Intense rainstorms as drivers of lacustrine turbidity currents: implications for paleoflood records

Flood turbidites in lake sediments are widely used to reconstruct past flood activity, yet the physical link between flood hydrology, sediment transport, and the resulting deposit remains incompletely constrained. In this study, we investigate the mechanisms controlling turbidity-current initiation in the subaquatic delta of the Muota River (Switzerland) and how they are reflected in the sedimentary record of Lake Lucerne. We integrate hydro-meteorological observations from the catchment, in situ measurements of turbidity currents using moored acoustic doppler current profilers, and sediment cores spanning the last approx. 50 years of deposition. Comparing event deposits identified in the basin with gauged floods indicates that the largest floods show clear correspondence with thick, extensive turbidites, whereas the sedimentary imprint of moderate floods exhibits inter-event variability in thickness or is not consistently preserved. Monitoring data demonstrate that turbidity-current initiation is not controlled by river discharge alone but is governed by suspended sediment concentration, which in turn depends on rainfall characteristics and sediment mobilisation within the catchment. Short-lived, high-intensity precipitation events can generate sediment-rich inflows that trigger discharge-decoupled turbidity currents, whereas some higher but less turbid discharge peaks are not associated with turbidity-current initiation. This decoupling between discharge magnitude and sedimentary response may challenge the interpretation of lacustrine flood archives. Our findings emphasise that robust paleoflood reconstructions benefit from process-based calibration using modern monitoring data.