bluuebunny/crossref_metadata_2025 huggingface dataset:
Basal-flow characteristics of a linear medium sliding frictionless over small bedrock undulations
Authors: Gudmundsson G. Hilmar
Published: September 2017

The basal deformation of a gravity-driven linear creeping flow sliding frictionless over slowly varying bed undulations in two dimensions is analysed analytically, using results from second-order perturbation theory. One of the key results is that, close to sinusoidal bedrock undulations, up to two different spatial regions of local extrusion flow may arise. The offset and onset of extrusion flow is controlled primarily by the amplitude-to-wavelength ratio. Above the crest of a sinusoidal bed line, a local maximum of the surface-parallel velocity develops for ε : = ak < 0.138, where a is the amplitude and k is the wave number. As ε increases from zerо to this critical value, the vertical position of the velocity maximum moves from kz = 1 to kz ≈ 1.98, where z is the vertical distance above the mean bed line. Within and above the trough of a sinusoid, a region of local minimum of the surface-parallel velocity component develops, which shifts from kz = 1 towards the bed line as ε increases front zero to 1/2. Below this velocity minimum, and for some distance above the velocity maximum, the surface-parallel velocity increases with depth. This type of extrusion flow will cause a reversal of borehole-inclination profiles close to the bedrock.
Some comments on climatic reconstructions from ice cores drilled in areas of high melt
Authors: Koerner Roy M.
Published: September 2017

Poor consideration has been given in many Arctic circum-polar ice-core studies to the effect of summer snow melt on chemistry, stable-isotope concentrations and time-scales. Many of these corps are drilled close to the firn line where melt is intense. Some come from below the firn line where accumulation is solely in the form of super-imposed ice. In all cases, seasonal signals are reduced or removed and, in some, time gaps develop during periods of excessive melting which situate the drill site in the ablation zone. Consequently, cross correlations of assumed synchronous events among the cores are invalid, so that time-scales along the same cores differ between authors by factors of over 2. Many so-called climatic signals are imaginary rather than real. By reference to published analyses of cores from the superimposed ice zone on Devon Ice Cap (Koerner, 1970) and Meighen Ice Cap (Koerner and Paterson, 1974), it is shown how melt affects all the normally well-established ice-core proxies and leads to their misinterpretation. Despite these limitations, the cores can give valuable low-resolution records for all or part of the Holocene. They show that the thermal maximum in the circum-polar Arctic occurred in the early Holocene. This maximum, effected negative balances on all the ice caps and removed the smaller ones. Cooler conditions in the second half of the Holocene have caused the regrowth of these same ice caps.
Glaciological and oceanographic evidence of high melt rates beneath Pine Island Glacier, West Antarctica
Authors: Jenkins Adrian , Vaughan David G. , Jacobs Stanley S. , Hellmer Hartmut H. , Keys John R.
Published: September 2017

Satellite imagery indicates that the floating terminus of Pine Island Glacier has changed little in extent over the past two decades. Data on the velocity and thickness of the glacier reveal that calving of 28 ± 4 Gta−1 accounts for only half of the ice input near the grounding line. The apparently steady configuration implies that the remainder of the input is lost by basal melting at a mean rate of 12 ± 3 ma−1. Ocean circulation in Pine Island Bay transports +1°C waters beneath the glacier and temperatures recorded in melt-laden outflows show that heat loss from the ocean is consistent with the requirements of the calculated melt rate. The combination of iceberg calving and basal melting lies at the lower end of estimates for the total accumulation over the catchment basin, drawing into question previous estimates of a significantly positive mass budget for this part of the ice sheet.
On the surface energy budget of sea ice
Authors: Wendler Gerd , Adolphs Ute , Hauser Adrian , Moore Blake
Published: September 2017

The surface energy budget was investigated during a cruise through the pack ice in the Southern Ocean. The time of observation was close to mid-summer. Some of the more important findings were:

The mean albedo varied from 11 % for open water to 59% for 10/10 ice cover. Hourly values span the range from 6% (open water) to 76% (total ice cover).

The net heat flux into the ocean (B) was on average 109 W m−2, If this energy were used solely for melting of sea ice, 30 mm could be melted each day.

For low surface albedos (ice concentration below 7/10), the net radiation increased with decreasing cloudiness. However, the opposite was the case for a high surface albedo.

The last point shows the importance of clouds on the surface energy budget. Not only should their presence or absence be known but also the reflectivity of the underlying surface, as it might change the net radiation in opposite ways.
Simulation of the historical variations in length of Unterer Grindelwaldgletscher, Switzerland
Authors: Schmeits M. J. , Oerlemans J.
Published: September 2017

The historical length variations in Unterer Grindelwaldgletscher have been simulated by coupling a numerical mass-balance model to a dynamic ice-flow model. As forcing functions, we used (partly reconstructed) local climatic records, which were transformed by the mass-balance model into a mass-balance history. The ice-flow model then computes the length variations that have occurred over the course of time.

In a model run from AD 1530 to the present, with both seasonal temperature and precipitation variations as forcing functions, the observed maximum length of the glacier around AD 1860 and the subsequent retreat are simulated. The observed AD 1600 maximum, however, does not show up in the simulation. This is probably due to an incorrect reconstruction of the mass balance for this period, as detailed climatic data are available only since 1865. The root-mean-square difference between the simulated and the observed front positions is 0.28 km. The simulated glacier geometry for 1987 fits the observed geometry for that year reasonably well.

