bluuebunny/crossref_metadata_2025 huggingface dataset:
The dramatic retreat of Mount Kenya’s glaciers between 1963 and 1987: greenhouse forcing
Authors: Hastenrath Stefan , Kruss Phillip D.
Published: September 2017

The retreat of the glaciers on Mount Kenya is quantitatively well documented for the intervals 1899–1963 and 1963–1987. The ice recession between 1899 and 1963 was strongly dependent on solar radiation geometry. By contrast, the ice thinning between 1963 and 1987 amounted to about 15 m for all glaciers regardless of topographic location. This suggests that climatic forcings other than solar radiation have become more prominent.

Sensitivity analyses indicate that the energy supply of about 5 W m−2, required to produce the observed ice thinning through melting, can be accounted for by a combination of climatic forcings. The direct effect of changing atmospheric composition (“greenhouse effect”) on the net longwave radiation could have contributed less than 1 W m−2. A warming of 0.0 to 0.2°C would translate into an additional downward-directed sensible heat transfer of 0.0 to 1.4 W m−2. A 0.1 to 0.2 g kg−1 increase in specific humidity would, through savings in the latent heat transfer, contribute 2 to 4 W m−2.

Long-term station records show little warming trend for East Africa itself. However, mid-tropospheric specific humidity trends of about 0.6 g kg−1 over the past two decades in the equatorial belt have been reported in the literature, and considered to be consequences of “global warming” and the “greenhouse effect”.

Viewed in perspective, the ice wastage on Mount Kenya between 1963 and 1987 appears to have been driven primarily by three climatic forcings, conceivably all steered by the “greenhouse effect”: a direct forcing through the net longwave radiation; an indirect forcing through warming and therefore enhanced sensible heat transfer; and another indirect forcing through warming (not necessarily in the region itself), leading to increased (advected) atmospheric moisture, and hence to reduced latent heat transfer, this last line of control being the most important.
Glacier lake outburst flood disasters in China
Authors: Yongjian Ding , Jingshi Liu
Published: September 2017

Floods caused by outbursts from lakes dammed either by end moraines or by glaciers are the most important disasters related to glaciers in China. The former occur mainly in Tibet, and the latter in Xinjiang Province. Exceptionally large outbursts from lakes dammed by end moraines have been reported 19 times since 1935 amd 30 outbursts from glacier-dammed lakes have been recorded since 1956. Outbursts from lakes dammed by end moraines are closely associated with ice avalanches, and 79% of all dam failures occur during July to August when ice avalanches are frequent. Outbursts from glacier-dammed lakes often occur in years of very high air temperature, and 63.3% of all failures are between August and September when the storage capacities of glacier lakes reach their limit. Whether or not the end moraine-dammed lakes are of potential danger depends on the flow of the glacier that feeds the lake and the vertical distance between the terminus of the glacier and the level of the lake. The frequency of periods of outbursts from glacier-dammed lakes corresponds to the periods of glacier advance. During the last 160 years, three periods of frequent outbursts from glacier-dammed lakes have occurred. Their duration has been 20 to 30 years and the interval between them about 40 years. The frequency of glacier lake outbursts could increase early in the next century if glaciers advance and dam up new marginal lakes in response to a cold period since 1940.
Trends and features of climatic changes in the past 5000 years recorded by the Dunde ice core
Authors: Tandong Yao , Thompson L. G.
Published: September 2017

Α δ18O record from Dunde Ice Cap, located in the Qilian mountains on the northeastern margin of the Tibetan Plateau, has been analyzed and interpreted. With an ice temperature of –7.3°C at a depth of 10 m and –4.7°C at the bottom of the ice cap, and an accumulation rate of 400 mm a−1, the Dunde core has provided interesting results. The upper part of this core, core D-l, can be easily dated by a combination of δ18O, microparticle concentration and conductivity. It can also be dated as far back as 4550 BP by counting dust layers in ice. Based on the time scale established by the above methods and on the δ18O–temperature relation, the δ18O fluctuations in the upper 120 m of the core can be interpreted as mainly due to climatic changes during the past ~ 5000 years. The warmest periods in the past ~ 5000 years in the core were found to be centered on the present, 3000, and 4100 BP, and the colder periods center around 500, 1200, 4000, and 4500 BP. It is clear from the ice-core record that the Little Ice Age was only one of many cold periods in the past, although it was the coldest period in the past 500 years.
Factors delaying spring runoff in the upper Ürümqi River basin, China
Authors: Kattelmann Richard , Daqing Yang
Published: September 2017

Although less than 100 mm of precipitation generally falls during the winter months in the upper Ürümqi River basin, an uneven snowpack of 20 to 100 cm depth is present in early spring. When the surface of this snow cover begins to melt in April, the meltwater is not immediately transformed into streamflow. Several processes are responsible for the five to 15 days of delay in streamflow generation: refreezing in the snow cover itself, creation of a basal ice layer at the snow-soil interface, growth of superimposed ice on the glaciers of the basin, ice formation in stream channels and restoration of high albedo by snowstorms that occur about once a week in spring.
Sources and spatial variation of the chemical composition of snow in the Tien Shan, China
Authors: Williams Mark W. , Tonnessen Kathy A. , Melack John M. , Daqing Yang
Published: September 2017

