bluuebunny/crossref_metadata_2025 huggingface dataset:
Artificial Release of Avalanches by Explosives
Authors: Gubler H.
Published: September 2017

The method of the artificial release of slab avalanches by explosives is investigated. The effect of a detonation on a seasonal snow cover is measured and discussed. The attenuation of the resulting stress waves as a function of the type of explosive used, the position of the charge relative to the snow surface, the snow-stratification profile, and the type of ground are determined in field experiments. The effective ranges of shots in potential fracture zones are estimated.
The Dynamics of Avalanching in the Khibins
Authors: Kotlyakov V.M. , Rzhevskiy B.N. , Samoylov V. A.
Published: September 2017

Results of ten-year measurements of avalanche impact upon a large-sized installation are shown. The installation is equipped with 20 pressure sensors using the principle of the intrusion of a steel cone into a duralumin plate. The impacts of 30 dry avalanches with volumes from 100 up to 50 000 m3 are analysed. A maximum pressure at “a point" of 1 100 kN/m2 and a pressure of 650 kN/m3 averaged over the area of the installation (24 m2) were recorded. It is found that 75% of the impact energy is concentrated in the lowest 2 m of the installation. Proceeding from these data, and also taking into account that the thickness of an avalanche body amounts to 10-20 m at the moment of impact, we may conclude, that there is a “dense core" and an upper ’"high aerosol" part in an avalanche body.

The use of slereo-photogrammetric surveys of moving avalanches revealed the “velocity depression" effect in the Khibin avalanches: Avalanche velocity decreases abruptly (by a factor 1.5 to 2) at the end of transit channel and then grows rapidly up to a maximum at the end of the avalanche cone. The greatest variations of velocity amount to 51 m/s.

The data obtained prove the inefficiency of anti-avalanche filling dams, especially because of their negative role in the generation of disasterous air waves, whose pressure varies from 20 up to 150 kN/m 2.
Breakage of Ice Sheets by Underwater Explosions
Authors: Vittoratos E. , Charles M. E.
Published: September 2017

We have attempted to develop a theoretical understanding of the field experience on the destruction of floating ice sheets by explosives, by performing small-scale laboratory explosions and developing a theory based on the elastic plate. Glass spheres 4.5 × 10¯2 m in diameter and c. 4 × 10¯4 m thick were immersed in water underneath a floating ice sheet c. 2 × 10¯2 m in thickness. The air pressure was raised till the sphere burst at pressures around 15 atmospheres. A high-speed camera (up to several thousand frames per second) recorded the details of the explosion: the growth of the gas bubble and the corresponding deformation and failure of the ice. We observed radial and circumferential cracks develop within 2 ms of the bursting of the sphere.

As a first step in the theoretical development, we have considered the response of an infinite elastic plate to impulsive pressure loading due to an underwater explosion. We have assumed potential, incompressible flow which is a valid approximation for the case of the above experiments and the analogous compressed-gas blasting in the field (Mellor and Kovacs, 1972). However the effects caused by the intense shock wave that is radiated by the detonation of a high explosive are thus not considered. We relate the maxima in the tensile stress with the crack pattern and the eventual damage, and have achieved qualitative agreement with the laboratory observations. The model does reproduce and clarify some aspects of the field data, in particular the role of the thickness (Mellor, unpublished); but it fails to relate the crater diameter to the weight of the explosive. It appears that at optimum blasting conditions with high explosives an incompressible-fluid, classical-plate-theory approach is inadequate.
A Study of Several Pressure Ridges and Ice Islands in the Canadian Beaufort Sea
Authors: Hnatiuk J. , Kovacs A. , Mellor M.
Published: September 2017

The environment conditions in the southern Beaufort Sea are described with special emphasis on pressure ridges and ice islands. Techniques for determining the geometric configurations and the physical and mechanical properties of sea-ice structures and ice islands are described. Profiles of pressure ridges were determined by surface surveys, drill-hole probes and side-looking sonar scanning. Multi-year pressure ridges with thicknesses up to 18 m and widths up to 110 m were examined in detail. The first-year ridge of 22 m thickness and 100 m width was studied. Results are given for several multi-year ridges and the first-year ridge. Information obtained from dives under the ice is also given. Corresponding data are given for grounded ice islands with particular attention being given to contact between the ice and sea bed. A 19 m thick ice-island fragment grounded in 13 m of water was one of several investigated. Measurements of temperature, salinity, tensile strength and compressive strength are given for ice taken from old pressure ridges and factors influencing the interpretation of test data are discussed. The data obtained in this study will be used in engineering design studies for off-shore structures for drilling and production of hydrocarbons from the Beaufort Sea area. Exploratory drilling in shallow water has already been carried out and off-shore drilling from drill ships is scheduled to commence in the study area during the open-water season of 1976.

This paper will be published in full in a future issue of Journal of Glaciology.
Experiments on the Heaving Force of Freezing Soil
Authors: Kinosita Seiiti
Published: September 2017

Frost heaving of soil is accompanied by a force which often causes severe damage to structures. It was suggested by Everett that this so-called “heaving force" can be attributed to the coexistence of ice and water in micropores among soil particles which characterize the soil type and can be computed thermodynamically. However, the actual heaving force changes in a complicated manner depending on various factors including freezing speed, constraining condition for a soil block, and, of course, soil type.

