bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of permafrost thickness using ground geophysical measurements, and its usage for defining vertical temperature variations in continental ice and underlying bedrock
Authors: Ruotoistenmäki Tapio , Lehtimäki Jukka
Published: September 2017

In bedlock covered by continental ice, the depth to electrically conductive saline waters enriched below permafrost can be defined by electromagnetic measurements. Thus, if the ice thickness is also measured we obtain estimates of permafrost thickness variations in the survey area. Moreover, using the relation between ice and permafrost thicknesses and approximations of the melting temperature of saline waters combined with the average annual temperature at the surface, we can estimate temperature variations within both the bedrock and the ice. These can further be used for estimating the temperature values at the ice base.

The method was developed for interpreting two geophysical field profiles measured on continental ice in western Dronning Maud Land, Antarctica. Gravity, magnetic and electromagnetic profiles were measured between the nunataks Basen and Plogen (≈22 km) and Basen and Fossilryggen (≈38km). In the Basen–Fossilryggen profile the electromagnetic soundings revealed good conductors in the bedrock beneath the ice. The significant correlation between the ice thickness and the depth of the conductor in the bedrock strongly suggests that the conductors are not sedimentary rock layers but rather saline groundwater in which salinity has been enhanced by permafrost processes. From the regression curve we can conclude that the temperature vs depth curve in the ice can be represented by a first-degree line and that the “warm” ice base of about −2° C is expected to occur at depths of about 650 m, the base of permafrost in outcropping bedrock being at about 1 km. The mean temperature gradients in the ice and in the bedrock can be estimated as being about 20°Ckm−1 and 13°C km−1 respectively.

In the Basen–Plogen profile, conductors were detected only in the beginning of the profile, where ice thickness was below 650m. In the main part of the profile where the ice thickness exceeds 650 m, no conductors were observed. In those areas our interpretation is that the icebase is “warm” and no saline waters enriched by permafrost are present.
Prediction of possible changes in glacio-hydrological characteristics under global warming: southeastern Alaska, U.S.A.
Authors: Davidovich N.V. , Ananicheva M.D.
Published: September 2017

We use the Wetherald and Manabe climate model to predict the response of mountain glaciers to a doubling of atmospheric carbon dioxide. The response is measured in terms of a change in the equilibrium-line altitude (ELA) and the glacier terminus altitude (GTA), net accumulation–ablation on these altitudes and the melt runoff for 12 mountain-glacier regions in southeastern Alaska, U.S.A. The methods we use involve extrapolating climate-model temperature fields to a glacier’s location, and empirical–statistical relationships between air temperature and percentage of solid precipitation, and between summer air temperature and ablation and melt runoff. Our study shows that, under global warming, glaciation in southeastern Alaska will not disappear, but mass exchange of glaciers will be more intensive and the ELA value will increase by 300–760 m, depending on the glacier’s distance from the ocean.
Late Pleistocene interactions of East and West Antarctic Ice-flow Regimes: evidence from the McMurdo Ice Shelf
Authors: Kellogg Thomas B. , Hughes Terry , Kellogg Davida E.
Published: September 2017

We present new interpretations of deglaciation in McMurdo Sound and the western Ross Sea, with observationally based reconstructions of interactions between East and West Antarctic ice at the last glacial maximum (LGM), 16000, 12000, 8000 and 4000 BP. At the LGM, East Antarctic ice from Mulock Glacier split; one branch turned westward south of Ross Island but the other branch rounded Ross Island before flowing southwest into McMurdo Sound. This flow regime, constrained by an ice saddle north of Ross Island, is consistent with the reconstruction of Stuiver and others (1981a). After the LGM, grounding-line retreat was most rapid in areas with greatest water depth, especially along the Victoria Land coast. By 12000 BP, the ice-now regime in McMurdo Sound changed to through-flowing Mulock Glacier ice, with lesser contributions from Koettlitz, Blue and Ferrar Glaciers, because the former ice saddle north of Ross Island was replaced by a dome. The modern flew regime was established ∼4000 BP. Ice derived from high elevations on the Polar Plateau but now stranded on the McMurdo Ice Shelf, and the pattern of the Transantarctic Mountains erratics support our reconstructions of Mulock Glacier ice rounding Minna Bluff but with all ice from Skelton Glacier ablating south of the bluff. They are inconsistent with Drewry’s (1979) LGM reconstruction that includes Skelton Glacier ice in the McMurdo-Sound through-flow. Drewry’s (1979) model closely approximates our results for 12000-4000 BP. Ice-sheet modeling holds promise for determining whether deglaciation proceeded by grounding-line retreat of an ice sheet that was largely stagnant, because it never approached equilibrium flowline profiles after the Ross Ice Shelf grounded, or of a dynamic ice sheet with flowline profiles kept low by active ice streams that extended northward from present-day outlet glaciers after the Ross Ice Shelf grounded.
Spatial variations in heat at the base of the Antarctic ice sheet from analysis of the thermal regime above subglacial lakes
Authors: Siegert Martin J. , Dowdeswell Julian A.
Published: September 2017

