The Ticino-Toce ice conveyor belts during the Last Glacial Maximum

The provenance and distribution of erratic boulders of the Ticino-Toce glacier network yields key information for determining glaciers’ paleoflow and highlights the interaction between two major Alpine glacier systems during the Last Glacial Maximum (LGM). Boulders in the central and western parts of the Verbano, as well as in the smaller Orta end moraine systems, originate from the Toce catchment. Erratics pertaining to the Ticino mountain basin characterize the eastern flank of the Verbano amphitheatre and the glacial deposits in the Ceresio system. The wide distribution of Toce lithologies in the Verbano end moraine system can, despite its smaller overall size, be ascribed to the hypsometry and valley course of the Toce catchment. Areas with highest-elevation (>4000 m a.s.l.) and a short flow path (<100 km), favored the early spread of the Toce glacier. In the first phase of the LGM, the preceding advance of the Toce glacier may have suppressed the larger, possibly inert, Ticino glacier towards the east forcing its diffluence into the prealpine area of Ceresio, which had no local glaciers and was likely impacted by a western branch of the Adda glacier. The dynamics of the Ticino-Toce glacier network during the LGM highlight the role of the topography and location of the accumulation areas in driving differential development of glaciers originating from high catchments that can force nearby glaciers with greater inertia towards a different path.