Because of the success of the historical simulation, an attempt is made to predict future glacier retreat on the basis of two different greenhouse-gas scenarios. For a Business-as-Usual scenario, only 29% of the 1990 volume would remain in AD 2100.
Modelling temperature variations in polar snow using DAISY
Authors: Morris Ε. M. , Bader H. -P. , Weilenmann P.
Published: September 2017

A physics-based snow model has been calibrated using data collected at Halley Bay, Antarctica, during the International Geophysical Year. Variations in snow temperature and density are well-simulated using values for the model parameters within the range reported from other polar field experiments. The effect of uncertainty in the parameter values on the accuracy of the predictions is no greater than the effect of instrumental error in the input data. Thus, this model can be used with parameters determined a priori rather than by optimization. The model has been validated using an independent data set from Halley Bay and then used to estimate 10 m temperatures on the Antarctic Peninsula plateau over the last half-century.
Crevasse Deformation and Examples from Ice Stream B, Antarctica
Authors: Vornberger P.L. , Whillans I.M.
Published: September 2017

Crevasses, once formed, are subject to rotation and bending according to the velocity field through which they travel. Because of this, crevasse shapes can be used to infer something about the velocity field of a glacier. This is done using a model in which each crevasse opens perpendicularly to the principal extensional strain-rate, when that strain-rate exceeds some specified critical value, and is then deformed according to the same velocity gradients that formed the crevasse. This model describes how crevasses are formed, translated, rotated, bent, and lengthened.

Velocity fields are sought for which calculations produce crevasses approximating those found in three example areas on Ice Stream B, Antarctica. The first example is the hook-shaped crevasses that occur just outside the chaotic shear zone at the ice-stream margin. They are used to infer a rate of lateral shearing, and side drag. The second example, a pattern of splaying crevasses, is satisfactorily simulated by a model with side-drag stress varying linearly across the ice stream. This confirms that this region is restrained almost entirely by side drag. The third example is transverse crevasses and their change in orientation, but many different velocity fields can produce the observed pattern. Of these three examples, the shapes of hook-shaped marginal crevasses and splaying crevasses can provide useful information whereas transverse crevasses are less helpful.
Thermal Response of a Small Ice Cap to Climatic Forcing
Authors: Hanson Brian
Published: September 2017

Two-dimensional finite-element calculations of velocity and temperature fields have been applied to the energy balance of a cross-section of Barnes Ice Cap, Baffin Island, Canada. The flow plane currently is cooling near the ice divide and warming near the margin. Long-term simulations show a net warming trend followed by a cooling trend with a steady-state average temperature similar to the present. Sensitivity studies on an idealized version of the flow plane show that the overall temperature responds less than surface-temperature forcing, because a negative feedback in temperature advection is substantially larger than a positive feed-back in strain heating. The response times of the flow plane by itself are somewhat faster but of the same magnitude as response times that would be estimated from one-dimensional modeling. When bedrock-temperature calculations are included, response times increase an order of magnitude, but these do not substantially affect the short-term response.
Subglacial Water Pressures and the Shape of Subglacial Conduits
Authors: Hooke Roger LeB. , Laumann Tron , Kohler Jack
Published: September 2017

Measured subglacial water pressures are frequently higher than theoretical values calculated by assuming that subglacial conduits are straight and either circular or semi-circular in shape. While this may be attributed to errors in the estimates of conduit roughness or ice viscosity, we suggest here an alternative explanation: namely, that the conduits are actually broad and low rather than semi-circular. Good agreement between measured and calculated pressures can be obtained by assuming that the cross-sectional shape of conduits resembles the space between the arc of a circle and its chord. The angle subtended by the arc, θ, is treated as an adjustable parameter. In four cases studied, θ ranged from 2° to 36°.
Instruments and Methods: A Digital Low-Frequency, Surface-Profiling Ice-Radar System
Authors: Wright David L. , Hodge Steven M. , Bradley Jerry A. , Grover Thomas P. , Jacobel Robert W.
Published: September 2017

A new short-pulse digital profiling radar system that operates at lower frequencies than most ice radars used in polar regions to date has been designed and built by the U.S. Geological Survey. The transmitter is an avalanche transistor pulser which drives a resistively loaded dipole transmitting antenna. A similar, but separate antenna is connected to the receiver. The receiver has adjustable sensitivity time control (STC) of as much as 60 dB to compensate for attenuation and geometric spreading factors. A fiber-optic cable is used to transmit both control signals and data. The data-acquisition and display system incorporates very high-speed digitizing and signal averaging, real-time profile display, and data storage on standard computer nine-track magnetic tape.