Research on the sources and spatial variation of the chemical content of snow was conducted in four headwater basins of the eastern Tien Shan, China. The mean SO42- concentration of 16.2 μeq L-1 was three-fold greater than background concentrations from other remote areas of the world. About 80% of the SO42- in snow was deposited in association with Ca2+ and Mg2+ , partially accounting for the relatively high pH of 6.34 in new snow. The variance of individualions in the snowpack ranged from 24 to 46%, measured as the standard deviation divided by the mean and based on 59 samples. Analysis of variance tests showed that solute concentrations varied significantly among sites within an individual basin and that the mean solute concentrations did not vary significantly among basins. Aeolian dust in the snowpack resulted in significant post-depositional alterations in the solute content of snow. Mineral weathering of the dust in the snowpack of the Tien Shan mproduced alkalinity and Ca2+, increasing conductance and buffering H+ .
Flood generation and destruction of “Drift” Glacier by the 1989–90 eruption of Redoubt Volcano, Alaska
Authors: Trabant D. C. , Meyer D. F.
Published: September 2017

Mid -winter flooding of the Drift River was caused by melting of snow and glacier ice during the 1989–90 eruption of Redoubt Volcano. “Drift” Glacier (unofficial name) was beheaded when 110 to 120 × 106 m3 of perennial snow and ice were mechanically entrained by the four largest volcanically initiated flows. The flow volumes were increased by incorporation of the seasonal snowpack on the lower glacier surface and in the flooded river valley. The seasonal snow contributed a volume equivalent to about 35 × 106 m3 of water to the flows, increasing the cumulative flood volume by almost 30%. No large amounts of meltwater were stored on or under the glacier before any of the flows took place. The threat of flooding was significantly reduced after the second major eruption removed the remainder of the easily erodible snow and ice.
Anthropogenic sulfate and Asian dust signals in snow from Tien Shan, northwest China
Authors: Wake Cameron P. , Mayewski Paul A. , Ping Wang , Qinzhao Yang , Jiankang Han , Zichu Xie
Published: September 2017

Snow samples were collected from a 0.5 m snowpack at Glacier No. 1 and near Bogda Feng, eastern Tien Shan, northwest China. Samples that were melted in the field were analyzed for chloride, nitrate, sulfate, sodium, potassium, magnesium, calcium, and microparticles. Eight samples were returned frozen and were analyzed for the above ions plus ammonium, acetate, formate, methylsulfonate, and hydrogen peroxide. There was no significant difference in measured major ion concentrations between the melted and frozen samples. Measured cations in both sets of samples were two to three times greater than measured anions. Calcium and sodium are the dominant cations while sulfate is the dominant measured anion. High ion burdens are associated with dusty layers in the snowpack, indicating that dust from the vast arid regions of central Asia is the dominant source for major ions in Tien Shan snow. The significant increase in sulfate and decrease in the cation : anion ratio in Bogda Feng snow relative to Glacier No. 1 snow suggest that anthropogenic emissions from Ürümqi are an important source of sulfate to precipitation downwind from the city.
A distributed snowmelt prediction model in mountain areas based on an energy balance method
Authors: Ohta Takeshi
Published: September 2017

A distributed snowmelt prediction model was developed for a mountain area. Topography of the study area was represented by a digital map. Cells On the map were divided into three surface-cover types; deciduous forest, evergreen forest and deforested area. Snowmelt rates for each cell were calculated by an energy balance method. Meteorological elements were estimated separately in each cell according to topographical characteristics and surface-cover type. Distributions of water equivalent of snow cover were estimated by the model. Snowmelt runoff in the watershed was also simulated by snowmelt rates calculated by the model. The model showed thai the snowmelt period and snowmelt runoff after timber harvests would be about two weeks earlier than under the forest-covered condition.
Bent icicles and spikes
Authors: Maeno N. , Makkonen L. , Takahashi T.
Published: September 2017

Formation mechanisms of bent icicles and thin spikes were studied by observations of natural icicles and by artificially growing icicles in a cold laboratory, and the results are discussed with reference to the general growth process of icicles. It is shown that icicles can be bent by the displacement of their roots, change in water supply rates, and wind. Spikes were observed to grow by the freezing of a water column captured at the centre of icicles after their length and diameter growth stopped.
Modelling of the ice-edge failure process with curved failure surfaces
Authors: Kujala Pentti
Published: September 2017

The failure process of a Wedge-shaped ice edge is modelled by dividing the process in crushing failures at the contact and flaking failures initiating from high pressure in the contact. This type of approach has been shown earlier by Daley to give an explanation of the physical background of the line-like contact observed in ice-crushing tests and in full-scale measurements. Daley's model is developed further by studying the stress field in ice in more detail when applying the Coulomb macroscopic failure criterion to determine the force required for flaking failures. The analysis indicates that the shape of the flaking failure surface to minimise the force required to cause failure follows a logarithmic spiral. The shape of the spiral is related to the inner friction angle of ice and to the geometry of the ice edge. The curved flaking surfaces require considerably less force than straight surfaces used previously, especially with wide wedge angles. Finally, the model developed is used to simulate the time history of a crushing force measured in laboratory crushing tests and a good correspondence is obtained.
Effects of microtopography on texture, temperature and heat flow in Arctic and sub-Arctic snow
Authors: Sturm Matthew , Holmgren Jonathan
Published: September 2017

