Timing of deglaciation and Late Glacial and Holocene infilling of the Ticino valley between Biasca and Lago Maggiore (Southern Switzerland)

Abstract

<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 (8.0–7.0 ka BCE). This role increased significantly since the Lower Neolithic (5.4–4.3 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 19.93–18.81 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 16.89–16.34 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 ± 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 8.36–8.17 ka cal BP and 7.43–7.26 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 (0.59–0.43 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 (2.20–1.55 ka BCE) and, rising significantly, since the Early Iron Age (0.90–0.45 ka BCE).</p>

Lake Maggiore: geomorphological genesis, lake-level evolution, and present and future ecosystems importance

“…3) and 18.15 ka b2k. The latter date corresponds to the upper chronological limit of the so-called Cugnasco Stadial, determined by Cosmogenic nuclide dating of erratic boulders (Scapozza et al, 2022). During the Cugnasco Stadial, the front of the Ticino paleo-glacier was already attested between Cadenazzo and Cugnasco in the middle of the Piano di Magadino, which at the time was entirely occupied by Lake Maggiore (Scapozza et al, 2014).…”

“…The progradation of the river Ticino delta into the Piano di Magadino during the Holocene was well documented thanks to numerous geological boreholes and radiocarbon dating (Tab. 3) of organic material found in fluvial deposits (Scapozza, 2016;Scapozza and Ambrosi, 2021;Czerski et al, 2022;Scapozza et al, 2022). Just before 10.75 ka b2k (UZ-5958/ETH-42562 in Tab.…”

Holocene Deformations at the Po Plain–Southern Alps Transition (Lake Maggiore, Italy): Inferences on Glacially vs. Tectonic-Induced Origin

“…However, the Holocene age of the deformed sediments (dated between 8760 and 8550 years BC), postdating the last glacial event in southern Lake Maggiore [64,127], seems to strongly preclude ice sheets as direct contributors to the observed deformations.…”