Snow mechanics and avalanche formation: field experiments on the dynamic response of the snow cover

1995 ◽  
Vol 16 (5-6) ◽  
pp. 621-633 ◽  
Author(s):  
J�rg Schweizer ◽  
Martin Schneebeli ◽  
Charles Fierz ◽  
Paul M. B. F�hn
Keyword(s):  
Dynamic Response ◽  
Snow Cover ◽  
Field Experiments ◽  
Avalanche Formation ◽  
Snow Mechanics

Frost heaving in a boreal soil in relation to soil scarification and snow cover

2001 ◽  
Vol 31 (6) ◽  
pp. 1084-1092 ◽  
Author(s):  
Urban Bergsten ◽  
France Goulet ◽  
Tomas Lundmark ◽  
Mikaell Ottosson Löfvenius
Keyword(s):  
Snow Cover ◽  
Field Experiments ◽  
Soil Surface ◽  
Control Treatment ◽  
Tree Seedlings ◽  
Frost Heaving ◽  
Humus Layer ◽  
Soil Scarification ◽  
Natural Snow ◽  
Surface Ice

Vertical uplift of seedlings and rods on the soil surface and at a depth of 5 cm, and of reference trees, was monitored using a theodolite from autumn to spring in two adjacent field experiments on a silt soil in northern Sweden. Treatments involving scarification (control and square patches of 0.1, 0.2, 0.4, and 0.8 m at natural snow cover) and snow cover (simulated maximum cover, snow free, and natural cover for control and 0.4-m patches) were compared. For snow free and natural snow cover, diurnal variation of soil surface temperature, duration and magnitude of freezing temperatures, and uplift increased with patch size. At the end of the winter under natural snow cover, uplift of the soil surface and shallow soil was between 4.4 and 5.3 cm for the control treatment without scarification and the 0.1-m patch while the uplift for the 0.4- and 0.8-m patches reached 7.6–11.5 cm. The highest uplift value, 14.6 cm, was observed for the snow-free treatment with 0.4-m patches. Maximum uplift of trees averaged 4.4 cm, which was similar to values observed for seedlings and rods with an intact humus layer and a natural snow cover, indicating that the highest observed uplift was mainly due to needle and soil surface ice. In conclusion, size of the scarified area and duration and thickness of snow cover largely influence frost heaving of tree seedlings in a susceptible soil.

scholarly journals Validating modeled critical crack length for crack propagation in the snow cover model SNOWPACK

2019 ◽  
Author(s):  
Bettina Richter ◽  
Jürg Schweizer ◽  
Mathias W. Rotach ◽  
Alec van Herwijnen
Keyword(s):  
Crack Length ◽  
Snow Cover ◽  
Field Experiments ◽  
Detection Method ◽  
Probability Of Detection ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Avalanche Forecasting ◽  
Snow Stratigraphy ◽  
Abstract Data

Abstract. Data on snow stratigraphy and snow instability are of key importance for avalanche forecasting. Snow cover models can improve the spatial and temporal resolution of such data, especially if they also provide information on snow instability. Recently, a new stability criterion, namely a parameterization for the critical crack length, was implemented into the snow cover model SNOWPACK. To validate and improve this parameterization, we therefore used data from three years of field experiments performed close to two automatic weather station above Davos, Switzerland. Monitoring the snowpack on a weekly basis allowed to investigate limitations of the model. Based on 145 experiments we replaced two variables of the original parameterization, which were not sufficiently well modeled, with a fit factor thereby decreasing the normalized root mean square error from 1.80 to 0.28. With this fit factor, the improved parameterization accounts for the grain size resulting in lower critical crack lengths for snow layers with larger grains. This also improved an automatic weak layer detection method using a simple local minimum by increasing the probability of detection from 0.26 to 0.91 and decreased the false alarm ratio from 0.89 to 0.47.

scholarly journals Validating modeled critical crack length for crack propagation in the snow cover model SNOWPACK

