The return period or average time between events as a function of position along an avalanche path is a primary determiner for zoning in snow avalanche terrain. Areas with long times between the occurrences are sought to enable permissions for occupied structures and placement of infrastructure facilities. Generally, both the avalanche frequency and potential destructive effects decrease proceeding down into the runout zone where applications reside. Both the avalanche frequency and the estimated destructive effects are used in zoning methods. In typical zoning problems, the allowable return period exceeds 25 years. In most cases, there are not enough prior data on avalanche occurrences for an avalanche path to specify return periods accurately which implies that models must be used. Both avalanche dynamics and empirical, probabilistic models are used to predict zones for rare avalanche occurrences. However, the return period is a probabilistic quantity which places emphasis on empirical models. In this paper, the common methods for determining return period of avalanches are reviewed. The main emphasis in this paper is on verification, accuracy and quantification of the methods for determining return period through use of case histories. From a scientific perspective, the results here suggest some deficiencies in commonly used zoning strategies.

In this article, we are going to investigate the effects of snow, rain, temperature and wind on the number of backcountry and off-piste avalanche accidents. The data base of our survey is restricted on the western part of Austria (federal states Tyrol and Vorarlberg) within the winter periods 1987/88--2008/09. We are able to stratify the daily data for municipalities in Tyrol and Vorarlberg. Employing spatial kriging and hurdle models, we found a positive significant effect of the snow water equivalent measurement on avalanche accident counts (if we consider the running average over the past 3 days). The variables rain and temperature 1800 meter above sea level showed negative effects on the number of accident counts. In the case of the variable wind - ERA5 global reanalysis data turned out not to be reliable -- we had a focus on the 3 avalanche accident hot spots of Austria St. Anton am Arlberg, Lech and Sölden observing wind data of the weather stations Galzig, Warth and Obergurgl. At least in the case of St. Anton and Lech, we found significant positive effects (daily velocity totals and west wind component) on the number of avalanche counts. Calculating the daily mean wind load showed a positive effect only in the case of St. Anton am Arlberg.Finally, we tried to find conclusions in connection with `avalanche problems' such as used by several avalanche information services only finding (beside `new snow') some evidence for a `spring scenario'.

Snow gliding is a key factor for snow-glide avalanche formation and soil erosion. This study considers atmospheric and snow variables, vegetation characteristics, and soil properties and determines their relevance for snow gliding at a test site (Wildkogel, Upper Pinzgau, Austria) during winter 2014/2015. The time-dependent data were collected at a high temporal resolution. In addition to conventional sensors, a snow melt analyzer was used.The analysis shows that the soil temperature 10 cm below the surface, the phytomass of mosses, the liquid water content in the snowpack, and the static friction coefficient of the glide shoes had significant influence on snow gliding during the whole winter. In the first period (October to January) the soil moisture at the surface and 1.5 cm below the surface and the length of the slope uphill of the glide shoes affected the snow gliding, too. In the second period (February to May) the soil temperature at the surface, the soil moisture 10 cm below the surface, and the slope angle had additional influence on snow gliding.The role of the vegetation in the snow-glide process is determined by the influence on the static friction coefficient caused by its composition and characteristics and by moss-rich and short-stemmed canopies being seemingly more interconnected with the snowpack.In addition to the soil and snow properties, the topography and the vegetation characteristics, further investigations may be focused on the freezing and melting processes in the uppermost soil layers and at the soil surface.

In this article we analyzed spatial and temporal patterns of fatal Austrian avalanche accidents caused by backcountry and off-piste skiers and snowboarders within the winter periods 1967/1968–2015/2016. The data were based on reports of the Austrian Board for Alpine Safety and reports of the information services of the federal states. Using the date and the location of the recorded avalanche accidents, we were able to carry out spatial and temporal analyses applying generalized additive models and Markov random-field models. As a result of the trend analysis we noticed an increasing trend of backcountry and off-piste avalanche fatalities within the winter periods 1967/1968–2015/2016 (although slightly decreasing in recent years), which is in contradiction to the widespread opinion in Austria that the number of fatalities is constant over time. Additionally, we compared Austrian results with results of Switzerland, France, Italy and the US based on data from the International Commission of Alpine Rescue (ICAR). As a result of the spatial analysis, we noticed two hot spots of avalanche fatalities (Arlberg–Silvretta and Sölden). Because of the increasing trend and the rather narrow regional distribution of the fatalities, initiatives aimed at preventing avalanche accidents were highly recommended.

