bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hot-Water Drilling in the Antarctic Peninsula (Abstract)
Authors: Cooper S. 
Published: September 2017

The British Antarctic Survey has developed a hot-water drilling system used chiefly for installing temperature sensors through ice shelves and for retrieving oceanographic equipment tethered through thick fast ice. The specification, design and operation of the drill for these two activities will be discussed and practical field problems will be highlighted.A novel aspect of the design is the use of reaming nozzles to enlarge a pilot hole. These nozzles eject water upwards along the surface of the nozzle cone, and drill most efficiently when they hang free and unsupported by the sides of the pilot hole. The nozzles incorporate a nozzle-mounted valve, activated when the nozzle cone contacts the ice, thus increasing the back pressure of the water flow. The pressure increase is monitored at the surface and the winch speed is reduced accordingly in order to ensure an efficient drilling operation.
Stable Water-Isotope Studies for Deciphering the Recent Structure and Holocene Evolution of the East Antarctic Ice-Sheet Margin Near 12° E (Abstract)
Authors: Hermichen W. -D. , Strauch G. , Vaikmäe R. 
Published: September 2017

Since 1978 scientists from the German Democratic Republic, in collaboration with members of Soviet Antarctic Expeditions, have been studying the isotopic composition of ice and snow, as well as the trapped gas content of glacier ice from northern Queen Maud Land near 12 °E, in order to decipher recent structures and Holocene evolution of this part of the margin of the East Antarctic ice sheet.Along a 180 km north-south profile three large bodies could be distinguished: (1) Novolazarevskaya Ice Shelf (100 km wide, ≲700 m thick); (2) the ice cover (30 km wide, ≲300 m thick) of the Skaly Instituta Geologii Arktiki nunataks [“Skaly IGA”], with a scarp to the Schirmacher oasis; and (3) a firn glacier (50 km wide, c. 1000 m thick), filling the depression between “lskaly IGA” and the Wohlthat massif.The ice-flow conditions of the surface layer are known. On the basis of isotope profiles from Soviet drilling sites on the ice shelf (447 m core) and on the firn glacier (809 m core), from the scarp and slope of the inland ice to the south of the Schirmacher oasis (ablation zone), and from numerous pits through the surface layer, a preliminary stratigraphic model has been developed.On the basis of recent flow conditions, the basal layer of Novolazarevskaya Ice Shelf and that of the inland ice of the “Skaly IGA” region were identified as relics of late Pleistocene ice cover by their mean deuterium content of −390 and −330% respectively. The old ice is covered by Holocene layers of regional origin (δD = −230 to −150%); in the ice shelf there are also layers derived from the interior of Antarctica (δD = −350 to −280%).The isotope profile of the firn glacier (range of δ18O variations −32.3 to −18.1%, identifiable annual layers of about 20 cm of ice to a depth of 500 m) represents a unique record of the last 7–8 ka for this region. It is also supported by measurements of the total air content trapped in ice samples (V = 107–127 cm3/kg) taken from the 809 m core. Details will be published elsewhere.More information is expected to be provided by isotope studies of extended blue-ice fields and ice-cored moraines.
The Variation in the Ice Sheet of Mizuho Plateau, East Antarctica (Abstract)
Authors: Mae Shinji , Nishio Fumihiko , Ohmae Hirokazu , Takahashi Shuhei , Nakawo Masayoshi , Kawada Kunio 
Published: September 2017

