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

Abstract

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 137 Cs (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 137 Cs method (13.4 Mg ha −1 yr −1 and 8.8 Mg ha −1 yr −1 ). The 137 Cs 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.

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

“…The site is affected by glide-snow avalanches occurring in springtime or late autumn, and is prone to snow gliding and subsequent glide crack formation. Soil erosion is very pronounced and clearly related to snow-soil interface dynamics (Ceaglio et al, 2012), as soil is frequently removed by avalanches and large soil deposits can be observed in the avalanche runout area. In the last four years, glide-snow avalanches have been documented almost yearly.…”

“…The upper soil horizons had a sand content ranging from 32 to 60 %, and a clay content ranging from 6 to 20 % (Ceaglio et al, 2012). The soil bulk density ranged between 0.66 Mg m −3 (SB) and 1.07 Mg m −3 (RA), and the skeleton content from 5 to 44 % (Ceaglio et al, 2012).…”

“…The runout area starts at 1200 m a.s.l., ends on an avalanche shed protecting the road and is characterized by decreasing slope steepness. An exhaustive description of the avalanche site and dynamics, as well as the sampling strategy in the area, is provided by Ceaglio et al (2012).…”

“…Fallout radionuclides are therefore largely used to assess the budget of soil erosion and sedimentation processes (Mabit et al, 2008;Mabit and Bernard, 2007;Matisoff and Whiting, 2011;Mabit et al, 2013). Ceaglio et al (2012) used this method to compare field-measured and 137 Cs-derived soil redistribution rates, highlighting the predominance of the snow-related phenomena in the total soil erosion for a mountain basin in the northwestern Italian Alps.…”

“…We will investigate sites where we expect different intensities of snow-induced erosion: the release area (RA), where avalanche release and slow snow cover movements take place; the track area (TA) directly affected by the avalanche run; and a third area, protected by avalanche defense structures (DS) that are designed to reduce snow cover movements, where avalanche release is excluded but slow snow cover movements can still occur. The specific objectives are (1) to apply the GIS-based RUSLE at a mountain site affected by recurrent glide-snow avalanches, (2) to compare the soil erosion estimates of the RUSLE with the 137 Cs-based erosion rates estimated from a previous field survey carried out by Ceaglio et al (2012), (3) to test a winter correction factor (winter factor, W ) calculated from the ratio of Ceasium-137 ( 137 Cs) to RUSLE erosion rates, referring to winter soil erosion contribution, and (4) to discuss and interpret the results also considering a 2-D avalanche dynamic model proposed by Christen et al (2010).…”