Powder Snow Research Articles

Analysis of the biomechanical characteristics of different swinging techniques in alpine skiing.

As a consequence of the increase in popularity of skiing as a leisure sport, ski teaching has become an important pedagogic and economic issue. Unfortunately, most ski teaching curricula lack a thorough evaluation of the most important swinging techniques. Therefore, this study analyses the biomechanical characteristics of swinging techniques in alpine skiing. The data were collected using biodynamic, kinematic and electromyographic methods, employing 21 test skiers, all of whom were state-certified Austrian ski instructors. For all techniques, the individual turns were divided into a steering phase and an initiation phase. In the main, the fundamental differences between the single techniques became apparent in the initiation phase. There it seemed useful to distinguish between turns with 'up-unweighting' and turns with 'down-unweighting'. It was found that turns with up-unweighting were initiated either from the downhill ski only or from both skis. Turns with down-unweighting were used primarily on mogul pistes and in deep powder snow. Finally, some conclusions for training methodology are given.

Passive microwave signatures of landscapes in winter

The successful application of passive microwave sensors requires signatures for the unambiguous inversion of the remote sensing data. Due to the large number of object types and large variability of physical properties, the inversion of data from land surfaces is a delicate and often ambiguous task. The present paper is a contribution to the assessment of multi-frequency passive microwave signatures of typical objects on land in winter. We discuss the behaviour of measured emissivities at vertical and horizontal polarization over the frequency range of 5 to 100 GHz (incidence angle of 50 degrees) of water and bare soil surfaces, grass and snowcovers under various conditions. These data and their variabilities lead us toward a classificaion algorithm for some, but not all object classes. Most snowcovers can easily be discriminated from other surfaces, difficulties occur for fresh powder snow if 94 GHz data are not available. The problem of wet snow has found a solution by using a certain combination of observables.

Experimental and theoretical study of the dynamics of powder snow avalanches

A powder snow avalanche is referred to as the turbulent flow of a cloud of dense fluid (suspension of snow particles) in an ambient one (the air) down an incline. This buoyant cloud can be channeled in a couloir (two-dimensional or 2-D buoyant cloud) or spread laterally on an open field (three-dimensional cloud). Between these two extreme cases one can meet all kinds of flow depending on mountain relief. Previous laboratory experiments in a water flume concerned only 2-D flows. 3-D flows are the subject of the present paper. From ‘thermal theory’ it is possible to obtain laws about velocity and density of the flowing cloud. A hundred experiments were carried out in a large tank containing fresh water along a tilting plane. It was shown that the height, length, and width growth rates of the clouds, between 15° and 90°, were linear functions of the slope. On the other hand the variation of the front velocity was shown to be in accordance with the proposed theoretical analysis. The results of this modeling can be applied to a real case of a powder snow avalanche flowing down a slope if there is no entrainment of the snow from the ground. This ‘no entrainment assumption’ corresponds generally to the last stage of the flow. Some practical examples are proposed.

Multiphase Flows in the Atmosphere

Phase change of water vapour in the atmosphere produces small water particles in the atmosphere. They are usually suspended quite densely in limited space and are called clouds. When the air temperature falls below -20°C, they are replaced by ice particles. Clouds play an important role in the meteorological processes from local to global scales.Pyroclastic flow is a complicated multiphase flow associated with volcanic eruptions. It consists of a mixture of air and hot volcanic ash and behaves like a gravity current along mountain slopes. Since the air is heated by hot ash, buoyancy in the pyroclastic flow increases like cumulus in which the air is heated by the latent heat of water.Powder snow avalanche is a kind of turbidity currents, which occurs when a large amount of powder snow accumulates in piles along the moutain slope. Once the avalanche begins, turbulence in the avalanche takes the piled snow into the air along the path and the effective density increases. The powder snow avalanche is very destructive, because the velocity reaches about 100m/s in the developed stage.