The system was successfully used on Ice Stream B in West Antarctica at centre frequencies of 1, 2, 4, 8, and 12.5 MHz. Bottom-return signal-to-noise ratios of more than 40 dB were obtained at 2 MHz through 800 m of ice. Convoluted internal surfaces not related to present bottom topography were resolved within the ice streams and anomalous strong reflections or “bright spots” were identified near the base of the ice. At present, there is no satisfactory glaciological explanation for either of these observations.
Creep Buckling of Ice Shelves and the Formation of Pressure Rollers
Authors: Collins I. F. , McCrae I. R.
Published: September 2017

Much of the surface of an ice shelf is covered with series of undulations. These undulations or “pressure rollers” are particularly noticeable in the neighbourhood of ice rises or ice streams. To date, there is no satisfactory theoretical model explaining the formation of these waves. As a contribution to understanding this phenomenon, this paper investigates the stability of ice shelves to perturbations in the background stress and strain-rate distributions.

The perturbation analysis is based on Glen’s creep law and leads to a continuous eigenvalue problem for the wavelength of the disturbance as a function of growth-rate. It is shown that, provided these strain-rates are sufficiently compressive, waves of the type observed can be expected to form. It is shown that lateral extensional strain-rates have a destabilizing effect and pressure rollers are more likely to form when these are present. Comparison of predicted wavelengths is made with available field data.
Dielectric Behaviour of Firn and Ice from the Antarctic Peninsula, Antarctica
Authors: Reynolds John M.
Published: September 2017

Dielectric experiments have been undertaken at temperatures between −2° and −70° C in the frequency range 10Hz to 100 kHz on 14 firn and ice samples retrieved from the Antarctic Peninsula. This investigation shows that the dielectric behaviour of polar samples from the Antarctic Peninsula is very similar to that of polar firn and ice from Greenland and from elsewhere in Antarctica. In contrast, temperate samples from the Antarctic Peninsula have relaxation times up to ten times shorter for a given temperature between –20° and –70°C, and have higher values of high-frequency conductivity than those of polar samples. Consequently, the thermal regime (temperate or polar) can be distinguished by the dielectric behaviour of the samples.

High-frequency conductivities of polycrystalline samples from the Antarctic Peninsula match the trends of published conductivity data for HF- and HCl-doped laboratory ice; higher conductivities are associated with coastal sites where greater concentrations of marine ions occur in snow.

Annealing polar firn above −10°C results in elevated conductivities across all frequencies measured and shortened relaxation times. Thus, samples for dielectric analysis should not be warmed to above –10°C for risk of irreversibly altering their dielectric behaviour.
A History of Jökulhlaups from Strandline Lake, Alaska, U.S.A.
Authors: Sturm Matthew , Benson Carl S.
Published: September 2017

Jökulhlaups, also known as outburst floods, have occurred every 1 to 5 years from Strandline Lake, one of the largest glacier-dammed lakes in North America. The development of a distinct calving embayment in the lobe of Triumvirate Glacier which dams the lake, as well as the filling of a number of supraglacier pools, appear to be reliable precursors to a jökulhlaup. Analysis of contour maps made from photographs taken immediately before and after the jökulhlaup of 17 September 1982 indicate that over 95% of the lake drains, a volume of approximately 7 × 108m3of water. The glacier lobe which dams the lake fractures and subsides during a jökulhlaup, indicating that the release mechanism is hydrostatic lifting of the ice off of a sub-glacial spillway. Evidence from the ice-free margins of the glacier suggests that the spillway may be controlled by bedrock. Large variation in the refilling period of Strandline Lake indicates that the subglacial drainage tunnels can remain open for as much as a few years after a jökulhlaup, before they become sealed by sediments and/or glacier ice.
Seasonal Surface-Velocity Variations on a Sub-Polar Glacier in West Greenland
Authors: Andreasen Jørn-Ole
Published: September 2017

Eight stakes situated in the ablation and the accumulation areas of a sub-polar glacier in West Greenland were surveyed at intervals of 10 days during the summers of 1982 and 1983, The horizontal velocity in both the ablation and the accumulation areas increased distinctly during the short summer season. This indicates that melt water reaches the bed and that the glacier is sliding. It is proposed that melt water produced in the ablation area is forced up-glacier through a subglacial water system. The vertical displacement of stakes showed variations indicating an apparent uplift of the glacier during the summer. However, this is interpreted as the result of seasonal variation in atmospheric refraction.
Mass–Balance and Ice–Flow–Law Parameters for East Antarctica
Authors: Hamley T.C , Smith I.N. , Young N.W.
Published: September 2017

A comprehensive set of ice-velocity and thickness data from traverses within the IAGP study area (bounded by long. 90°E. and 135°E., and north of lat. 80°S.) is compared with steady-state mass-flux calculations based on Scott Polar Research Institute (SPRI) map compilations.

The results of previous regional mass-budget estimates are reviewed and followed by a description of the new field measurements and the basis upon which a computer “grid–point” program is used to calculate balance fluxes.

A comparison of measured and balance fluxes indicates that the ice sheet in this region of East Antarctica is unlikely to be significantly out of balance.

The ratio of average column to surface velocity is discussed and calculated to be 0.89.