Arctic and sub-Arctic snow is deposited on ground that can have significant microrelief due to tundra hummocks and tussocks. The microrelief, a substantial fraction of the total snow depth, causes basal layers of snow (usually depth hoar) to be discontinuous. In-situ measurements made at four locations in Alaska indicate lateral temperature gradients up to 60°C m −1 exist at the snow/ground interface due to the microtopography. For all sites, the winter average range of temperature along a 1.5 m transect at the interface varied from 4°C to greater than 7°C. Heat-flux transducers placed at the tops and bases of tussocks indicated that vertical heat flow was consistently 1.4 to 2.1 times higher at the top than the base. Results of a conductive model based on tussock height are consistent with these measurements.
Glacial quarrying: a simple theoretical model
Authors: Hallet B.
Published: September 2017

Glacial quarrying remains enigmatic despite being long recognized as a primary, perhaps the dominant, process by which glaciers erode bedrock. The rate-limiting process appears to be subglacial rock fracture due to ice-induced mechanical stresses.

To study this erosional process, a simple model of quarrying is developed for a glacier sliding over a periodic series of bedrock steps. Consideration of the balance of forces at the ice/rock interface and of the rate of cavity closure permits evaluation of ice-induced stresses on bedrock surfaces. The resulting stress distribution where ice loads are most concentrated near the corner of bedrock steps is evaluated using a simple elastic solution for the state of stress in a loaded quarter-plane. It is then used to determine whether fractures in the rock will grow, and to estimate the rate of progressive crack growth. Based on these crack-growth rates, an index of the quarrying rate is then calculated as a function of glaciological variables effective pressure and sliding velocity—and various bed parameteres. Considerable incentive exists for further analysis of quarrying, and for seeking field data to test the model.
The role of bedrock topography, structure, ice dynamics and preglacial weathering in controlling subglacial erosion beneath a high-latitude, maritime ice field
Authors: Rea Brice R. , Whalley W. Brian
Published: September 2017

It is known that regions of warm- and cold-based ice sheets modify and protect the Landscape, respectively. Investigations on a small plateau-top ice field, Øksfjordjøkelen (40 km2), in north Norway have indicated that this situation can exist at a small scale. Margins of the plateau, exposed by ice retreat since AD 1850, provide evidence of a complex basal thermal regime: in some localities blockfields with patterned ground and, in others, abraded and quarried bedrock forelands have been exposed. Exposed blockfields are interpreted as areas covered by cold-based, non-erosive ice. In areas of sliding ice, substantial quantities of erosion are evident. Locally, bedrock shows three joint sets intersecting which produce joint-bounded blocks. Removal of these blocks during the Little Ice Age has produced small rock steps about 5–10 m long and 1–3 m high. Present-day basal sliding velocities at the snout are low (15 m a–1) and ice thickness over the whole glacier is < 190 m. Simple modelling for block removal shows a direct relationship with glacier-sliding velocity and inverse relationship with ice thickness. Preglacial weathering is shown to influence the size of removable blocks.
Scales and rates of glacial sediment removal: a 20 km long, 300 m deep trench created beneath Breiðamerkurjökull during the Little Ice Age
Authors: Björnsson Helgi
Published: September 2017

A 20 km long, 2-5 km wide trench, which extends to 300 m below sea level, is believed to have been created by removal of sediment during the advance of Breiðamerkurjökull in the Little Ice Age. Between 1732 and 1890, the glacier advanced by 9 km, covered an area of 45 km2 and excavated a volume of 5 × 109 m3, equivalent to an average of 110 m over this area. Average sediment-removal rate during the 158 years was 32 × 106 m3 a−1 or 0.7 m a−1 km−2 averaged over the area covered by the advancing glacier. Calculated over the whole drainage area of the eastern branch of the glacier of 750 km2, the denudation rate would be 4 × 10−2 m a−1 km−2. Fluvial processes are estimated to have carried about 30 × 106 m3 a−1, and the sediment fluxes within the ice and by the deforming subglacial till are estimated to be 105 and 106 m3 a−1, respectively. The average sediment concentration in the glacial streams would have been about 10 kg m−3. Such concentrations have been measured in Icelandic rivers during jökulhlaups and surges. Several surging events took place during the advance of Breiðamerkurjökull, and jökulhlaups drain regularly beneath the glacier from ice-dammed marginal lakes. The present rate of transport, although considerable, seems to be about 10 × 106 m3 a−1, of which 30% is transported by the river to the sea and 70% is dumped into a proglacial lake.
The influence of englacial drainage on sediment-transport pathways and till texture of temperate valley glaciers
Authors: Kirkbride Martin , Spedding Nick
Published: September 2017

