<p>The definition of the timing of infilling and environmental evolution of Alpine valleys is essential in the knowledge of the mountain geomorphological systems response to the climate oscillations after the Last Glacial Maximum. This assessment is necessary in the comparison of a system controlled only by natural factors, dominated by paraglacial and paraperiglacial erosion models, and the increasing role played by anthropogenic factors modifying the environment. In the Southern Swiss Alps, anthropogenic factors start playing a role since the frequentation of the valley bottoms and main Alpine passes during the Middle Mesolithic (8.0&#8211;7.0 ka BCE). This role increased significantly since the Lower Neolithic (5.4&#8211;4.3 ka BCE), with the first permanent settlements.</p><p>Radiocarbon dating in Lago di Monate (Varese, Italy) starts the deglaciation of the Lago Maggiore basin just before 19.93&#8211;18.81 ka cal BP (BE 8023.1.1, Rey <em>et al</em>. 2020, Clim. Past 16; cf. Kamleitner <em>et al</em>. 2022, Quat. Sci. Rev. 279). Complete deglaciation of the Lago Maggiore basin by no later than 16.89&#8211;16.34 ka cal BP is indicated by radiocarbon dating of an organic lacustrine deposit in the lower Riviera valley in Castione (north of Bellinzona). <sup>10</sup>Be surface exposure dating of three erratic boulders located upslope of Claro (left side of Riviera valley) point to deglaciation slightly earlier. These chronological elements show a 70 km retreat of the Ticino glacier between Lago di Monate and Castione in 2.6 &#177; 1.0 ka. The deglaciation was followed by a significant debris supply from the slopes to the valley bottoms, contributing to the development of large alluvial fans. Valley bottom damming exercised by rapidly growing alluvial fans allowed the creation of a series of lake basins of increasing level upstream. Radiocarbon dating performed in Castione points out the lake formation just during the deglaciation, and its complete infilling by fluvial deposits between 12.72 and 12.76 ka cal BP, as indicated by the woods found in fluvio-deltaic deposits.</p><p>From Castione to Lago Maggiore, the progradation of the Ticino (and Moesa) river delta completely filled the valley bottom step by step. This infilling was dated: in Bellinzona (13.9 km from the actual river mouth) between 13.48 and 13.31 ka cal BP, when the Castione palaeo-lake was still present; in Giubiasco (10.6 km) between 10.70 and 10.49 ka cal BP; in Gudo (7.6 km) between 8.36&#8211;8.17 ka cal BP and 7.43&#8211;7.26 ka cal BP; in Riazzino (2.9 km) between 3.89 and 3.58 ka cal BP; and in Magadino di Sopra (1.3 km), according to historical information, between 1365 and 1518 CE (0.59&#8211;0.43 ka cal BP).</p><p>Both depositional rates in the alluvial plain and delta progradation rates follow the paraglacial erosion model from the Late Pleistocene to the beginning of the Meghalayan. During the Meghalayan, anthropogenic factors, such as deforestation and reforestation, are added to morpho-climatic factors and indicate an increasing human pressure on the erosional/depositional dynamics since the Early Bronze Age (2.20&#8211;1.55 ka BCE) and, rising significantly, since the Early Iron Age (0.90&#8211;0.45 ka&#160;BCE).</p>
<p>The occurrence of large rock slope failures in an Alpine environment is influenced not only by morpho-structural and lithological characteristics of slopes, but also by the regional glacial history. The latter plays a significant role on slope stability, as the glaciers pressure exerts a variable load on the valley flanks and may lead to weakening of slope strength. To understand the strong relationship between the deglaciation and the large rock slope failures following it, a detailed geochronological assessment of both processes is essential.<br>In the Southern Swiss Alps, in the territory between the five valleys north of Bellinzona (Riviera, Valle Leventina and Valle di Blenio in Canton of Ticino, Val Calanca and Valle Mesolcina in Canton of Graub&#252;nden), several debris accumulations of large rock slope failures can be observed. The objective of this research is to define the exposure-age of three rockslide/rock avalanche deposits in Ludiano (Valle di Blenio), Norantola (Valle Mesolcina) and Bodio-Cauco (Val Calanca), through Schmidt hammer exposure-age dating (SHD).<br>Schmidt hammer, also called concrete sclerometer, allows to measure a rebound value (R-value), which is directly proportional to the strength of the rock surface. Under the same climate conditions and for the same lithology, this can be directly correlated with the surface weathering and therefore to exposure-age.