Measurements of heaving force were carried out on various soil samples (sand, sandy loam, sandy clay loam, and two kinds of clays) under various freezing conditions: freezing speed in a range from 0.10 cm/h to 0.35 cm/h, presence or absence of water supply, complete or loose axial constraint applied to a soil block. In each experiment, soil was packed in a cylindrical container with a diameter of 11 cm and a height of 10 cm. A disk was placed on top of the soil contained in the container to constrain the sample either rigidly (a complete axial constraint) or less rigidly through a spring (a loose axial constraint). Main results of the measurements were as follows:

(1)

Under complete axial constraint, the heaving force decreased with decrease in the freezing speed and with the increase in the size of soil particles (from 6 bars to 1 bar for clay; from 4 bars to 1 bar for sandy clay loam; from 4 bars to 0.8 bar for sandy loam; from 1.5 bars to 0.6 bar for sand).

(2)

Without the constraint, the heave amount was almost independent of the freezing speed when there was no water supply (8 mm for clay; 6.5 mm for sandy clay loam; 3.5 mm for sandy loam; 1 mm for sand).

(3)

The heaving force decreased very rapidly with the loosening of the axial constraint by weakening the spring.

The results indicate that it is practical to treat the heaving force phenomenologically as a kind of resistive force exerted by freezing soil on a container holding the soil. Because of a volumetric increase due to the transformation of water into ice at the freezing front, both unfrozen and frozen parts of the soil suffer some strain if the soil is somehow constrained by the container. The strains cause stresses which appear as the heaving force. A formula for the heaving force is given in which both the frozen and the unfrozen soil are treated as viscoelastic bodies.
Using Linear Discriminant Analysis to Classify Snowfall Situations into Avalanching and Non-Avalanching Ones
Authors: Drozdovskaya N.F.
Published: September 2017

The existing methods of predicting avalanche danger often do not meet users’ demands because of the empiric character of the insufficient volume of information used. In such forecasts the contribution of each individual parameter into the prognostic information is unknown, and this is very important when studying such an event as avalanche formation, which is conditioned by a complex interaction of numerous factors, including snow accumulation, the state of snow thickness, and the conditions of its development.

It is obvious that such problems can be successfully solved by statistical methods, and that explains the growing interest in numerical methods of avalanche forecasting. Problems of multi-dimensional observations arises in many scientific fields. The method suited for this problem is discriminant analysis, the purpose of which is to divide a multi-dimensional observation vector into predetermined classes.

This study considers the prognostic (diagnostic) problems of fresh-snow avalanches released during snowfall or in the two days after it has ceased. The theoretical basis is a complex of statistical methods: correlation and dispersion analysis, “sifting" for the choice of predictors’ informative groups, construction of linear parametric discriminant functions, predictions based on training sample, and verification of discriminant functions based on independent material.

The archive used in the study consisted of 500 avalanching cases and 1 300 non-avalanching ones. All situations were grouped according to geomorphological characteristics. Each situation is described by eight meteorological characteristics. The results of classification of snowfall situations into avalanching and non-avalanching ones are as follows: reliability of ρ is from 75% to 91%, H from 0.15 to 0.51; based on independent material the reliability of ρ is from 63% to 85%, H from 0.10 to 0.56.

This paper has been accepted in revised form for publication in a later issue of the Journal of Glaciology.
Image-Analysis Techniques for Determination of Morphology and Kinematics in Arctic Sea Ice
Authors: Lee Meemong , Yang Wei-Liang
Published: September 2017

The synthetic aperture radar (SAR) data have been used to study sea ice with respect to its motion and formation/deformation. With the prospect of the Alaska SAR Facility development in the near future, there is a great need for robust and efficient sea-ice analysis techniques. This paper presents a sea-ice motion analysis technique that can be used for (1) local motion analysis of a selected ice patch and (2) a global ice motion over the entire image area. Though there are several sea-ice motion tracking techniques, they do not provide the required operational speed or robustness. In order to meet the operational speed requirement (over fifty images per day), we have developed a sea-ice motion analysis technique which requires very little human interaction and much simplified computation. The proposed technique uses a subset of easily distinguishable features to predict global motion characteristics and apply template matching over a predicted search area. We applied the developed technique to two pairs of SEASAT SAR images, one pair with a minor motion of “ice pack” and another with a larger and discontinuous motion of “fast ice”. The two major achievements of the new approach are: first, development of a set of computer-aided tools for feature selection and registration and, secondly, implementation of an optimal search strategy for automatic template matching via a motion prediction model.
Satellite Remote Sensing of Vatnajökull, Iceland
Authors: Williams Richard S.
Published: September 2017