Field studies at Mueller and Tasman Glaciers in New Zealand and in Iceland have revealed extensive ice-marginal moraine sequences fed by a series of debris bands containing characteristic rounded debris. We interpret these debris bands as meltwater deposits from relict conduits. The process of sediment accumulation described requires that debris undergoing basal or high-level ice transport is entrained by running water, becoming comminuted and rounded before being returned to high-level ice transport and eventual deposition in marginal moraines. Tins sequence of events suggests a link between glacier hydrology and ice-marginal sedimentation, possible mechanisms for which are explored. Pronounced moraines with rounded debris can be expected if (a) large quantity of debris is carried within the englacial drainage network; (b) there is a tendency for this debris to be abandoned within the ice; and (c) ice-flow trajectories and ablation ensure that this debris congregates at the ice surface. Streams which flow at high level within the ice can intercept and entrain englacial debris derived from rock fall. However, debris sources at Gigjökull and Steinholtsjökull in Iceland are restricted to the glacier bed, suggesting that, in certain cases, the presence of a basal overdeepening acts as a key factor controlling the accumulation of these moraines. Water pressure rises as channels encounter an overdeepening, forcing debris-laden streams to leave the bed and take an englacial route. That debris may pass from ice to water and back into ice before deposition has gone largely unrecognised in accounts of glacial process systems, yet it provides an explanation of how temperate alpine glaciers can include water-worked debris in their marginal depositional facies.
On the sedimentological character of Alpine basal ice facies
Authors: Hubbard Bryn , Sharp Martin , Lawson Wendy J.
Published: September 2017

Seven basal ice facies have been defined on the basis of research at eleven glaciers in the western Alps. The concentration and texture of the debris incorporated in these facies are described. Grain-size distributions are characterised in terms of their: (i) mean size and dispersion, (ii) component Gaussian modes, and (iii) self-similarity.

Firnified glacier ice contains low concentrations (≈0.2 g 1−1) of well-sorted and predominantly fine-grained debris that is not self-similar over the range of particle diameters assessed. In contrast, basal ice contains relatively high concentrations (≈4–4000 g 1−1 by facies) of polymodal (by size fraction against weight) debris, the texture of which is consistent with incorporation at the glacier bed. Analysis by grain-size against number of particles suggests that these basal facies debris textures are also self-similar. This apparent contradiction may be explained by the insensitivity of the assessment of self-similarity to variations in mass distribution. Comparison of typical size–weight with size–number distributions indicates that neither visual nor statistical assessment of the latter may be sufficiently rigorous to identify self-similarity.

Apparent fractal dimensions may indicate the relative importance of fines in a debris distribution. Subglacially derived basal facies debris has a mean fractal dimension of 2.74. This value suggests an excess of fines relative to a self-similar distribution of cubes, which has a fractal dimension of 2.58. Subglacial sediments sampled from the forefield of Skalafellsjökull, Iceland, have fractal dimensions of 2.91 (A-horizon) and 2.81 (B-horizon). Debris from the A-horizon, which is interpreted as having been pervasively deformed, both most closely approaches self-similarity and has the highest fractal dimension of any of the sample groups analyzed.
20th-century glacial-marine sedimentation in Vitus Lake, Bering Glacier, Alaska, U. S. A.
Authors: Molnia Bruce F. , Post Austin , Carlson Paul R.
Published: September 2017

Vitus Lake, the ice-marginal basin at the southeastern edge of Bering Glacier, Alaska, U.S.A., is a site of modern, rapid, glacial-marine sedimentation. Rather than being a fresh-water lake, Vitus Lake is a tidally influenced, marine to brackish embayment connected to the Pacifie Ocean by an inlet, the Seal River. Vitus Lake consists of five deep bedrock basins, separated by interbasinal highs. Glacial erosion has cut these basins as much as 250 m below sea level. High-resolution seismic reflection surveys conducted in 1991 and 1993 of four of Vitus Lake’s basins reveal a complex, variable three-component acoustic stratigraphy. Although not fully sampled, the stratigraphy is inferred to be primarily glacial-marine units of (1) basal contorted and deformed glacial-marine and glacial sediments deposited by basal ice-contact processes and submarine mass-wasting; (2) acoustically well-stratified glacial-marine sediment, which unconformably overlies the basal unit and which grades upward into (3) acoustically transparent or nearly transparent glacial-marine sediment. Maximum thicknesses of conformable glacial-marine sediment exceed 100 m. All of the acoustically transparent and stratified deposits in Vitus Lake are modern in age, having accumulated between 1967 and 1993. The basins where these three-part sequences of “present-day” glacial-marine sediment are accumulating are themselves cut into older sequences of stratified glacial and glacial-marine deposits. These older units outcrop on the islands in Vitus Lake.

