The measurement of snow accumulation and distribution is one of the primary objectives of a study on the melt of snow-drifts and erosion in the phosphate mining region of south-eastern Idaho. The study area is located in an active phosphate mine and is limited to the sites of waste dumps, a product of the surface mining technique used in this area. Four sites are included in the overall study with one dump selected for intensive snow measurement. Snow deposition data have been collected for one winter season (November 1977—June 1978) on a grid pattern over this dump. The area of the study site has been expanded and similar measurements are planned for the coming snow season.

The snow measurements were made monthly on a pre-established 23 m (75 ft) square grid overlaid on the dump. The analysis of the snow data consists of contour mapping of any one or all the snow properties measured—snow depth, density, or water equivalent. In addition, since the measurements are made on the same grid each month, mathematical manipulation of grid data allows contour maps of the residual of the monthly snow properties to be plotted. A similar analysis of terrain properties collected on the same grid results in contour maps displaying ground slope, concavity-convexity of the surface, aspect, or distance from snow- deposition obstacles.

The aim of the analysis using these types of data is to arrive at a model which will compute patterns of snow accumulation and distribution on the ground surface given a description of terrain type and probable meteorological properties of the region. A preliminary comparison of the maps shows a similar pattern of snow deposition occurring each month with the exposed areas of the dump swept clean and the greatest snow depth occurring in the sheltered concavities.

This paper describes the various maps concerned with avalanche hazards in Switzerland and gives examples of parts of specimen maps. These include the Wald- und Lawinenkarte der Schweiz (1907) at 1 : 250 000 which marks actual avalanche paths, the Karte der lawinengefährdeten Gebiete (1972) at 1 : 30 0000 which gives a summary view of avalanche hazard, the Gefahrenkarte der Schweiz (1975) at 1 : 100 000 which is intended to give an over-all view of all natural hazards that will influence land use, the Lawinenatlas/Lawinenkarte Uri (1978) at 1 : 25 000 which contains all identifiable avalanche paths in the Canton, the Kombinierte geomorphologische Gefahrenkarte 1: 10 000 von Grindelwald (1977), a Pilot study of mapping natural hazards in a mountain area, and the Lawinengefahrenkarten des Eidg. Institutes für Schnee- und Lawinenforschung at 1 : 10 000 included in 26 advisory reports on 561 individual avalanche paths, and which can act as pilot studies to assist cantons in preparing their own maps.

This paper is being published in full in German in Interpraevent 1980, Bd. 3, as part of the proceedings of the symposium held at Bad Ischl, Austria, 8-12 September 1980.

In conducting tension and compression tests on snow samples, strains and strain-rates are usually determined from the displacements of the ends of the samples. In this work, a strain-gage which mounts directly onto the snow sample during testing, was developed and was found to give accurate and direct measurements of strain and strain-rates.

A commercially available 0-28 pF variable capacitor was modified to perform the required strain measurements. It is a polished metallic plunger sliding inside a metal-coated glass tube. The plunger and tube were each soldered to the end of a spring-steel wire arm. To the other end of these arms were soldered to 10 mm square pads made of thin brass shim stock. The whole device weighs 2.5 g and the low coefficient of friction in the capacitor resulted in a very low actuation force. To mount the strain gage, the pads are wetted and frozen onto the snow sample.

A high degree of sensitivity was achieved through the use of “phase-lock-loop” electronic circuitry. The capacitance change caused by the strain in the sample, changes the frequency of output signal from an oscillator and thus causes the change in output from the system. In the locked state, to which the system is constantly driven by a feed-back loop, the system output is almost ripple free.

The strain gages were calibrated in the field in order to take into account the effects of very low field temperatures. The calibration curves were almost linear over the travel of 15 mm, the maximum limit. The sensitivity of the system is 4 mV per strain unit, but this could be increased by an order of magnitude by minor adjustments in the circuit.