The slow downhill motion of snow on the ground, referred to as snow gliding, impairs afforestation, increases the predisposition for landslides, fosters winter soil erosion, and coincides with the occurrence of glide-snow avalanches. This study identifies areas with a high chance for severe snow gliding for an area covering > 20,000 km(2) in the Central and Eastern Alps. The Spatial Snow-Glide Model (SSGM) was used to map potential snow gliding areas (i.e. snow gliding distances). The results revealed 56% of the investigated area to be potential snow gliding areas. Nearly 2000 km(2) (17%) were prone to snow gliding distances of > 112 cm per winter period, indicating a high vulnerability for both glide cracks and glide-snow avalanches. Taking the inter-annual variability of winter precipitation into account, which turned out to be highest in the usually drier southern part, another 5690 km(2) were found to have a high risk for snow gliding damages. For planning purposes of on-site mitigation measures the Guidelines to Identify Snow-Glide Areas (GISGA) were validated to corroborate the sequential application of SSGM and GISGA for comprehensive assessment of snow gliding at landscape scale. We conclude that the application of SSGM and GISGA provides an appropriate evaluation framework for regional stakeholders to implement adequate steps to prevent critical snow gliding.

Avalanches are one of the principal natural hazards in alpine regions, frequently resulting in property damage and fatalities. This paper indicates and analyses avalanche accidents and particularly avalanche fatalities within the last 70years in Austria.

Avalanches are one of the principal natural hazards in alpine regions, resulting frequently in disastrous accidents. In this paper accidents with 5 or more than 5 fatalities were defined as a disastrous event. Taking into account this definition, 47 disastrous avalanches occurred in the last 70 years. These 47 events claimed 474 fatalities. The events with the highest number of fatalities occurred in Blons (1954) where two huge avalanches within 9 hours reached the village and killed 56 inhabitants, and in Galtür (1999) where 31 people lost their lives. Both events rank to the so-called ‘catastrophic avalanches’. The most serious `tourist avalanche‘ took place in 1982 near to Werfenweng where 13 skiers have been killed. The most recent event was an accident in the Wattener Lizum with 5 fatalities which occurred in February 2016. While `catastrophic avalanches ́ generally are correlated with heavy snowfall, `tourist avalanches ́ can be associated not only with new snow but also with a weak snowpack and increasing temperatures. The decreasing trend in the case of `catastrophic avalanches ́ undoubtedly is a result of the high standard of technical protective measures in Austria; however, fatalities caused by ‘tourist avalanches’ predominated in the last 35 to 45 years which can be explained by a rising number of skiers and mountaineers.

Snow gliding is a downhill motion of snow on the ground; it is able to affect afforestation (uprooting of plants) and to cause soil erosion. Once the glide motion turns into an avalanche movement, the process is called a glide avalanche. Winters with continuing snow gliding and a high activity of glide avalanches might be called ‘glide winters’. The most recent ‘glide winter’ in the European Alps was 2011/2012. Glide avalanches have the ability to cause damage to buildings and infrastructure. This review describes the progress in research, from basic snow glide measurements via the design of sophisticated models through to comprehensive investigations concerning glide avalanche formation. However, despite the great progress made in this field of research, there are still some unsolved problems, such as the influence of soil conditions on snow gliding or the prediction of glide avalanches.

Snow gliding is a downhill motion of snow on the ground; observations have shown gliding to be possible not only on open slopes but also in forest stands. Larch stands, with their low canopy density and open forest structure with clearings and gaps, are particularly prone to high glide rates. Snow gliding may have negative effects on juvenescent trees which can be damaged by extraction from the ground.