2019 ◽  
Vol 13 (12) ◽  
pp. 3353-3366 ◽  
Author(s):  
Bettina Richter ◽  
Jürg Schweizer ◽  
Mathias W. Rotach ◽  
Alec van Herwijnen
Keyword(s):  
Grain Size ◽  
Crack Propagation ◽  
Crack Length ◽  
Snow Cover ◽  
Field Experiments ◽  
Critical Crack ◽  
Critical Crack Length ◽  
Avalanche Forecasting ◽  
Weak Layer ◽  
Snow Stratigraphy

Abstract. Observed snow stratigraphy and snow stability are of key importance for avalanche forecasting. Such observations are rare and snow cover models can improve the spatial and temporal resolution. To evaluate snow stability, failure initiation and crack propagation have to be considered. Recently, a new stability criterion relating to crack propagation, namely the critical crack length, was implemented into the snow cover model SNOWPACK. The critical crack length can also be measured in the field with a propagation saw test, which allows for an unambiguous comparison. To validate and improve the parameterization for the critical crack length, we used data from 3 years of field experiments performed close to two automatic weather stations above Davos, Switzerland. We monitored seven distinct weak layers and performed in total 157 propagation saw tests on a weekly basis. Comparing modeled to measured critical crack length showed some discrepancies stemming from model assumption. Hence, we replaced two variables of the original parameterization, namely the weak layer shear modulus and thickness, with a fit factor depending on weak layer density and grain size. With these adjustments, the normalized root-mean-square error between modeled and observed critical crack lengths decreased from 1.80 to 0.28. As the improved parameterization accounts for grain size, values of critical crack lengths for snow layers consisting of small grains, which in general are not weak layers, become larger. In turn, critical weak layers appear more prominently in the vertical profile of critical crack length simulated with SNOWPACK. Hence, minimal values in modeled critical crack length better match observed weak layers. The improved parameterization of critical crack length may be useful for both weak layer detection in simulated snow stratigraphy and also providing more realistic snow stability information – and hence may improve avalanche forecasting.

scholarly journals Experiment and Numerical Simulation of the Dynamic Response of Bridges under Vibratory Compaction of Bridge Deck Asphalt Pavement

2019 ◽  
Vol 2019 ◽  
pp. 1-16 ◽  
Author(s):  
An-Ping Peng ◽  
Han-Cheng Dan ◽  
Dong Yang
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Field Experiments ◽  
Bridge Deck ◽  
Asphalt Pavement ◽  
Dynamic Responses ◽  
Structural Safety ◽  
Cross Sectional ◽  
Bridge Structures ◽  
Vibratory Compaction

Vibratory compaction of bridge deck pavement impacts the structural integrity of bridges to certain degrees. In this study, we analyzed the dynamic response of different types of concrete-beam bridges (continuous beam and simply supported beam) with different cross-sectional designs (T-beam and hollow-slab beam) under vibratory compaction of bridge deck asphalt pavement. The dynamic response patterns of the dynamic deformation and acceleration of bridges under pavement compaction were obtained by performing a series of field experiments and a three-dimensional finite element simulation. Based on the finite element model, the dynamic responses of bridge structures with different spans and cross-sectional designs under different working conditions of vibratory compaction were analyzed. The use of different vibration parameters for different bridge structures was proposed to safeguard their structural safety and reliability.

scholarly journals SNOW AVALANCHES ON THE SEREBRYANSKAYA DISTANCE OF THE WAY

2021 ◽  
Vol 81 (3) ◽  
pp. 112-118
Author(s):  
A.K. Ibraimov ◽  
◽  
A.K. Kurbenova ◽  
O.D. Seitkazinov ◽  
◽  
...  
Keyword(s):  
Snow Cover ◽  
Natural Disaster ◽  
Slope Angle ◽  
Snow Avalanches ◽  
Avalanche Formation ◽  
The Way

This article presents the probability of avalanche formation, possible damages depending on the volume of the avalanche, the volume of snow avalanches, the type of snow avalanches, slope angle, slope roughness, snow cover height. The analysis of conditions and factors accompanying such a natural disaster as snowfalls and snowdrifts on the railway is made. Effective ways of dealing with snowdrifts on the railway are highlighted.

