Individual flood events detected in the recent sediments of the Petit Lac d'Annecy,eastern France

Abstract

A 90-cm long freeze core from the Petit Lac d'Annecy was sampled at 1-cm intervals and studied using magnetic measurements, chemical element and pollen analysis. The results reveal four distinctive horizons in each of which the different lines of evidence point to deposition during a single, major flood event. The magnetic evidence shows that the sediment deposited in each event included a high proportion of surface-soil derived material and this inference is consistent with the geochemical and pollen records from these layers. No firm dates can be ascribed to these inwash events at present, but a tentative chronology derived for the core from ²¹⁰Pb measurements, varve counting where possible, and correlation with a nearby, previously dated core, suggest that these flood events date from the late seventeenth to early nineteenth centuries. A tentative correlation is suggested between the single-event deposits and the record of summer/autumn floods during the period.