The Japanese Antarctic Research Expedition (JARE) has conducted glaciological studies on Mizuho Plateau since 1981. We have already reported that the ice sheet flowing from Mizuho Plateau into Shirase Glacier is thinning at a rate of about 70 cm/year and that the profile of the distribution of basal shear stress is similar to that of surging glaciers.A 5 year glaciological programme on Mizuho Plateau and in east Queen Maud Land is now being carried out and we have obtained the following new results:(1) The ice sheet in the down-stream region (where ice elevation is lower than about 2400 m) is thinning, based on measurements of horizontal and vertical flow velocity, strain-rate, the slope of the ice surface, the accumulation rate and densification of snow.(2) δ18O analysis of deep ice cores obtained at Mizuho Station (2240 m a.s.l.) and point G2 (1730 m a.s.l.) shows that δ18O increased about 200 years ago at Mizuho Station and about 400 years ago at point G2. If we can assume that the increase in δ18O is caused by the thinning of the ice sheet, then this result means that this thinning propagates to up-stream areas.(3) Radio-echo-sounding measurements on Mizuho Plateau show that the ice base in the down-stream region is wet. This supports the result described in (1), since the basal sliding due to a wet base causes ice-sheet thinning, as proposed in our previous studies.In summary, a possible explanation of ice-sheet variation on Mizuho Plateau is as follows: the thinning of the ice sheet, caused by the basal sliding due to basal ice melting, started at Shirase Glacier and has been propagating up-stream to reach its present position. A simple calculation, using flow velocities, shows that the thinning started at Shirase Glacier about 1500–2000 years ago.
Snow Accumulation and Oxygen-Isotope Records at the Law Dome Summit, Antarctica (Abstract)
Authors: Morgan V. I. 
Published: September 2017

At the summit of Law Dome (66°44′S, 112°50′E) the annual snow accumulation is equivalent to 0.7 m of water, and seasonal cycles of oxygen-isotope ratio are preserved clearly in the firn. Isotope-ratio measurements on three 28 m deep ice cores taken 15 m apart near the summit show that although annual layer thicknesses are well correlated between the cores, the actual isotope values (even when averaged over several years’ accumulation) are poorly correlated.Since the three sites must obviously receive the same precipitation, the differences in isotope ratio imply that the amounts of the precipitation retained as accumulation from individual snow-falls throughout the year must vary. The large seasonal variation in isotope ratio then easily accounts for the offsets.In the Law Dome region, precipitation occurs mainly as a result of cyclonic activity in spring, winter and autumn. The stronger winds experienced at these times cause the snow to be formed into large dunes, which are the stable (although moving) surface configuration under these conditions. The movement of dunes by erosion on one face and deposition on the other causes the snow in them to be well mixed. Isotope measurements on a 0.7 m high dune on the inland ice cap showed that it was composed of “winter” snow, with an average isotope value of −28.2% and a range of only 1%. The harder underlying snow had values which varied between −24.2 and −27.4%.During periods of relatively calm or warm conditions the dunes become consolidated and their movement is greatly reduced. Further snow-falls then do not add accumulation to the top and up-wind side of the dunes but tend to fill them in on the down-wind side. In particular it is observed that for Law Dome the surface profile is quite rough in winter and spring, but the more gentle winds and light snow-falls experienced in summer produce a very smooth surface at the beginning of autumn, with all the surface hollows filled in.The ice-core isotope profiles confirm the evenness of the summer accumulation, compared to that of winter. Correlation coefficients are typically 0.26 for the winter minima and 0.65 for the summer peak in isotope ratio. This means that somewhat shorter averaging times can be used when compiling “climatic” records from isotope profiles if only the “summer” isotope values are used. This is useful in comparison of isotopic and meteorological data when only a limited time span is available.Apart from the short-term effects, which can be reduced as desired by longer averaging periods, these core studies also demonstrate how any process which can modulate the precipitation or accumulation will also affect the isotopic composition of the accumulated snow.
Tiltmeter Observations From Doake Ice Rumples, Ronne Ice Shelf, Antarctica (Abstract)
Authors: Smith A. M. 
Published: September 2017

