The lacustrine depression at Annecy (France), geological setting and Quaternary evolution

The Annecy lacustrine depression lies in a tectonic transverse valley of st ructural origin, linking the present day towns of Annecy and Ugine and boun ded by tl ie Bauges and Bornes massifs. Only the last two major glacial per iods are represented in the stratigraphic and geomorphic evidence from the area, but its successive glaciations that have been largely responsible for the form of the valley within which the present day lake lies. Of particul ar importance were the lobes of the Arve glacier, one shaping the depressio n from the south-east; the other from the north. The retreat of the glacier s left behind a more extensive precursor of the present day Lac d'Annecy, w hich latter constitutes the residual body of open water after lake level lo wering, partial infilling and drainage diversions within the catchment. The drainage basin of the extended lake formed shortly after the last glacial maximum (LGM) in the region. Its extent can be determined from field sampli ng and coring and its elevation can be established at 460 m above present d ay sea level. The present day lake is more isolated, since the Fier river, to the north, no longer drains into it. To the southeast, the course of the Chaise river has also been diverted, leaving the lake's drainage basin red uced to half its post-LGM size. The major paleogeographical events in the L ate-Quaternary evolution of the basin are described in chronological sequen ce.