In 1967, as the result of a major surge, glacier ice completely filled all five basins. Subsequent terminus retreat, which continued through August 1993, exposed these basins, providing new locations for glacial-marine sediment accumulation. A correlation of sediment thicknesses measured from seismic profiles at specific locations within the basins, with the year that each location became ice-free, shows that the sediment accumulation at some locations exceeds 10 m year−1.
The jökulhlaup from Katla in 1918
Authors: Tómasson Haukur
Published: September 2017

The greatest event in the 20th-century glaciological history of Iceland has been the glacier burst of Katla on Saturday 12 October 1918. Several cubic kilometres of water and ice were transported by the burst, and over 0.5 km3 of magma surfaced from the Katla caldera. The volcanic material was transported by air and water, and part of it probably formed pillow lava at the eruption site. The volcanic material transported by water was deposited mostly on the Mýrdalssandur plain and at the coast, but part of it was probably carried out to greater depths by gravity currents as the water entered the sea. The peak flow rate during the jökulhlaup was probably over 3 × 105 m3 s−1 of water, with a further 25 Kt s−1 of ice and a similar amount of sediment.
Subglacial chemical erosion: seasonal variations in solute provenance, Haut Glacier D’Arolla, Valais, Switzerland
Authors: Brown G. H. , Sharp M. , Tranter M.
Published: September 2017

This paper determines the provenance of solute in bulk meltwaters draining Haut Glacier d’Arolla, Valais, Switzerland, during the 1989 ablation season. Dissolved species are partitioned into components derived from sea salt, acid aerosol, dissolution of atmospheric CO2, and lithogenic sources, namely carbonates, sulphides and aluminosillicates. A major conclusion is that trace geochemically reactive minerals in the bedrock contribute the bulk of the solute found in runoff. Seasonal changes in solute provenance and in the dominant chemical weathering process are observed. Whereas the chemical weathering of aluminosillicate minerals by carbonation reactions remains relatively constant during the ablation season, the chemical erosion of carbonates shows distinct seasonal variations, reflecting changes in the nature of the subglacial drainage system. Subglacial drainage structure and bedrock type are key controls on the extent of subglacial chemical weathering.
Implications of till-provenance studies for glaciological reconstructions of the paleoglaciers of Wildhorse Canyon, Idaho, U.S.A.
Authors: Brugger Keith A.
Published: September 2017

Detailed till-provenance studies of moraine complexes in the Wildhorse Canyon area, Idaho, U.S.A., allow inferences to be made regarding the flow paths and dynamics of Wildhorse and Fall Creek Glaciers, the two principal tributaries constituting a late-Pleistocene compound glacier. In particular, the distribution of statistically defined pebble and mineral assemblages within moraine complexes suggests that Wildhorse Glacier contributed a substantially greater volume of ice to the trunk glacier than did Fall Creek Glacier.

An initial group of glaciological reconstructions yields estimates for the equilibrium-line altitude (ELA) of the compound glacier that are consistent with those independently arrived at using other methods of ELA determination. Ice-flux calculations imply, however, that for each reconstruction the relative contributions of ice from Wildhorse and Fall Creek Glaciers were about equal, which is inconsistent with the inferences drawn from the till-provenance data. An alternative reconstruction incorporated possible orographic effects on accumulation and ablation by using different ELAs for the two tributary glaciers. Calculations for this reconstruction suggest that the ice flux of Wildhorse Glacier was about twice that of Fall Creek Glacier. This reconstruction is more consistent with the till-provenance data, and furthermore suggests that such data might be invaluable in choosing between seemingly equally viable glaciological reconstructions of paleoglaciers.
Relationship between snowdrift development and drifted snow during a wind episode
Authors: Mases M. , Font D. , Vilaplana J. M.
Published: September 2017

Snowdrift formation has been monitored in the eastern Spanish Pyrenees since 1992 at an experimental study plot at the La Molina ski resort between 2000 and 2400 m. Several instruments were installed to characterize the wind, quantify snow-mass flux, detect snowdnfting episodes and measure the evolution of a natural snowdrift.

This plot is situated within a natural snowdrift and is equipped with measuring instruments such as snow poles, three columns of snow collectors (prismatic boxes) facing the dominant winds and an anemographic station.

During the 4 years of data acquisition, the thickness of the snowdrift has been measured and the snow collectors checked once each week. An active interest has been taken in the relationship between snowdrift development and drifting snow during a wind episode.

The relationship observed between wind, drifting snow and the development of the snowdrift is presented The results show: (1) the amount of snow collected in the snow collectors is related to wind intensity and to the availability and the quality of drifting snow, and (2) wind intensity principally affects the relative location of maximum snowdrift growth rather than controlling the thickness of the snowdrift.

By comparing the evolution of the snowdrift with Tabler’s (1975) model, we observed that it fits with the topographic features of our study area for the three seasons shown.
Solute in high arctic glacier snow cover and its impact on runoff chemistry
Authors: Hodgkins Richard , Tranter Martyn
Published: September 2017