Iceland’s largest ice cap, Vatnajökull, has been the test site for a series of airborne and satellite remote-sensing studies since 1966. Various types of image data acquired by the Landsat Multispectral Scanner (MSS) and the Seasat Synthetic Aperture Radar (SAR) are assessed for their value to glaciological studies of Vatnajökull. A low Sun angle winter 1973 MSS band 7 Landsat image of Vatnajökull provides information about the distribution and size of subglacial volcanic calderas, cauldron subsidence caused by subglacial geothermal and (or) intrusive volcanic activity, and delineation of the probable position of surface ice divides. Two types of multi-spectral digital enhancements were applied to a late summer 1973 MSS image of Vatnajökull. The first type was used to prepare a planimetric base map showing the location of the principal surface features and an inventory of 38 named outlet glaciers, one internal ice cap (Öraefajökull), and two detached glaciers which comprise this complex ice cap, and to measure its area (8300 km2). The second type provides information about the position of the snow line at the approximate end of the 1973 melt season, the areas encompassed by the ice fades of the ablation area and the slush zone and wet-snow facies/percolation facies of the accumulation area. More information about the surface morphology of Vatnajökull was available from the Sow Sun angle winter and the digitally enhanced summer Landsat image of the ice cap than from the Seasat SAR image.
Impulse Radar Sounding of Fossil Ice within the Kuranosuke Perennial Snow Patch, Central Japan
Authors: Yamamoto K. , Yoshida M.
Published: September 2017

The impulse radar was found to be useful in surveying the internal structures of wet snow patches in mountain regions. Radar profiles revealed that the thickness of the perennial ice was 30 m, possibly the thickest in Japan. An unconformity widely extended nearly parallel to the surface at the depth of 2 to 9 m and divided the ice into two parts.
A Study of the Fluctuations in Sea-Ice Extent of the Bering and Okhotsk Seas with Passive Microwave Satellite Observations (Abstract)
Authors: Cavalieri D.J. , Parkinson C.L.
Published: September 2017

The seasonal sea-ice cover of the combined Bering and Okhotsk Seas at the time of maximum ice extent is almost 2 × 106 km2 and exceeds that of any other seasonal sea-ice zone in the Northern Hemisphere. Although both seas are relatively shallow bodies of water overlying continental shelf regions, there are important geographical differences. The Sea of Okhotsk is almost totally enclosed, being bounded to the north and west by Siberia and Sakhalin Island, and to the east by Kamchatka Peninsula. In contrast, the Bering Sea is the third-largest semi-enclosed sea in the world, with a surface area of 2.3 × 106 km2, and is bounded to the west by Kamchatka Peninsula, to the east by the Alaskan coast, and to the south by the Aleutian Islands arc.

While the relationship between the regional oceanography and meteorology and the sea-ice covers of both the Bering Sea and Sea of Okhotsk have been studied individually, relatively little attention has been given to the occasional out-of-phase relationship between the fluctuations in the sea-ice extent of these two large seas. In this study, we present 3 day averaged sea-ice extent data obtained from the Nimbus-5 Electrically Scanning Microwave Radiometer (ESMR-5) for the four winters for which ESMR-5 data were available, 1973 through 1976, and document those periods for which there is an out-of-phase relationship in the fluctuations of the ice cover between the Bering Sea and the Sea of Okhotsk. Further, mean sea-level pressure data are also analyzed and compared with the time series of sea-ice extent data to provide a basis for determining possible associations between the episodes of out-of-phase fluctuations and atmospheric circulation patterns.

Previous work by Campbell and others (1981) using sea-ice concentrations also derived from ESMR-5 data noted this out-of-phase relationship between the two ice packs in 1973 and 1976. The authors commented that the out-of-phase relationship is “... surprising as these are adjacent seas, and one would assume that they had similar meteorologic environments”. We argue here that the out-of-phase relationship is consistent with large-scale atmospheric circulation patterns, since the two seas span a range of longitude of about 60°, corresponding to a half wavelength of a zonal wave-number 3, and hence are quite susceptible to changes in the amplitude and phase of large-scale atmospheric waves.
Satellite-Altimeter Measurements of Surface Height in Sea-Ice Areas
(Abstract)
Authors: Laxon S.W. , Rapley C.G.
Published: September 2017

The Seasat radar altimeter was designed to operate over the open ocean and encountered problems over sea ice. In particular, the on-board measurements of surface height were noisy and unreliable. As a consequence, published mean sea-surface and geoid maps based on the Seasat on-board height estimates either omit sea-ice-covered areas or include suspect data. We have identified and investigated the problems encountered by the Seasat altimeter over sea ice and have developed a technique for extracting accurate surface-height values from the sea-ice echo wave-form data. The retracking method is based upon fitting real wave forms to a library of model returns.
Evolution of the Illecillewaet Glacier, Glacier National Park, B.C., Using Historical Data, Aerial Photography and Satellite Image Analysis
Authors: Champoux André , Ommanney C.S.L.
Published: September 2017

The Illecillewaet Glacier (British Columbia) has been surveyed in a variety of ways since the end of the 19th century. A summary of the different information - archive photographs, field surveys, photo-interpretation, and remote sensing - reveals that between 1887 and 1962, the glacier had retreated more than one kilometre. However, since 1972, it has advanced about 100 m. The techniques used and the results are discussed.
Glacier Volume Estimation on Cascade Volcanoes: An Analysis and Comparison with Other Methods
Authors: Driedger C.L. , Kennard P.M.
Published: September 2017

During the 1980 eruption of Mount St. Helens, the occurrence of floods and mudflows made apparent a need to assess mudflow hazards on other Cascade volcanoes. A basic requirement for such analysis is information about the volume and distribution of snow and ice on these volcanoes.

