A large tsunami in Lake Geneva in AD 563 was linked to a rockfall event in the Alps and caused considerable destruction around the lake, reports a Correspondence published online this week in Nature Geoscience. The authors suggest that the densely populated shore of Lake Geneva - and potentially of other lakes - may be at risk of future tsunamis.
Katrina Kremer and colleagues surveyed the deepest part of Lake Geneva, taking seismic reflection profiles and sediment cores. They identified a distinct lens-shaped sediment deposit, which they link in time to a documented rockfall event in AD 563. The rockfall occurred in the mountains near the Rhone delta, 70 kilometres from Geneva. The researchers suggest that the rockfall caused part of the delta to collapse, triggering the tsunami. According to numerical simulations, an 8-metre-high wave would have reached Geneva within 70 minutes of the rockfall.