The chemical composition of snow and meltwater in the 13 km2 catchment of Scott Turnerbreen, Svalbard, was investigated during the spring and summer of 1993. This paper assesses the provenance of solute in the snowpack and its impact on runoff chemistry. Dry snow contains 420μeql-1 of solute, is slightly acidic (pH 5.4) and is dominated by Na+ and Cl-. Wet snow is more dilute (total concentration 340μeql-1), and less acidic (pH 5.9). This is consistent with the elution of ions from the snowpack by meltwater. Snowpack solute can be partitioned into the following fractions: sea-salt aerosol, acid aerosol and crustal. About 98% of snowpack solute is sea salt, yielding 22000 kg km-2a-1. The behaviour of snowpack-derived Cl- in runoff is distinctive, peaking at over 800 μeql-1 early in the melt season as runoff picks up, before declining quasi-exponentially. This represents the discharge of snowmelt concentrated by elution within the snowpack which subsequently becomes relatively dilute. A solute yield of 140 kg km-2 a-1 can be attributed to anthropogenically generated acid aerosols, representing long-range atmospheric transport of pollutants, a potential contributor to Arctic runoff acidification.
Turbulent fluxes above the snow surface
Authors: Martin Eric , Lejeune Yves
Published: September 2017

Measurements of sensible- and latent-heat fluxes under stable conditions are rare. In order to obtain indirect measurements of turbulent fluxes, meteorological data measured at the Col de Porte laboratory (1320 m a.s.l, France) under very stable conditions (cold, clear night with low wind) are used. The radiative fluxes are measured, the conduction within the snowpack is calculated using the snow model Crocus and the turbulent fluxes are determined as a residual term of the surface-energy balance equation. These data were used to fit a new parameterization of the turbulent fluxes for the snow model. The turbulent fluxes are increased as compared to the theory. Crocus was also applied to the data from the LEADEX92 experiment and the turbulent fluxes calculated by the model were compared to the fluxes measured using sonic anemometers/thermometers on the site.
Numerical simulation of drifting snow: erosion and deposition models
Authors: Naaim Mohamed , Naaim-Bouvet Florence , Martinez Hugo
Published: September 2017

Earlier works on numerical modelling are analysed. Anderson and Haff (1991) proposed a model using the “splash” function which was defined for cohesionless sand. The Uematsu and others (1989, 1991) and Liston and others (1993,1994) approaches are based on fluid-mechanics conservation laws where the snow is transported and diffused by the air flow. These models consider the saltation layer as a boundary condition.

For the flow, and for the suspension, we adopt the same model as that of Uematsu and Liston. For mass exchange between the flow and snow surface, we have developed an erosion–deposition model where mass exchange is defined in relation to flow turbulence, threshold-friction velocity and snow concentration. Our snow-erosion model was calibrated using Takeuchi's(1980) field measurements. The deposition model was tested by comparing numerical results with wind-tunnel ones, for sawdust-accumulation windward and leeward of a solid snow fence with a bottom gap. The numerical results obtained are close to the experimental results. The main results of the various sensitivity experiments are: the leeward accumulation is very sensitive to the ratio (u*/u*t) (it appears for (u*/u*t) close to 1 and disappears for (u*/u*t) > 1.2), the global accumulation produced by the fence increases as (u*/u*t) decreases and the back reaction of particles on turbulence extends slightly the windward accumulation.
Charge-to-mass ratio of individual blowing-snow particles
Authors: Schmidt D. S. , Dent J. D. , Schmidt R. A.
Published: September 2017

Determining the electrostatic force acting on saltating snow particles requires knowledge of the electric field in the saltation region and the charge on the particle. To date, measurements of average charge-to-mass ratios for blowing-snow samples have been made but Schmidt and Schmidt (1993) have indicated these may underestimate charge-to-mass ratios for individual particles due to a mixture of positive and negative charge in the samples. This paper reports on measurements of charge-to-mass ratio for individual blowing-snow particles during a moderate blowing-snow storm in southwestern Wyoming. We measured charge-to-mass ratios as large as -208 μC, kg-1, significantly higher than the -10μC kg -1 measured by Latham and Montagne (1970) and -50 μC kg-1 measured by Wishart (1970). This large charge-to-mass ratio was accompanied by a distribution of positive and negative charge on the particles, supporting the conclusions of Schmidt and Schmidt (1993).
Crocus test results for snowpack modeling in two snow climates with respect to avalanche forecasting
Authors: Mingo Laurent , Mcclung D. M.
Published: September 2017

Overall results comparing field observations and Crocus simulations during the winters 1993–94 and 1994–95 in two different climate zones are presented. We present information on: snow depth, snow-temperature profiles, density profiles, liquid-water content profiles and grain metamorphism. Snow profiles illustrating the typical behavior of the model are presented and are shown to illustrate the sensitivity of Crocus to different mountain climates. Heat-exchange simulation, together with qualitative analysis of meteorological data, give promising results for surface-hoar prediction.
A preliminary numerical investigation of the micromechanics of snow compaction
Authors: Johnson Jerome B.
Published: September 2017