An analysis of the mean shear strain-rate (VS/Z), versus down-slope basal shear stress (τb = ρgᾱZ), suggests that power flow-law parameters of n = 3.21 and k = 0.023 bar−n m−1 are appropriate for the effective basal shear zone in this region of the Antarctic ice sheet.
Studies On Crescentic Fractures and Crescentic Gouges with the Help of Close-range Photogrammetry
Authors: Wintges Theodor
Published: September 2017

Studies on cresceatic fractures and crescentic gouges were carried out in the central part of the Alpine piedmont glaciation and the Quaternary Alpine mountain ice sheet. The test sites were situated in the pro-glacial area of the Hornkees south Berliner Hütte (Oberer Zemmgrund, Zillertal, Tyrol, Austria). This is also the area of the former confluence with another glacier which flowed at about 90° to Hornkees during the late-glacial period. It was therefore possible to make a comparison between different older glacier systems, different flow directions, and different ice thicknesses. About 12 000 minor features were measured by close-range photogrammetry; the result was 240 pairs of stereophotographs which were interpreted on first-order equipment. The single forms were registered point by point by coordinates. It was therefore possible to obtain three-dimensionally registered forms. One important result was that the late-glacial and the post-glacial glaciers of the Zemmgrund produced minor features with a large variation in size. A further result was the definition of possible glacier-flow directions by interpretation of the different directions of crescentic fractures and crescentic gouges. By this means it was possible to obtain several working reconstructions of the late- and post-glacial stream lines of the merged glaciers.
Ice-Core Drilling at 5700 m Powered by a Solar Voltaic Array
Authors: Koci Bruce R.
Published: September 2017

During the summer of 1983 a 2 kW array of solar voltaic panels was used to power a drill which collected two cores of 154 m and 163 m length to bedrock on the Quelccaya ice cap in Peru. The operation and performance of this array are discussed, considering the need for future requirements in remote pristine areas of the world.
A System for Mounting End Caps on Ice Specimens
Authors: Cole D. M. , Gould L. D. , Burch W. B.
Published: September 2017

This short note describes the equipment and procedures we have developed to mount end caps on ice-core specimens. The system typically achieves end-plane parallelism within 0.5 μm/mm of specimen diameter (i.e. a total indicator run-out of 0.002 in for a 4.0 in diameter specimen). The essential elements of the system are a holder and an alignment fixture. The holder firmly grips the ice core about its circumference by the compression of two series of O–rings. The alignment fixture clamps the holder to align the ice core precisely with the end caps. To bond the ice to the end cap we form a layer of 0°C water on the end cap; the water freezes immediately upon contact with the ice and forms a strong intimate bond. To date, we have used this system to install phenolic end caps on 101.6 mm diameter cores and aluminum end caps on 76.2 mm diameter cores of saline ice. We obtained a somewhat better tolerance with the aluminum caps (0.33 μm/mm of end-cap diameter), due primarily to the geometric stability of that material under the prevailing conditions. These specimens have been successfully tested in uniaxial and triaxial compression, and we expect that with appropriate end caps the system will be suitable for preparing tension specimens as well.
Isotope Ratios of Large Ice Masses
Authors: Jones A.S.
Published: September 2017

A model is proposed for determining the relative proportions of 16O and 18O in large ice sheets. Values calculated using this model are in agreement with published values for Antarctica and Greenland. It is intended to use the model for comparisons between the known ocean isotopie records and postulated ice-sheet masses during the last ice age.
Decay of a High Arctic lake-ice cover: observations and modelling
Authors: Heron Richard , Woo Ming-Ko
Published: September 2017

The decay of a lake-ice cover in the Canadian High Arctic was studied for 2 years. Melt at the upper surface accounted for 75% of the decrease in ice thickness, while 25% occurred at the ice–water interface. An energy-balance model, incorporating density reduction due to internal ice melt, was used to simulate the decay of the ice cover. The overall performance of the model was satisfactory despite periods when computed results differed from the observed ice decay. Energy-balance calculations indicated that the absorption of shortwave radiation within the ice provided 52% of the melt energy while 33 and 15% came from the surface-energy balance and heat flux from the water.
Growth rates of icicles
Authors: Maeno N. , Makkonen L. , Nishimura K. , Kosugi K. , Takahashi T.
Published: September 2017

Experimental and theoretical studies on the growth rate of an icicle were carried out as a function of temperature, water-supply rate and wind speed; the relative humidity was also taken into account. The length of an icicle increases by the downward growth of thin dendritic crystals into the supercooled pendant water drop at the tip, and thus the growth is in the crystallographic a-axis direction. The diameter, on the other hand, increases by the freezing of a water film flowing down along the icicle wall. The ratio of measured length-and diameter-growth rates was large, namely 8–32.

Both growth rates increased with decreasing temperature and increasing wind speed. The increase in water-supply rate led to the decrease in the length-growth rate but no significant change in the diameter-growth rate. These results could be well described by a numerical model of icicle growth which takes account of the dendritic growth at the tip and the wall and the effective heat transfer within the turbulent boundary layer around the icicle. A formation mechanism of ribs and hollows is discussed in relation to the flowing and freezing process of water on an icicle wall.
Textural characteristics and impurity content of meteoric and marine ice in the Ronne Ice Shelf, Antarctica
Authors: Eicken Hajo , Oerter Hans , Miller Heinz , Graf Wolfgang , Kipfstuhl Josef
Published: September 2017

