Powder fever and its impact on decision-making in avalanche terrain

We examined the effect of emotions, associated with “powder fever”, on decision-making in avalanche terrain. Background: Skiing in avalanche terrain is a voluntary activity that exposes the participant to potentially fatal risk. Impaired decision-making in this context can therefore have devastating results, often with limited prior corrective feedback and learning opportunities. Previous research has suggested that arousal caused by emotions affects risk assessment and intentions to engage in risky behavior. We propose that powder fever may induce similar responses. Methods: We used the following two experimental methods: laboratory studies with visual visceral stimuli (ski movies) and a field study with real stimuli (skiing exciting terrain). We evaluated the effect of emotions on attention, risk assessment, and willingness to expose oneself and others to risk. Results: Both the laboratory studies and the field study showed that skiing-related stimuli had a relatively strong effect on reported emotions. However, we found very few significant effects on decision-making or assessment of risk. Conclusions: Skiing activities make people happier. However, despite the clear parallels to sexual arousal, powder fever does not appear to significantly impair decision-making in our study. More research on the effects of powder fewer on milder forms of risk-taking behavior is needed

Can big data and random forests improve avalanche runout estimation compared to simple linear regression?

Accurate prediction of snow avalanche runout-distances in a deterministic sense remains a challenge due to the complexity of all the physical properties involved. Therefore, in many locations including Norway, it has been common practice to define the runout distance using the angle from the starting point to the end of the runout zone (α-angle). We use a large dataset of avalanche events from Switzerland (N = 18,737) acquired using optical satellites to calculate the α-angle for each avalanche. The α-angles in our dataset are normally distributed with a mean of 33◦ and a standard deviation of 6.1◦, which provides additional understanding and insights into α-angle distribution. Using a feature importance module in the Random Forest framework, we found the most important topographic parameter for predicting α-angles to be the average gradient from the release area to the β-point. Despite the large dataset and a modern machine learning (ML) method, we found the simple linear regression model to yield a higher performance than our ML attempts. This means that it is better to use a simple linear regression in an operational context

Representing spatial variability of snow water equivalent in hydrologic and land-surface models: a review

This paper evaluates the use of field data on the spatial variability of snow water equivalent (SWE) to guide the design of distributed snow models. An extensive reanalysis of results from previous field studies in different snow environments around the world is presented, followed by an analysis of field data on spatial variability of snow collected in the headwaters of the Jollie River basin, a rugged mountain catchment in the Southern Alps of New Zealand. In addition, area-averaged simulations of SWE based on different types of spatial discretization are evaluated. Spatial variability of SWE is shaped by a range of different processes that occur across a hierarchy of spatial scales. Spatial variability at the watershed-scale is shaped by variability in near-surface meteorological fields (e.g., elevation gradients in temperature) and, provided suitable meteorological data is available, can be explicitly resolved by spatial interpolation/extrapolation. On the other hand, spatial variability of SWE at the hillslope-scale is governed by processes such as drifting, sloughing of snow off steep slopes, trapping of snow by shrubs, and the nonuniform unloading of snow by the forest canopy, which are more difficult to resolve explicitly. Subgrid probability distributions are often capable of representing the aggregate-impact of unresolved processes at the hillslope-scale, though they may not adequately capture the effects of elevation gradients. While the best modeling strategy is case-specific, the analysis in this paper provides guidance on both the suitability of several common snow modeling approaches and on the choice of parameter values in subgrid probability distributions.Martyn P. Clark, Jordy Hendrikx, Andrew G. Slater, Dmitri Kavetski, Brian Anderson, Nicolas J. Cullen, Tim Kerr, Einar Örn Hreinsson and Ross A. Wood

An examination of the snow and avalanche hazard on the Milford Road, Fiordland, New Zealand