A dynamic finite-element computer program was used to examine the evolution of microstructure and its effect on continuum-scale deformation for the constant-speed uniaxial-strain compaction of an aggregate of roughly spherical elastic-plastic particles. Simulation results are used to explain some micromechanical aspects of snow compaction. Different compaction rates were used to examine the limits of quasi-static response and the effects of inertial stresses. Four stages of microstructurally controlled compaction were observed for quasi-static loading: particle re-arrangement, elastic deformation and two stages of plastic deformation. Elastic deformation follows the first critical density caused by the stable random loose-particle packing of rough spheres. Stage III compaction occurs by plastic deformation once stresses acting on particles exceed yield. Stage IV compaction follows a second critical density caused by the stable packing of deformed particles and is also through plastic deformation of particles. During high-speed compaction, inertial stresses propagate particle deformation from the loading platen into the aggregate. As a consequence, particle re-arrangement is limited so that the pressure-density ratio is larger for high-speed compaction than for quasi-static compaction at the same density. Hence, critical densities and the compaction-rate dependence of the pressure-density ratio during compaction of an aggregate of particles composed of rate-independent material are determined by the evolution of microstructure at different compaction rates. Observed pressure-density profiles for polar snow exhibit the same features of critical density and changes in the pressure-density ratio as found in the simulation and consist of four compaction stages: particle re-arrangement and three stages of creep particle deformation each following a critical density. Shear stresses appear to enhance the compaction during the stage III creep deformation of snow.
Wavy temperature and density distributions formed in snow
Authors: Sokratov Sergey A. , Maeno Norikazu
Published: September 2017

Precise measurements of temperature and density distributions in snow under an applied temperature gradient showed that alternation of evaporation and condensation zones is formed and causes the wavy patterns in quasi-steady temperature and density distributions. In samples with a snow density of 200–500 kg2 m−3 the wavelength was 3–7 cm and the amplitude was roughly 2°C. The present result gives a clue to explaining the wide range of previously measured water-vapor diffusion coefficients in snow.
Laboratory experiments on shear failure of snow
Authors: Schweizer Jürg
Published: September 2017

Using a direct simple-shear apparatus, snow samples (115 mm in diameter, 16–18 mm in height) taken from a so-called homogeneous layer (small rounded particles, density: 290 kg m−3) were tested in a cold laboratory. Experiments were performed for strain rates between 7 × 10−6 s−1 and 5 × 10−3 s−1 at test temperatures of −5°C, −10°C and −15°C. The effects of strain rate and temperature on failure stress, failure strain, stiffness (initial tangent modulus) and toughness were studied. The transition between the ductile and brittle (sudden fracture) state of failure was found to be at about 1 × 10−3 s−1 for the snow types tested, independent of temperature. Stiffness proved to be the most temperature-dependent property of alpine snow. It strongly increases with decreasing temperature. Failure strain and toughness decrease with decreasing temperature. Failure stress was found to increase slightly with decreasing temperature. The effect is not very distinct but close to statistically significant and might be partly hidden by the scatter in the stress data due to variations inherent in sampling and testing.
Channelized subglacial drainage over a deformable bed
Authors: Walder Joseph S. , Fowler Andrew
Published: September 2017

We develop theoretically a description of a possible subglacial drainage mechanism for glaciers and ice sheets moving over saturated, deformable till. The model is based on the plausible assumption that flow of water in a thin film at the ice-till interface is unstable to the formation of a channelized drainage system, and is restricted to the case in which meltwater cannot escape through the till to an underlying aquifer. In describing the physics of such channelized drainage, we have generalized and extended Röthlisberger’s model of channels cut into basal ice to include “canals” cut into the till, paying particular attention to the role of sediment properties and the mechanics of sediment transport. We show that sediment-floored Röthlisberger (R) channels can exist for high effective pressures, and wide, shallow, ice-roofed canals cut into the till for low effective pressures. Canals should form a distributed, non-arborescent system, unlike R channels. For steep slopes typical of alpine glaciers, both drainage systems can exist, but with the water pressure lower in the R channels than in the canals; the canal drainage should therefore be unstable in the presence of channels. For small slopes typical of ice sheets, only canals can exist and we therefore predict that, if channelized meltwater flow occurs under ice sheets moving over deformable till, it takes the form of shallow, distributed canals at low effective pressure, similar to that measured at Ice Stream B in West Antarctica. Geologic evidence derived from land forms and deposits left by the Pleistocene ice sheets in North America and Europe is also consistent with predictions of the model.
Miniature high-power impulse transmitter for radio-echo sounding
Authors: Narod B. Barry , Clarke Garry K.C.
Published: September 2017

We have developed a miniature high-power impulse transmitter for radio-echo sounding of glaciers. It features two synchronous second break-down pulse generators operating in a differential configuration. Specifications include bipolar 550 V pulses having rise times less than 2 ns, 512 Hz repetition rate, 180 mA at 10-14 V d.c. operating power, 5 mA standby current and maximum dimension of 12 cm. Because of its small size and low power consumption, the transmitter is suitable for back-portable systems and for towed arrays. The transmitter first saw service in 1990 on Trapridge Glacier, Yukon Territory. Subsequent copies have been used on Agassiz Ice Cap, Northwest Territories, Bering Glacier, Alaska and elsewhere. To date, the maximum ice thickness measured using this transmitter is 825 m, on temperate Bering Glacier.
δD-δ18O Relationships and the Thermal History of Basal Ice Near the margins of two Glaciers in Lyngen, North Norway
Authors: Gordon J.E. , Darlinc W.G. , Whalley W.B. , Gellatly A.F.
Published: September 2017

