinct down-glacier propagation of a characteristic strain pattern and associated zone of acoustic emissions at speeds of 0.1–0.6 km h−1. During mini-surges, extensile and compressive strain-rates exceed 10 × 10−4 d−1 and 40 × 10−4 d−1, respectively; typical strain-rates between mini-surges were less than 2 × 10−4d−1 in magnitude. Seismic activity jumped by two orders of magnitude and was distinctly audible during a mini-surge. Maximum strain-rate during mini-surges decreased from year to year. The high time resolution of the strain allows short time-scale structure of velocity variations to be deduced. As a propagating mini-surge passes, the velocity anomaly at a fixed location is characterized by a rapid initial rise over a few hours to two distinct peaks separated by a few hours, followed by a slower return to normal velocity taking up to a day. The double peak in velocity may arise from a single, very sharp, transient peak in the basal slip velocity associated with the initial opening of cavities at the base in response to a sudden rise in basal water pressure (observed by Kamb and Engelhardt). This supports an important role for basal cavitation in the mini-surge mechanism.
Modeling the Influence of Till Rheology on the Flow and Profile of the Lake Michigan Lobe, Southern Laurentide Ice Sheet, U.S.A.
Authors: Beget James E. 
Published: September 2017

AbstractThe late Wisconsin Shelbyville till was deposited in southern Illinois c. 20 000–21 000 year B.P. and records the maximum southern advance of the Lake Michigan lobe of the Laurentide ice sheet. The yield strength calculated for a representative till debris flow found just south of the ice margin is 8 kPa (0.08 bar), and probably approximates yield strength of basal Shelbyville till. An ice-profile model assuming plastic behavior in basal till suggests the southern Lake Michigan lobe may have been unusually thin. Reconstructed Laurentide glacier profiles from the south-west and western Great Plains (South Dakota, Alberta, Minnesota, and Montana), and the MacKenzie Delta, N.W.T., are similar to those inferred for the southern Great Lakes area, and much thinner than those of most modern ice sheets. The Pleistocene Laurentide ice sheet may have been asymmetric: thicker in the east than in the west. Glaciers resting on weak sediments can move both by subglacial sediment deformation (creep) and sliding at the sediment–ice interface. Till rheology is complex; shearing of till by over-riding glaciers would increase porosity and further reduce yield strength.
Stress-Gradient Coupling in Glacier Flow: II. Longitudinal Averaging in the Flow Response to Small Perturbations in Ice Thickness and Surface Slope
Authors: Echelmeyer Keith A. , Kamb Barclay , Kamb Barclay 
Published: September 2017

AbstractAs a result of the coupling effects of longitudinal stress gradients, the perturbations ∆u in glacier-flow velocity that result from longitudinally varying perturbations in ice thickness ∆h and surface slope ∆α are determined by a weighted longitudinal average of ϕh∆h and ϕα∆α, where ϕh and ϕα are “influence coefficients” that control the size of the contributions made by local ∆h and ∆α to the flow increment in the longitudinal average. The values of ϕh and ϕα depend on effects of longitudinal stress and velocity gradients in the unperturbed datum state. If the datum state is an inclined slab in simple-shear flow, the longitudinal averaging solution for the flow perturbation is essentially that obtained previously (Kamb and Echelmeyer, 1985) with equivalent values for the longitudinal coupling length l and with ϕh = n + 1 and ϕα + n, where n is the flow-law exponent. Calculation of the influence coefficients from flow data for Blue Glacier, Washington, indicates that in practice ϕα differs little from n, whereas ϕh can differ considerably from n + 1. The weighting function in the longitudinal averaging integral, which is the Green’s function for the longitudinal coupling equation for flow perturbations, can be approximated by an asymmetric exponential, whose asymmetry depends on two “asymmetry parameters” μ and σ, where μ is the longitudinal gradient of ℓ(= dℓ/dx). The asymmetric exponential has different coupling lengths ℓ+ and ℓ− for the influences from up-stream and from down-stream on a given point of observation. If σ/μ is in the range 1.5–2.2, as expected for flow perturbations in glaciers or ice sheets in which the ice flux is not a strongly varying function of the longitudinal coordinate x, then, when dℓ/dx > 0, the down-stream coupling length ℓ+ is longer than the up-stream coupling length ℓ−, and vice versa when dℓ/dx < 0. Flow-, thickness- and slope-perturbation data for Blue Glacier, obtained by comparing the glacier in 1957–58 and 1977–78, require longitudinal averaging for reasonable interpretation. Analyzed on the basis of the longitudinal coupling theory, with 4ℓ + 1.6 km up-stream, decreasing toward the terminus, the data indicate n to be about 2.5, if interpreted on the basis of a response factor Ѱ + 0.85 derived theoretically by Echelmeyer (unpublished) for the flow response to thickness perturbations in a channel of finite width. The data contain an apparent indication that the flow response to slope perturbations is distinctly smaller, in relation to the response to thickness perturbations, than is expected on a theoretical basis (i.e. ϕα/ ϕh + (n/n + 1) for a slab). This probably indicates that the effective ℓ is longer than can be tested directly with the available data set owing to its limited range in x.
Effects of climatic perturbations on the equilibrium-line altitude, West Greenland
Authors: Ambach Walter 
Published: September 2017

