LGM Glaciation of the Central Southern Alps - a Regional LGM Glacier Chronology derived from the Ticino-Toce Glacier System

The large end moraine systems along the southern fringe of the Alps are among the most prominent Quaternary landforms. Typically consisting of multiple, concentric ridges, made up of ice-marginal glaciogenic deposits, they are often referred to as (morainic) amphitheatres. The characteristic close spacing between individual ridges complicates the recognition of different glaciations within the end moraine systems. Suggested LGM (and pre-LGM) glacier extents in many of the Italian amphitheatres are consequently strongly divergent. By means of surface exposure and radiocarbon datings, recent studies were able to resolve ‘true’ LGM glacier limits in several forelands-reaching glacier systems in NW and NE Italy (Monegato et al., 2007; Gianotti et al., 2015; Monegato et al., 2017; Ivy-Ochs et al., 2018). It was thereby recognised that the morphology of the eastern amphitheatres (e.g., Garda, Tagliamento) is mainly a result of the last glaciation. To the west, however, moraine ridges of previous glaciations are preserved downstream of identified LGM ice margins (e.g. Ivrea, Rivoli-Avigliana). Despite the key position within the Alpine chain, LGM extent and timing within the central Southern Alps (corresponding to the Ticino-Toce and Adda glacier systems) remain ambiguous. The presented study aims to overcome this gap by introducing a regional glacier chronology based on cosmogenic nuclide dating of the Ticino-Toce glacier and the corresponding Verbano amphitheatre. Our chronological data promotes an LGM piedmont lobe significantly larger than recently proposed (Bini et al., 2009). Paired with geomorphological observations, the age constraints further suggest a ∼5000-year lasting period of stable glacier conditions and an active ice margin close to the LGM maximum extent. Shortly after the glacier abandoned its LGM maximum position, a glacier re-advance cycle set in as shown by the sedimentological record on site. Final glacier withdrawal from the foreland is assumed to set in no later than 19 ka.