An analysis was made of the volume-estimation methods developed by previous authors and a volume- estimation method was developed for use in the Cascade Range. A radio echo-sounder, carried in a backpack, was used to make point measurements of ice thickness on major glaciers of four Cascade volcanoes (Mount Rainier, Washington; Mount Hood and the Three Sisters, Oregon; and Mount Shasta, California), These data were used to generate ice-thickness maps and bedrock topographic maps for developing and testing volume-estimation methods. Subsequently, the methods were applied to the unmeasured glaciers on those mountains and, as a test of the geographical extent of applicability, to glaciers beyond the Cascades having measured volumes.

Two empirical relationships were required in order to predict volumes for all the glaciers. Generally, for glaciers less than 2.6 km in length, volume was found to be estimated best by using glacier area, raised to a power. For longer glaciers, volume was found to be estimated best by using a power law relationship, including slope and shear stress. The necessary variables can be estimated from topographic maps and aerial photographs.
Recession of Grasshopper Glacier, Montana, Since 1898
Authors: Ferrigno Jane G.
Published: September 2017

Grasshopper Glacier is a cirque glacier in the central Rocky Mountains of the United States. It is a remnant of the “Little Ice Age”, rather than the more widespread and older Pinedale Glaciation. The glacier has not been monitored on a regular basis and very few maps have been published of the area, but it has been studied, photographed, occasionally mapped, and described by scientific and non-scientific groups, at different times since 1898. These photographic, cartographic, and written records make it possible to trace the fluctuations of this glacier since 1898. Grasshopper Glacier has had periods of positive mass balance, but the overall trend has been negative, with accelerated melting in recent years. It is estimated that Grasshopper Glacier has lost about 50% of its area and as much as 90% of its volume, since 1898. Other Rocky Mountain glaciers are experiencing similar wastage and, if current conditions continue, these glaciers will disappear by the middle of the next century.
Short Period Motion Events On Variegated Glacier as Observed By Automatic Photography and Seismic Methods
Authors: Harrison W.D. , Raymond C.F. , MacKeith P.
Published: September 2017

A network of automated time-lapse cameras was deployed on Variegated Glacier, Alaska, to establish the temporal and spatial patterns of velocity change at a one-day time resolution. Results from the summers of 1979, 1980, and 1981 are presented; a surge occurred in 1982 and 1983. The principal velocity variations were pulses of increased speed, lasting about one day and referred to as “early”- or “late”-season motion events. The former recurred quasi-periodically on the upper part of the glacier in the early part of the melt season; the latter occurred later in the summer and were correlated with major storms or melting. Supplemental information about the occurrence of motion events was obtained from monitoring of seismic activity. Evidence for several other types of velocity changes was found.
Survey and Mapping of Recent Ice Shelf Changes and Landfast Sea Ice Growth Along the North Coast of Ellesmere Island, NWT, Canada
Authors: Jeffries M.O. , Serson H.V.
Published: September 2017

Ground and aerial surveys along the north coast of Ellesmere Island confirm that a considerable area of shelf ice remains, although it is not as extensive as it once was due to periodic ice island calvings. However, the lost ice shelf is quickly replaced by landfast sea ice. The sea ice often persists for many years and thickens sufficiently to be considered as the restoration of former ice shelf. The landfast ice quickly assumes an undulating topography, similar to the ice shelves, the development of which is encouraged by melt water and wind action. Even under the present conditions of negative mass balance, the sea ice reaches considerable, undeformed thicknesses. The thick sea ice forming today could be the precursor of an expansion of the ice shelves.
Glacier Mapping for an Inventory of the Indus Drainage Basin: Current State and Future Possibilities
Authors: Kick W.
Published: September 2017

A large problem of the World Glacier Inventory is the Pakistan part which is still missing. The available official quarter-inch and half-inch maps of the Survey of India and Pakistan are not adequate for the purpose. The maps of some expeditions provide reliable data for a few areas. Landsat imagery does not yield heights and has other disadvantages. At the present time, the Spacelab mission, in September 1986, with its metric camera, seems to offer a rather good opportunity.
Photogrammetric and Satellite Mapping of the Margin of the Inland Ice, West Greenland
Authors: Thomsen H.H.
Published: September 2017

Glaciological investigations have been carried out in areas proposed for local hydro-power stations in Greenland, A mapping programme was set up, to provide data for mass balance and simulation of run-off, as well as glacier dynamics.

Two types of glacier map have been produced, covering the margin of the Inland Ice: detailed photogrammetric maps, based on plotting from vertical aerial photographs and a new type of surface feature map, based on digitally-processed Landsat data. The photogrammetric maps, plotted on a scale of 1:25 000, include surface topography and surface features, such as crevasses, lakes, moraines etc. The surface feature maps, plotted on a scale of 1:100 000, show surface features related to ice and melt-water drainage, as well as subtle, topographic features, related to the subglacial topography.