Antarctic subglacial lakes provide аn important boundary condition for thermal analysis of the ice sheet in that the basal ice temperature over lakes may be assumed to be at the pressure-melting point. We have used a one-dimensional vertical heat-transfer equation to determine theoretical temperature values for the ice-sheet base above 77 subglacial lakes identified from airborne radio-echo-sounding data covering 50% of Antarctica. Variations in our temperature results to below the pressure-melting temperature over lakes are due to either our estimate of the geothermal heat flux or a neglect of heat derived from (a) internal ice deformation and (b) basal sliding, in the thermal model. Our results indicate that, when the geothermal heat flux is set at 54 m W m−2, the ice-sheet base above 70% of the known Antarctic subglacial lakes is calculated to be at the pressure-melting value. These lakes are located mainly around Dome C, Ridge B and Vostok station. For the ice sheet above subglacial lakes located hundreds of kilometres from the ice divide, using the same thermal model, loss of heat due to vertical advection is calculated to be relatively high. In such regions, if the ice-sheet base is at the pressure-melting point, heat lost due to vertical advection must be supplemented by heat from other sources. For the three lakes beneath Terre Adélie and George V Land, for instance, the basal thermal gradient calculated to produce pressure melting at the ice-sheet base is equivalent to 1.5–2 times the value obtained when 54 m W m−2 of geothermal heat is used as the sole basal thermal component. We suggest that, as distance from the ice divide increases, so too does the amount of heat due to internal ice deformation and basal sliding. Moreover, by considering the ice-sheet basal thermal characteristics above subglacial lakes which lie on the same ice flowline, we demonstrate empirically that the heat due to these horizontal ice-motion terms varies pseudo-exponentially with distance from the ice divide. The location along a flowline where a rapid increase in the basal heat gradient is calculated may correspond to the onset of large-scale basal sliding.
Geometry, motion and mass balance of Dyer Plateau, Antarctica
Authors: Raymond Charles , Weertman Bruce , Thompson Lonnie , Mosley-Thompson Ellen , Peel David , Mulvaney Rob
Published: September 2017

Geodetic surveying and ground-based radar profiling were used to determine geometry and surface motion of the ice sheet on the Dyer Plateau, Antarctica, in the vicinity of an ice-core site on a local dome. Vertical strain measurements in the core hole constrain the depth profile of vertical velocity. These geophysical measurements are used to analyze the profiles of density and annual layer thickness measured on the ice core to estimate the current mass balance of the ice column and the past history of accumulation rate. Consideration of horizontal and vertical mass-flow divergence shows that the profiles of density and vertical velocity are not fully consistent with steady state. Mean density of the firn layer appears to be increasing, which leads to the deduction of a small rate of mass increase (≈ 0.02 m a− 1 ice-equivalent thickness). Over the last 200a there has been a gradual increase in accumulation rate from about 0.46 m a− 1 to 0.54 m a− 1 ice-equivalent thickness in recent time.
Stress-induced foliation in the terminus of Variegated Glacier, Alaska, U.S.A, formed during the 1982–83 surge
Authors: Tad Pfeffer W.
Published: September 2017

Two sets of bubble-density foliation, one vertical and transverse to flow and one vertical and parallel to flow, developed in the ice of the terminus lobe of Variegated Glacier, Alaska, during the passage of the final stages of the 1982–83 surge in June and July 1983. The transverse foliation is ubiquitous in the lower part of the terminus lobe affected by the surge, but disappears abruptly over a 5 m wide zone at the boundary of the surge, as delineated by measurable strain rates during the surge. The ice at the outermost limit of the transverse foliation experienced compressive total strains no greater than −0.10 (logarithmic), but did briefly experience high strain rates, corresponding to compressive stresses in excess of 0.6 MPa. It is concluded that the transverse foliation was developed as a consequence of high compressive stress rather than high total strains. Experimental evidence of Kamb indicates that bubble migration occurs under similar tectonic conditions to those in the terminus lobe during the surge, and that bubble migration is related to stress rather than finite deformation or rotation of pre-existing structures. Bubble migration may be the mechanism by which the transverse foliation developed during the passage of the surge front.
Climate sensitivity of glaciers in southern Norway: application of an energy-balance model to Nigardsbreen, Hellstugubreen and Alfotbreen
Authors: Oerlemans J.
Published: September 2017

Three glaciers in southern Norway, with very different mass-balance characteristics, are studied with an energy-balance model of the ice/snow surface. The model simulates the observed mass-balance profiles in a satisfactory way, and can thus be used with some confidence in a study of climate sensitivity. Calculated changes in equilibrium-line altitude for a 1 K temperature increase are 110, 108 and 135 m for Nigardsbreen, Hellstugubreen and Alfotbreen, respectively. The corresponding changes in mass balance, averaged over the entire glacier area, are −0.88, −0.715 and −1.11 m year−1 (water equivalent).

