Snow Gliding Research Articles

Physical Modeling of Snow Gliding: A Case Study in the NW Italian Alps

Snow gliding, a slow movement downhill of snow cover, is complex to forecast and model and yet is extremely important, because it drives snowpack dynamics in the pre-avalanching phase. Despite recent interest in this process and the development of some studies therein, this phenomenon is poorly understood and represents a major point of uncertainty for avalanche forecasting. This study presents a data-driven, physically based, time-dependent 1D model, Poli-Glide, able to predict the slow movement of snowpacks along a flow line at the daily scale. The objective of the work was to create a useful snow gliding model, requiring few, relatively easily available input data, by (i) modeling snowpack evolution from measured precipitation and air temperature, (ii) evaluating the rate and extent of movement of the snowpack in the gliding phase, and (iii) assessing fracture (i.e., avalanching) timing. Such a model could be then used to provide hazard assessment in areas subject to gliding, thereby, and subsequent avalanching. To do so, some simplifying assumptions were introduced, namely that (i) negligible traction stress occurs within soil, (ii) water percolation into snow occurs at a fixed rate, and (iii) the micro topography of soil is schematized according to a sinusoidal function in the absence of soil erosion. The proposed model was then applied to the “Torrent des Marais-Mont de La Saxe” site in Aosta Valley, monitored during the winters of 2010 and 2011, featuring different weather conditions. The results showed an acceptable capacity of the model to reproduce snowpack deformation patterns and the final snowpack’s displacement. Correlation analysis based upon observed glide rates further confirmed dependence against the chosen variables, thus witnessing the goodness of the model. The results could be a valuable starting point for future research aimed at including more complex parameterizations of the different processes that affect gliding.

Shallow erosion on grassland slopes in the European Alps – Geomorphological classification, spatio-temporal analysis, and understanding snow and vegetation impacts

Erosion with the subsequent loss of soil and soil fertility is one of the urgent environmental problems worldwide. On grassland slopes from the montane to the alpine elevation zones of the European Alps, shallow erosion is a widespread and regionally increasing phenomenon. This group of mechanical denudation processes includes shallow landslides and nival abrasion (i.e., by snow gliding and avalanches), which are displacing patches of vegetation, soil and unconsolidated material. The resulting bare ground areas as well as the dislocated material are susceptible to further transport by water, snow, or wind. Our review summarizes the current knowledge on the main geomorphological processes for Alpine grassland erosion, namely shallow landslides and abrasion by snow movements as well as combinations of both processes. We shortly discuss the basic and variable controlling factors and further present a comprehensive approach for identifying and classifying shallow erosion phenomena and processes. In this context, the possibilities, limitations, and challenges for identification, classification and analysis of these processes by remote sensing are discussed in detail. Furthermore, the article focuses particularly on the role of snow-related processes, the relationship of erosion and vegetation, and the re-stabilization of affected areas by plants. Finally, we outline the discussion on the impact of land-use and climate change on these shallow erosion processes and identify the main research gaps that should be bridged in order to both better understand and deal with these erosion types on Alpine slopes.

Towards a better understanding of shallow erosion resistance of subalpine grasslands

Shallow erosion is caused by processes such as landsliding, snow gliding, avalanches, animal trampling, or human activities and frequently occurs on high mountain grasslands. It can lead to significant long-term losses of grassland and related ecosystem services, e.g. fodder production, or water retention. Since restoration of subalpine and alpine ecosystems is difficult, prevention of shallow erosion is of vital importance for damage control. However, current knowledge on relationships between grassland ecology, management and shallow erosion resistance is very limited. In this study, we assessed relationships between the surface-mat stability of the topsoil (0–10 cm depth), vegetation cover, species diversity, growth patterns, indicator plant species for high and low tensile strength, soil texture, total nitrogen, and soil organic carbon.Vegetation composition significantly influenced the surface-mat stability of subalpine grasslands. Some key species were associated with higher reinforcement than other species. However, surface-mat stability neither depended on the vegetation type (grass or forb), nor on the root type, but rather on individual species characteristics such as roots and clonal structures as well as a certain plant and structural diversity. A balanced nutrient supply was associated with higher surface-mat stability, while soil texture had no effect. We hypothesized that stabilizing effects of plant-plant connections in tightly interwoven, dense root and clonal structure systems dominate over effects of root-soil connections. Thus, effects of soil texture may be negligible for the surface-mat stability. In general, our results show that adapted grassland management can be used as preventive erosion control measure on subalpine grasslands.