This paper deals with an analysis of backcountry avalanche events in Austria. In particular the cumulation of accidents in certain periods will be investigated. During the last 50 years an average of 30 persons per year were killed by avalanches in Austria; about two third of all fatalities occurred as a result oftourist avalanches´. The most fatal event in the backcountry was in January 1982 when 13 skiers (mainly students) were killed by an avalanche near to Werfenweng (Salzburg). The majority oftourist avalanchesoccurs in a few (short) periods; generally one to four periods per winter can be identified. In many cases the cumulation of accidents is correlated with new snow and drift snow.

This somewhat provocative title induces a couple of further provocative questions: Are well- tried findings which were already identified 80 to 100 years ago no more sufficient for skiers? What further improvements became relevant for mountaineers and backcountry skiers? What is new in today's avalanche education? One of the first appropriate books was Zdarsky's "Elements of Avalanche Awareness" published in 1916; in the 1920s and 1930s the most important influencing factors on avalanches were already well-known; the books from Paulcke (1938), Seligman (1936) and Welzenbach (1930) are milestones in the field of snow and avalanches. Bilgeri (1934) mentioned six most important points which have to be considered when travelling through avalanche terrain (angle of the slope, terrain, ground, depth of the snow, consistency of the snow and anchorage of the snow). In the 1980s Conway et al. found that within short distances stability may be subject to strong variations. However, mountaineers and backcountry skiers could not use the findings because no one was able to identify those areas of instability. A major discussion on avalanche education was initiated as the strategic methods came up end of the 1990s (Munter, Larcher, Engler…); these methods only used another design but did not provide new results. This paper describes the most important findings with regard to the relevance for mountaineers and backcountry skiers and reviews them in terms of their practical application.

Snow hardness is an important parameter in avalanche forecasting; however, hardness has not that relevance as the shear strength of snow. On the other hand hardness measurements are easier to operate and they are more suitable for practitioners. The snow hardness correlates approximately with the shear strength of snow; low hardness may be an indicator for weak layers (e.g. depth hoar). This study aims to quantify the shear strength with data of hardness measurements. For that purpose both, traditional hand hardness observations and objective hardness measurements were carried out. The snow hardness was measured in horizontal direction with a digital push-pull gauge. The shear strength was measured with a shear frame (size 0.05m 2 ). All measurements were done at intervals of 10cm vertically. The analysis of the scattering data allows an interpretation of the relationship between the snow hardness and the shear strength. Especially lower hardness levels (up to 100kPa) show a clear correlation.

During the last 50 years, an average of 30 persons per year was killed by avalanches in Austria. About one-third of all avalanche fatalities occurred as a result of so-called ‘catastrophic avalanches’. ‘Catastrophic avalanches’ are spontaneously released avalanches that affect villages and cause damage to property (buildings, roads and other infrastructure). The biggest avalanche events in Austria were in 1950/1951 (135 fatalities), in 1953/1954 (143 fatalities) and in February 1999, when 38 persons were killed in Galtür and Valzur. This article deals with an analysis of nine major avalanche cycles in the last 55 years. An avalanche cycle in this article is defined as 50 recorded avalanches of at least size 3 in two days and/or 5 persons killed in villages within two days. The basis of this study are the well-documented records from Fliri (1998), who analysed natural disasters in the western part of Austria and the Trentino, including floods, mudflows, earthquakes and avalanches. The meteorological data were taken from two relevant observation sites in the northern part of the Austrian Alps, from two sites in an intermediate and continental region, respectively and from one site in the southern part of the Austrian Alps. Atmospheric patterns were analysed by using weather charts for the relevant periods. Both the meteorological data and the weather charts were provided by the Central Institute for Meteorology and Geodynamics (ZAMG). It was found that there was a major cycle every 6 years (on average). Two-thirds of all investigated cycles were characterised by a continuous increase of snow depth over a period of at least three days. In only three periods (1975, 1986, 1988), daily extreme values could be observed. More than 40% of all the cycles occurred in January. In two-thirds, a north-westerly oriented frontal zone was responsible for the formation of a major cycle. The remaining cycles were released by low-pressure areas over Central Europe and the Mediterranean Sea, respectively.

