bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self-Similarity of Wind Profiles in Blowing Snow Allows Outdoor Modeling
Authors: Tabler Ronald D. 
Published: September 2017

AbstractDrifts formed by snow fences appear to be scaled in proportion to fence height over a height range of nearly two orders of magnitude. This paper examines natural scaling in terms of commonly accepted similitude criteria. It is suggested that requirements for dynamic similarity of flow fields are satisfied over a period of time because surface roughness heightz0varies approximately as the square of shear velocityu⋆2for saltating flows in air. This is demonstrated by intensive measurements of wind profiles over snow and ice surfaces. Satisfaction of similitude requirements for scaling particle motion is less certain, although natural sorting may effectively scale particles over a restricted range of wind speeds. Natural scaling of drifts suggests snow erosion and deposition can be studied with reduced-scale models on smooth surfaces outdoors. The feasibility of this technique is demonstrated by results from 1 : 30 scale models of 1.8 and 3.8 m snow fences on both level lake ice and irregular terrain constructed from compacted snow.
A Slip-velocity Hypothesis Applied to Hydraulically Smooth Wind Flow Over a Snow cover
Authors: Bergen James D. 
Published: September 2017

AbstractAn hypothesis relating the slip velocity for laminar flow over a porous surface to the specific permeability of the surface proposed by Beavers and Joseph (1967) is applied to the problem of estimating the surface shear stress on an extensive snow surface at low wind speeds. Vertical profiles of wind speed and the air permeability of the surface snow layer were recorded for five periods of neutrally stable, hydraulically smooth flow. The variation of the ratio of the slip velocity to the surface shear stress with the specific permability was examined. The data are compatible with the hypothesis, although they are too sparse to allow valid estimates of the coefficients in the hypothesis.
Threshold Wind-Speeds and Elastic Impact in Snow Transport
Authors: Schmidt R. A. 
Published: September 2017

AbstractCohesive forces are added to the analysis of forces on sand and soil particles to show that fluid drag, alone, often cannot initiate movement of a snow surface. The impact force of saltating ice spheres, however, can easily provide the force to break cohesive bonds, according to these calculations. The argument suggests a balance between the distribution of bond strengths of exposed surface particles and the distribution of saltation trajectory heights.
Snow Transport Over Mountain Crests
Authors: Föhn Paul M. B. 
Published: September 2017

AbstractIn order to gain more insight into the mountain snow-transport mechanisms wind and drift flux measurements have been executed on a ridge crest (mainly during snow-storms). Horizontal wind-speed profiles, measured between 0.3 and 6 m above snow surface, show a hump-shaped course especially for strong winds. Theoretical approximations substantiate that the Bernoullian pressure decrease on the crest may be the main cause for this type of wind profile. Roughness parameters (Z0, u⋆) are determined with the aid of the wind profiles and compared with those reported in the literature. Corresponding drift density profiles coincide with steady-state drift theories as long as wind speeds are low (u1≤ 7-10 m s-1), at greater wind speeds snow plumes of 1 to 1.5 m thickness develop immediately above snow surface. Areal measurements on snow mass-balance differences between windward and lee slopes are used to approximate the total transport over the ridge crest and to derive a quantitative relationship between crest winds and drift-snow deposition on lee slopes.
The Energy-Line Method in the Mechanics of avalanches
Authors: Körner H. J. 
Published: September 2017

AbstractThe energy-line method results from the graphical representation of the energy law as applied in hydraulics. It makes it easier to understand the entire process of the movement of an avalanche from where it breaks away to where it is deposited. The technique, the energy lines, and the average slope of avalanches, as well as the theoretical energy lines of the one-coefficient and two-coefficient models of avalanche dynamics, are described. The method is explained by means of an example.
Snow–Pack Structure: Stability Analyzed by Pattern–Recognition Techniques
Authors: LaChapelle Edward R. , Ferguson Sue A. 
Published: September 2017