Runs with an ice-flow model for Nigardsbreen, to which calculated mass-balance profiles arc imposed, predict that the front will advance by 3 km for a 1 K cooling, and will retreat by as much as 6.5 km for a 1 K warming. The response to a 10% increase in precipitation would be a 2 km advance of the snout, whereas a 4 km retreat is predicted for a 10% decrease. This large sensitivity (as compared to many other glaciers) is to a large extent due to the geometry of Nigardsbreen.
Hintereisferner, Austria: mass-balance reconstruction and numerical modelling of the historical length variations
Authors: Greuell W.
Published: September 2017

In this study, an attempt is made to simulate the historical length variations of Hintereisferner (Austria). Key elements in the model are: (1) reconstruction of the local climate (Vent); (2) multiple linear regression analysis between measured climate and mass-balance variations; (3) reconstruction of the mass balance with (1) and (2); (4) a one-dimensional numerical ice-flow model forced by the mass-balance history. Progress relative to the previous, similar studies can be summarized as two points: (1) the mass balance is reconstructed more carefully, and (2) sensitivity experiments show that uncertainties and assumptions in the flow model hardly affect the response of the glacier to climate fluctuations with a time-scale of the order of (or larger than) the response time of the glacier (around 100 year).

In the regression equation, mass-balance fluctuations are determined by the temperature during the ablation season and the annual precipitation. Cloudiness has no effect. The local temperature can be reconstructed as far back as 1755 with the temperature series from Basel, but the reconstruction of precipitation is unreliable prior to 1900. Mainly due to this point, a simulation starting in 1755 failed completely. However, in a run starting in 1894, the total retreat since then (2.2 km) was reproduced within 10%.
Flow-law hypotheses for ice-sheet modeling
Authors: Alley Richard B.
Published: September 2017

Ice-flow modeling requires a flow law relating strain rates to stresses in situ, but a flow law cannot be measured directly in ice sheets. Microscopic processes such as dislocation glide and boundary diffusion control both the flow law for ice and the development of physical properties such as grain-size and c-axis fabric. These microscopic processes can be inferred from observations of the physical properties, and the flow law can then be estimated from the microscopic processes.

A review of available literature shows that this approach can be imperfectly successful. Interior regions of large ice sheets probably have depth-varying flow-law “constants”, with the stress exponent, n, for power-law creep less than 3 in upper regions and equal to 3 only in deep ice; n probably equals 3 through most of the thickness of ice shelves and ice streams.
Calculated variations of annual ice ablation at the margin of the Greenland ice sheet, West Greenland, 1961–90
Authors: Braithwaite Roger J. , Olesen Ole Β. , HøJmark Thomsen Henrik
Published: September 2017

Annual ice ablation has been measured at three locations at the margin of the Greenland ice sheet: Nordbogletscher (for 6 years: 1977–78 to 1982– 83), Qamanârssûp sermia (8 years: 1979–80 to 1986–87) and at Paakitsup Akuliarusersua (7 years: 1982–83 to the present). As the data sets cover different periods, it is difficult to compare ablation directly between the three sites. However, measured series at each site can be extended over the last 30 years (1961–90) by simulations using climatic data, and the extended data series can be compared. The pattern of calculated ablation variations at the three locations is remarkably similar with no sign of any trend towards increased ablation in recent years. There was generally low ablation from the mid-1970s to the mid-1980s that may explain the recent thickening of the ablation area which has been detected by satellite radar altimetry. Ablation varies substantially from year to year, e.g. with a standard deviation of the order of ±0.5 m water a−1, and any future monitoring programme must detect trends of increasing ablation against this background of natural variations.
The Western Barents Sea and the Svalbard archipelago 18 000 years ago – a finite-difference computer model reconstruction
Authors: Isaksson Elisabeth
Published: September 2017

A finite-difference computer model was used to reconstruct a steady-state ice sheet over the western Barents Sea and the Svalbard archipelago at the last glacial maximum 18 000 BP. Flowlines were reconstructed from the ice margin to the ice dome based on information about glacial geology, bedrock topography, basal thermal regime and the present precipitation pattern. The modelling result suggests a 1700 m high marine ice dome east of Spitsbergen and a 1350 m high terrestrial dome over northwest Spitsbergen. Over most of the terrestrial areas, the bed is frozen while in the marine areas the bed is thawed. This is in agreement with both the terrestrial and the marine glacial geology records. The height of the terrestrial dome implies that the ice sheet was thin and left several of the higher mountain peaks as nunataks. Three major ice streams were reconstructed in the most pronounced over-deepened marine channels. This modelling experiment did not allow any major ice streams in the fjords of Spitsbergen during steady-state conditions.
Thermal conductivity of porous ice in hailstone shells
Authors: Zheng Guoguang , List Roland
Published: September 2017