New tiltmeter data from Doake Ice Rumples on Ronne Ice Shelf are presented. The tiltmeters detected flexing of the ice shelf close to the grounding line, due to tidal forces. In earlier studies on Rutford Ice Stream, flow was from grounded ice into the floating ice shelf. In contrast, the area studied on Ronne Ice Shelf exhibits flow from the ice shelf on to grounded ice rumples.The data span 5 km of the up-stream ice shelf and much of the grounded ice. Approximately 30 d of continuous tilt data are available for one site on the ice shelf. Analysis of this record can determine the dominant tidal frequencies present.A number of shorter records cover periods normally of a few days. These were obtained from sites both up-stream and down-stream of the long-term site. They have been used to investigate the variation in tilt amplitude with distance from the grounding line.The approximate position of the grounding line was located from the position of strand cracks and by using surface-elevation and ice-thickness data. The tiltmeters helped to confirm this position. Over grounded ice, tidal flexing is clearly present up to about 2 km from the grounding line. Beyond this it appears to be absent. The signal recorded by tiltmeters on grounded ice farther than 2 km from the grounding line is attributed, at present, to a temperature dependency of the tiltmeters.The flexing of ice shelves at tidal frequencies has previously been treated as an elastic problem. Available models which use beam theory require the use of a time-dependent function and a reduced “effective” ice thickness in the elastic modulus. On preliminary analysis, data from the ice shelf and grounding line of Doake Ice Rumples appear to be consistent with these theories. More detailed analysis and interpretation is required in order to confirm the level of agreement and to determine possible variations due to the “reversed” nature of the flow direction.
Single Folds at the Margins of Dry-Based Glaciers as Indicators of a Glacial Advance
Authors: Chinn T.J.H. 
Published: September 2017

Single folds which enclose the marginal “inner moraines” of the dry-based Jeremy Sykes and Alberich Glaciers, Dry Valleys area, Antarctica, are deduced to have formed during an advance of the margins of these glaciers where the thin, stiff marginal ice has obstructed glacier flow and expansion.It is suggested that the occurrence of this type of fold can be an indicator of an advance in many fully dry-based glaciers. On Alberich Glacier, the fold and associated margin forms suggest that a sequence of margin forms evolves when a small cirque glacier expands outward from a sloping ramp front to a tongue terminating in a calving ice cliff.
Dynamics of the Law Dome Ice Cap, Antarctica, as Found From Bore-Hole Measurements
Authors: Etheridge D.M. 
Published: September 2017

The internal dynamics of the Law Dome ice cap have been investigated by measuring the deformation of three bore holes located on an approximate flow line. Bore holes BHC1 (300 m deep) and BHC2 (344 m) were drilled in the coastal area to within several metres of bedrock and BHQ (418 m) was drilled about half-way towards the dome centre to about 50% of the ice thickness. Detailed measurements of orientation (inclination and azimuth), diameter, and temperature were taken through each bore hole over a 1 year span for BHC1 and BHC2 and a 10 year span for BHQ. The orientation data were reduced to obtain ∂u/∂z, a measure of the shear strain-rate. Changes in the depth of features located by bore-hole diameter measurements were used to obtain vertical velocity profiles. Other measurements discussed are temperatures, oxygen isotopes, crystal structure, surface velocities, and surface and bedrock topography.At the coastal sites, the ∂u/∂z profiles show two maxima in the lower third of the ice sheet. Flow due to the measured deformation accounts for about 55% of the surface velocity, the remainder being due to deformation and sliding in the basal zone. The vertical velocity profiles show mostly firn compression. The deeper ∂u/∂z maximum occurs in ice from the Wisconsin period which appears to deform more rapidly than the Holocene ice immediately above. The upper ∂u/∂z maximum may be related to the stress history of the ice, which can also explain the presence of significant shear strain and crystal-fabric development at only half the ice thickness at the BHQ site.
Isotropic and Anisotropic Flow Relations for Ice Dynamics
Authors: Jacka T.H. , Budd W.F. 
Published: September 2017

A flow relation for the minimum strain-rates for isotropic ice is presented. This flow relation has been compiled from laboratory tests in shear and compression, and covers the temperature and stress ranges typical of natural ice masses. However, the ice in natural ice masses is mostly anistropic. Three cores drilled at Law Dome, Antarctica, are used as examples to illustrate some of the different anisotropies that develop in ice masses in relation to the stress configurations and accumulated strains.For the shear- or compression-stress configurations, anistropic flow rates can be derived as enhancements of the minimum isotropic flow rates for the particular stress, temperature, and stress configuration. For compression, this enhancement asymptotically approaches 3. For shear, the enhancement may be as high as 8. For combinations of shear and compression, further tests are required.
Model Studies on Ice-Stream Surging
Authors: Radok U. , McInnes B.J. , Jenssen D. , Budd W.F. 
Published: September 2017