scholarly journals Salination of Snow on Sea Ice and Formation of Snow Ice

1985 ◽  
Vol 6 ◽  
pp. 309-310 ◽  
Author(s):  
Takatoshi Takizawa
Keyword(s):  
Sea Ice ◽  
Snow Cover ◽  
Field Experiments ◽  
Sea Water ◽  
Ice Surface ◽  
Wet Snow

Field experiments were carried out to investigate a change in salinity of the snow cover on sea ice and of the snow ice. Snow which covered thin sea ice was flooded with the brine that was pushed out onto the sea ice surface, resulting in a rise in salinity to more than 32‰, which was higher than that of sea water. On the day after the salination of the snow, the flooded snow was found to have been either frozen into snow ice or kept unfrozen. In either case the brine was excluded in turn from the flooded snow. As a result, the wet snow or snow ice had a salinity somewhat above 20‰. It is suggested that subsequently the wet snow keeps the salinity at more than 20‰, while the salinity of the snow ice decreases gradually with time.

scholarly journals Artificial Release of Avalanches by Explosives

1977 ◽  
Vol 19 (81) ◽  
pp. 419-429 ◽  
Author(s):  
H. Gubler
Keyword(s):  
Snow Cover ◽  
Field Experiments ◽  
Stress Waves ◽  
Snow Surface ◽  
Fracture Zones ◽  
Seasonal Snow ◽  
Seasonal Snow Cover

Abstract The method of the artificial release of slab avalanches by explosives is investigated. The effect of a detonation on a seasonal snow cover is measured and discussed. The attenuation of the resulting stress waves as a function of the type of explosive used, the position of the charge relative to the snow surface, the snow-stratification profile, and the type of ground are determined in field experiments. The effective ranges of shots in potential fracture zones are estimated.

scholarly journals Modal Parameters Identification of Bridge Structures from GNSS Data Using the Improved Empirical Wavelet Transform

2021 ◽  
Vol 13 (17) ◽  
pp. 3375
Author(s):  
Zhen Fang ◽  
Jiayong Yu ◽  
Xiaolin Meng
Keyword(s):  
Wavelet Transform ◽  
Dynamic Response ◽  
Field Experiments ◽  
Suspension Bridge ◽  
Modal Parameters ◽  
Structural Dynamic ◽  
Response Data ◽  
Empirical Wavelet Transform ◽  
Bridge Structures ◽  
Gnss Data

It is difficult to accurately identify the dynamic deformation of bridges from Global Navigation Satellite System (GNSS) due to the influence of the multipath effect and random errors, etc. To solve this problem, an improved empirical wavelet transform (EWT)-based procedure was proposed to denoise GNSS data and identify the modal parameters of bridge structures. Firstly, the Yule–Walker algorithm-based auto-power spectrum and Fourier spectrum were jointly adopted to segment the frequency bands of structural dynamic response data. Secondly, the improved EWT algorithm was used to decompose and reconstruct the dynamic response data according to a correlation coefficient-based criterion. Finally, Natural Excitation Technique (NExT) and Hilbert Transform (HT) were applied to identify the modal parameters of structures from the decomposed efficient components. Two groups of simulation data were used to validate the feasibility and reliability of the proposed method, which consisted of the vibration responses of a four-storey steel frame model, and the acceleration response data of a suspension bridge. Moreover, field experiments were carried out on the Wilford suspension bridge in Nottingham, UK, with GNSS and an accelerometer. The fundamental frequency (1.6707 Hz), the damping ratio (0.82%), as well as the maximum dynamic displacements (10.10 mm) of the Wilford suspension bridge were detected by using this proposed method from the GNSS measurements, which were consistent with the accelerometer results. In conclusion, the analysis revealed that the improved EWT-based method was capable of accurately identifying the low-order, closely spaced modal parameters of bridge structures under operational conditions.

scholarly journals Model simulations of the modulating effect of the snow cover in a rain on snow event