Use of Sentinel-1 radar observations to evaluate snowmelt dynamics in alpine regions

Abstract. Knowing the timing and the evolution of the snow melting process is very important, since it allows the prediction of (i) the snowmelt onset, (ii) the snow gliding and wet-snow avalanches, (iii) the release of snow contaminants, and (iv) the runoff onset. The snowmelt can be monitored by jointly measuring snowpack parameters such as the snow water equivalent (SWE) or the amount of free liquid water content (LWC). However, continuous measurements of SWE and LWC are rare and difficult to obtain. On the other hand, active microwave sensors such as the synthetic aperture radar (SAR) mounted on board satellites are highly sensitive to LWC of the snowpack and can provide spatially distributed information with a high resolution. Moreover, with the introduction of Sentinel-1, SAR images are regularly acquired every 6 d over several places in the world. In this paper we analyze the correlation between the multitemporal SAR backscattering and the snowmelt dynamics. We compared Sentinel-1 backscattering with snow properties derived from in situ observations and process-based snow modeling simulations for five alpine test sites in Italy, Germany and Switzerland considering 2 hydrological years. We found that the multitemporal SAR measurements allow the identification of the three melting phases that characterize the melting process, i.e., moistening, ripening and runoff. In particular, we found that the C-band SAR backscattering decreases as soon as the snow starts containing water and that the backscattering increases as soon as SWE starts decreasing, which corresponds to the release of meltwater from the snowpack. We discuss the possible reasons of this increase, which are not directly correlated to the SWE decrease but to the different snow conditions, which change the backscattering mechanisms. Finally, we show a spatially distributed application of the identification of the runoff onset from SAR images for a mountain catchment, i.e., the Zugspitze catchment in Germany. Results allow us to better understand the spatial and temporal evolution of melting dynamics in mountain regions. The presented investigation could have relevant applications for monitoring and predicting the snowmelt progress over large regions.

Investigating morphodynamics on Little Ice Age lateral moraines in the Italian Alps using archival aerial photogrammetry and airborne LiDAR data

The rapid glacier recession in the European Alps exposes large amounts of unconsolidated sediment. Several processes are involved in the reworking of this sediment on steep lateral moraines, e.g. small slides on the upper slopes, sheet erosion by snow gliding, fluvial erosion and debris flows. To gain deeper insight into the dependence of the morphodynamics on lateral moraines on the time since deglaciation, we analysed erosion rates and geomorphological processes occurring at different distances from the present-day glacier termini. Moreover, we assessed the significance of parameters like slope gradient, altitude a.s.l. and the presence of dead ice for the morphodynamics. We used historical (1959) as well as contemporary (2016) aerial images and airborne laserscanning data (2006) to derive orthophotos, 3D point clouds (SfM) and Digital Elevation Models of Difference (DoD). These models cover the entire lateral moraine sections of two glaciers in South Tyrol, Italy, but detailed analysis was restricted to five test areas which deglaciated at different times. We were able to detect areas with decreasing geomorphological activity showing an erosion rate below 1 cm per year mainly on moraine sections remote from the contemporary glacier tongue. Simultaneously, moraine sections with continuous high levels of morphodynamics or even increasing activity were observed. The latter show heavy gullying on the upper slopes with erosion rates of 5.9–10.1 cm per year and no indications of decreasing rework rates could be found. We suppose a strong influence of degrading debris-covered dead ice, which all these slope experienced over many years after glacier melting. However, moisture availability and the slope angles, amongst others, also affect the geomorphological processes forming the moraine slopes. Thus, our results are only partly consistent with the literature, because we found areas with decreasing activity, as assumed in the paraglacial adjustment model, as well as moraine sections where no stabilization can be observed to date.