A self-surging glacier model (Budd and McInnes, 1974;Budd, 1975), in which basal sliding is parameterized in terms of energy per unit area dissipated by basal friction, TbVb, has been extended to model the steady-state and time-dependent behaviour of eight Antarctic ice streams. Their basic characteristics were established with the working hypothesis of steady-state mass balance for the ice sheet as a whole, using a 20 km grid digitization of the surface and bedrock-elevation contours in Antarctica: glaciological and geophysical folio (Drewry, 1983). When the viscosity of the ice is lowered to values that are somewhat unrealistic for the present Antarctic ice, all the model ice streams enter a pulsating fast-sliding mode of flow in which the velocity reaches several km/year for periods ranging from fractions οf a year to tens of years. Except for one ice stream (Slessor Glacier), no substantial surge-like advances were found, and even in that case no periodic surging regime developed. The pulses are tentatively attributed to processes at the grounding line, with the converging width-parameterization scheme in the surging velocity calculation as another complexity that is still being investigated. For the cyclic surging Medvezhi Glacier model (Budd and Mclnnes, 1978), it has been found that the model surges change to shorter pulses as the width-convergence rate is increased.It is concluded that the special regime and topography of ice streams — net accumulation increasing along the strongly converging flow and removal of the ice by calving rather than ablation — impede the onset of periodic surging. However, more sophisticated parameterizations of the basal hydraulics now in development may well show that ice-stream surges after all are possible.
Investigation on Wet-Snow Metamorphism in Respect of Liquid-Water Content
Authors: Brun E. 
Published: September 2017

Up to the present time, quantitative investigations on wet-snow metamorphism have mostly been conducted on water-saturated snow, because of the difficulty in getting large enough wet-snow samples at a uniformly low liquid-water content. Using the dielectric properties of snow at a frequency in the range 20–100 kHz, a warming device has been developed which has enabled us to bring samples of 7 × 10−3 m3 snow to any desired liquid-water content. A maximum value of 8% by volume was reached within 2 h.The warming device was used to reproduce natural wetness conditions in the laboratory in order to investigate wet snow metamorphism at low liquid-water content. Snow samples were brought to different liquid-water contents and held in that condition for about 2 weeks, during which grain-size was characterized using a picture-analysis system able to derive the mean radius of curvature of the cluster circumference. At any given liquid-water content value, the growth rate of the mean volume of the crystals building the clusters was constant, a pattern which has also been observed in water-saturated snow by previous investigators. This growth rate is well described by a power function of liquid-water content.
Avalanche Starting-Zone Analysis by use of a Knowledge-Based System
Authors: Buisson Laurent , Charlier Claude 
Published: September 2017

This paper presents the first step in the development of a new kind of computer-based tool which can help a specialist consultant in avalanche path analysis, a knowledge-based or expert system. In considering an avalanche path, the specialist often needs a simulation of possible avalanches on this path in order to obtain data for probable velocities and pressures. Use of classical numerical tools by an engineer requires a great deal of experience and knowledge. Such knowledge exists, but until the development of knowledge-based systems no computer-based tool was available.After a short review of such systems, we describe a knowledge-based system currently being developed in CEMAGREF. Its problem-solving environment includes methods of analysis developed by a senior consultant, and also numerical and qualitative models. In the first step, which is presented here, it analyses the starting zone of an avalanche path. By means of a digital terrain model and a description of vegetation and main ridges (a model which still needs to be improved) this system can make use of the experience of specialists to produce an avalanche-starting simulation based on specified meteorological conditions. Quite simple rules are employed in order to take into account snow drift. First results are shown on accompanying maps of this qualitative modelling and these will need to be tested for validity.
Measurements of Friction Coefficients of Snow blocks
Authors: Casassa G. , Narita H. , Maeno N. 
Published: September 2017

Snow blocks were slid down natural snow slopes and filmed with a video camera. Friction coefficients were calculated from time-distance curves and the equation of motion. Dry-friction coefficients ranged from 0.57 to 0.84, and could be separated into Coulomb friction and a friction component proportional to the contact area of the blocks (adhesion). These values are greater than the values usually used in avalanche dynamics, but are consistent with previous coefficients obtained for snow blocks sliding over snow.When uniform ploughing occurred and a shear layer developed along the track the apparent friction coefficients increased with velocity, and could be modelled by considering the kinematic viscosity of the snow. The values of kinematic viscosity ranged from 10−3 to 10−4 m2/s and agreed well with those values obtained by other researchers.
Spatial Variability of Snow-Pack Outflow at a Site in Sierra Nevada, U.S.A.
Authors: Kattelmann Richard 
Published: September 2017