Study on the Release and Flow of Powder Snow Avalanches

Study on the Release and Flow of Powder Snow Avalanches

On the powder snow avalanche, which occurred in Maseguchi, Nou-machi, Niigata prefecture, 1986

On the powder snow avalanche, which occurred in Maseguchi, Nou-machi, Niigata prefecture, 1986

On the powder snow avalanche which occurred in Shimamichi-kohsen, Nou-machi, Niigata Prefecture, 1986

On the powder snow avalanche which occurred in Shimamichi-kohsen, Nou-machi, Niigata Prefecture, 1986

Analytical study of powder snow avalanches

Appropriate expressions describing the motion of powder snow avalanches are derived. The model consists of four equations, i.e. the conservation equations of air, snow particles, momentum of avalanches, and kinetic energy of turbulence. The total buoyancy of powder snow avalanches changes freely via erosion and deposition of bed material. In the model presented, the snow entrainment rate from bed is directly linked to the level of tubulence.The rate of development of strongly accelerated avalanches is obtained with the aid of numerical integration. The model gives a good explanation of the characteristics of the powder snow avalanche, i.e. the quick formation of thick clouds and the very fast speed of the front. To the extent that observations exist, the prediction of powder snow avalanches obtained herein is in general agreement with those observations.

Philip P. Upton, 1919-1984

... In 1960, [Phil Upton] ... was invited to join the Arctic Institute's Icefield Ranges Research Project as a pilot. It was an inspired choice, for Phil's contributions and loyalty to the Arctic Institute and the Kluane Research Station were immeasurable. He made the Saint Elias Mountains his parish, and became the finest mountain and glacier pilot in North America. He explored countless landing sites throughout the range in support of Arctic Institute research projects and private mountaineering expeditions. ... Skill he had in abundance. Of greater importance, his judgment was superb, his intuition uncanny. For 24 years he operated without serious mishap, tempering courage with caution, understanding fully the limits of himself and his machine. In 1968 he made the first landing on Mount Logan, at an altitude of 5300 m asl. This and subsequent landings that season inaugurated and developed the Institute's capability to run the High Altitude Physiology Study. It was an astonishing feat, and we who followed had the enormous psychological advantage of knowing that it could be done, and the benefit of his advice and leadership. ... To the eternal credit of Philip and the Institute, the safety record of the HAPS project was without parallel. After 12 years of operations, and after passing a considerable number of research and support personnel through one of Earth's more inhospitable sites, not one serious injury was sustained. Crises there were, of course, and although I took a larger share of the flying in later years, it was always Phil who chose to plough the aircraft into deep powder snow after a storm, who made the quite dreadful approach over the Northwest Col when the wind demanded, who picked his way over the undercast to a sick climber. ...

Seismic and Impact–Pressure Monitoring of Flowing Avalanches

Abstract Continuous records have been made during the passage of dry–snow avalanches of both seismic signals, which allows the avalanche speed to be estimated, and impact pressures on load cells with surface areas of 645 and 6 450 mm2. The impact pressure recordings show an initial peak followed by a base pressure. The observed initial and base pressures vary strongly within avalanches and from one avalanche to another, but, on average, they can be correlated with the frontal speed and the density of the deposited avalanche snow. It is concluded that well–developed dry–snow avalanches have an unsteady wave motion similar to the slug flow observed in ultra–rapid flow of water, and that they consist of three stratified components: dense flowing snow at the bottom, light flowing snow, and powder snow.

Seismic and Impact–Pressure Monitoring of Flowing Avalanches

AbstractContinuous records have been made during the passage of dry–snow avalanches of both seismic signals, which allows the avalanche speed to be estimated, and impact pressures on load cells with surface areas of 645 and 6 450 mm2. The impact pressure recordings show an initial peak followed by a base pressure. The observed initial and base pressures vary strongly within avalanches and from one avalanche to another, but, on average, they can be correlated with the frontal speed and the density of the deposited avalanche snow. It is concluded that well–developed dry–snow avalanches have an unsteady wave motion similar to the slug flow observed in ultra–rapid flow of water, and that they consist of three stratified components: dense flowing snow at the bottom, light flowing snow, and powder snow.