The texture and physical properties of an ice core, recovered to 215 m depth from the Ronne Ice Shelf, Antarctica, have been studied with regard to formation and transformation of the ice. At a depth of 152.8 m, a sharp discontinuity marks the transition between meteoric ice accumulated from above and marine ice accreted from below, as testified by electrolytical conductivity and stable-isotope measurements as well as geophysical field surveys. Automated image analysis of thin sections indicates that the decrease in grain-boundary density and the increase in grain cross-sectional area with depth is commensurate with though not necessarily caused by thermodynamically driven grain growth down to 120 m depth, corresponding to a vertical strain of roughly 65% as computed with a simple temperature-history, particle-path model. The observed increase of grain-boundary density (i.e. a decrease of grain-size) with age in the marine ice is in part explained by the thermal history of this layer. Sediment inclusions at the top of the marine-ice layer affect the observed grain-boundary density profile by inhibiting grain growth and dynamic recrystallization. This may allow some conclusions on the role of temperature, particulate inclusions, stress and strain rate in controlling the grain-size evolution of deforming ice, supplementing earlier laboratory experiments conducted at much shorter time-scales. Salinities (0.026%), brine volumes (0.09–0.2%) and solid-salt concentrations have been computed from electrolytical conductivity measurements (mean of 51.0 × 10−6 S cm−1) for the marine ice. An assessment of salt incorporation and desalination rates shows that these low salinities can at present only be explained by a unique densification mechanism of under-water ice crystals at the base of the ice shelf.
Radio Echo-Sounding of Spitsbergen Glaciers: Problems in the Interpretation of Layer and Bottom Returns
Authors: Dowdeswell J. A. , Drewry D.J. , Liestøl O. , Orheim O.
Published: September 2017

Airborne radio echo-sounding of Spitsbergen glaciers during 1980 used 60 MHz SPR1 Mk IV equipment. On several glaciers results showed unambiguous bottom returns at depths 2–3 times those reported in previous Soviet echo-sounding at 440 and 620 MHz. Comparison of 60 MHZ records and independent gravity-surveyed ice thickness for two glaciers agreed to within 10%, whereas Soviet ice thicknesses were only 30–60% of gravity depths. Soviet bed echoes often coincided closely with an internal reflecting horizon recorded by the SPRI Mk IV system, and it is shown that Soviet U.H.F. equipment failed to penetrate to the true glacier bed on a number of ice masses (e.g. Finsterwalderbreen, Kongsvegen, Negribreen). This was probably due to increased absorption and scattering at higher radio frequencies, related to the inhomogeneous nature of Spitsbergen glaciers, which are often at or near the pressure-melting point. Both 60 MHz and U.H.F. equipment seldom recorded bed echoes in ice-cap accumulation areas (e.g. Isachsenfonna), where firn soaking during summer and 10 m temperatures of zero degrees have been observed. An isolated internal reflecting horizon was recorded on many glaciers. It is unlikely to be a moraine layer, but may be related to ice with a water content of 1–2% observed at a similar depth (115 m) in a drill core from Fridtjovbreen.
Solute Acquisition in Glacial Melt Waters. I. Fjallsjökull (South-East Iceland): Bulk Melt Waters with Closed-System Characteristics
Authors: Raiswell R. , Thomas A.G.
Published: September 2017

Variations in dissolved cations, total alkalinity, sulphate, and field pH are recorded for samples of precipitation, supraglacial melt, and bulk melt waters (those emerging at the portal) from Fjallsjökull (south-east Iceland). The composition of supraglacial melt indicates derivation from precipitation by the acquisition of solutes from the weathering and dissolution of rock debris, in a system open to atmospheric carbon dioxide. Bulk melt waters have variable compositions, approaching saturation with calcite, which can be derived from supraglacial melt water by continued solute acquisition in a system closed to atmospheric carbon dioxide. Solute–discharge relationships suggest that chemical evolution of the bulk melt waters occurs when aggressive englacial waters are mixed with the solute and sediment-rich subglacial component. Simple mixing behaviour occurs over intermediate discharges as long as variations in the extent of post-mixing evolution are small compared to changes in the mixing ratio.
A Model for Pollutant Concentrations During Snow-Melt
Authors: Hibberd S.
Published: September 2017

In recent years extensive measurements of pollutant concentrations within the environment have been made over Western Europe following reports of unusually high pollution levels within rivers and lakes, especially after the start of the spring melting period. A simple model is presented to describe theoretically the pollutant efflux within the first fractions of melt water released from a snow-pack at the start of the melting season. The dominant features included are the appearance of a wave-front as heading the unsaturated flow of melt water and the pollutant dispersion arising from the interaction of the flow with the porous structure of the snow-pack and molecular diffusion. Computed results are shown describing the evolution of pollutant concentration profiles in the first run-off stage from a snow-pack subjected to an applied uniform surface heating.
Experiments in the Machining of Ice at Negative Rake Angles
Authors: Lieu D.K. , Mote C.D.
Published: September 2017

The cutting force components and the cutting moment on the cutting tool were measured during the orthogonal machining of ice with cutting tools inclined at negative rake angles. The variables included the cutting depth (< 1 mm), the cutting speed (0.01 ms−1 to 1 ms−1), and the rake angles (–15° to –60°). Results of the experiments showed that the cutting force components were approximately independent of cutting speed. The resultant cutting force on the tool was in a direction approximately normal to the cutting face of the tool. The magnitude of the resultant force increased with the negative rake angle. Photographs of ice-chip formation revealed continuous and segmented chips at different cutting depths.
Morphology, Stratigraphy, and Genesis of Small Drumlins in Front of the Glacier Mýrdalsjökull, South Iceland
Authors: Krüger Johannes , Thomsen Henrik Højmark
Published: September 2017

Investigations have been made of the geomorphology, internal structure, and till fabric of small drumlins in a drumlin field exposed in front of the retreating northern part of Mýrdalsjökull, Iceland. The drumlins either comprise irregular drumlin complexes or they show clearly the shape of typical drumlins with their highest points at the up-glacier ends of streamlined hills.