Water flow through natural snow-packs is generally accepted to be extremely variable even over short distances. Differences in snow properties, and discontinuities in the horizontal and vertical structures of snow-packs, are responsible for variations in the effective area of the snow surface associated with outflow from a part of the base of the snow-pack. At the Central Sierra Snow Laboratory snow-pack outflow has been monitored using four snow-melt lysimeters of 6 m2 area each; two of these collectors were subdivided into three sections of equal area.Substantial variations in daily and monthly outflow volumes were noted between the individual collectors and also to a greater degree between the 2 m2 sub-units of the divided containers. The relative collecting efficiency of the snow-melt lysimeters also changed over time. In the deep warm snow-packs of the Sierra Nevada forest zone, snow-pack water routing appears to be highly variable, and this variability is on a much larger scale than was previously recognized. The large differences in snow-pack outflow measured in this study suggest that structural discontinuities and microtopography of snow strata can redirect percolating water over an area of several square meters.
Flow Characteristics of an Unconstrained, Non-Cohesive, Granular Medium Down an Inclined, Curved Surface: Preliminary Experimental Results
Authors: Lang R.M. , Leo B.R. , Hutter K. 
Published: September 2017

Some preliminary experimental results are presented, which characterize the behaviour of small-scale artificial avalanches. The laboratory simulation consisted of releasing a finite mass of non-cohesive granular material to flow without restriction down an inclined surface which includes a curved part at the base where the run-out zone is encountered. Three contrasting materials, of 3 mm and 5 mm diameter size sortings, and also two different bed roughnesses were used.Results indicate that a theoretical model which presumes a flow-regime-type avalanche may be too restrictive, in the sense that it describes a limiting case which does not often occur even under controlled conditions. Some suggestions are made for amendments to current theoretical concepts.
Calculation of Maximum Snow-Avalanche Run-Out Distance by use of Digital Terrain Models
Authors: Lied K. , Toppe R. 
Published: September 2017

Digital maps and terrain models are used to calculate maximum snow-avalanche run-out distance based on topographic parameters. Maps of 1:50 000 scale are found to be accurate enough for the purpose. 113 well-known avalanches are discussed in this paper. A computer system is used to calculate terrain parameters such as rupture area (A), avalanche-path length (L), avalanche-track lengths (L1L2), and run-out lengths (L3). Maximum run-out angle (α), avalanche-track angle (β). and average angle of rupture zone (γ) are also found by computer. The use of computer and terrain model reduces subjective judgement of parameters to a minimum. Run-out distance was found to be best expressed by the regression equation:α = 0.91β + 0.08γ–3.5°. R2 = 0.94, S = 1.4°.L = 0.93L1 + 0.97L2 + 0.61A + 182 m. R2 = 0.96, S = 137 m.
Slush-Flow Questionnaire
Authors: Onesti Lawrence J. , Hestnes Erik 
Published: September 2017

Questionnaires concerning slush flows were distributed globally. The purpose of the questionnaire was to determine the geographic distribution of slush-flow activity and also to collect information concerning the most commonly used nomenclature, release conditions, the season of occurrence, the type of terrain most susceptible to slush-flow occurrences, the characteristics of starting zones, paths and run-out zones, geomorphic activity, type of damage likely to result, and hazard control.Individuals having first-hand experience of the slush-flow process have been identified. The answers to the questionnaire established that slush flows definitely occur in lower latitudes as well as in the Arctic, and that the slush-flow hazard has not yet received the emphasis that it deserves. Heavy rainfall may cause slush flows at any time during winter, especially in areas with a marine west-coast type of climate. Stream channels and shallow depressions are the most common locations of starting zones, while slush-flow frequency seems to be closely related to the permeability of the substratum. Slush flows are a significant geomorphic agent, and it is noteworthy that there has been an increasing encroachment into potential slush-flow zones as a consequence of human activity.