AbstractInternal snow–cover structure depicted by conventional snow profiles is commonly held to be important for avalanche forecasting but it is largely omitted from numerical forecasting schemes owing to quantification difficulties. A subjective test given to practising forecasters illustrated the complex roles of measured profile parameters in describing instability. A clustering technique of pattern recognition, after introducing a snow–profile training set, has demonstrated an objective ability to sort correctly 86% of the layer boundaries associated with slab–avalanche bed surfaces or lubricating layers. Further improvement in stability recognition comes from a newly devised shear test driven by a wedge which quickly locates failure planes within the snow cover. The cluster analysis is then able to sort with similar accuracy between stable and unstable (avalanching) failure planes so located.
The Avalanches of December 1966 in Western T’ien-shan, China
Authors: Jiaqi Qiu , Ruji Hu 
Published: September 2017

AbstractThe exceptional avalanches of December 1966 in the basins of the Gunes and Kashi Rivers caused much damage and blocked the highway for several months. The general avalanche conditions in this area and the exceptional weather which caused the exceptional avalanches are described.
Recent Progress and New Applications of the Dynamics of Avalanches
Authors: Brugnot Gerard 
Published: September 2017

AbstractThis paper reports the present stage in our research programme. We have used two very different models : (i) A numerical model treating the avalanche as a Newtonian liquid with a free surface; this model describes qualitatively the velocity fluctuations both of avalanche particles and of the front and gives some quantitative predictions, but much experimentation is needed to determine the large number of parameters involved. (ii) An analogue model in which powder avalanches have been simulated in an underground tunnel, taking account of the densimetric Froude number; this model reproduces the pressure rise which precedes the visible front, and also the pressure wave as the front passes which causes so much damage to engineering works—and human beings. These models have been applied to two cases—a bridge and a snow shed.The interplay between models and experimentation is discussed and the need for improved data on the mass output of an avalanche, of its detailed velocity history, and of the force on large objects is emphasized. Methods being used to try to supply this information are discussed ; gamma-ray measurements for specific mass, high-speed stereophotogrammetry for velocity, and various pressure sensors for the force. The possibility of releasing real powder avalanches to enable such measurements to be made more reliably is being investigated.
Topographical effects of Snow Deposition on Restructured Land
Authors: Chaco E. , Molnau M. 
Published: September 2017

AbstractThe measurement of snow accumulation and distribution is one of the primary objectives of a study on the melt of snow-drifts and erosion in the phosphate mining region of south-eastern Idaho. The study area is located in an active phosphate mine and is limited to the sites of waste dumps, a product of the surface mining technique used in this area. Four sites are included in the overall study with one dump selected for intensive snow measurement. Snow deposition data have been collected for one winter season (November 1977—June 1978) on a grid pattern over this dump. The area of the study site has been expanded and similar measurements are planned for the coming snow season.The snow measurements were made monthly on a pre-established 23 m (75 ft) square grid overlaid on the dump. The analysis of the snow data consists of contour mapping of any one or all the snow properties measured—snow depth, density, or water equivalent. In addition, since the measurements are made on the same grid each month, mathematical manipulation of grid data allows contour maps of the residual of the monthly snow properties to be plotted. A similar analysis of terrain properties collected on the same grid results in contour maps displaying ground slope, concavity-convexity of the surface, aspect, or distance from snow- deposition obstacles.The aim of the analysis using these types of data is to arrive at a model which will compute patterns of snow accumulation and distribution on the ground surface given a description of terrain type and probable meteorological properties of the region. A preliminary comparison of the maps shows a similar pattern of snow deposition occurring each month with the exposed areas of the dump swept clean and the greatest snow depth occurring in the sheltered concavities.
A Preliminary System to Predict Snow Instability using Acoustic Emissions
Authors: Sommerfeld R. A. 
Published: September 2017