The thermal conductivity and diffusivity of porous ice accreted on spherical and spheroidal hailstone models were measured over a density range of 620–915 kg m−3. By scanning the evolving surface temperature distributions during cooling in a cold airflow the thermal conductivity was varied in iterative fashion until the internal heat flux produced the correct surface temperature distribution. The results indicate a linear dependence of the thermal conductivity, ki, and diffusivity, αi, on density. For example, lowering the density by 10% lowers ki by 15%. Within the range of cloud conditions, the density variations affect the thermal parameters more than temperature does. The results also indicate a continuous decrease of the thermal conductivity from bulk ice via consolidated porous ice to loosely packed snow.
Temperate ice permeability, stability of water veins and percolation of internal meltwater
Authors: Lliboutry L.
Published: September 2017

In temperate glacier ice, in situ, besides water veins, there are water lenses, on grain boundaries more or less perpendicular to the direction of maximum pressure p1 (at the grain scale). Geometry of veins is developed. Grains are modelled as equal tetrakaidecahedra. The stress and temperature fields around a vein at a smaller, microscopic scale are estimated and the water discharge by a Vein is calculated. The time-derivative of the cross-sectional area S of a vein is governed neither by energy dissipation in the water nor by plasticity, but by capillarity effects and salinity. A “vasodilator threshold” pd for water pressure pw in the veins is defined. Normally, Pw < Pd, then S has a stable value, the same for any orientation of the vein, and the microscopic temperature is uniform. The coefficient of permeability is proportional to (Pd-pw)−4, and thus a true Darcy law does not hold. As an application, the percolation of internal meltwater is studied; in an upper boundary layer about 2 m thick this meltwater flows upwards, because in the bulk of the glacier pw is very close to P1, whereas it is zero at the surface. When, exceptionally, pw > pd, S increases irreversibly. Whether it leads to the formation of “worm-holes” is discussed.
Diagnosing the imbalance of Glaciar Santa Rosa, Cordillera Raura, Peru
Authors: Ames Alcides , Hastenrath Stefan
Published: September 2017

For Glaciar Santa Rosa, in the Cordillera Raura, Peru, the extent and volume are determined for 1980 and 1961 from topographic mapping, and for two undated earlier stages LME and MAX from moraines. The regime of the glacier in terms of ice flow and mass balance is evaluated for the 1977–83 period. More than half of the water discharge from the glacier is not renewed by precipitation but supplied by the ice thinning. The rate of surface lowering of 2 m a−1 liquid-water equivalent corresponds to an energy amount for melting of 22 W m−2. Sensitivity analyses of Glaciar Yanamarey in the nearby Cordillera Blanca show that such a decrease of energy available for melting could be produced by a cloudiness increase of one-tenth, an air temperature decrease of more than 2°C, a decrease in specific humidity of 1 g kg−1, or some combination of heat-budget processes. Such changes in the atmospheric environment would be required to stabilize the glacier at its recent volume. As another indication of the recent imbalance, the maximum volume flux is found about 100 m below the equilibrium-line altitude. Under continuation of recent climatic conditions, the glacier may disappear within a few decades. These inferences coorroborate a recent assessment for the neighboring Cordillera Blanca.
Structural evolution of Variegated Glacier, Alaska, U.S.A., since 1948
Authors: Lawson Wendy
Published: September 2017

Аn excellent photographic database, comprising 12 sets of vertical aerial photographs taken between 1948 and 1993, has enabled the structural glaciology of surge-type Variegated Glacier, Alaska, U.S.A., tо be analyzed for a period that spans two surge cycles and includes the effects of three surges. The glacier-wide patterns of crevasse development at the end of each of these surges, which occurred in 1947–48, 1964–65 and 1982–83, were remarkably similar, despite differences in surge intensities and extents. At the end of each surge a three-fold longitudinal zonation of crevasse orientation characterised that part of the glacier that had been affected by surge activity. This zonation comprises: (i) transverse crevasses in a narrow upper zone, (ii) superimposed longitudinal and transverse crevasses in an extensive middle zone, and (iii) longitudinal crevasses in a narrow lower zone. The main difference between patterns produced by successive surges was small variations in the extent оf the three zones. During quiescence, the most intense crevasse development occurs in the upper glacier in the latter part of quiescence, and is a function of increasingly steep down-glacier velocity gradients developing in the buildup to the impending surge. Some crevassing also develops in the central part of the glacier in mid-quiescence that is not related to the surge nature of the glacier, but to normal flow processes over bedrock. There is no structural evidence to indicate that any of the tributaries of Variegated Glacier surge. This observation suggests that the bulb-like loops in the medial moraines at Variegated Glacier form during quiescence as a result of the steady flow of the tributaries into the stagnant trunk glacier, rather than as a result of tributary surges.
Avalanche forecasting — an expert system approach
Authors: Schweizer Jürg , Föhn Paul M. B.
Published: September 2017

