"Slope stability hazard in Alpine areas": a look back on the 4EU+ field trip in Italy

by Nikola Derková, Jaroslav Dufek, Jiří Kocum, Ondřej Racek (students of Charles Unviersity)

From 11 to 17 July 2021, students of the Faculty of Science of Charles University took part in a summer school organized by the University of Milan. The field exercise, entitled "Slope stability hazard in Alpine areas", was designed for Master's and PhD students. Our faculty was represented by students from the Department of Physical Geography and Geoecology: two master's students - Nikola Derková and Jaroslav Dufek, and two doctoral students - Ondřej Rack and Jiří Kocum. In addition, two German students from Heidelberg University joined our international group.

Image 1: Location of the Val San Giacomo. (Tantardini et al., 2013)The course took place in the Valle Spluga (also known as Val San Giacomo), Val Bregaglia and Valchiavena in the Italian Alps north of Milan in the province of Sondrio - Lombardy. The base for all trips in the city of Chiavenna was the Valchiavenna University Station for the study of the alpine environment - Valchiavenna Station for the Studio dell´Ambiente Alpino, Dipartimento di Scienza della Terra.

Four groups of Czech, German and Italian students were led in the field by doctoral students from the University of Milan. The whole course was focused on engineering geology and physical geography. The course started with a two-day joint part, where students were introduced to all the methodologies, which were to be used by students during teamwork in the field at four different locations.

During the first activity, the students were acquainted with a several-hour geological description of geological outcrops. The result was the characterization of the rock slope using the RMR (Rock Mass Rating) index. The main discontinuities, their azimuth, inclination and frequency were described. Furthermore, the mechanical and geochemical properties of the relevant rocks, such as composition, hardness, degree of weathering, etc., were investigated. All findings were recorded in pre-prepared sheets. A large Image 2: Display of main discontinuities. (Morcioni et al., 2020)number of materials and tables, according to which the individual parameters were assessed, served to facilitate the filling in of the sheets. With the exception of one student, who has been dealing with the rock slope for a long time, this activity was new and enriching for foreign students. Nevertheless, Czech students did not get lost working with the geological compass and Schmidt's hammer. Minor complications were perhaps caused only by the prepared materials, which were only in Italian. The RMR index created in this way serves as key information about the properties of the rock mass. From the results, it is possible to determine how stable the massif is and what technical procedures are necessary or possible to use so that the resulting engineering work is stable for a long time.

Other activities were already well known to Czech and German students (specialized on physical geography). Hydrology was represented by measuring the properties of water in a watercourse with a multiparametric probe. Temperature, pH, conductivity, dissolved oxygen, and solids were measured. Furthermore, the flow velocity was measured using a hydrometric propeller and an analysis of sediments in the riverbed was performed. First, in order to determine the proportion of the largest fractions, samples were taken, which were dried in the laboratory and then sieved for the final determination of the representation of individual fractions. Hydropedology was also represented by measuring the infiltration of water into the soil using two-circuit infiltrometers. Soil samples were also taken to determine bulk density. The last, but by far the most time-consuming part was the cartographic-geomorphological part, when landslides of different origin and in various environment (glacial, gravitational, fluvial sediments) were drawn in the maps. The maps were A1 format and the teams had the task of mapping their entire allocated area.

Image 3: From left - measurement with a multiparametric probe, analysis of sediments in a riverbed, measurement of infiltrations, soil sampling and mapping of surrounding slopes.

During the joint part of the course, the lecturers introduced the localities where research or monitoring is currently being carried out. During the joint program, the specifics of the Italian nature manifested itself in form of "coffee breaks", some of the teams maintained this habit in the following days. At research sites, students were always introduced to research that was already completed or still ongoing and learnt about natural hazards of each site.

Image 4: The tower of the temple in the village of Gallivagio. In the lower-left corner you can see a protective wall with stone foundations.Most studies examine ongoing slope movements using continuous monitoring or model approaches (Apuani et al., 2007; Morcioni et al., 2012; etc.).

Part of the program was also devoted to a detailed description of the slope processes that took place in the past. It was, for example, a description of a paleo-rockslide. Others map the ancient activity of glaciers (Tantardini et al., 2013). The dynamics of some processes is very low. However, in the case of the dynamics of slope movements, the speed is very high. An example of such a process and its relationship with anthropogenic structures is the rescue of the monastery in the village of Gallivaggio. Thanks to the continuous monitoring that takes place here (Carlà et al., 2019; Dei Cas et al., 2018), it was clear from the measured irreversible displacements of the rock blocks that a rock fell over the village. A several-meter-high protective wall was built between the rock wall and the monastery, serving as a barrier against rock falls. On 30 May 2018, there was a rockfall and thanks to the timely construction of a protective wall, the monastery was protected. The rock fall was recorded and can be watched.

The second study presented was a case study of the famous and beautiful Lake Azzurro di Motta. In 2005 and 2006, due to the drier period, the lake almost dried up and was partially saved thanks to artificial filling. In October 2018, however, it dried up completely and was supposed to disappear.

Image 5: Comparison of lake level from the same period in 2017 and 2018.The Italian Environment Fund (Fondo Ambiente Italiano - FAI) has included the site on a list of "heart sites" that must be saved, and studies have begun to determine the causes of drying up and the future of the lake. No source flows into the lake and is naturally fed directly by groundwater. In the spring, thanks to increased inflows of groundwater, it fills up, and then the level drops until winter. In 2018, due to a severe drought, the groundwater level dropped below the bottom of the lake and the lake dried up. Due to the large drop in groundwater, artificial watering did not help either. However, the lake did not disappear forever and with the coming precipitation began to fill again. Tourists can admire the azure blue lake hidden in the middle of the forest to this day. However, we were not so lucky, because due to bad weather we had to leave the site at an altitude of 1835 m above sea level and instead of walking around the lake and exploring the relationship between hydrogeological water circulation and extensive deep slope deformation above the lake, another coffee break followed, at which the whole process was explained to us.

After a two-day joint part, during which the students got to know each other and learnt about the tasks, tools and methods, each team was assigned a location for individual research. Each group was assigned one doctoral student from the Italian side, who assisted the team. For the rest of the day, the work was carried out separately and the teams met only for breakfast and dinner, where they often processed and evaluated the data from the previous day until late at night. The data measured by the hydrometric propeller and the analysis of river sediments were used to characterize the water flow from the point of view of builders and engineers, where it is possible to determine both the erosion capabilities of the flow and the properties of fluvial sediments as a foundation. From the speed of the water flow, it is possible to deduce the abrasive force of water in a given place, and from river sediments, it is then possible to observe which largest pieces of rock the water flow in a given locality is able to displace. This is important to consider due to the possible interaction of both water masses and transported sediments with engineering works. Infiltration tests and analyzes of sediment and soil samples were performed on moraines, aggregation ramparts, and parts of landslides in order to determine the composition of these sediments, their stability and water permeability.

Image 6: Serpentines rising to Passo Stelvio. Source: CK/image/2020/06/Passo_dello_Stelvio_east_08_opening_3.jpg.The summer school brought a lot of new knowledge to the participants, especially about the dynamics, monitoring, and methods used in geohazard research in the Alpine environment. Students also established valuable contacts that will be beneficial in his further activities related to the dissertation. These established contacts will lead in the future to closer cooperation and possible internships at the University of Milan.