AbstractResults From the last four winters’ studies on acoustic emissions from snow slopes have shown that periods of higher noise in the frequency band 5 to 125 Hz are associated with periods of instability, but that the phenomenon of acoustic emissions from unstable snow is very weak. Interference with the acoustic emissions from extraneous sources such as chairlifts, trucks, and airplanes causes ambiguities in the data which interfere with the straightforward prediction of instability.Spectra of the noises were examined, with the idea that filters might improve the signal-to-noise ratio. It was found that the noise generated by unstable snow can occur over a fairly wide range of frequencies and that there is no band of frequencies which is unique to unstable snow. It was found that the noise from the chairlift had a very stable spectrum and that it had a band from 50 to 65 Hz which was pronounced and in which the snow noise was fairly low. The r.m.s. voltage in the band 5 to 125 Hz can therefore be reduced by subtracting a proportion of the r.m.s. output of a narrow-band 55 Hz filter. By adjusting the constant of proportionality, it was possible to eliminate interference from the chairlift almost entirely, and this will be used.Spectral analyses have also shown that ambiguities are generated by variations in the 60 Hz power-line noise. It is possible to suppress this with the use of filters, but without complex digital data manipulation, it is not possible to eliminate it.The fact that the snow noise does not transmit over large distances means that events of interest should not occur simultaneously on two, widely spaced geophones. The system will include a geophone in an unstressed region whose r.m.s. voltage will be subtracted from that of the geophone in the stressed region to eliminate signals which are common to both. It is hoped that this technique will eliminate ambiguities caused by extraneous sources such as trucks and airplanes.
Prevention of Avalanches in the Gunes Valley in T’ien-Shan, China
Authors: Yanlong Wang , Zichu Xie , Zhizhong Zhang 
Published: September 2017

AbstractA section of the highway through the Gunes valley can be seriously interrupted by avalanching; in 1966-67 traffic was interrupted for four months. About 86 places are threatened by avalanches, most of which are channelled avalanches that do not reach the highway every year.A comprehensive programme to study the avalanches was begun in 1967 on the basis of which avalanche protective works were undertaken in 1974-75 and their effectiveness analysed in 1976-77. Most of these depend on local material; the main rock deposits available are andesite, which has good permeability and is very suitable for earthworks.The most common type of defence used is the building of mounds, 4-6 m high, 10-12 m wide, and 20-30 m long with a ditch dug in front. Such mounds have the effect of braking the avalanche flow and also of capturing snow on the uphill side. A second system is the terracing of slopes; beginning from the avalanche fracture line, earth is dug parallel to the contours. In two places dykes have been built to guide the snow, and in a few places avalanche sheds have been constructed, though because of expense these have been kept to a minimum. As the soil and climatic conditions are very suitable, tree planting around structures is a successful way of increasing avalanche protection.During the analysis of effectiveness snow-fall as recorded was heavy, but the defences were effective and avalanches did not seriously interrupt the highway.
Tectonic processes in Svalbard tide-water glacier surges: evidence from structural glaciology
Authors: Richard Hodgkins , Dowdeswell Julian A. 
Published: September 2017

AbstractThe tectonic effects of a glacier surge differ from those of steady state because flow is driven by longitudinal stresses rather than shear stresses. The orientations of recently formed crevasses, indicating the directions of the principal stresses, have been used to investigate tectonic processes in glacier surges recorded by repeat aerial photography. Long-term, large-magnitude shifts in stress regime are demonstrated, as are short-term propagation features. Two types of tide-water glacier advance are identified, depending on the position of the surge front relative to a low effective-pressure zone at the glacier terminus.
Ice Flow along the Byrd Station Strain Network, Antarctica
Authors: Whillans I. M. 
Published: September 2017

AbstractThe flow of the Antarctic ice sheet near Byrd Station is modeled using surface net accumulation-rate data, surface strain-rate data, and core-hole tilting results. The model empirically allows for the progressive development of ice fabric and for values of the vertical strain-rate nearer to zero at depth, and adjusts the strain-rates according to the effect of the climatic warming at the beginning of the Holocene.The validity of the model is supported by the agreements between calculated bed form and that measured by radar sounding, and between calculated and measured present-day ice-sheet thinning-rates. The ice was about 200 m thicker before thinning.The depth-age relationship for the Byrd Station ice core shows that the climatic change represented by the oxygen isotopic ratio of the ice began some 5000 years sooner than in north Greenland (Hammer and others 1978), but ended at about the same time.
Stability of Temperate Ice Caps and Ice Sheets Resting on Beds of Deformable Sediment
Authors: Boulton G. S , Jones A. S 
Published: September 2017