Avalanche forecasting for a given region is still a difficult task involving great responsibility. Any tools assisting the expert in the decision-making process are welcome. However, an efficient and successful tool should meet the needs of the forecaster. With this in mind, two models, were developed using a commercially available software: CYBERTEK-COGENSYSTM, a judgment processor for inductive decision-making–a principally data-based expert system. Using weather, snow and snow-cover data as input parameters, the models evaluate for a region the degree of avalanche hazard, the aspect and altitude of the most dangerous slopes. The output result is based on the snow-cover stability. The new models were developed and have been tested in the Davos region (Swiss Alps) for several years. To rate the models, their output is compared to the a posteriori verified hazard. the first model is purely data-based. Compared to other statistical models, the differences are: more input information about the snow cover from snow profiles and Rutschblock tests, the specific method to search for similar situations, the concise output result and the knowledge base that includes the verified degree of avalanche hazard. The performance is about 60%. The second, more-refined model, is both data- and rule-based. It tries to model the decision-making process of a pragmatic expert and has a performance of about 70%, which is comparable to the accuracy of the public warning.
Visible and near-infrared reflectivity during the ablation period on Peyto Glacier, Alberta, Canada
Authors: Cutler Paul M. , Scott Munro D.
Published: September 2017

Models for calculating glacier mass balance are sensitive to surface reflectivity variation. Fieldwork carried out on Peyto Glacier, Alberta, Canada, contributes to the data set available for ice-reflectivity parameterization in such models. Hemispherical reflectivity in the visible and near-infrared parts of the solar spectrum was obtained for rock, snow and three contrasting glacier surfaces to examine temporal and spatial variations. Glacier-ice near-infrared reflectivity displays only minor spatial variation (0.12–0.17) in comparison with the visible range (0.23–0.40), the latter being influenced primarily by surface impurity content. Surface roughness is of minor importance compared with impurities. Temporal variation of reflectivity was weak at all glacier-ice and rock locations; slight variations observed were due to changes in either solar zenith angle or cloud amount. Snow reflectivity displayed pronounced diurnal asymmetry and a larger response to cloud cover. The minimal temporal variation in glacier-ice reflectivity simplifies its parameterization. This behaviour is additionally useful for satellite-based measurements of the reflectivity field on larger glaciers, as images obtained within a 6 h window centred on solar noon are likely to yield values which are within 2–3% of daily mean values.
First results from a pre-operational system for automatic detection and recognition of seismic signals associated with avalanches
Authors: Leprettre Benoit J. P. , Navarre Jean-Pierre , Taillefer Alain
Published: September 2017

A system for automatic, reliable, semi-instantaneous estimation of avalanche activity is presented in an attempt to check deterministic models and improve the surveillance of risk zones. The principle is the seismic detection of avalanches. Two experimental sites equipped with standard seismological equipment are described. Avalanche seismic signals are recorded, as well as many extraneous signals of natural or human origin. After several years of a posteriori identification of the signals, we are now able to set up criteria for the automatic recognition of non-avalanche signals. We have therefore developed an automatic analysis/decision system to discriminate between avalanche signals and others. This system worked satisfactorily in pre-operational conditions during the winter of 1995-96. The results are presented and compared with other data related to avalanche activity. Although there is still room for improvement, our system seems to be able to estimate avalanche activity better than human visual observations.
Tidewater calving
Authors: Van Der Veen С.J.
Published: September 2017

Data from Columbia Glacier are used to identify processes that control calving from a temperate tidewater glacier and to re-evaluate models that have been proposed to describe iceberg calving. Since 1981, Columbia Glacier has been retreating rapidly, with an almost seven-fold increase in calving rate from the mid-1970s to 1993. At the same time, the speed of the glacier increased almost as much, so that the actual rate of retreat increased more slowly. According to the commonly accepted model, the calving rate is linearly related to the water depth at the terminus, with retreat of the glacier snout into deeper water, leading to larger calving rates and accelerated retreat. The Columbia Glacier data show that the calving rate is not simply linked to observed quantities such as water depth or stretching rate near the terminus. During the retreat, the thickness at the terminus appears to be linearly correlated with the water depth; at the terminus, the thickness in excess of flotation remained at about 50 m. This suggests that retreat may be initiated when the terminal thickness becomes too small, with the rate of retreat controlled by the rate at which the snout is thinning and by the basal slope. The implication is that the rapid retreat of Columbia Glacier (and other comparable tidewater glaciers) is not the result of an increase in calving as the glacier retreated into deeper water. Instead, the retreat was initiated and maintained by thinning of the glacier. For Columbia Glacier, the continued thinning is probably associated with the increase in glacier speed and retreat may be expected to continue as long as these large speeds are maintained. It is not clear what mechanism may be responsible for the speed-up but the most likely candidate is a change in basal conditions or subglacial drainage. Consequently, the behavior of tidewater glaciers may be controlled by processes acting at the glacier bed rather than by what happens at the glacier terminus.
Radiometric Chronology of Changme-Khangpu Glacier Sikkim
Authors: Nijampurkar V.N. , Bhandari N. , Borole D.V. , Bhattacharya U.
Published: September 2017