&#160;<br>R-values were calibrated thanks to measurements carried out on surface of known age, determined from historical sources and from cosmogenic nuclide dating (CND). In the first category, boulders from the Monte Crenone rock avalanche of 30<sup>th</sup> September 1513 were used (De Pedrini <em>et al</em>. 2022, Geogr. Helv. 77). Surfaces interested by CND are several boulders of the Chironico rock avalanche (Claude <em>et al</em>. 2014, Swiss J. Geosci. 107) and four erratic boulders deposited by the Ticino glacier above Claro (Riviera valley) and in Gudo (Piano di Magadino) (Scapozza <em>et al</em>. 2022, this volume).<br>By linear regression, the following SHD of the investigated surfaces could be obtained: 16.15 &#177; 0.98 ka for the Ludiano rock avalanche deposit; 15.97 &#177; 1.04 ka for the Norantola rock avalanche deposit; 15.77 &#177; 1.07 ka for the glacial erosion surface (<em>roches moutonn&#233;es</em>) in Serravalle (Semione); 13.98 &#177; 1.26 ka for the Bodio-Cauco rockslide deposit. All these exposure ages indicate a collapse of the investigated rock slope failures only a few centuries after the deglaciation, which occurred for the lower and middle parts of the Valle Mesolcina, Valle di Blenio and Valle Leventina between 16.94 and 16.25/15.96 ka b2k.<br>Both deglaciation and dated rock slope failures occurred during the Greenland Stadial GS-2.1a of the INTIMATE event stratigraphy, dated between 17.48 and 14.69 ka b2k (Rasmussen <em>et al</em>. 2014, Quat. Sci. Rev. 106) or, at least, at the beginning of the Greenland Interstadial GI-1 (14.69&#8211;12.90 ka b2k), in particular during the events GI-1e (14.69&#8211;14.08 ka b2k), GI-1d (14.08&#8211;13.95 ka b2k) and GI-1c (13.95&#8211;13.31 ka b2k), characterized by the first significant temperature increase after the Last Glacial Maximum.</p>
<p>Understanding the past river dynamics, their relationship with the climate oscillations, and their impact on humans as a resource and/or natural risk, is very crucial. In recent times many studies were carried out to determine the evolution of the hydro-sedimentary dynamics of Alpine rivers in the past, trying to predict the future effect of the increased fluvial activity leading to repeated floods, especially in the current context of climate change.</p><p>The present contribution is the object of a recent publication (Czerski <em>et al.</em> 2022, Geogr. Helv. 77) on the evolution of the fluvial environments of the Ticino river alluvial plain (Southern Switzerland). The research is based on historical sources, previous investigations on three sites based in the Ticino river floodplain, and data collected on six archaeological sites located on four alluvial fans. The results revealed a complex interaction of the Ticino river and its lateral tributaries with the human communities since the Neolithic (5400&#8211;2200 BCE). The lithostratigraphy and the archaeological evidence described on the field were constrained by radiocarbon dating, providing the interpretation of the depositional context of the studied sequences and their correlation with the geological epochs and the cultural periods defined for the Southern Swiss Alps. The combined approach allowed for the definition of 13 phases of enhanced hydro-sedimentary activity covering a period between the Neolithic and the contemporary period. The palaeoenvironmental and palaeoclimatic causes of these phases and their impacts on the human settlements are evaluated.</p><p>Most of the enhanced hydro-sedimentary phases could be linked to the regional or continental palaeoenvironmental and palaeoclimatic context, recorded in correspondence with periods of climate degradation with the establishment of cold and humid conditions, evidence of glacier advances in the Swiss Alps, and/or by an increase in the flood activity on the southern side of the Alps. The more recent phases, in particular, are attributed to the coldest and moistest phases of the Little Ice Age (LIA) climate oscillation. The collected data allowed us also to assess the impacts of these enhanced alluvial phases on the human communities and to explain many of the sedimentological and archaeological observations on the field. For example, the torrential events attributed to the LIA had a strong impact on the construction and destruction phases observed for the archaeological site of Giubiasco Palasio.</p><p>The study is still ongoing; the summary on the evolution of the hydro-sedimentary dynamics of the Ticino river and its tributaries presented herein will be continuously refined and updated with further sedimentological and archaeological observations.</p>
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