AbstractAlthough theories of glacier movement generally assume that glaciers flow over rigid rock beds, there are many places where glaciers rest on beds of deformable sediment, and the great Pleistocene ice sheets which extended from time to time over much of Northern Europe and North America were largely underlain by such beds. Observations show that a large proportion of the forward movement of a glacier lying on such a bed may be contributed by deformation of the bed rather than the glacier. A theory is developed in which the glacier surface profile is related to the hydraulic and strength properties of potentially deformable bed materials. If these have a high hydraulic transmissibility, melt water is readily discharged sub-glacially, the bed is stable, and the profile is a normal parabolic one, governed by the rhcological properties of ice. If bed transmissibility is low, water pressures build up, the bed begins to deform, and a lower equilibrium profile will develop, so that in an extreme case the glacier approximates to a thin flat sheet, similar to an ice shelf. It is suggested that such behaviour may have occurred at the margins of large Pleistocene ice sheets over North America and Europe, and evidence in support of this is drawn from the reconstructed shapes of these ice margins, anomalously small amounts of isostatic rebound, anomalously high retreat-rates, and the presence of glaciotcctonic structures. Reasons are suggested to explain why this behaviour should have been important for Pleistocene glaciers which penetrated into currently temperate latitudes but does not appear to be important in large modern glaciers.
Ice-Sheet Flow Properties Derived from Bore-Hole Shear Measurements Combined With Ice-Core Studies
Authors: Russell-head D. S. , Budd W. F. 
Published: September 2017

AbstractA 345 m deep bore hole in ice about 385 m thick, near the edge of Law Dome, Antarctica, was drilled in 1974 about 3 km up-stream from the site of a previous bore hole, nearly reaching the bed, obtained in 1969. The core from this new bore hole has been studied comprehensively, particularly with regard to the ice-crystal orientation fabrics. Samples of the ice core were subjected to simple shear at temperatures and deviatoric stresses which match the in situ conditions of the ice sheet.Similar studies of randomly-oriented laboratory-made polycrystalline ice were undertaken. Long-term tests, lasting for up to two years, were required to determine minimum strain-rates. The flow law for the anisotropic ice was thus determined as a function of that for the isotropic ice together with a measure of c-axis fabric strength perpendicular to the shear plane.Core studies indicate that the upper part of the ice sheet has a polycrystalline structure appropriate to the surface longitudinal stress. Deeper in the core a strong concentration of near-vertical c-axes develops. Ice having very large crystals with multiple maxima fabrics was found in the lower quarter of the ice thickness.Shear measurements in the bore hole indicate the existence of high strain-rates in the zone of vertical c-axes, and of lower shear-rates below that level. The low values of shear-rates in the basal region cannot be explained in terms of crystallographic changes alone, and therefore it is inferred that the shear stress decreases in this layer–a result which also provides a possible explanation for the development of the observed basal crystal structure.
Antarctic Ice-Sheet Volume at 18000 Years B.P. and Holocene Sea-Level Changes at the West Antarctic Margin
Authors: Lingle Craig S. , Clark James A. 
Published: September 2017

