A 7,500-year-long record of extreme wave events from tidal Lake Hamana, south-central Japan 

<p>Lake Hamana is a brackish lake with an area of 64 km², facing the eastern Nankai Trough and connected to the Pacific Ocean. The lake has experienced tsunami intrusion during historical Nankai Trough megathrust earthquakes, and it therefore has the potential to contain a valuable sedimentary archive of wash-over events caused by tsunamis, but also by storms. Analysis of geophysical surveying data and several sediment cores has allowed a 7.5-kyr-long record of &#8805; 22 event deposits to be extracted from the lake&#8217;s sedimentary infill. Event deposits are embedded in fine-grained (silty) lacustrine sediments and have a thickness between 1 and ~50 cm. They are often sandy and typically display an erosive base, a fining-upward sequence, semi-parallel to chaotic or deformational layering, stronger X-ray attenuation, an increased magnetic susceptibility and high values for ratios of Ca/Fe and Sr/Fe. They correspond to strong reflectors on seismic images and are interpreted as products of possible wash-over events (sandy, fining-upward) and earthquake shaking (silty, deformed). Wash-over event beds become thinner or even disappear and/or become finer-grained towards ocean-distal lake sites. Radionuclide dating and independent tephrostratigraphy show that ages of event deposits go back to 7.5 ka BP, with main recurrence modes of 150-200 years. Especially going back beyond 5 ka BP, the Lake Hamana record has the potential to help fine-tune the existing megathrust records along the eastern Nankai Trough subduction zone.</p>