AbstractPerturbation analysis is applied to the heat balance at the EGIG line (West Greenland) with respect to climatic changes. The shift of the equilibrium-line altitude is obtained for perturbations of temperature, absolute humidity, cloudiness and annual accumulation. The total net ice ablation at the EGIG line increases by 45% with a perturbation of + 1 K. Applying this figure to the entire ice sheet, the total ablation equals the total accumulation at a warming of + 2 K, if refreezing of melt water is neglected.
Internal melting and ice accretion at the bottom of temperate glaciers
Authors: Lliboutry L. 
Published: September 2017

AbstractTemperate glacier ice is neither dry nor impermeable, as the standard theory of glacier sliding assumes. This fact leads to the already published concept of locally stress-controlled temperatures. Why the temperature is determined by the highest principal pressure, why the microscopic stress equals more or less the macroscopic one, and why water may flow in the capillary network even when water lenses at grain boundaries are freezing is explained. The new concept is applied to ice sliding on a hard bed having a sine profile, without cavitation. First, the stress field for a Newtonian viscous material and a vanishing roughness are used; next, an improved one, that takes into account the non-linear viscosity of ice and the finite amplitude of the micro-relief. It appears that water migrates from the stoss sides of the bumps to the lee sides within a bottom layer of thickness hw. Moreover, there is less ice melting at the sole on the former ones than ice accretion on the latter, a fact that yields a trend of ice accretion at the glacier sole. It is balanced by internal melting near the bed and water oozing at the interface from the soaked ice. Consequently, a thin layer of accreted regelation ice with a constant mean thickness hi should exist at the interface. Modelling realistically mountain glaciers, hw ∼ 20 cm and hi ∼ 3.5 cm are found.
The mass balance of a cirque glacier in the Italian Alps (Ghiacciaio Della Sforzellina, Ortles–Cevedale Group)
Authors: Catasta G. , Smiraglia C. 
Published: September 2017

AbstractThe net mass balance (1986/87–1989/90) was calculated for a small cirque glacier in the Italian Alps (Ghiacciaio della Sforzellina, 0.42 k m2, Ortles–Cevedale Group). Four annual mass balances are presented here. All four balances were negative (mean value: –0.90 m year−1), with a maximum deficit of –1.16 m year−1 in 1989–90. The climatic conditions (which are analyzed using data from the S. Caterina Valfurva Station) consisted of a succession of cold, dry winters with little snowfall. Frontal-variation data available since 1925 show a constant retreat until 1966, followed by a brief advance period which has already terminated.
Global change, Antarctic meteorite traps and the East Antarctic ice sheet
Authors: Delisle G. 
Published: September 2017

AbstractNumerical models to assess the principal response of large ice caps to climatic changes are used as a guide to the interpretation of field evidence of changes in the glaciological regime in the coastal areas of Victoria Land and north Victoria Land, Antarctica. Based on the theoretical work, the following scenario is proposed: areas within about 300 km from the coast of Victoria Land experienced (i) significantly shallower ice slopes and a lesser degree of glaciation during most of the late Tertiary, (ii) steep slopes and thicker ice than today during glacial stages, and (iii) moderate thinning of the ice in intervening interglacial stages.The model predicts, for central regions of Antarctica, a slightly thinner ice cap (lower snow-accumulation rate) during glacial stages, but an estimated 200 m thicker ice cap in warmer Tertiary climates than today. The calculated “Tertiary ice caps” indicate a probable tendency of periodic surges due to basal melting at the outer fringes.Only modest changes of the ice thickness in reasonably good agreement with the model predictions for the current interglacial stage have been observed on four blue-ice fields, all located within 250 km of the coastline. Investigated ice fields include two meteorite traps — the Allan Hills Icefield and the Frontier Mountain meteorite fields. Antarctic meteorite traps are sustained by very specific glaciological conditions — in particular, only moderate changes in ice thickness over time. The sub-ice topography of these fields was determined by radar measurements and reveals a former, very different glaciological regime, which is interpreted as being associated with glacial processes, operative during the late Tertiary.Field evidence for a hypsithermal event during the Holocene is presented.
Surface Movement and its Relationship To The Average Annual Hydrological Budget of Lemon Creek Glacier, Alaska
Authors: Wilson Charles R. 
Published: September 2017

AbstractThe object of the 1957 program of the Juneau Ice Field Research Project on Lemon Creek Glacier was (1) to obtain data on surface movement in the accumulation region, and (2) to relate the movement to the average annual hydrological budget. Results show a net loss of ice over the past four years, although this deficit does not appear to be reflected by the movement of the ice. Lemon Creek Glacier appears to be in approximate equilibrium.
Preliminary Results of the Glaciological Work on the Trans-Antarctic Expedition, 1955–58
Authors: Stephenson P. J. , Lister H. 
Published: September 2017