Constant strain-rate tensile tests were performed on natural snow at Berthoud Pass, Colorado, U.S.A., in the density range of 140-290 kg m-3. Four strain gages were mounted onto the samples to sense any non-uniform deformation which otherwise would have gone unnoticed or caused scatter in the data. The average indication of these gages was used to construct stress—strain curves for various types of snow at different strain-rates. The effect of strain-rate on the behavior of snow was studied.

“Ratcheting” in the stress-strain curve in the region where the snow becomes plastic was observed first by Kinosita in his compression tests. A similar phenomenon was observed in these tension tests. It was found that directly measured strain is quite different from that which would be calculated from sample end movement. Strain softening was not observed in these tests up to total strains of 8%. The strain-rate effects found were comparable to the results of other investigators.

Results From the last four winters’ studies on acoustic emissions from snow slopes have shown that periods of higher noise in the frequency band 5 to 125 Hz are associated with periods of instability, but that the phenomenon of acoustic emissions from unstable snow is very weak. Interference with the acoustic emissions from extraneous sources such as chairlifts, trucks, and airplanes causes ambiguities in the data which interfere with the straightforward prediction of instability.

Spectra of the noises were examined, with the idea that filters might improve the signal-to-noise ratio. It was found that the noise generated by unstable snow can occur over a fairly wide range of frequencies and that there is no band of frequencies which is unique to unstable snow. It was found that the noise from the chairlift had a very stable spectrum and that it had a band from 50 to 65 Hz which was pronounced and in which the snow noise was fairly low. The r.m.s. voltage in the band 5 to 125 Hz can therefore be reduced by subtracting a proportion of the r.m.s. output of a narrow-band 55 Hz filter. By adjusting the constant of proportionality, it was possible to eliminate interference from the chairlift almost entirely, and this will be used.

Spectral analyses have also shown that ambiguities are generated by variations in the 60 Hz power-line noise. It is possible to suppress this with the use of filters, but without complex digital data manipulation, it is not possible to eliminate it.

The fact that the snow noise does not transmit over large distances means that events of interest should not occur simultaneously on two, widely spaced geophones. The system will include a geophone in an unstressed region whose r.m.s. voltage will be subtracted from that of the geophone in the stressed region to eliminate signals which are common to both. It is hoped that this technique will eliminate ambiguities caused by extraneous sources such as trucks and airplanes.

A section of the highway through the Gunes valley can be seriously interrupted by avalanching; in 1966-67 traffic was interrupted for four months. About 86 places are threatened by avalanches, most of which are channelled avalanches that do not reach the highway every year.

A comprehensive programme to study the avalanches was begun in 1967 on the basis of which avalanche protective works were undertaken in 1974-75 and their effectiveness analysed in 1976-77. Most of these depend on local material; the main rock deposits available are andesite, which has good permeability and is very suitable for earthworks.

The most common type of defence used is the building of mounds, 4-6 m high, 10-12 m wide, and 20-30 m long with a ditch dug in front. Such mounds have the effect of braking the avalanche flow and also of capturing snow on the uphill side. A second system is the terracing of slopes; beginning from the avalanche fracture line, earth is dug parallel to the contours. In two places dykes have been built to guide the snow, and in a few places avalanche sheds have been constructed, though because of expense these have been kept to a minimum. As the soil and climatic conditions are very suitable, tree planting around structures is a successful way of increasing avalanche protection.

During the analysis of effectiveness snow-fall as recorded was heavy, but the defences were effective and avalanches did not seriously interrupt the highway.

This paper is concerned with the variation of snow glide and its predictability in full-depth avalanches. From field measurements of snow glide using a newly developed gear-type glide-meter which is fixed to the ground and which measures the amount of glide as the angle of rotation of a gear, the following characteristics are deduced: (1) the variation of gliding rate is composed of both short-term and long-term variations, and (2) the existence of correlation between the short-term variation and the relative frequency of avalanches is recognized.