Swiss lake tsunamis are disasters in waiting, warns Geneva University researcher Guy Simpson, co-author of a study into a giant tsunami on Lake Geneva in 563 AD triggered by a rock fall and underwater landslide.

According to new research published in the Nature Geoscience journal, a massive rock fall - probably from the Le Grammont mountain close to where the Rhone flows into lake at its eastern end - caused part of the river delta to collapse and slide into the lake.

Historical accounts describe how huge waves then inundated everything on the lake shores, devastated villages, destroyed a bridge and mills in Geneva and passed over the city walls; it is not known how many people were killed...

...Lake Geneva is particularly at risk of a tsunami in the future, the team claims, as riverine sediment continues to build up on the slopes of the Rhone delta, and a rock fall, earthquake or large storm could have a similar impact.
 
At least a million people live along the shores of Lake Geneva. The city of Geneva is especially vulnerable because on the one hand its elevation is not much higher than the level of the lake itself, and on the other it is located at the tip of the funnel-shaped body of water, which means the waves would be greatly amplified.
 
A wave of similar height today would completely inundate large parts of the city centre, the paper points out.