AbstractThe Antarctic ice sheet has been reconstructed at 18000 years b.p. by Hughes and others (in press) using an ice-flow model. The volume of the portion of this reconstruction which contributed to a rise of post-glacial eustatic sea-level has been calculated and found to be (9.8±1.5) × 106 km3. This volume is equivalent to 25±4 m of eustatic sea-level rise, defined as the volume of water added to the ocean divided by ocean area. The total volume of the reconstructed Antarctic ice sheet was found to be (37±6) × 106 km3. If the results of Hughes and others are correct, Antarctica was the second largest contributor to post-glacial eustatic sea-level rise after the Laurentide ice sheet. The Farrell and Clark (1976) model for computation of the relative sea-level changes caused by changes in ice and water loading on a visco-elastic Earth has been applied to the ice-sheet reconstruction, and the results have been combined with the changes in relative sea-level caused by Northern Hemisphere deglaciation as previously calculated by Clark and others (1978). Three families of curves have been compiled, showing calculated relative sea-level change at different times near the margin of the possibly unstable West Antarctic ice sheet in the Ross Sea, Pine Island Bay, and the Weddell Sea. The curves suggest that the West Antarctic ice sheet remained grounded to the edge of the continental shelf until c. 13000 years b.p., when the rate of sea-level rise due to northern ice disintegration became sufficient to dominate emergence near the margin predicted otherwise to have been caused by shrinkage of the Antarctic ice mass. In addition, the curves suggest that falling relative sea-levels played a significant role in slowing and, perhaps, reversing retreat when grounding lines approached their present positions in the Ross and Weddell Seas. A predicted fall of relative sea-level beneath the central Ross Ice Shelf of as much as 23 m during the past 2000 years is found to be compatible with recent field evidence that the ice shelf is thickening in the south-east quadrant.
Late Wisconsin Reconstruction for the Ross Sea Region, Antarctica
Authors: Drewry David J. 
Published: September 2017

AbstractIf sea-level depression in the Ross Sea embayment were: (1) < 120–130 m, or (2) > 120–130 m but sustained for < 104 a, it is unlikely that the Ross Ice Shelf would have become fully grounded over the whole continental shelf during Wisconsin times. Sediments flooring the Ross Sea and recent estimates of sea-level lowering and post-glacial emergence yield little support for grounded ice but do provide some evidence for expanded ice-shelf conditions. A reconstruction is presented based on this premise. The model is compatible with glacial geologic results, especially those in the McMurdo Sound area.
A Catastrophe Model of the Paleoglimate
Authors: MacAyeal Douglas Reed 
Published: September 2017

AbstractA simple qualitative model of global ice cover is presented to account for the apparent catastrophic transitions between glacial and interglacial climates. Unlike the Budyko (1972) and Weertman (1976) models, the catastrophe model employs a second control parameter besides the oribtally induced insolation fluctuations to differentiate between fast and slow glaciological response mechanisms. It is conjectured that this second control parameter is linked to isostatic actions occurring beneath the continental crust which shift the dynamic emphasis from terrestrial to marine ice margins.
Ice-thickness Patterns and the Dynamics of the Ross Ice Shelf, Antarctica
Authors: Bentley Charles R. , Glough John W. , Jezek Kenneth C. , Shabtaie Sion 
Published: September 2017

AbstractAs part of the Ross Ice Shelf Geophysical and Glaciological Survey, a detailed map of ice thickness has been produced from airborne radar measurements closely tied to the network of survey stations on the ice-shelf surface. The map, drawn with a 20 m contour interval, reveals a highly complex pattern of thickness variations reflecting presumably, at least in part, complex ice-shelf dynamics. Many features of the thickness variation pattern appear to be associated with zones of grounded ice, but not all. Features of interest include many ice thickness minima, with closures up to 120m; a narrow, greatly elongated ridge-trough system 450 km or more in length; a few ice thickness maxima; steep regional gradients of 10 m/km in freely floating ice; highly contorted contours suggesting a large-scale “turbulence”; and at least two remarkable step-like changes in ice thickness. The irregularity of many of these features suggests dynamic non-equilibrium, i.e. the existence of transients in the dynamic system, so that the ice shelf as a whole suggests a state of rather rapid change. Flow-bands constructed on the basis of the strengths of the echo from the ice-water interface clearly delineate the outflow from the main East Antarctic outlet glaciers in the grid eastern part of the shelf. A discontinuous flow band originating in a small mountain glacier (Robb Glacier) suggests a variable mesoclimate in the vicinity of the glacier within the last thousand years. Strong reflections near the ice front suggest bottom melting of saline ice previously frozen on to the underside of the ice. Several rifts or incipient rifts in the ice shelf characteristically show two lateral bands of strong reflections with a non-reflecting zone in between.