New constraints on the postglacial evolution of Lago Maggiore, Northern Italy

Lago Maggiore is situated in an overdeepened valley reach at the southern margin of the European Alps, and its thick sediment infill allows the reconstruction of the postglacial valley and lake evolution. We study here the sedimentary succession in the lower Ossola Valley, which is infilled by ~500 m of deposits. In a marginal position, a core of the International Continental Scientific Drilling Program (ICDP) recovered a 58‐m‐long sediment succession that is investigated by sedimentological and geotechnical analyses, luminescence and radiocarbon dating, and contextualised by reflection‐seismic data. The succession consists of a basal coarse‐grained interval that is overlain by ~35 m of silts and sands, reflecting an ice‐retreat sequence and the establishment of glaciolacustrine conditions. A distinct transition from homogeneous silt‐dominated to sandier, more heterogeneous lake deposits is attributed to a dam breach and lake‐level drop resulting in sudden delta progradation at ca. 9 ka. A clustering of mass movements in other Alpine lakes at 9.5–10 ka might point to a major earthquake as a common source event. At ca. 7 ka, the site fell dry and was covered by colluvial deposits. Our findings complement reconstructions of the regional glacial and postglacial evolution; however, the causes of lake‐level drops require further research.