The 32Si concentration in a sample of surface ice from the snout of Changme-Khangpu glacier is 0.36 disintegrations per minute/tonne compared to the fall-out value of 0.7 d.p.m./tonne. If this decrease is assumed to be solely due to decay of 32Si, an age off c. 100 years is estimated for the surface ice of the snout, leading to an average flow velocity of c. 40 m/year for the past century. A vertical profile of 210Pb in a core taken at an altitude of 5040 m shows two horizons where this isotope is enriched, one between 3 and 4 m and another between 11 and 12 m, indicating that the primary concentration of 210Pb can change by physico-chemical processes like adsorption on dust. None the less, a longitudinal profile along the glacier shows a systematic decrease of 210Pb activity with decreasing altitude, the surface ice of the snout giving a value of 0.2 d.p.m./l, corresponding to an age of 100 years which is concordant with the 32Si age. This surface flow-rate of the glacier is much larger than the average contemporary flow-rate (c. 13m/year). The difference can be understood in terms of the past history of advance and recession of the glacier as revealed by the geomorphic evidence.
A Re-Assessment of the Mass Balance of the Lambert Glacier Drainage Basin, Antarctica
Authors: McIntyre N. F.
Published: September 2017

Re-definition of the interior drainage basin Lambert Glacier, using the most recent sources of ice-surface elevations, has shown its area to be 902000 km2, that is, 17% less than previous estimates. Landsat imagery of the steepest sloping part of the basin shows there is bare ice over an area of 56000 km2. Other evidence also indicates exceptionally low mass inputs and the distribution of accumulation rates has been up-dated. The result is a positive mass balance for the interior basin (+2 Gt a–1 ) and error limits which fall below zero. This is 47% less than the most recent calculation and illustrates the difficulty in deriving mass budgets in regions where data are scarce.
Superplasticity Owing to Grain Growth in Polar Ices
Authors: Duval Paul , Lliboutry Louis
Published: September 2017

Deep coring in polar ice sheets has only located the well-known recrystallized ice with a fabric peculiar to tertiary dislocation creep in bottom layers. At lesser depths, anisotropic ice with steady grain-sizes is found; secondary dislocation creep is the dominant process and an anisotropic third-power relation viscosity should ensue. In this paper, ices from the surface down to several hundred metres in depth are considered. Their grain-size increases with time owing to free energy at grain boundaries. This continuous boundary migration appears to be a much more efficient process for relative displacements of the grains than boundary sliding accommodated by diffusional processes between grains of constant size. Locally heterogeneous superplastic deformation leading to moderate viscosities is therefore expected. This deformation mechanism can explain the field data which seem to show a viscosity more than one order of magnitude lower than would result from Nabarro–Herring creep or secondary dislocation creep.
Tabular Icebergs: Implications from Geophysical Studies of Ice Shelves
Authors: Shabtaie Sion , Bentley Charles R.
Published: September 2017

Recent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridge/troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration in the course of transport.

The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.

Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.

We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.

Radar profiles of the ice shelf front at four sites in flow bands of very different characteristics are shown. In some places rifting up-stream from the front shows regular spacings, suggesting a periodic calving. Differential bottom melting near the front causes the icebergs to have an uneven surface and bottom (i.e. dome shaped).

Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass balance rates of tabular icebergs.
A Plasticity Theory Approach to the Steady-State Shape of a Three-Dimensional Ice Sheet
Authors: Reeh Niels
Published: September 2017

The differential equation determining the elevations of a perfectly plastic three-dimensional steady-state ice sheet is set up. Analytical solutions of the equation are obtained in two simple case, (1) an ice sheet on a horizontal base with an arbitrary edge curve, and (2) an ice sheet on a plane sloping base with a rectilinear ice margin. The solutions are discussed, particularly with reference to the development of ice divides and ice streams.

For arbitrary base and ice-margin geometries, solutions are obtained by means of the method of characteristics, which reduces the problem to solving simultaneously three ordinary first-order differential equations. The integration, which is performed by numerical methods, is generally commenced at the ice margin, where the necessary boundary conditions are known.