Avalanches pose a significant natural hazard in many parts of the world. Worldwide the hazard is being managed in a number of new and traditional methods. In New Zealand, the Milford Road, Fiordland, has a significant avalanche problem which has been managed by the Transit New Zealand Milford Road Avalanche Programme since 1984. This avalanche programme has generated a database of all avalanche occurrences and associated meteorological parameters for the time period 1985 to 2002. Elsewhere around the world, similar and more extensive data sets have been used to examine a wide variety of aspects in relation to the snow cover, avalanching and avalanche hazard. The availability of the Milford Road database has provided the opportunity use new and traditional approaches to examine many aspects of avalanching including; the trends in and relationships with the snow and avalanche regime, evaluation of the avalanche hazard, statistical forecasting of avalanches and the visualisation of avalanche occurrence information in a GIS. Statistical and graphical examination of the inter-annual variation in the snow and avalanche regime revealed relationships between the snow depth, avalanche occurrences and atmospheric circulation similar to those found elsewhere around the world, but not previously examined in New Zealand. Furthermore, the analysis resulted in strong correlations despite using a database significantly shorter than those used elsewhere. Atmospheric circulation types that bring strong winds and precipitation were found to be highly significantly correlated with avalanche occurrences and snow depth. Avalanche occurrences were more highly correlated with atmospheric circulation than snow depth was, reflecting the strong maritime avalanche climate. Risk evaluation was undertaken using two approaches, the avalanche hazard index (AHI) and the probability of death to individuals (PDI) method. The present avalanche risk was compared to a theoretically uncontrolled avalanche regime, using 2002 traffic volumes for AHI and PDI. The AHI analysis highlighted the reduction in the AHI resulting from the control programme, and the significantly lower AHI when compared to Rogers Pass, B.C., Canada. The PDI analysis using equations modified to allow for a range of consequences indicated that the Milford Road is similar in risk to roads in Switzerland, but is far more accessible, with fewer closed days. A new equation for PDI, which accounted for waiting traffic was derived, and suggested that the calculated risk was high and unacceptable compared to standards applied to other hazards. Statistical forecasting using classification tree analysis has been successfully applied to avalanche forecasting in other climatic settings. This study has applied an extension to this technique through 10-fold cross validation to permit classification of an avalanche day in this direct action maritime climate. Using varying misclassification costs two classification trees were generated. The tree that used only wind speed and wind speed and precipitation combined in a temperature sensitive wind drift parameter obtained an overall accuracy of 78%, with correct prediction for an avalanche day at 86%. These predictor variables are considered to be the fundamental controls on avalanche forecasting in this climate, and coincide with important variables inferred from the atmospheric circulation analysis. Following the investigation of various methods for the creation of a high resolution digital elevation model (DEM), a GIS was used for the visualisation and examination of avalanche occurrences. Similar to other studies, qualitative and quantitative analysis of the spatial distribution in terms of aspect of avalanche occurrences was undertaken using the GIS. Colour coding of occurrences highlighted the influence of two storm directions, while an excess ratio showed the clear influence of aspect on avalanche occurrences in relation to two dominant storm directions, avalanche size and avalanche paths. Furthermore, the GIS has many applications for operational forecasting, teaching and the maintenance of institutional memory for the avalanche programme

FIVE SEASONS OF DETAILED SURFACE HOAR OBSERVATIONS: WHAT HAVE WE LEARNED?

ABSTRACT: Since the start of the 2011-12 season the Yellowstone Club Ski Patrol have diligently been collecting detailed observations of surface hoar (SH) presence or absence at 16 sites across Pioneer Mountain in SW Montana, USA. These manual observations have been taken on at least three days per week, and on many additional days when SH formation seemed possible. We now have over 280 days of SH / non-SH observations at 16 sites, at varying elevations, with different aspects and sky view exposures. To our knowledge there is no other data set on manual observations of SH at the mountain range scale, with this combined spatial and temporal coverage. In addition to the manual observations, we have 15 minute observations of temperature and humidity at 1.5m, sky view exposure at all sites, and 15 minute wind speed and direction at half of the sites. Using these data we have examined the dominant controls that explain the spatial patterns of surface hoar at the plot to mountain range scale. Our results show that small-scale site characteristics which influence micrometeorological conditions and the local site level sky view exposure can greatly influence the spatial variability of surface hoar, over and above that which aspect alone can explain. Furthermore, synoptic scale analysis using NCEP/NCAR synoptic composite maps provides insight for SH absence on days when conditions would seem to be conducive for SH formation. These results highlight our incomplete, but growing understanding of some of the complexities of surface hoar formation processes at this scale, and have implications for both regional and local scale avalanche forecasting

Slope scale spatial variability across time and space: Comparison of results from continental and maritime climates