The core of each drumlin consists either of undisturbed glacio-fluvial deposits or glacio-dynamically deformed drift. The distribution of the first type often has a characteristicen échelonarrangement, similar to the interstream areas in the upper reaches of outwash fans. The second type forms a pattern with a predominant trend conforming to the glacier margin; this type is superimposed on overridden ice-margin push-moraine ridges. It is shown that the material in the drumlin cores is only slightly eroded by the glacier that formed the drumlins. The core is mantled by subglacial lodgement till about 0.1–1.5 m in thickness.

Seventeen fabric analyses of 25 clasts each were performed on material from within the till mantle. These analyses show a preferred long-axis orientation but indicate a considerable between-site variability ranging up to 45° even between samples taken a few metres apart. The preferred clast orientation for samples taken along the drumlin crests only deviates 0–10° from the regional ice-flow direction indicated by fluted moraines, whereas the deviation for samples from the flanks and the stoss-sides is up to 35°. However, the fabrics show a characteristic pattern relative to the shape of the drumlin; on their tops, the clast fabric parallels the ice-flow direction, whereas it tends to follow the contour direction on the flanks and stoss-sides.

It is concluded that the cores of the drumlins consist of pre-existing deposits, whereas the mantles are composed of subglacial till. Regarding the processes involved, the material contained in the core is mainly eroded by pro-glacial melt-water streams and not by ice. During the subsequent flow of ice across the area, the most prominent terrain elements have acted as subglacial obstacles, leading to localized till deposition and drumlin formation. Thus, the drumlins were formed mainly by subglacial deposition of till but the obstacles acted as an essential factor favouring their initiation.
Experiments Relating to the Fracture of Bedrock at the Ice-Rock Interface
Authors: Smith Jennifer M.
Published: September 2017

MacClintock (1953) has suggested that arcuate features formed on glass by the impression of steel ball bearings may be analogous to crescentic gouges observed on formerly glaciated rock surfaces. He noted that cracks, convex in the direction of movement, are formed as bearings roll over a glass surface but not as they slide over it. MacClintock therefore proposed that the similarly orientated crescentic gouges may owe their origin to abrading clasts rolling along a glacier bed. This note describes simple experiments designed to test this view by generating friction cracks artificially. Cracks convex and concave in the direction of movement were produced by a non-rolling bearing — a result apparently incompatible with MacClintock’s proposal. It is suggested that the orientation of such cracks is less dependent on bearing rotation and more the result of pressure variation. Cracks analogous to crescentic gouges may form as a result of unloading.
Application of a Flow Model to the Ice-divide Region of Devon Island Ice Cap, Canada
Authors: Reeh N. , Paterson W.S.B.
Published: September 2017

The steady-state flow model of Reeh (1988) is applied to a flow line that starts at the highest point of the Devon Island ice cap, follows the surface crest for 7.6 km, and then runs down the slope for a further 3.7 km. The effects of bedrock undulations, divergence of the flow lines, the variation of temperature with depth, and a basal layer of “soft” ice-age ice are taken into account. A flow law with n = 3 and a value of A close to that of Paterson (1981) is used. Longitudinal stress variations are neglected so that shear stress is calculated by the usual formula. It is estimated that these calculated values may be in error by at most 30%. Depth profiles of effective shear stress, and of the components of velocity and normal strain-rate, are presented at selected points along the flow line. These illustrate the large variations that occur near an ice divide and over bedrock undulations of amplitude comparable with the mean ice thickness. The model gives good predictions of the surface profile and of longitudinal and transverse surface strain-rates measured at ten points along the flow line. Predicted depth profiles of horizontal and vertical velocity components are compared with those measured in a bore hole. Comparison is limited by the fact that the model works in ice equivalent, whereas about 20% of the ice column consists of firn with different rheological properties from ice. The vertical velocity prediction is good. However, the model does not reproduce well the shape of the horizontal velocity profile, although measured and calculated fluxes differ only slightly. Predicted annual-layer thicknesses are within 15% of the measured ones in the upper half of the ice column, which consists of ice deposited in the last 1000 years. Predicted thicknesses in older ice are too small and the discrepancy increases with depth. This might indicate increased precipitation or, more likely, a thinner ice cap in the climatic optimum. However, it could also result from the fact that the layer of “soft” ice has been thinning continuously since the end of the ice age, so that the ice cap has never been in a steady state.
Localized Basal Freezing Within George VI Ice Shelf, Antarctica
Authors: Pedley M. , Paren J.G. , Potter J.R.
Published: September 2017

