Another lake. Another ancient disaster. In 563, a tsunami devastated Lake Geneva. A massive rockfall near the mouth of the Rhone at the opposite end from the city of Geneva sent a huge wave crashing from one end of the lake to the other.
Lausanne was hit by a 40 foot wave, and by the time it reached Geneva, it was still towering to 25 feet. A contemporary chronicler wrote that the water burst over the city walls and swept away a bridge. Along the lake, villages were destroyed, and many people perished. The accepted explanation for the disaster is that a rockfall had created a natural dam across the river, which eventually gave way, unleashing the wave.
But scientists at the University of Geneva have offered another idea. They suggest that sediment had accumulated at the mouth of the Rhone, forming an underwater delta with a number of deep channels.
When the rocks fell they destroyed these canyons, and this generated the tsunami. In 1806, a landslide into another Swiss lake, Lake Lauerz, triggered a 60 foot wave which killed ten people.