Cross-Country Skiing

To the Editor.— I appreciate Lyons and Porter's article Cross Country Skiing: A Benign Sport? I managed to sustain a spiral fracture of the tibia as the result of a twisting fall in deep, powder snow while wearing ankle-top boots and cable bindings when I was indulging in this completely safe sport in 1970. Since then my veracity has been in serious doubt, as I have been told by innumerable cross-country skiers that they have never heard of anyone fracturing anything in this most benign of sports. I can now restore my reputation as a reasonably reliable informant even if not an outstanding cross-country skier.

La dynamique des avalanches d'après les résultats des expériences de déclenchement artificiel au Lautaret

Results of tests carried out at an experimental site on the Lautaret Pass during the 1974/75 snow season are described. Two avalanche corridors are fitted with instrumentation ; one starts at an altitude of 2,320 m and ends 90 m below, and the other drops 210 m from an altitude of 2,340 m. Snow depths vary from 0.7 m to 2.8 m. The avalanches are set off by explosives positioned by a conveyor cable and fired by a special safety unit designed by Laboratoire A.S.P. Avalanches were triggered in powder snow on the 22nd and 31st January 1975 and in powder and sheet snow on the 12th March 1975. Test measurements are as follows : 1) Particle velocities in the avalanche, using hydraulic currentmeters and cinematographic equipment. Average velocity is around 7 m/s and peak velocities up to 16 - 18 m/s. 2) Impact pressure, using strain-gauges. Peak values are recorded behind the avalanche front, ranging from 0.6 bar to 1.3 bar. 3) Specific mass of the flowing snow, by gamma attenuation and comparison with gravimetric measurement data obtained before and after the avalanche. The coefficient of increase is approximately 1.3. Measured data for various depths are shown on tables. 4) Specific mass of the aerosol, by gamma attenuation (cesium 137, activity 37 mCi, horizontal distance 2.24 m) at 5m above the bottom. However, the proportion of aerosols in the avalanche is too small for the measurements to carry significant weight. 5) Snow temperature in the avalanche, using platinum temperature probes. Temperature rises of 1.6°C, 1.4°C and 1.0°C have been recorded. Snow temperatures at various depths are listed on tables. 6) Aerosol velocity, using a standard French Meteorological Service Type W106 propeller anemometer. 7) Avalanche front velocity, depth and size of the avalanche. These are determined by photography at 4 frames/second with reference to appropriate markers along the corridor. With this equipment, an avalanche can be observed over much of its length. 8) Electrostatic charges carried by the avalanche. Attempts have been made to measure these with a Rotschild electrometer a few metres from the edge of the avalanche, but so far without significant results. Data obtained for twelve avalanches in 1973, 1974 and 1975 are listed in a general table.

Physico-chemical phenomena in comets—I: Experimental study of snows in a cometary environment

The existence and thennodynamic stability of the clathrate hydrate of methane is checked in the 100°K temperature range, and its dissociation pressure is measured. Contrarily to ordinary ice or snow of water, it has the morphological appearance of a peculiar powder snow made of small icy grains. Their apparent density is between 0.33 and 0.54 g cm −3. Their actual size distribution is established and has a sharp peak for grains between 0.1 and 1 mm in dia. In a vacuum simulating cometary conditions, grains are constantly stripped from the main body of snow, by gases originating from the dissociation of the hydrate. As it is likely that all known clathrate hydrates behave in the same way, it is submitted that they could build up a halo of ice grains within the inner coma of comets. This halo may play an important role in the understanding of the cometary phenomena.

On the Construction and Comparison of Difference Schemes

On the Construction and Comparison of Difference Schemes

Propeller Sledges on the German Greenland Expedition, 1930–31

Modern polar research calls for a much more specialised and efficient travel technique than did polar exploration of even a few years ago; and, as a result, great strides have been made in perfecting the modern mechanical methods of transport. The old method of dog-sledging, with its comparatively low speeds and light loads, is already being replaced, to some extent, by mechanically driven sledges and aeroplanes. Several expeditions at work in the Arctic and Antarctic during the last few years have been able to make excellent use of air transport, but the first mechanically driven sledges were at best only moderately successful, and each reached its limit according to its construction either as a result of bad ice, slush, or deep powder snow, where the wheels or caterpillar band became bogged.