Hobbs Pool is an area of thin ice shelf situated within George VI Ice Shelf, Antarctica. Thicker ice shelf surrounding Hobbs Pool isolates the upper 155 m of the water column from water lying at the same depth else-where under the ice shelf. Summer melt-water lakes drain through crevasses at Hobbs Pool forming a 155 m thick layer of low-salinity water close to its freezing point. Colder and more saline water in the lower part of this layer leads to in-situ freezing of fresher water lying above it. Below 155 m depth, the water temperature and salinity are linearly related by basal melting which is observed elsewhere under the ice shelf. The surface ice shows areas of deformation and deposits of subglacial rock debris which may result from upward particle paths in the area. The raising of subglacial rock debris on to the ice surface may provide a mechanism for the transport of erratics across the ice shelf to Alexander Island from the base of Palmer Land glaciers.
Drainage of the Austre Okstindbreen Ice-dammed Lake, Okstindan, Norway
Authors: Knudsen N. Tvis , Theakstone Wilfred H.
Published: September 2017

Observations of the discharge, electrical conductivity, cationic content, and isotopic composition of glacier-river water indicate that drainage of the lake dammed at the margin of the glacier Austre Okstindbreen, Okstindan, Norway, is preceded by disruption of the glacier’s drainage system(s). Annual studies over a period of 12 years have demonstrated that intense storm precipitation, changes of ablation conditions, and the stage of development of drainage systems all may play a role in triggering drainage of the ice-dammed lake. Water temperature may influence the course of the outburst. The lake has drained on at least ten occasions in the last 12 years. Three of the events (1979, 1985, and 1986) occurred early in the summer, whilst melting of the winter’s snow cover was contributing substantially to glacier-river discharge: high basal water pressure and rapid sliding may have facilitated disruption of drainage conditions within the glacier. In 1982, the lake drained during a severe storm, in 1977 and 1984 shortly after a period of heavy rainfall. During the 1977 and 1984 events, water under pressure burst up through the glacier surface. The lake basin remained partly filled throughout one summer (1980): in-flow of water was balanced by out-flow into the glacier.
Seismic Evidence for a Weak Basal Layer During The 1982 Surge of Variegated Glacier, Alaska, U.S.A
Authors: Richards Mark A.
Published: September 2017

Wide-angle seismic reflections from a glacier bed are sensitive to the presence of subglacial water and to the mechanical strength of the basal zone. The phase of a compressional to shear (P-SV) converted wave is particularly sensitive to the shear coupling between the glacier and its bed. Both shear (SV) and compressional (P) reflections from the bottom of Variegated Glacier were obtained before the 1982–83 surge event using explosive sources, and the phases of these reflections (relative to the source) were positive as expected for an ice/bedrock interface. During surge, P-wave reflections from the deepest part of the glacier bed were phase reversed, while somewhat shallower P-wave reflections were not. SV reflections were not clearly observed during surge and cannot be interpreted with confidence, even though the experiments were designed to detect them using three-component geophones. The unexpected P-wave phase reversal might be explained by a thin, mechanically weak or fluidized basal debris layer during surge which acts as a strong seismic absorber and suppresses multiple reflections within the layer. However, the required amount of seismic attentuation in the layer seems unreasonably large. An alternative explanation requiring ∼4–8 m or more of water or water-saturated debris (without strong attenuation) is implausible.
Ice-shelf Response to Ice-stream Discharge Fluctuations: I. Unconfined Ice Tongues
Authors: MacAyeal Douglas R. , Barcilon Victor
Published: September 2017

Ice-stream discharge fluctuations constitute an independent means of forcing unsteady ice-shelf behavior, and their effect must be distinguished from those of oceanic and atmospheric climate to understand ice-shelf change. In addition, ice-stream-generated thickness anomalies may constitute a primary trigger of ice-rise formation in the absence of major sea-level fluctuations. Such triggering may maintain the current ice-rise population that, in turn, contributes to long-term ice-sheet stability. Here, we show that ice-stream-generated fluctuations of an ideal, two-dimensional ice shelf propagate along two characteristic trajectories. One trajectory permits instantaneous transmission of grounding-line velocity changes to all points down-stream. The other trajectory represents slow transmission of grounding-line thickness changes along Lagrangian particle paths.
Ice Flow and Mass Changes of Lewis Glacier, Mount Kenya, East Africa: Observations 1974–86, Modelling, and Predictions to the Year 2000 AD
Authors: Hastenrath Stefan
Published: September 2017

The study is based on an observation program since 1974, including the continuous monitoring of net balance during 1978–86. The 8 year vertical net-balance profile, characterized by negative values throughout and an increase of absolute amounts from the higher towards the lower elevations, defines the recent climatic forcing.

A model is developed with a spatial resolution by 100 m wide bands, relating glacier morphology, ice flow, and mass economy, using as input ice thickness, surface slope, width of height contours, area of 100 m wide bands, volume flux, and net balance as a function of elevation. In 1 year time steps, the model calculates the changes in ice thickness and surface topography commensurate with the difference between net balance and longitudinal divergence of volume flux, and then the corresponding changes in surface slope, contour width, area of 100 m wide bands, volume flux, and net balance corresponding to the new surface elevations. This information serves as input for the next time step.