When plotted on a δD-δ18O diagram, the isotope values of basal ice formed by refreezing of melt water beneath the cold-based margin of a corrie glacier lie on a straight line with a slope of 5.5. This freezing slope differs from a slope of 7.2 for the basal ice layer of the cold-based ice cap, Balgesvarri, which has not undergone refreezing. The latter slope is similar to that of 7.7 for the local precipitation. Co-isotope measurements from the two glaciers support the association of subglacial debris entrainment with refreezing processes.
Simulation of Historic Glacier Variations with a Simple Climate-Glacier Model
Authors: Oerlemans Johannes
Published: September 2017

Glacier variations during the last few centuries have shown a marked coherence over the globe. Characteristic features are the maximum stand somewhere in the middle of the nineteenth century, and the steady retreat afterwards (with some minor interruptions depending on the particular region). In many papers, qualitative statements have been made about the causes of these fluctuations. Lower temperatures associated with solar variability and/or volcanic activity are the most popular explanations. In particular, the statistical relation between glacier activity and major volcanic eruptions appears to be strong.

In this paper, an attempt is made to simulate recent glacier fluctations with a physics-based model. A simple climate model, calculating perturbations of surface-radiation balance and air temperature (not necessarily in phase!), is coupled to a schematic time-dependent glacier model. The climate model is forced by volcanic activity (Greenland acidity and/or Lamb’s dust-veil index) and greenhouse warming. Solar variability was not considered, because its effect on climate has still not been demonstrated in a convincing way. The output is translated into variations in equilibrium-line altitude, driving the glacier model.

The simulated variations in glacier length show good agreement with the observed record, but the amplitude is too small. This is improved when mass-balance gradients are assumed to be larger in warmer climates. Compared to recently published modelling studies of particular glaciers, in which series oflocalparameters (e.g. tree-ring width and temperature) were used as forcing, the present simulation is better. This suggests that the radiation balance is a decisive factor with regard to glacier variations on longer time-scales. The model experiments lend support to the results of Porter (1986), who concluded from a more qualitative study that a strong relation exists between periods of increased volcanic activity and glacier advances.

A comparison of some selected runs shows that, according to the present model,the greenhouse warming would be responsible for about 50% of the glacier retreat observed over the last 100 years.
The Effects of Ice Thickness on the Exchange of Solar Radiation Over the Polar Oceans
Authors: Grenfell Thomas C.
Published: September 2017

Total transmission, absorption, and reflection of solar radiation have been determined for bare blue and white ice between 0.02 and 0.8 m in thickness as well as for blue ice covered with 0.01 to 0.4 m of dry packed snow. The calculations were performed at 45 wavelengths between 400 nm and 2150 nm using a two-stream model to account for the finite thickness of the ice and snow layers. Total radiative energies were found by numerical integration over wavelength. The results were compared with corresponding calculations for optically thick ice of the same types. Albedos increase from about 0.05 for open water to a maximum of 0.9 for thick snow. For 0.8 m blue and white ice, predicted albedos on cloudy days are 0.28 and 0.67 respectively. Under clear skies these albedos decrease by 10 to 30%. Total transmission through thin ice (less than 0.8 m) is from 50% to 300% greater than is predicted by Beer’s law depending on ice type and cloud cover. Radiative energy absorption at the surface is independent of thickness, but significant departures from Beer’s law of as much as 200% are evident in all cases below a depth of 2.5 mm. A parameterization scheme is presented for incorporating these results into heat- and mass- balance studies.
In-Situ Estimates of the Tensile Strength of Snow Utilizing Large Sample Sizes
Authors: McClung David M.
Published: September 2017

Experimental procedure and measured estimates of the tensile strength of snow are given by a new method utilizing large sample sizes of naturally deposited snow. Data are presented as a function of average sample density, temperature, loading rate, and snow type. The results show less scatter in the data than previous in-situ estimates and lower mean strength values as a function of density. The relevance of the data to tensile fracture as observed in slab avalanche release is discussed.
Accelerating Strain Preceding an Avalanche
Authors: Sommerfeld Richard A.
Published: September 2017

Strain gages set in the snow on an avalanche track recorded accelerating strain for four hours preceeding a naturally released avalanche. On a second occasion when the strain-rate was similar, the strain decelerated and no avalanche occured.
Observations of the Antarctic ice sheet with the Seasat scatterometer: relation to katabatic-wind intensity and direction
Authors: Ledroit M. , Remy F. , Minster J.-F.
Published: September 2017

The Seasat A satellite scatterometer radar, initially designed to measure ocean-wind intensity and direction, also provided observations on the Antarctic ice sheet. The signal of the back-scatter coefficient decreases strongly from 10 to −20 dB when the incidence angle of the observations increases from 0° to 65°. An additional 5 dB signal is found, which is correlated with the direction and intensity of katabatic winds, independent of the incidence angle and polarization of the signal. By using simplified models of the volume-scattering within the snowpack (which is mostly sensitive to snow grain-size) and surface-scattering from the air-snow interface (which depends on roughness), it is evident that the signal of the scatterometer could result from the effects of snow dunes at low incidence angle, and of micro-roughness and volume back-scatter at incidence angles greater than 25°. The instrument therefore provides a means of measuring the direction and intensity of katabatic winds.