The maps have so far been used for preliminary delineation of drainage areas on the Inland Ice and for planning tracks of radio echo-soundings.
The Problem of “Hidden” Ice in Glacier Mapping
Authors: Whalley W.B. , Martin H. Elizabeth , Gellatly Anne F.
Published: September 2017

Ice can become “hidden”, i.e. buried, by the superimposition of rock debris on a glacier or where rock debris may incorporate interstitial ice. Because it is obscured, problems result from a lack of understanding of the extent and continued activity of such ice. Landforms may be associated with this phenomenon and can be used as indirect evidence of its existence. A rock glacier can contain glacially-derived, buried ice as well as interstitial ice. We show, with examples, how such rock glaciers can be identified and provide information on the extent and possible volume of hidden ice in marginally glacierized and permafrost areas. In most cases, recognition of topography is sufficient, although time-separated aerial photographs may be necessary to locate the extent of ice. These are generally preferable to, and more cost effective than, most detailed on-site determinations of ice extent. It is possible to incorporate and extend knowledge of hidden ice in glacier mapping and inventory projects.
The Role of Debris-Rich Ice in Flow Near the Margins of Glaciers (Abstract)
Authors: Baker R.W.
Published: September 2017

The margins of many ice sheets and ice caps are marked by the presence of alternating layers of debris-laden and clean ice. The role of this ice in flow and sediment transport near the margins of glaciers has been the subject of considerable controversy between glacial geologists and glaciologists for over three decades.

Glacial geologists (Goldthwait, 1951, 1960, 1971, 1975; Bishop, 1957; Souchez, 1967, Boulton, 1970, 1972; Hambrey, 1976) commonly refer to the debris-bearing ice bands as “thrust planes” or “shear planes”, apparently seeing them as reverse faults which transport rock debris from the glacier bed to the surface in a “conveyor-belt-like” manner (Goldthwait, 1975, p. 192). As supporting evidence for the shear-plane mechanism, glacial geologists have offered only qualitative observations and none seem to have actually observed it in action. Glaciologists on the other hand, particularly Weertman (1961), Hooke (1968; 1973), and Hooke and Hudleston (1978), have objected to this concept on physical grounds and have presented convincing arguments for doubting that it is mechanically sound. In spite of the controversy surrounding it, the shear-plane mechanism has gained wide acceptance among geologists and physical geographers and has been perpetuated in recent years through a number of popular introductory geology and physical geography textbooks (e.g. Embleton and King, 1975; Judson, Deffeyes, and Hargraves, 1976; Leet, Judson, and Kauffman, 1978; Press and Siever, 1982; Hamblin; 1982).
Strain Rates On Rutford Ice Stream, Antarctica (Abstract)
Authors: Stephenson N. , Doake C.S.M.
Published: September 2017

In a study of the Rutford Ice Stream, strain rates were measured on a transverse section. Magnitudes ranged up to 40 × 10−3 a−1 but were typically in the order of 3 × 10−3 a−1 with an error of 0.1 χ 10−3 a−1. Variations in the strain rate between adjacent stakes of 0.2 χ 10−3 a−1 to 2 × 10−3 a−1 were matched to the thickness variations on the glacier.

For each set of three adjacent stakes, the velocity gradient components of the surface strain rate tensor were calculated by assuming that the gradients were linear over the distance between adjacent stakes. When plotted against distance across the ice stream, each strain rate component revealed different aspects of the flow field. The longitudinal strain rate was compressive, with an almost constant magnitude of 10−3 a−1. The lateral strain rate is extensive, with an average value of 1.1 × 10−3 a−1 which agreed with the angle between the divergent flow lines observed on a Landsat image. Peaks in the lateral strain rate, corresponding to longitudinal bands of thicker ice, showed that these thicker bands were spreading more rapidly at the expense of thinner areas. The two velocity gradient components of the shear rate tensor also reflected differences in ice thickness.
Mapping Coastal Ice Cliffs and Icebergs From Altimetry Data (Abstract)
Authors: Thomas R.H. , Zwally H. Jay
Published: September 2017

In a recent paper, Thomas et.al. (1984) showed how the coast of Antarctica could be mapped using satellite altimetry data. As the satellite approached the continent from the ocean, the Seasat altimeter obtained strong reflections from sea ice, even for a short time after passing over the ice front. Measured ranges are actually oblique distances to the nearest portion of sea ice, yielding a false drop in surface elevation. From the sequence of oblique ranges during a single orbit crossing of the ice cliff, the horizontal position of a segment of the ice cliff is mapped. Currently, the entire Seasat data set is being analyzed to map most of the Antarctic coastline north of 72 °S to an accuracy of ± 0.1 to 1 km, which is a major improvement over existing surveys. The altimeter waveforms corresponding to each range measurement are computer analyzed (“retracked”), using procedures that account for the specular reflections from sea ice and the diffuse reflections from firn. Each waveform analysis, along with the corrected range for data obtained in the vicinity of an ice cliff crossing, is verified or recomputed on an interactive computer, which also computes and maps the position of the ice front. The locations of several tabular icebergs have also been mapped with the same procedures, which can ultimately be used to obtain an estimate of iceberg population density in polar waters, initial results include the mapping of the Larsen ice shelf on the eastern side of the Antarctic Peninsula, showing, for example, the protrusion at approximately 68.5 °S. Estimates of errors in the derived horizontal position are obtained from the analysis of data from repeating orbit tracks. Comparison of these results with results from future altimetry missions will reveal changes in the position of coastal ice cliffs, due to ice movement and/or iceberg calving. Systematic measurements over several years would probably distinguish the effects of iceberg calving, which is intermittent, from those of ice movement, which is continuous.
Measurements on Air Porosity of Sea Ice
Authors: Nakawo Masayoshi
Published: September 2017