Snow gliding and glide-snow avalanches: recent outcomes from two experimental test sites in Aosta Valley (northwestern Italian Alps)

Abstract. Snow gliding and glide-snow avalanches are gaining importance among scientists as global warming might induce conditions favourable to those phenomena. Our aim is to analyse such processes with a particular focus on the potential driving factors associated with the soil conditions. We equipped two experimental test sites in the Aosta Valley region (NW Italy) with glide-snow shoes, temperature and volumetric liquid water content (VLWC) sensors in the soil and in the basal snowpack layer; snow and weather parameters were also collected by automatic weather stations and at manual snow measuring sites. In the two monitoring seasons 2013–2014 and 2014–2015 we registered nine glide-snow avalanches, two cold and seven warm events, which were characterized by different snow and soil conditions. In the only warm glide-snow avalanche event, which presented a continuous gliding before, the daily glide rate showed a significant exponential relationship with the soil VLWC. We also found, though without a general trend, that gliding and non-gliding periods (either considering warm and cold periods separately or together) were characterized by significantly different predisposing factors. This study contributes to the assessment of the importance of soil VLWC, which seems to be one of the most important driving factors for gliding processes. Therefore, it supports the need, already suggested by other scientists, for analysing such processes with an interdisciplinary approach which integrates snow and soil sciences.

Determining the drivers for snow gliding

Abstract. 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.

Spatial evaluation of snow gliding in the Alps

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 km2 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 km2 (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 km2 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.

The role of soil volumetric liquid water content during snow gliding processes

In recent years, our understanding of snow gliding and glide-snow avalanches has improved; however, the contributing factors are still poorly understood and difficult to measure. In particular, the role of soil properties has not been considered as much as other environmental parameters (e.g. air temperature). Focusing on soil properties we established a monitoring site in the Italian Alps, in the release zone of a WSW-facing avalanche path. The area is typically characterized by intense snow gliding that results in the formation of large glide cracks, often leading to the release of a glide-snow avalanche. The site was equipped with four glide-snow shoes to measure snow gliding movement. Temperature and water content sensors were located at the snow-soil interface and at different depths within the soil. Meteorological data were recorded by a nearby automatic weather station, and snowpack properties were evaluated using manual snow profiles and SNOWPACK simulations; additionally, soils were characterized with special emphasis on the physical properties of the upper soil horizons. During two monitoring seasons, we registered a cold-temperature event characterized by gradual and continuous snow gliding and three warm-temperature events with glide-crack formation and evolution, in one case resulting in a glide-snow avalanche. Univariate (Mann-Witney U test) and multivariate (Classification Trees) analyses allowed us to find significant differences between gliding and non-gliding periods, and confirmed the importance of distinguishing between cold and warm-temperature events. In particular, for warm-temperature events we found that the most significant parameters were a large snow depth, strong settlement and high air temperature. For cold-temperature events we found that, together with a large snow depth, the volumetric liquid water content, both at the snow-soil interface and within the soil, played a fundamental role. Moreover, for the cold-temperature events we found a strong correlation between daily glide rates and the soil volumetric liquid water content, with an exponential relationship at the snow-soil interface and at 5cm depth within the soil. These results highlight the relationship between the snow gliding process and the soil conditions, which have been identified among the main environmental factors related to the development of snow gliding.

Snow gliding susceptibility: the Monterosa Ski resort, NW Italian Alps

ABSTRACTSnow gliding, though a slow process, should be considered as important as the faster snow avalanche flows, as it can similarly produce severe damage to buildings and infrastructure. Snow gliding depends on snowpack properties, land cover and terrain parameters. Among these driving factors, in this work, we focus on stationary factors, that is, those that are considered features related to terrain and land cover, in particular those that could be derived from a Digital Elevation Model or land use/cover maps: slope angle, aspect, roughness and land cover. We propose a geographical information system-based procedure to create a snow gliding susceptibility index and to produce a related snow gliding susceptibility map. We tested this procedure in the Aosta Valley (NW Italian Alps), where the Monterosa Ski resort is located. The map covers an area of about 338 km2 at a scale of 1:50,000. The proposed procedure is seen as a valuable tool to help safety personnel at ski resorts as well as in other scenarios (e.g. road management) in the identification of areas most prone to snow gliding.