The method has been applied to model the elevation contours and the flow pattern of the central Greenland ice sheet, using the bottom topography revealed by radio echo soundings and the present ice margin geometry. The result is in surprisingly good agreement with our knowledge of the ice-sheet topography and flow pattern, all significant ice divides and ice streams being reproduced. This suggests, that the method can be applied to model the shape and flow pattern of ice sheets under glacial conditions, using information about former ice-margin positions.
Modification of Clasts in Lodgement Tills by Glacial Erosion
Authors: Sharp Martin
Published: September 2017

7.8% of 1 105 clasts with a B-axis diameter of >32 mm in lodgement tills from Skálafellsjökull, south-east Iceland, had a stoss-and-lee form. Clasts deeply embedded in the tills were more likely to have such a form than those resting lightly on the surface. Deeply embedded basalt and andesite clasts were also more rounded than lightly embedded clasts of similar lithology, and more striated and more likely to have a stoss-and-lee form than deeply embedded gabbro and granophyre clasts. Lightly embedded basalt and andesite clasts were more striated than lightly embedded gabbro and granophyre clasts. Within each lithological class, larger clasts were more likely to have a stoss-and-lee form. It is suggested that deeply embedded boulders acquire their rounded stoss-and-lee form by abrasion and fracture by over-riding debris-laden ice. This occurs after they have become firmly lodged by ploughing into the subglacial till bed, and before they become buried by lodgement of debris around them. The degree of modification depends in part upon clast size and lithology. The long-axis orientation of deeply embedded boulders is a good indicator of former ice-flow directions.
The Importance of Pressurized Subglacial Water in Separation and Sliding at the Glacier Bed
Authors: Bindschadler Robert
Published: September 2017

The effect of pressurized subglacial water on the sliding process is examined by a parameter called the “bed separation index”. This index indicates the relative extent of cavity formation by combining the effects of variation of bed-normal stress across undulations (Kamb, 1970) and steady-state water pressure in a Röthlisberger conduit at the glacier bed. Data from three glaciers of widely varying size are used to test the correlation of the bed separation index with inferred sliding rates. For Columbia Glacier and Ice Stream B in West Antarctica it is shown that high water pressure enhances sliding. More complete data from the third test case. Variegated Glacier, are used to compare a number of possible formulations of a “sliding law”. A Weertman-type power law (exponent c. 3), modified for the effect of subglacial water pressure, appears to be most preferable. Other formulations, including the “lubrication factor” hypothesis used by Budd (1975) are tentatively rejected. Consideration of the temporal variations of the “bed separation index” indicate that, on short time scales of days and weeks, variations of water pressure can dominate the sliding process. A rapid order-of-magnitude increase in water discharge causes a hundredfold transient increase in the water pressure. A bi-modal hydraulic regime is revealed for water flow transverse to the direction of main ice flow. This behavior is in accord with the observation of a sudden acceleration of the ice due to increased sliding in early summer or following heavy rainstorms.
Longitudinal Variations in Glacial Flow: Theory and Test Using Data from the Byrd Station Strain Network, Antarctica
Authors: Whillans I. M. , Johnsen S. J.
Published: September 2017

A theory advanced by Budd (1970) for ice-flow variation due to bed effects is improved and applied to the flow of the ice sheet leading to Byrd Station, Antarctica. Linear viscous rheology is used and a biharmonic equation for stress and strain-rate variation is solved. Basal boundary conditions include an undulating bottom topography and longitudinal variations in basal sliding and shear stress. Near Byrd Station it is found that variations in basal sliding and shear stress have more important direct effects than does the bed topography. This result is important to considerations on the stability of glacial flow. Distortions of internal layers are calculated and these closely match the distortions observed in the internal layers detected by the NSF-SPRI-TUD radar. The phase relationship between internal layer distortion and surface topography provides a positive test for the theory. The theory does not predict a spectral power maximum in surface topographic relief at a wavelength of three ice thicknesses. Such wavelengths however dominate and we speculate that this may be due to the dynamics of glacial erosion and deposition or with subglacial water motion.
Field Studies of Bottom Crevasses in the Ross Ice Shelf, Antarctica
Authors: Jezek Kenneth C. , Bentley Charles R.
Published: September 2017

Surface and airborne radar sounding data were used to identify and map fields of bottom crevasses on the Ross Ice Shelf. Two major concentrations of crevasses were found, one along the grid-eastern grounding line and another, made up of eight smaller sites, grid west of Crary Ice Rise. Based upon an analysis of bottom crevasse heights and locations, and of the strength of radar waves diffracted from the apex and bottom corners of the crevasses, we conclude that the crevasses are formed at discrete locations on the ice shelf. By comparing the locations of crevasse formation with ice thickness and bottom topography, we conclude that most of the crevasse sites are associated with ice rises. Hence we have postulated that six ice rises, in addition to Crary Ice Rise and Roosevelt Island, exist in the grid-western sector of the ice shelf. These “pinning points” may be important for interpreting the dynamics of the West Antarctic ice sheet.
Inventory of Arctic Laser Terrain Profiles
Authors: Radl C. J. , Welsh J. P.
Published: September 2017

Ten maps show where and when 90 000 km of airborne laser terrain profiles of Arctic sea ice have been obtained. The laser terrain profiling system is briefly described. The data reduction procedure is also briefly described.
Flexural–Gravity Waves on Floating Stratified Ice
Authors: Robinson Edwin S.
Published: September 2017

