A new experimental snow avalanche test site at Seehore peak in Aosta Valley (NW Italian Alps) - Part II: Engineering aspects

The estimate of the effects produced by the impact of a snow avalanche against an obstacle is of the utmost importance in designing safe mountain constructions. For this purpose, an ad-hoc instrumented obstacle was designed and built in order to measure impact forces of small and medium snow avalanches at Seehore peak (NW Italian Alps). The structural design had to consider several specific and unusual demands dictated by the difficult environment. In this article, the new test facility is described from the engineering point of view, discussing the most important aspects of the analyzed problems which were solved before and after the construction. The performance of the instrumented obstacle in the first two operating seasons, and some proposals for future upgrading are eventually illustrate

Quantifying the contribution of the root system of alpine vegetation in the soil aggregate stability of moraine

One fifth of the world's population is living in mountains or in their surrounding areas. This anthropogenic pressure continues to grow with the increasing number of settlements, especially in areas connected to touristic activities, such as the Italian Alps. The process of soil formation on high mountains is particularly slow and these soils are particularly vulnerable to soil degradation. In alpine regions, extreme meteorological events are increasingly frequent due to climate change, speeding up the process of soil degradation and increasing the number of severe erosion processes, shallow landslides and debris flows. Vegetation cover plays a crucial role in the stabilization of mountain soils thereby reducing the risk of natural hazards effecting downslope areas. Soil aggregate stability is one of the main soil properties that can be linked to soil loss processes. Soils developed on moraines in recently deglaciated areas typically have low levels of soil aggregation, and a limited or discontinuous vegetation cover making them more susceptible to degradation. However, soil structure can be influenced by the root system of the vegetation. Roots are actively involved in the formation of water-stable soil aggregation, increasing the stability of the soil and its nutrient content. In the present study, we aim to quantify the effect of the root system of alpine vegetation on the soil aggregate stability of the forefield of the Lys glacier, in the Aosta Valley (NW-Italy). This proglacial area provides the opportunity to study how the root system of ten pioneer alpine species from different successional stages can contribute to soil development and soil stabilization. To quantify the aggregate stability of root permeated soils, a modified wet sieving method was employed. The root length per soil volume of the different species was also determined and later correlated with the aggregate stability results. The results showed that soil aggregate stability was significantly increased by the presence of roots. The lowest soil aggregate stability was found with Epilobium fleischeri followed by Minuartia recurva and Leucanthemopsis alpina. The highest aggregate stability was found with the graminoid species. These results show a close relationship between the development of root systems of the studied species and soil aggregate stability, a factor which can be taken into consideration in order to improve the accuracy of existing susceptibility mapping for early warning and civilian protection

Driving factors of soil microbial ecology in alpine, mid-latitude patterned grounds (NW Italian Alps)

Patterned ground (PG) is one of the most evident expressions of cryogenic processes affecting periglacial soils, where macroscopic, repeated variations in soil morphology seem to be associated with small-scale edaphic and vegetation gradients, potentially influencing also microbial communities. While for high-latitude environments only few studies on PG microbiology are available, the alpine context, where PG features are rarer, is almost unexplored under this point of view. We followed a double approach, based on denaturing gradient gel electrophoresis (DGGE) and quantitative PCR (qPCR), in order to investigate microbial community composition and abundance of phylogenetic markers and functional genes (bacterial and archaeal amoA) within single PG features and among different sites from four areas in the Western Italian Alps, characterized by different lithotypes. Bacterial, archaeal, and fungal community composition was quite homogeneous within single features, with more differences among samples collected from different lithologies. The abundance of phylogenetic and functional markers was uniform at different sites, except for the highest altitude one showing the lowest bacterial, archaeal, and ammonia-oxidizing archaea abundance. Nevertheless, at a small-scale level, a concentric distribution of microbial markers was described within single features, paralleling soil chemical property trends. These first results support the hypothesis that microbial ecology in alpine, periglacial ecosystems is driven by a complex series of environmental factors, such as lithology, altitude, and cryogenic activity, acting simultaneously on community shaping both in terms of diversity and abundance

Liquid and plastic limits of mountain soils as a function of the soil and horizon type

Soil degradation by processes such as soil erosion, shallow landslides, debris-flows etc. is a significant problem in mountain areas, and is a crucial issue for natural hazard assessment in mountain areas. Several soil properties, among which are the liquid and plastic limits, i.e. moisture contents for which a soil passes from the plastic to liquid state (liquid limit, LL) and from the semisolid to plastic state (PL, plastic limit), have been proposed as indicators for soil vulnerability to degradation processes, both of natural and anthropogenic origin. In this research we investigated the liquid and plastic limits of the main soil groups ofWorld Reference Base for Soil Resources (WRB) classification present in Aosta Valley (N–WItalian Alps) from a pedogenic perspective. In particular, we compared 1) soils at different stages of development; and 2) different genetic horizons. Our main aim was to provide and interpret data on soils' consistency and mechanical behavior that may be used as indexes for the assessment of soil vulnerability. Despite its relatively small area, the Aosta Valley is characterized by a wide range of soil types. Sixty-two soils with different profile evolution stages, representative of 7 WRB soil groups,were investigated and LL and PL in genetic horizons were studied at the soil type and genetic horizons level. In general, soil consistency was largely determined by the organic matter content (both in topsoils and organic matter-enriched subsurface horizons), but in spodic horizons and some C horizons a role of poorly crystalline and pedogenic iron oxides was observed too. Considering the vulnerability to consistency loss, that can result in erosion processes and overall soil degradation, surface horizons were generally less vulnerable, as could be expected on the basis of previous research, i.e. showed higher LL and PL values, than the deeper ones, generally characterized by a reduction of soil consistency. Therefore, topsoil could receive higher water inputs while still preserving their consistency and strength. This was not confirmed in Podzols, where the organic matter enrichment of spodic horizons determined a discontinuity in physical properties between the E horizons (more vulnerable) and the underlying, spodic ones. The same trend was observed for Calcisols with a deep cemented Bkm horizon. The research provided a novel overview on LL and PL in the common soil types present in the Alpine region, integrating the already existing research on topsoil vulnerability to degradation processes (erosion, consistency losses, losses of strength), and the regional soil database. The use of LL and PL as indicators of soil physical quality was approached with a pedogenic perspective, which might be helpful for a better definition of hazard assessment at the regional scale