Dynamics of glide avalanches and snow gliding

AbstractIn recent years, due to warmer snow cover, there has been a significant increase in the number of cases of damage caused by gliding snowpacks and glide avalanches. On most occasions, these have been full‐depth, wet‐snow avalanches, and this led some people to express their surprise: how could low‐speed masses of wet snow exert sufficiently high levels of pressure to severely damage engineered structures designed to carry heavy loads? This paper reviews the current state of knowledge about the formation of glide avalanches and the forces exerted on simple structures by a gliding mass of snow. One particular difficulty in reviewing the existing literature on gliding snow and on force calculations is that much of the theoretical and phenomenological analyses were presented in technical reports that date back to the earliest developments of avalanche science in the 1930s. Returning to these primary sources and attempting to put them into a contemporary perspective are vital. A detailed, modern analysis of them shows that the order of magnitude of the forces exerted by gliding snow can indeed be estimated correctly. The precise physical mechanisms remain elusive, however. We comment on the existing approaches in light of the most recent findings about related topics, including the physics of granular and plastic flows, and from field surveys of snow and avalanches (as well as glaciers and debris flows). Methods of calculating the forces exerted by glide avalanches are compared quantitatively on the basis of two case studies. This paper shows that if snow depth and density are known, then certain approaches can indeed predict the forces exerted on simple obstacles in the event of glide avalanches or gliding snow cover.

Soil erosion by snow gliding – a first quantification attempt in a subalpine area in Switzerland

Abstract. Snow processes might be one important driver of soil erosion in Alpine grasslands and thus the unknown variable when erosion modelling is attempted. The aim of this study is to assess the importance of snow gliding as a soil erosion agent for four different land use/land cover types in a subalpine area in Switzerland. We used three different approaches to estimate soil erosion rates: sediment yield measurements in snow glide depositions, the fallout radionuclide 137Cs and modelling with the Revised Universal Soil Loss Equation (RUSLE). RUSLE permits the evaluation of soil loss by water erosion, the 137Cs method integrates soil loss due to all erosion agents involved, and the measurement of snow glide deposition sediment yield can be directly related to snow-glide-induced erosion. Further, cumulative snow glide distance was measured for the sites in the winter of 2009/2010 and modelled for the surrounding area and long-term average winter precipitation (1959–2010) with the spatial snow glide model (SSGM). Measured snow glide distance confirmed the presence of snow gliding and ranged from 2 to 189 cm, with lower values on the north-facing slopes. We observed a reduction of snow glide distance with increasing surface roughness of the vegetation, which is an important information with respect to conservation planning and expected and ongoing land use changes in the Alps. Snow glide erosion estimated from the snow glide depositions was highly variable with values ranging from 0.03 to 22.9 t ha−1 yr−1 in the winter of 2012/2013. For sites affected by snow glide deposition, a mean erosion rate of 8.4 t ha−1 yr−1 was found. The difference in long-term erosion rates determined with RUSLE and 137Cs confirms the constant influence of snow-glide-induced erosion, since a large difference (lower proportion of water erosion compared to total net erosion) was observed for sites with high snow glide rates and vice versa. Moreover, the difference between RUSLE and 137Cs erosion rates was related to the measured snow glide distance (R2 = 0.64; p < 0.005) and to the snow deposition sediment yields (R2 = 0.39; p = 0.13). The SSGM reproduced the relative difference of the measured snow glide values under different land uses and land cover types. The resulting map highlighted the relevance of snow gliding for large parts of the investigated area. Based on these results, we conclude that snow gliding appears to be a crucial and non-negligible process impacting soil erosion patterns and magnitude in subalpine areas with similar topographic and climatic conditions.

Soil erosion in an avalanche release site (Valle d'Aosta: Italy): towards a winter factor for RUSLE in the Alps