The air content of sea ice can be measured directly by melting a sample and collecting the released air, provided the air saturation ratio in the meltwater is known. The saturation ratio was found experimentally to be a function of three parameters: the time after an ice sample was melted, the average bubble size, and the air porosity of the sample. Since the last parameter is the term to be determined, an iteration method was employed in calculations of porosity. The bubble pressure was assumed to be at one atmospheric pressure. The vertical profile of air porosity was thus obtained for first-year sea ice in the Arctic. The results were in good agreement with estimations of porosity made from density values measured for the same samples. This indicates that the bubble pressure is near one atmospheric pressure.
The Lobe Structure in Ice Accreted on an Aluminium Conductor in The Presence of a Dc Electric Field
Authors: Phan Luan C. , Laforte Jean-Louis , Nguyen Du D.
Published: September 2017

Supercooled droplets of 38 μm mean volume diameter are accreted on a smooth aluni mum cylinder of 3.15 cm in diameter in order to study the effect of an electrostatic field upon ice formation on a power-line conductor. The results obtained show that ice grown in the presence of an applied negative field of 15 kV cm−1 exhibits a cusped-lobe structure characterized by surfacial outward knobs, convex rings of fine air bubbles and radial lines of large air bubbles; in the same conditions, a positive electric field of 15 kV cm−1 does not produce such lobe features. On the other hand, accretion tests performed in the absence of an electric field with a 33 μm droplet spectrum show that the well-developed cusped-lobe structure appears in ice at low ambient temperature and air velocity. In the present experimental conditions, the formation of cusped lobes observed in the presence of a negative electric field could be explained by a decrease in the temperature of the deposit due to a reduction of impact velocity of the charged droplets and/or an increase in the local heat-transfer coefficient at the surface of the ice accretion. Corona wind from ice points, always in the opposite direction to the impinging droplets, may also reduce their impact velocities. In addition, corona wind and roughness of the surface may contribute to a better evacuation of the latent heat and thus decrease the deposit temperature. The difference between the effects of a negative DC field and those of a DC positive field of the same strength comes from a stronger ionization intensity and/or a stronger deformation of water drops in the negative electric field.
An Evaluation of Shock Waves in Unsaturated Wet Snow
Authors: Sato A. , Brown R. L.
Published: September 2017

The propagation of shock waves in unsaturated wet snow is investigated, both analytically and experimentally.

The experimental program was carried out in the laboratory with an electromagnetic stress-wave generator. During each test, impact velocity was measured at the base of the specimen by means of a contacting wire system. Also, pressure was measured at the opposite end with a piezo-resistive pressure transducer with a flat response from below 0.5 to above 100 kHz.

Densities of snow samples in the range from 200 to 500 kg m−3 were tested. Impact velocities at the base were varied from 20 to as high as 100 rns −1. Propagation distances (specimen lengths) were varied from 2 to 5 cm. Also, for each test, the free water moisture content in the test specimen was carefully measured so that the effect of this property could be evaluated. The test results are reported and the wave attenuation rates are characterized in terms of the parameters discussed above. In addition, these results are compared to test results for dry snow.

Finally, wave propagation theory is used to evaluate the material tangent modulus. The theory is also used to calculate particle velocity and density increases produced by the shock waves. The results are compared to those obtained earlier for dry snow.
Snow Avalanches and Acoustic Emissions
Authors: Sommerfeld R. A. , Gubler H.
Published: September 2017

Analyses of several years of data show that acoustic emission activity is greater from unstable snowpacks than from stable snowpacks. Two types of signals have been identified: type I spikes and type II long-term elevation of the noise level. It is thought that the type I signals originate from macroscopic cracks. The type II signals may originate from differential movement on shearing surfaces, but this is less certain. Increased noise levels of both types correlate well with slope instability, when the slope stability is known. In some climates the limited range of signal detection might be a significant problem. A foam-mounted geophone set into the snow near active layers appears to be the best sensor available at present.
Mapping Ice-Sheet Margins from Radar Altimetry Data
Authors: Thomas Robert H , Martin Thomas V. , Zwally H. Jay
Published: September 2017

The Seasat radar altimeter, which was designed to measure ranges to the sea surface, has also provided the most accurate available maps of ice-sheet elevation. Seasat operated for three months during the austral winter of 1978, when Antarctica was girdled by sea ice. As the satellite approached the continent from the ocean, the altimeter obtained very strong reflections from the sea ice, and it continued to measure ranges to the sea ice even for a short time after passing over the ice front. The measured ranges are oblique distances to the nearest portion of sea ice, and the sequence of oblique ranges gives the position of the sea ice along the ice front. After the satellite crossed the ice front travelling seaward, oblique ranges were measured to the nearest portion of ice shelf. Examples are given from Seasat orbits crossing the Amery and Fimbul ice shelves. The entire Seasat data set provides an opportunity for mapping most of the East Antarctic coastline to an absolute horizontal accuracy of ±(0.1 → 1) km. The resulting map would effectively be an instantaneous view of the ice margin, requiring no adjustment for ice movement during the survey period.
Uniaxial and Plane-Strain Compressive Strength of Model Ice
Authors: Timco G. W.
Published: September 2017