Flexural–gravity waves in the 3 ms to 50 ms period range were recorded on floating layers of ice ranging from 6 cm to 52 cm in thickness. These inversely dispersive waves are analogous to Rayleigh waves propagating on a multi-layered structure. Therefore, flexural–gravity wave dispersion curves can be calculated by the well-known Haskell–Thompson method. This approach allows the effects of snow layers and stratification of the ice to be evaluated. In earlier methods of calculating flexural–gravity wave dispersion. the structure was restricted to a single homogeneous solid layer over a homogeneous fluid. The effect of a low-velocity snow layer is to reduce the short-period phase velocity, and to increase the velocity at long periods. Dispersion curves for ice layers with and without a snow cover cross at an intermediate period that increases as ice thickness increases. These effects are measurable in seismic experiments on frozen ponds and lakes.
Sediment Transport During an Outburst from Glacier De Tsidjiore Nouve, Switzerland, 16–19 June 1981
Authors: Beecroft Ian
Published: September 2017

Between 16 and 19 June 1981 a large water pocket of volume 183 000 m3burst from glacier de Tsidjiore Nouve. From hourly stream discharge and suspended sediment concentration observations a suspended sediment output of 1 674 × 103kg was calculated. The transport of bed-load was estimated at 3 840 × 103kg, hence a total quantity of around 5 500 × 103kg of sediment were removed from the catchment, including the pro-glacial field, in the four days of the outburst.
Micro-Meteorological Conditions for Snow Melt
Authors: Kuhn M.
Published: September 2017

The energy budget of a snow or ice surface is determined by atmospheric variables like solar and atmospheric long-wave radiation, air temperature, and humidity; the transfer of energy from the free atmosphere to the surface depends on the stability of the atmospheric boundary layer, where vertical profiles of wind speed and temperature determine stability, and on surface conditions like surface temperature (and thus surface humidity), roughness, and albedo.

This paper investigates the conditions exactly at the onset or the end of melting using air temperature, humidity, and as the radiation term the sum of global and reflected short-wave plus downward long-wave radiation. For the turbulent exchange in the boundary layer, examples are computed with a transfer coefficient of 18.5 W m−2 K−1 which corresponds to the average over the ablation period on an Alpine glacier. Ways to estimate the transfer coefficient for various degrees of stability are indicated in the Appendix.

It appears from such calculations that snow may melt at air temperatures as low as –10°C and may stay frozen at +10°C.
Evidence of a Periodic Ice-Cliff Avalanche on North-West Ellesmere Island, N.W.T., Canadian High Arctic
Authors: Evans D. J. A. , Fisher T. G.
Published: September 2017

Evidence of a recent (1985) ice-cliff avalanche from an outlet lobe of a small plateau ice cap on north-west Ellesmere Island is discussed. Former avalanche events are evidenced by debris lying outside the 1985 avalanche material. Periodic activity seems to be linked to the build-up of melt water in the crevasses of the outlet lobe during the melt season. The exact magnitude and frequency of events are unknown. Some implications to geomorphology and the sedimentology of sub-polar glaciers are discussed.
Snow-stratification investigation on an Antarctic ice stream with an X-band radar system
Authors: Forster Richard R. , Davis Curt H. , Rand Timothy W. , Moore Richard K.
Published: September 2017

An X-band FM-CW radar was used to determine the feasibility of observing annual snow-accumulation layers in Antarctica with a high-resolution inexpensive radar system. The formation of layering boundaries, their resultant electromagnetic discontinuity and their detection by reflected energy are presented. Large returns from depths corresponding to reasonable positions for annual layers were found. The average accumulation rates calculated from the radar returns agree with those measured in a previous pit study done in the same area. The detection of the annual accumulation layers with this system implies a simple, inexpensive mobile radar could be used to profile large areas allowing the distorting effects of local topography to be removed.This type of system with a concurrent pit study could provide insight into the effect of sub-surface strata on spaceborne or airborne microwave remote sensing.
Freezing-rate effects on the physical characteristics of basal ice formed by net adfreezing
Authors: Hubbard Bryn
Published: September 2017

A number of theoretical and empirical studies have indicated that many individual characteristics of ice formed by processes of net basal adfreezing may be sensitive to the rate of propagation of the freezing front through the reservoir concerned. The effects of freezing rate on the the stable-isotope chemistry and crystallography of ice, in addition to the disposition and character of included debris and gas are reported. Unidirectional freezing through a cylindrical reservoir containing various water–sediment mixtures has been conducted in the laboratory and the resulting cores analysed for debris and gas disposition and ice-crystal size and fabric. The data lend support to inferences drawn from studies concerned with specific ice properties and an idealized suite of characteristics is developed which may be diagnostic of basal ice formed by net adfreezing.