Abstract. Soil erosion in Alpine areas is mainly related to extreme topographic and weather conditions. Although different methods of assessing soil erosion exist, the knowledge of erosive forces of the snow cover needs more investigation in order to allow soil erosion modeling in areas where the snow lays on the ground for several months. This study aims to assess whether the RUSLE (Revised Universal Soil Loss Equation) empirical prediction model, which gives an estimation of water erosion in t ha yr−1 obtained from a combination of five factors (rainfall erosivity, soil erodibility, topography, soil cover, protection practices) can be applied to mountain areas by introducing a winter factor (W), which should account for the soil erosion occurring in winter time by the snow cover. The W factor is calculated from the ratio of Ceasium-137 (137Cs) to RUSLE erosion rates. Ceasium-137 is another possible way of assessing soil erosion rates in the field. In contrast to RUSLE, it not only provides water-induced erosion but integrates all erosion agents involved. Thus, we hypothesize that in mountain areas the difference between the two approaches is related to the soil erosion by snow. In this study we compared 137Cs-based measurement of soil redistribution and soil loss estimated with RUSLE in a mountain slope affected by avalanches, in order to assess the relative importance of winter erosion processes such as snow gliding and full-depth avalanches. Three subareas were considered: DS, avalanche defense structures, RA, release area, and TA, track area, characterized by different prevalent winter processes. The RUSLE estimates and the 137Cs redistribution gave significantly different results. The resulting ranges of W evidenced relevant differences in the role of winter erosion in the considered subareas, and the application of an avalanche simulation model corroborated these findings. Thus, the higher rates obtained with the 137Cs method confirmed the relevant role of winter soil erosion. Despite the limited sample size (11 points), the inclusion of a W factor in RUSLE seems promising for the improvement of soil erosion estimates in Alpine environments affected by snow movements.

Snow gliding and glide avalanches: a review

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 and loading under two different forest stands: a case study in the north-western Italian Alps

The presence of a thick snowpack could interfere with forest stability, especially on steep slopes with potential damages for young and old stands. The study of snow gliding in forests is rather complex because this phenomenon could be influenced not only by forest features, but also by snow/soil interface characteristics, site morphology, meteorological conditions and snow physical properties. Our starting hypothesis is that different forest stands have an influence on the snowpack evolution and on the temperature and moisture at the snow/soil interface, which subsequently could affect snow gliding processes and snow forces. The aim of this work is therefore to analyse the snowpack evolution and snow gliding movements under different forest covers, in order to determine the snow forces acting on single trees. The study site is located in a subalpine forest in Aosta Valley (NW-Italy) and includes two plots at the same altitude, inclination and aspect but with different tree composition: Larch (Larix decidua) and Spruce (Picea abies). The plots were equipped with moisture and temperature sensors placed at the snow/soil interface and glide shoes for continuous monitoring of snow gliding. The recorded data were related to periodically monitored snowpack and snow/soil interface properties. Data were collected during two winter seasons (2009–10 and 2010–11). The snow forces on trees were analytically calculated either from snowpack data and site morphology or also from measured snow gliding rates. Different snow accumulations were observed under the two different forest stands, with a significant effect on temperature and moisture at the snow/soil interface. The highest snow gliding rates were observed under Larch and were related to rapid increases in moisture at the snow/soil interface. The calculated snow forces were generally lower than the threshold values reported for tree uprooting due to snow gliding, as confirmed by the absence of tree damages in the study areas.

Snow gliding on a south-facing slope covered with larch trees

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. The goal of this study was to determine whether snow gliding depends on forest cover (canopy) and size of clearings. Snow gliding was measured during eight winter periods at six measuring positions (ranging from ‘dense forest’ to ‘open slope’) in and beside a larch stand in the Stubai Valley, Tyrol, Austria. The results showed that gliding is strongly influenced by forest cover. Snow gliding increases with decreasing canopy density. The difference between the six measuring positions was highly significant (p < 0.005). The identified glide cracks on at least two measuring positions, indicating extreme glide rates and, therefore, strong negative effects on juvenescent trees. To prevent glide rates of a magnitude such as this requires a mature forest with at least 300 stems/ha.

Estimation of soil redistribution rates due to snow cover related processes in a mountainous area (Valle d'Aosta, NW Italy)