In order to interpret reliably the results of model tests which involve compressive (crushing) failures, the compressive strength of the model ice must be known. In this paper, the uniaxial and plane-strain compressive strengths of carbamide (urea) model ice are documented for scale factors of 40>λ>5. In addition, the influences of stress and strain-rates, platen materials and direction of loading are discussed. The results of the tests are interpreted in terms of the structure of the ice.
The Predicted Behavior of Griesgletscher, Wallis, Switzerland, and its Possible Threat to a Nearby Dam (Abstract only)
Authors: Bindschadler Robert
Published: September 2017

The behavior of Griesgletscher, Switzerland, is studied by application of a numerical model of temperate glacier flow. The analysis addresses the possible danger posed to a hydroelectric dam which is 600 m from the calving terminus of the glacier. Model parameters are adjusted to fit data collected over eleven years. A calving law relating the calving flux to the water depth at the front provides a good fit of the data. Assuming a continuation of the present climate, the terminus is predicted to retreat 200 m over the next forty years, followed by an advance of 150 m lasting several centuries. Numerous experimental climate alterations show that the dam will not be threatened by short-term climatic changes. A long-term mass-balance increase of 0.12 m of ice per year (or a drop of 0.2°C in mean annual air temperature) would be sufficient to fill the reservoir with ice. With an additional increase of 0.07 m of ice per year the terminus would reach the dam. Data from the 1923 and 1850 moraines are used to suggest lower-bound estimates of temperature changes (-0.4 and -0.6°C respectively) during these periods of glacial maxima.
Properties of Debris-Laden Ice: Application to the Flow Response of the Glaciers on Mount St Helens
Authors: Brugman Melinda M.
Published: September 2017

Intense deformation within an extensive englacial debris layer appears to be a dominant flow mechanism for glaciers on Mount St Helens, Washington. Observations of this phenomenon have been made on Shoestring Glacier and more recently on other glaciers on the volcano. Transverse velocity profiles on Shoestring Glacier have shown a marked plug flow behavior occurring between narrow marginal zones of crevassing. Both longitudinal and transverse velocity profiles on Shoestring Glacier were measured during the year before and the two years after the cataclysmic eruption of the volcano on 18 May 1980.

The geometry and regime of every glacier on Mount St Helens dramatically changed during the eruption. The entire accumulation area of Shoestring Glacier was removed by a volcanic landslide and blast, and the glacier surface was deeply incised through the action of pyroclastic flows and mudflows. Surface velocity measurements were supplemented by vertical profiles taken along the newly exposed ice cliffs. Large velocity gradients seen in the transverse, longitudinal and vertical profiles coincided with the mapped location of a recently exposed englacial debris layer. Further detailed measurements on the vertical profiles show that the intense shear occurs by deformation internal to the debris layer, A study of the properties of debris-laden ice was undertaken to determine the mechanism for localization of deformation to the debris layer and for the associated response of the glacier to a sudden change in stress.
Trace Elements in Antarctic Air and Snowfall
Authors: Dick A.L. , Peel D.A.
Published: September 2017

Measurements of trace elements in snow and ice are frequently used to describe past atmospheric composition although there is no firm basis for assuming a direct connection. Trace-element concentrations have been measured on samples of aerosol and freshly fallen snow collected simultaneously from two sites in the Antarctic Peninsula during summer. Following improvements in contamination control, the reported concentrations and crustal enrichment factors of Cd, Cu, Pb and Zn in the aerosol are lower than any values previously reported from Antarctica. Even tighter controls will be required in the future.

For a crustal element (A1) and for the marine cations (Na, Ca and K) a consistent ratio (0.48±0.31) for the concentration in air (pg m−3)/concentration in snow (pg g−1) is obtained for simultaneously collected samples. This supports a simple model of aerosol scavenging proposed by Junge which considers aerosol removal over polar ice sheets to be dominated by in-cloud processes. Averaged data for Cd, Cu, Pb and Zn from samples collected at different times appear to behave similarly. These findings suggest that there is no preferential scavenging by snowfall of either crustal or heavy metal components in contemporary aerosol. If proved more general in Antarctica this may help to simplify the interpretation of time series data from ice cores.
Volcanic Ash Layers in Bare Ice Areas near the Yamato Mountains, Dronning Maud Land and the Allan Hills, Victoria Land, Antarctica
Authors: Nishio Fumihiko , Katsushima Takayoshi , Ohmae Hirokazu
Published: September 2017

Dirt layers of tephra were found on the bare ice surface in the Meteorite Ice Field near the Yamato Mountains, Dronning Maud Land, and near the Allan Hills, Victoria Land, Antarctica. The grain-size analyses of volcanic ash fragments show that the mean grain size in the Allan Hills region is larger than that in the Yamato Mountains region. This fact indicates that the volcanic sources of the dirt layers in the Yamato Mountains region are farther away than those in the Allan Hills. Their constituent fragments are well-sorted and composed mainly of volcanic glass shards with minor amounts of crystal fragments.