The model was applied to the intervals 1974–78, 1978–82, and 1982–86, as training periods, to explore the diagnostics of ice flow and mass economy, and to ascertain the model performance in treating long-term evolution in glacier behavior. The experiments yielded a reasonable agreement between calculated and observed changes in ice thickness, velocity, and volume flux, over the three aforementioned 4 year periods of field monitoring. Two sets of prediction experiments beyond 1986 were then undertaken. The first used as input the observed 1978–86 vertical net-balance profile (a), and thus simulated the future evolution of the glacier given continuation of the recent climatic forcing. In the second set of experiments, the 1978–86 net-balance values were doubled to yield a more extreme net-balance profile (b), representing climatic conditions considerably more adverse to the maintenance of the glacier.

Predictions are presented for the epochs 1990, 1994, 1998, and 2000. Given continuation of the recent climatic conditions (profile a), the following changes are anticipated from 1986 to the year 2000: a shrinkage of the volume from 4 to 1 x 106 m3; an area decrease from 25 to 17 χ 104 m2; a shortening of the glacier from 990 to less than 800 m; a slow-down of fastest ice flow from 2.5 to less than 1ma−1; a decrease of the maximum volume flux from 13 to less than 3 χ 103 m3 a−1; and substantial up-glacier displacements of the velocity and volume-flux maxima. Under more extreme negative net-balance conditions (profile b), the decay would be so greatly accelerated that Lewis Glacier may completely disappear well before the end of the millennium. This prospect is inherent in a possible change from recent climatic conditions.
Morphology and Dynamics of Ice Rises
Authors: Martin P. J. , Sanderson T. J. O.
Published: September 2017

Profile surveys are presented of four ice rises on the east coast of the Antarctic Peninsula. On Butler Island velocity measurements were also made. The ice rises behave as miniature ice caps frozen to flat horizontal bedrock and provide a simple system for the study of laws of ice flow. Deformation is principally by shear through the ice mass. Velocity measurements provide a value of n = 3.13±0.52 for the flow law . Each ice rise is bounded on one side by ice shelf and on the other side by open sea. Towards open sea the profiles are found to agree well with steady-state theoretical profiles and they supply a value of for temperature – 13.5°C and stress range 0.5–1.3 bar. Towards ice shelf the profiles are elongated and they deviate from the theoretical profile. This may be due to compressive stress in the ice shelf causing migration of the grounding line down sloping bedrock. No significantly anomalous behaviour is found in the summit region.
The Creep of Ice, Geothermal Heat Flow, and Roosevelt Island, Antarctica
Authors: Thomas Robert H. , MacAyeal Douglas R. , Bentley Charles R. , Clapp James L.
Published: September 2017

Measurements of ice velocity, thickness, and surface topography on the large ice rise known as Roosevelt Island are consistent with Glen’s flow law, , for values of τ between 5 × 104 N m–2 and 1.4 × 105 N m–2, and there is no indication of a reduction in n at low stresses. If n = 3 there must be progressive softening of the ice towards the edge of the ice rise, and this probably represents the combined effects of warming and recrystallization leading to a fabric favoring shear. Assuming that near the centre of the ice rise, where the effects of recrystallization are probably negligible, the ice behaves in the same way as randomly-oriented polycrystalline ice, then the geothermal flux G in this area is approximately 0.06 W m–2. In the absence of measurements of deep-ice temperatures, the distribution of G across the ice rise cannot be determined. However, the simplest interpretation of the movement data requires:

(1)

a linear increase in G from 0.05 W m–2 on the north-east side of Roosevelt Island to 0.07 W m–2 in the south-west, and

(2)

strain-rate enhancement, due to recrystallization, that increases outward from the centre of the ice rise to reach a maximum value of approximately two near the edges.

The calculated values of G are larger than the world average, but this is consistent with the probably granitic core beneath Roosevelt Island. An increase in G of 0.02 W m–2 in a distance of 60 km would require an increase in granite thickness of about 5 km.
Glaciological Investigations of the Tropical Quelccaya Ice Cap, Peru
Authors: Thompson Lonnie G.
Published: September 2017

Glaciological results of the continuing investigations of the Quelccaya ice cap located at lat. 13° 56’ S., long. 70° 50’ W., in the Cordillera Oriental of southern Peru are presented. Ice cores to a depth of 15 m have been retrieved from the summit dome (5650 m), middle dome (5543 m), and south dome (5480 m) and sampled in detail for microparticle, oxygen-isotope, and total-β-activity measurements. Results of these core analyses indicate that although the summit of this ice cap is only 300 m above the annual snow line and the firn is temperate, an interpretable stratigraphic record is preserved. The marked seasonal ice stratigraphy is produced by the marked seasonal variation in regional precipitation. High concentrations of microparticles and β- radioactive material occur during the dry season (May-August). Microparticles deposited during the rainy season are larger than those deposited during the dry season. On the Quelccaya ice cap the most negative δ18O values occur during the warmer rainy season (the opposite occurs in polar regions). The near-surface mean δ value of – 21‰ is remarkably low for this tropical site where the measured mean annual air temperature is – 3°C The seasonality of the microparticles, total β activity, and isotope ratios offers the prospect of a climatic ice-core record from this tropical ice cap.