Abstract. Mountain areas are widely affected by soil erosion, which is generally linked to runoff processes occurring in the growing season and snowmelt period. Also processes like snow gliding and full-depth snow avalanches may be important factors that can enhance soil erosion, however the role and importance of snow movements as agents of soil redistribution are not well understood yet. The aim of this study was to provide information on the relative importance of snow related processes in comparison to runoff processes. In the study area, which is an avalanche path characterized by intense snow movements, soil redistribution rates were quantified with two methods: (i) by field measurements of sediment yield in an avalanche deposition area during 2009 and 2010 winter seasons; (ii) by caesium-137 method, which supplies the cumulative net soil loss/gain since 1986, including all the soil erosion processes. The snow related soil accumulation estimated with data from the deposit area (27.5 Mg ha−1 event−1 and 161.0 Mg ha−1 event−1) was not only higher than the yearly sediment amounts, reported in literature, due to runoff processes, but it was even more intense than the yearly total deposition rate assessed with 137Cs (12.6 Mg ha−1 yr−1). The snow related soil erosion rates estimated from the sediment yield at the avalanche deposit area (3.7 Mg ha−1 and 20.8 Mg ha−1) were greater than the erosion rates reported in literature and related to runoff processes; they were comparable to the yearly total erosion rates assessed with the 137Cs method (13.4 Mg ha−1 yr−1 and 8.8 Mg ha−1 yr−1). The 137Cs method also showed that, where the ground avalanche does not release, the erosion and deposition of soil particles from the upper part of the basin was considerable and likely related to snow gliding. Even though the comparison of both the approaches is linked to high methodological uncertainties, mainly due to the different spatial and temporal scales considered, we still can deduce, from the similarity of the erosion rates, that soil redistribution in this catchment is driven by snow movement, with a greater impact in comparison to the runoff processes occurring in the snow-free season. Nonetheless, the study highlights that soil erosion processes due to the snow movements should be considered in the assessment of soil vulnerability in mountain areas, as they significantly determine the pattern of soil redistribution.

Process identification of soil erosion in steep mountain regions

Abstract. Mountainous soil erosion processes were investigated in the Urseren Valley (Central Switzerland) by means of measurements and simulations. The quantification of soil erosion was performed on hill slope scale (2·20 m) for three different land use types: hayfields, pastures with dwarf shrubs and pastures without dwarf shrubs with three replicates each. Erosion rates during growing season were measured with sediment traps between June 2006 and November 2007. Long-term soil erosion rates were estimated based on Cs- 137 redistribution. In addition, soil moisture and surface flow were recorded during the growing season in the field and compared to model output. We chose the WEPP model (Water Erosion Prediction Project) to simulate soil erosion during the growing season. Model parameters were determined in the field (slope, plant species, fractional vegetation cover, initial saturation level), by laboratory analyses (grain size, organic matter) and by literature study. The WEPP model simulates sheet erosion processes (interrill and splash erosion processes, please note that no rill erosion occurs at our sites). Model output resulted in considerable smaller values than the measured erosion rates with sediment traps for the same period. We attribute the differences to observed random gravity driven erosion of soil conglomerates. The Cs-137 measurements deliver substantially higher mean annual erosion rates, which are most likely connected to snow cover related processes such as snow gliding and avalanche activities.

Schutzwälder der Nördlichen Kalkalpen: Verjüngung, Mikroklima, Schneedecke und Schalenwild | Protection forests in the Northern Limestone Alps: stand regeneration, microclimate, snow cover and ungulates

Relationships among ungulate pressure, stand regeneration, microclimate, and snowpack dynamics were investigated at three protection forest sites in the mixed mountain forest zone of the Bavarian Limestone Alps. The study was conducted at plots located inside and outside ungulate exclosures which had been established about 35 years ago. Air and topsoil temperatures were recorded for one year in hourly intervals. In winter 2005/2006, the thickness, constitution, and mobility of the snowpack were investigated. Inside the exclosures, which were stocked with dense regeneration of mixed mountain forest, mean air and topsoil temperatures were up to 0.9 °C (air) and 1.9 °C (soils) lower than outside. Maximum daily values of air and topsoil temperatures were up to 1.4 °C (air) and 5.2 °C (soils) lower inside the exclosures compared to the respective outside plots. The temperature differences were dependent on the aspect (NW &amp;lt; ESE &amp;lt; S). Snowpack thickness during winter increased more slowly inside the exclosures than outside due to snow interception by the young trees which had developed during stand regeneration; in late winter, snowpack melting was retarded. Inside the exclosures the snowpack was more heterogeneous (“column structure”) than outside (laminated structure). Consequently, inside the exclosures a large portion of the melting water drained vertically to the bottom of the snowpack and infiltrated into the soil, and the snow gliding activity was significantly smaller than outside. In summary, particularly at S-exposed sites, exclosure of ungulates resulted in a cooler, less extreme microclimate, a more heterogeneous and stable snowpack, and reduced snow gliding. Therefore, an adequate regulation of ungulate density by appropriate hunting activity is a key factor for a sustainable provision of important protection services of the mixed mountain forest in the Northern Limestone Alps.

Snow forces on forest plants due to creep and glide

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°) 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.