AbstractAt the inland station “Southice” (at approximately lat. 82° S., long. 29° W.) investigation in firn to 45m. included profiles of temperature, density, granularity and crystal size. Mean annual accumulation and temperature are interpolated and crystal fabric analyses briefly discussed. A study of drifting snow is outlined.Similar studies, but without crystal observations, were continued across the continent using snow cores to 11 m. depth and supplemented by Rammsonde soundings. These sub-surface observations with the sastrugi forms noted, permit the interpolation of the mean accumulation, temperature and wind direction at different heights across the continent. Radiation flux, wind speed and air and snow temperature profiles were recorded at various halts.
Some Observations on the Glaciers of Mt. Kenya
Authors: Charnley F. E. 
Published: September 2017

AbstractThe glaciological work of the I.G.Y. Mt. Kenya Expedition, 1957–58, is described and some results are given.The stages of retreat of the Mt. Kenya glaciers from their former limits are considered with reference to moraine evidence and existing records. A chronology is suggested for fluctuations during the last century.Mapping of the present glaciers has been carried out. The changes undergone by the Lewis Glacier since a previous survey in 1934 are considered. The surface movement of the Lewis Glacier has been measured and its economy examined in relation to the meteorological and climatic environment.
Accumulation and Temperature on The Inland Ice of North Greenland, 1959
Authors: Langway Chester C. 
Published: September 2017

AbstractTwelve deep pits (5 to 5.5 m.) revealed between 6 and 13 years of snow accumulation. The results show an average net accumulation of 18.5 g./cm.2 per year. Accumulation decreases inland at a mean rate of 1.5 g./cm.2 per 100 m. rise in elevation. Temperature measurements at 100 m. in all pits give a mean temperature-altitude gradient of 0.77° C. per 100 m. Evidence of melt was observed in all pits, the most pronounced melt occurring in 1954. The mean density reflects the local climate. Other empirical correlations of these data show linear trends that vary systematically with surface slope and local climate.
The Glide Direction in Ice
Authors: Kamb W. Barclay 
Published: September 2017

AbstractThe failure to detect experimentally a glide direction in the ice crystal is satisfactorily explained by assuming that the crystal glides simultaneously in three symmetry-equivalent directions with a response to the shear stress component in each direction that is the same as that observed for the crystal as a whole or for polycrystalline aggregates—the typical non-linear, power-type flow law. A hexagonal crystal responding to stress by this type of “non-linear crystal viscosity” behaves very differently from a tetragonal one. For a tetragonal crystal, the glide directions are well defined in the response of the crystal if the power-flow-law exponent n exceeds n ~ 1·5, whereas for a hexagonal crystal a well-defined glide direction can be observed only if n > c. 5. The response of a hexagonal crystal is entirely independent of a-axis orientation if n = 3 exactly. For 3 < n < c. 5 the true glide direction should be weakly apparent, whereas for 1 < n < 3 the crystal should show a response weakly suggestive of preferred glide in a direction perpendicular to the true glide direction. In the observed range of n values for ice, 2 < n < 4, the expected response to simultaneous glide differs so slightly from the hitherto-postulated a-axis-independent, “non-crystallographic” glide as to be practically undetectable experimentally. This circumstance makes it possible to identify <>as the glide direction, from structural considerations alone, and to accommodate the plastic properties of the ice crystal into the modern concepts of crystal plasticity. It may be expected that hexagonal close packed and face-centred cubic metals at high temperatures, in steady state creep, will show translation gliding without well-defined glide directions.
Milton Mt. Mckinley Range Expedition, 1960
Authors: Carter Adams , Atherton David 
Published: September 2017

AbstractThe paper describes the expedition’s work on the north fork of the Eldridge Glacier, which is found to be of the temperate alpine type. Velocity profiles show both slip at the glacier’s edge and shear in the adjacent layers. A summer accumulation pattern is demonstrated which makes the glacial balance unusually delicate. It is concluded that glaciers in this region are near their recent maxima because the high altitude accumulation offsets the shrinking of the lower tributary glaciers. Examination of an ice-dammed lake shows the main Eldridge Glacier to be near the maximum of the last major advance which raised the level of the ice at least 60 m.
Bubble Pressure in Greenland Icebergs
Authors: Scholander P. F. , Nutt D. C. 
Published: September 2017

AbstractA simple technique for measuring the pressure in individual bubbles of gas in glaciers is described. By this technique, bubble pressures in twenty-six west Greenland icebergs were measured. The bubbles were for the most part tubular in shape and oriented parallel, lending a fibrous and sometimes stratified appearance to the ice. Various suggestions are offered for the formation of these bubbles. Most bubbles had a pressure of 4–5 atmospheres, and pressures as high as 20 atmospheres were recorded. In closely adjacent bubbles differences of 2–5 atmospheres were often measured, which indicated diffusion tightness and lack of plasticity in the ice. When the ice surface melts, the bubbles expand at the cost of water extrusion. The various factors contributing to the maintenance of vertical walls characteristic of tabular bergs are discussed.