M. Maggioni

Soil Erosion Caused by Snow Avalanches: a Case Study in the Aosta Valley (NW Italy)

Abstract Snow avalanches can exert considerable erosive forces on soils. If a snow avalanche flows directly over bare ground, basal shear forces may scrape away and entrain soil. Soil material entrained by the avalanche is transported to the deposition zone, changing the chemical composition of the soils and potentially contributing to unique landforms. The quantity of soil material eroded and accumulated depends on avalanche characteristics and on morphological features, as well as soil properties and vegetation cover. We monitored a channeled avalanche path in the Aosta Valley of NW Italy in order to assess the contribution of avalanche debris to the formation of soils in the runout zone. Sediment concentration estimates and measurements of the avalanche deposit volumes were used to estimate the total sediment load. The collected sediments were separated into fine sediments (<2 mm) and large (>2 mm) organic and mineral fractions. Results, obtained from the winter seasons of 2006, 2007, and 2008, showed that the amount of sediment deposited on the preexistent soil at the foot of the avalanche path was mainly the fine sediments fraction. The total carbon and nitrogen content in the fine sediment fraction ranged respectively from 6.6 to 9.0% and 0.37 to 0.42%. The total sediment load transported out of the 3.5 km2 basin was estimated to be 7585 kg in 2006, 27,115 kg in 2007, and 2323 kg in 2008. This mass transport resulted in basin averaged denudation rates ranging from 0.67 g m−2 event−1 in 2008 to 7.77 g m−2 event−1 in 2007. Annual accumulation in the runout zone was 240 Mg ha−1 in 2006, 38 Mg ha−1 in 2007 and 10 Mg ha−1 in 2008. The inorganic N concentration of the snow in the runout zone was significantly greater than in the starting zone and was correlated with the organic fraction accumulated by the avalanche. By redistributing snow, avalanches not only redistribute water but also nutrients that can be available for plants in the growing season. Moreover, avalanche paths are places where soil accumulates in some areas and erodes in others, contributing to potentially unique pedo-environmental conditions.

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 susceptibility: the Monterosa Ski resort, NW Italian Alps

ABSTRACT Snow 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.

Snow Cover Effects on Glacier Ice Surface Temperature

Abstract Snowpack evolution and glacier ice surface temperatures were studied on the Indren glacier (Northwestern Alps, Italy) under different meteorological conditions: in winter 2002–2003, rich in snow from the beginning of the season, and in winter 2005–2006, poor in snow until February. Periodical snow profiles were made to measure the physical properties of snow, while data loggers measured the snow/ice interface temperature. Furthermore, in winter 2002–2003, the influence on the snowpack evolution of an artificial increase in the snow density was evaluated. During the season rich in snow there was a prevalence of rounded crystals originated by melt-freeze metamorphism, while in the season poor in snow depth hoar and faceted crystals prevailed, due to the higher temperature gradient. From these two winter seasons, it appeared that a deep snow cover of at least 100 cm was able to maintain the snow/ice temperature at around −5°C until the snow cover reached isothermal conditions, whereas, during the winter of 2005–2006, the shallow depth of snow did not allow basal temperature to reach an equilibrium value and the snow/ice interface temperature oscillated between −2 and −8°C. The altered snow density had no effect on the snow/ice interface temperature, whereas it caused a delay in the time of reaching isothermal conditions, thus allowing snow cover on the glacier to persist longer.