Snow forces impede afforestation in the subalpine region; in particular juvenescent trees can be damaged by extraction from the ground. Such forces are mainly triggered by intense snow gliding which is a frequent phenomenon on slopes with a smooth ground surface.In this article we have investigated the effects of snow gliding processes on forest plants. The study area was situated on a south-facing slope (altitude 1900 m, inclination 30 degrees) in the Stubai valley, Tyrol, Austria. The site is characterized by a smooth ground surface (stagnation depth of about 10 m) and high glide rates leading to a great number of damaged plants almost every winter season.The investigations included snow gliding measurements and experiments to determine those forces which are necessary to uproot juvenescent trees from the ground. The experiments were carried out on Swiss stone pine and larch trees with a height of 0.6-0.9 m (diameter 0.02 and 0.045 m).Our measurements revealed glide rates of up to 46.5 mm d(-1) and forces between 1000 and 3500 N as sufficient to uproot juvenescent trees.The downslope force was determined by the applicable snow pressure equations and compared with the results of our experiments. The investigations show that the calculated values are in close agreement with those measured on the plants. Provided that an impact of 50% of the measured forces will no longer result in damage to the trees (extraction or breakage), we calculated that the stagnation depth has to be reduced to about 1.5 m. (C) 2008 Elsevier B.V. All rights reserved.

The shear strength plays an important role in avalanche formation. However, investigations on shear strength in the field are time-consuming, in particular these measurements require experienced avalanche professionals. Main objective of this study was to estimate shear strength by using indirect methods which are more user-friendly than the traditional tests. We assumed that hardness and density of snow must be the two most appropriate parameters. Three different methods were implemented to determine snow hardness: the conventional hand hardness test, measurements with the Swiss Rammsonde, and a method with a digital force gauge where we measured hardness in horizontal direction (to find out hardness ranges in the different layers of the snowpack). The snow density was measured with the common standard cylinder and the shear strength was determined with a shear frame. The results indicate a encouraging relationship between snow hardness and shear strength; however, the strong scattering of the data requires further investigations to specify these relations.

At all times natural hazards like torrents or avalanches pose a threat to settlements and infrastructures in the Austrian Alps. Since 1950 more than 1,600 persons have been killed by avalanches in Austria, which is on average approximately 30 fatalities per year. In particular, the winter periods 1950/1951 and 1953/1954 stand out with more than 100 fatalities. Those events led to an increase of avalanche control programmes in the following decades. While from the 1950s to the 1970s emphasis was placed on permanent measures (technical structures, afforestations, hazard zoning ...) additional programmes such as avalanche warning and forecasting have supplemented avalanche control measures in the last decades. Current research is focused on avalanche simulation, risk management and the influence of the forest on avalanche formation. An important area of future research is to develop improved methods for avalanche forecasting and to intensify the investigation of the dynamics of avalanches.

Snow gliding is a key component leading to natural hazards, i.e. avalanches and erosions, and due to ongoing global changes has become a topic of major concern. Spatial information on snow gliding is important for management purposes, but, to date, lack of knowledge about key drivers for the snow-glide process hindered the development of a spatial snow-glide model (SSGM). We report the most important drivers for snow gliding derived from analyzing snow-glide distances taken over five winter periods in two climatically different study areas by ordinary least-squares regression. Six variables (forest stand, slope angle, winter precipitation, surface roughness, slope aspect west, slope aspect east) were revealed as key drivers and enabled us for the first time to establish a SSGM. Both model development (R2=0.838) and model validation (R2=0.823) exhibit outstanding accuracy of prediction. Hence, the SSGM was used to model snow-glide maps for both study areas: the ‘Kaserstattalm’ (Stubai Valley, North Tyrol, Austria) and the drier and warmer area of the ‘Waltner Mähder’ (Passeier Valley, South Tyrol, Italy). The reliability of these maps was validated by intersection with mapped erosions attributed to snow gliding. Therewith, such potential snow-glide maps have management relevance and are useful and necessary for risk assessment as well as to raise awareness about snow gliding to the land owners and regional managers.