Reconstructing deglaciation dynamic and environmental changes in the Italy-Switzerland transboundary area of the Val Viola Pass

The deglaciation following the Last Glacial Maximum (LGM) is one of the most important climate-driven surface processes that occurred in the Alps. The deglaciation contributed to shape the landscape of high-mountain areas. In the Lateglacial and during the Holocene, water-related, slope, and periglacial processes have interplayed with pedogenesis, shaping the landscape of the deglaciated alpine valleys. In order to reconstruct the deglaciation history and environmental changes occurred in the Val Viola area (Upper Valtellina-Poschiavo Valley), we used a multidisciplinary approach including a detailed geomorphological mapping of the area (Bollati et al., 2018) and field and laboratory characterization of post-LGM deposits and soils. As regards the analysis of deposits and soils, six soil profiles were sampled and analysed along an altitudinal transect between 2325 m and 2430 m a.s.l.; this helped elucidating the process of soil development and detecting the presence of different pedological units. Moreover, Schmidt’s hammer measurements were performed in order to establish the degree of surface weathering and thus the exposure-age of rock glacier debris and bare rock surfaces. Debris and rock surfaces suitable for Schmidt’s hammer exposure dating were selected according to the results of geomorphological mapping. Finally, two peat bog deposits and charcoals found in one soil profile were dated with AMS-14C dating. Analyses of soil profiles allowed the identification of the occurrence of different slope instability phases, which are recorded as buried surfaces, suggested by the presence of stone lines and/or granulometric discontinuity. A pristine phase of surface stability, likely characterized by increasing soil forming processes, is dated at 8120±30 BP, corresponding to the radiocarbon date of the bottom of a peat bog. Subsequently, this phase of stability has been affected by rexistasy phase probably due to the worsening of climate conditions. This instability phase occurred after the 4650 ± 30 BP, radiocarbon date of the charcoal found in a soil horizon buried below a stone line. A similar radiocarbon age (4320±30 BP) was found also at the bottom of a second peat bog. Above the stone line, covering the charcoal, a more recent soil unit testifies the occurrence of new environmental conditions promoting pedogenesis. In nearby areas, Schmidt’s Hammer was used to date bare surfaces (e.g. Scotti et al., 2017), and the regression lines obtained by the authors were used to calibrate rebound values collected in our study area. The data show that the rock weathering processes on the top of two exharated granitic gneiss outcrops started around 17 ky BP being in accordance with the timing of deglaciation since the Last Glacial Maximum and with soil developments. Schmidt’s hammer rebound values and soils analysis provided additional data useful for reconstructing the landscape evolution of the region

High mountain landscape and climate change. Analysis of the deglaciation history in an Italy-Switzerland cross-border area: the val Viola (Upper Valtellina-Poschiavo Valley)

The stage, financially supported by AIGeo, by Swiss Geomorphological Society (SGmG), by Dep. of Theoretical and Applied Sciences of Insubria University and by Dep. Earth Sciences of Milan University, was addressed to Young Geomorphologists (YGms) and the main topic of the IVth edition was to investigate the deglaciation history of the Val Viola Pass (VVP), This area is located at the border between Italy (Upper Valtellina) and Switzerland (Poschiavo Valley). The position of the study area favoured the participation of Swiss YGms, thus permitting a fruitful exchange of ideas on this specific research topic. The fieldtrip took place between the 29th and 31st July 2016. On 1st August a workshop was organized in Bormio (Upper Valtellina) to compare data collected on the field by the different working groups and to plan further data elaborations and a second round of field campaign (organized in September and October 2016), for refining and widening our dataset. According to the specific sub-aims of the stage, different methodologies were applied in the field by YGms; the participants were subdivided into groups and supervised by senior researchers. The first activity regarded the design of a detailed geomorphological map of the study area. During the field survey and the drawing up of a legend to be applied for landforms representation, the comparison between Italian (ISPRA, 1994; 2007) and Swiss legend systems was fundamental. A preliminary version of the geomorphological map, covering a surface of 3,7 kmq and a range of altitudes comprised between 2300 and 3300 m a.s.l., at a finer scale respect to previous ones (Pozzi et al., 1990), is ready. The second focus was the large Paradisin rock glacier located on the Swiss side of the VVP, which was investigated by means of electrical resistivity tomography (ERT). This activity led to the elaboration of two ERT profiles allowing the prospecting of the deep structure and stratigraphy. Moreover, on both the rock glacier debris and on many exposed rocky surfaces all around the VVP, Schmidt hammer measurements were carried out and elaborated in order to establish the surface weathering degree and subsequent exposure-age dating, which is a chronological proxy-data for deglaciation age. Direction of glacial palaeoflow indicators (striae) were also measured in the VVP area. Moreover, six soil profiles, developed after the deglaciation, were described in the field, laboratory analyses on collected samples are in progress and two Peat bog deposits were dated with AMS radiocarbon dating. During the different phases, to accurately interpret field results, data on climate variations were collected from Swiss and Italian meteorological stations and analyzed to observe climatic conditions of the VVP. Information about the glaciers history were sought from glaciers inventories, glaciological surveys, historical maps and aerial photos. Interdisciplinary approaches, involving difference skills can be considered important in the framework of the evolution of high mountain environment in response to climate change