Glass shards of the tephra from the Yamato Mountains region have a composition of tholeiitic andesite which is low in alkali and high in iron but not so enriched in titanium, and the associated crystal fragments consist of calcic plagioclase, subcalcic clinopyroxene, orthopyroxene and magnetite. The nature of island arc tholeiite of the tephra indicates that its source is some volcano in the South Sandwich Islands.

On the other hand, the tephra from the Allan Hills region is composed of glass shards of trachybasaltic composition and crystal fragments of titanaugite calcic plagioclase, kaersutite, olivine, rhönite and titanomagnetite. A young volcano of the McMurdo volcanic group is suggested as a possible source of this tephra.
Particle Morphology, Composition and Associated Ice Chemistry of Tephra Layers in the Byrd Ice Core: Evidence for Hydrovolcanic Eruptions
Authors: Palais J.M.
Published: September 2017

In 1968 an ice core 2164 m long was recovered from Byrd station in West Antarctica. About 2000 tephra layers were observed in the core and have been differentiated into ash and dust bands according to the grain size and concentration of particles in the layers. Mount Takahe, a local volcano in Marie Byrd Land, Antarctica is the probable source.

Detailed examinations of the particle morphology, composition and ice chemistry associated with some of the tephra layers have led to the conclusion that the eruptions which produced the layers were probably hydrovolcanic. Melted glacier ice is considered the most likely source of the water involved in the eruptions.

Processes associated with hydrovolcanism such as particle aggregation (causing premature deposition of fine particles), rapid conversion of sulfur dioxide to sulfuric acid (in the presence of abundant moisture) and scavenging of acid droplets by the fine dust particles are inferred to have taken place. Such processes would greatly reduce the atmospheric residence time of the eruptive products and thus their atmospheric and climatic impact.
Sulphuric and Nitric Acid Concentrations and Spikes Along A 200 m Deep Ice Core at D 57 (Terre Adélie, Antarctica)
Authors: Zanolini Françoise , Delmas Robert J. , Legrand Michel
Published: September 2017

D 57 station in Terre Adélie lies between the coast and the central Antarctic plateau. A 200 m ice core was recovered in summer 1980–81 at this location and analyzed by an electroconductometric method to detect exceptional acid levels linked to fallout from major volcanic eruptions. Several signals were indeed found. The corresponding ice-core sections were then analyzed for mineral acids (H2SO4 and HNO3). We detected several large volcanic events, in particular two eruptions identified as Tarabora (1815) and Galunggung (1822). The background concentration of sulphate was found to be relatively low (about 0.5 μeq 1−1). On the other hand nitrate values were higher than at coastal or central Antarctic locations (except for the Sauth Pole). Two spikes were found in the nitrate profile at depths of 140 and 148 m. It is thought that they could be either linked to the 1604 and 1572 supernovae Kepler and Tycho or correspond to epochs of particularly high solar activities. With the aid of these sulphate and nitrate exceptional events, a dating of the D 57 ice core can now be proposed which corresponds to a mean snow accumulation rate of 22 cm of ice equivalent per year over the last four centuries.
Can High-Altitude Ice Masses in Temperate Areas Provide Useful Climatic Records?
Authors: Mayewski Paul A. , Lyons W. Berry
Published: September 2017

Since 1979 we have been conducting a program of glaciochemical sampling and analysis in selected portions of the Indian Himalayas. The primary purpose of this work has been the retrieval of data that are of specific use in assessing the signal expressed by the chemistry of air masses entering the Himalayas. The techniques used for this purpose provide data sets for the following: chloride, sodium, reactive iron, reactive silicate, reactive phosphate, nitrite-plus-nitrate, ammonium, pH, oxygen isotopes, deuterium, microparticles, total β-activity, density and scanning electron microscopy. The results of this work appear in a series of papers (Lyons and others 1981, Lyons and Mayewski 1983, Mayewski and others 1981, 1983, 1984 and Goss and others 1985). In summary this work demonstrates: (1) problems encountered in high-altitude ice-core recovery, (2) effects of percolation on chemical records, (3) specific requirements necessary for the retrieval of unaltered glaciochemical records from Himalayan glaciers, (4) potential spatial variability of chemical species concentrations and interpretation of this with respect to time series, (5) usefulness of various glaciochemical indicators as applied to relative dating (seasonality) and air mass tracking, (6) specific details of the chemical and physical properties in Himalayan ice, and (7) recommendations for future Himalayan ice-core studies.
Applications of Isotope Geochemistry to Research On Chinese Glaciers
Authors: Ping Wang
Published: September 2017

We report trace element, tritium, and hydrochemical analyses for glaciers in mountain regions of western China, based on about 200 samples collected between 1980 and 1983. Conclusions are drawn about the origin of water vapour contributing to precipitation (local or otherwise) and about the contributions to glacier run-off (meltwater or precipitation), based on the tritium measurements.