2014 ◽  
Vol 11 (5) ◽  
pp. 4971-5005
Author(s):  
N. Wever ◽  
T. Jonas ◽  
C. Fierz ◽  
M. Lehning
Keyword(s):  
Snow Cover ◽  
Liquid Water ◽  
Field Experiments ◽  
Water Storage ◽  
Swiss Alps ◽  
Snow Melt ◽  
Point Scale ◽  
Meteorological Forcing ◽  
Dual Nature ◽  
Model Simulations

Abstract. In October 2011, the Swiss Alps encountered a marked rain on snow event when a large snowfall on 8 and 9 October was followed by intense rain on the 10th. This resulted in severe flooding in some parts of Switzerland. Model simulations were carried out for 14 meteorological stations in two regions of the Swiss Alps using the detailed physically-based snowpack model SNOWPACK. The results show that the snow cover has a strong modulating effect on the incoming rainfall signal on the sub-daily time scales. The snowpack runoff dynamics appears to be strongly dependent on the snow depth at the onset of the rain. Deeper snow covers have more storage potential and can absorb all rain and meltwater in the first hours, whereas the snowpack runoff from shallow snow covers reacts much quicker. It has been found that after about 4–6 h, the snowpack produced runoff and after about 11–13 h, total snowpack runoff becomes higher than total rainfall as a result of additional snow melt. These values are strongly dependent on the snow height at the onset of rainfall as well as precipitation and melt rates. An ensemble model study was carried out, in which meteorological forcing and rainfall from other stations were used for repeated simulations at a specific station. Using regression analysis, the individual contributions of rainfall, snow melt and the storage could be quantified. It was found that once the snowpack is producing runoff, deep snow covers produce more runoff than shallow ones. This could be associated with a higher contribution of the storage term. This term represents the recession curve from the liquid water storage and snowpack settling. In the event under study, snow melt in deep snow covers also turned out to be higher than in the shallow ones, although this is rather accidental. Our results show the dual nature of snow covers in rain on snow events. Snow covers initially absorb important amounts of rain water, but once meltwater is released by the snow cover, the snowpack runoff rates strongly exceed precipitation rates due to snow melt and a contribution from the liquid water storage. This effect is stronger in deeper snow covers than in shallow ones and is probably more pronounced in rain on snow events following closely after a snowfall than for rain on snow events on spring snow. These results are specifically valid for the point scale simulations performed in this study even though field experiments are lacking to further support the model simulations. Finally, the response of catchments can be different from the response at the point scale.

scholarly journals Variations in snow surface properties at the snowpack-depth, the slope and the basin scale

2008 ◽  
Vol 54 (188) ◽  
pp. 846-856 ◽  
Author(s):  
Jürg Schweizer ◽  
Achim Heilig ◽  
Sascha Bellaire ◽  
Charles Fierz
Keyword(s):  
Snow Cover ◽  
Surface Properties ◽  
Penetration Resistance ◽  
Snow Surface ◽  
Tree Line ◽  
Multi Scale ◽  
Basin Scale ◽  
Depth Scale ◽  
Snowpack Properties ◽  
Avalanche Formation

AbstractVariations of snow surface and snowpack properties affect avalanche formation. In up to four north-facing slopes above the tree line near Davos, Switzerland, snow surface properties were characterized. Penetration resistance was measured with a snow micro-penetrometer. The sampling scheme was designed to allow a multi-scale approach covering the snowpack depth scale (0.5–5 m), the slope scale (5–100 m) and the basin scale (100–1000 m). Observations and measurements were compared to the data of a nearby automatic weather station (AWS). The AWS data were also used to model snow-cover stratigraphy and its evolution with the numerical snow-cover model SNOWPACK. Comparing the four slopes showed that surface properties observed manually were similar among the three slopes that were sheltered, and often different from the slope that was wind-exposed. However, the penetration resistance of the surface layer was in most cases significantly different among slopes, although most values were <0.1 N, indicating very low hardness. These seemingly contradictory results follow from the different measurement support of the two methods. It is presently unclear which amount of variation at a given scale is relevant for avalanche formation. The geostatistical analysis and an analysis aimed at identifying the causes of variability were not conclusive. No patterns emerged that would allow conclusions regarding the effect on avalanche formation. Finding the causes of variability seems to require high-resolution terrain and weather models that are presently not readily available.

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