ABSTRACT: Understanding the spatial variability of the snowpack is a crucial step to improve accuracy in field data collection and avalanche forecasting. While there has already been a large volume of literature assessing the spatial variability of the snowpack, inconsistent sampling designs make comparing results difficult. This work uses an overlapping 10 by 10 m grid to collect Extended Column (ECT), Compression (CT) and Stuffblock (SB) test data at the slope scale across a range of environmental settings and climatic regimes in Montana and New Zealand. The overlapping grid methodology standardizes data collection between our sites, as well as allowing for repeat data collection on the same slope, thereby providing a new method for attempting to assess changes in spatial variability over time. Preliminary results suggest that the spatial variability of fracture propagation and fracture initiation may increase over time, and that the spatial variability of the fracture propagation propensity may be related to the processes causing the instability. As we collect more data, these results will provide further insight into the problem of snow pit location and representivity, both in terms of space and time

Risky positioning–social aspirations and risk-taking behaviour in avalanche terrain

We test if positionality, i.e., the desire to gain social status, is associated with an increased willingness to take risk among backcountry riders. If positional preferences drive risk-taking behaviour in avalanche terrain, this is especially problematic because the stakes are high and can be fatal. Our analysis is based on data for hypothetical choices from an online survey (N = 648) in North America. We find that positional riders are significantly more likely to boast about riding bold lines, more likely to associate steep riding with social respect, and more likely to say that they would accept to ride a potentially risky line. The positionality effect is present regardless of level of avalanche training. We discuss implications for avalanche training and education

Spatial Heterogeneity of Snow Density and Its Influence on Snow Water Equivalence Estimates in a Large Mountainous Basin

Accurate representation of the spatial distribution of snow water equivalent (SWE) in mountainous basins is critical for furthering the understanding of snow as a water resource, especially in the Western United States. To estimate the spatial distribution and total volume of SWE over mountainous basins, previous work has either assumed uniform snow density or used simple approaches to estimate density. This study uses over 1000 direct measurements of SWE and snow depth (from which density was calculated) in sampling areas that were physiographically proportional to a large (207 km2) mountainous basin in southwest Montana. Using these data, modeled spatial distributions of density and depth were developed and combined to obtain estimates of total basin SWE. Six estimates of SWE were obtained using varying combinations of the distributed depth and density models and were compared to the average of three different models that utilized direct measurements of SWE. Models utilizing direct SWE measurements varied by approximately 1% around their mean, while SWE estimates derived from combined depth and density models varied by over 14% around the same mean. This study highlights the need to carefully consider the spatial variability of density when estimating SWE based on snow depth in these environments

Are they experts? Self-assessed backcountry skills among backcountry skiers in Norway and North America

Proceedings, International Snow Science Workshop, Innsbruck, Austria, 2018We analyze how backcountry skiers’ perceived ability to manage avalanche terrain correlate with more objective measures of experience and skills, among 1209 backcountry riders in Norway and North America. We further analyze if self-assessed backcountry skills are affected by past experience of avalanches and close calls, risk attitudes, and demographics. Our results suggest that self-assessed skill to a large extent is a function of experience and knowledge, which is encouraging. However, we also find that men perceive their skills to be substantially higher than women when compared equally, at all levels of training and experience. Finally, we find that individuals with past experiences of avalanches and close calls rate their skills as higher than individuals without such experiences. Ourfindings provide suggestive evidence of a miss-match between perceived and actual skill, but more research is needed to control for selection effects and differences in objective skill levels

Keeping up with Jeremy Jones: Positional preferences and risky terrain choices

We use results from an online survey distributed in North America (N = 796), to analyze if backcountry riders’ level of contentment is affected by others’ backcountry activities, i.e., if they are positional, and if positionality for backcountry experiences is associated with increased risk-taking behavior. Our findings suggest that many are positional, and that positional preferences for challenging terrain is correlated with relatively high risk exposure. The positionality effect is present regardless of level of avalanche training, and suggests that current avalanche education does not change ones positionality related to risk taking behavior. Our results provide support for the hypothesis that social comparisons, and perhaps the fear of losing out, affects risk-taking behavior, and that current avalanche education does not change this. It further suggests that avalanche courses should be adapted to deal with the "keeping up with the Joneses" effect by incorporating some comprehension of personality type in the presentation of course material