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Photo: Marc Mongenet

Should people living near large lakes worry about tsunamis? New research shedding light on an ancient tsunami triggered by an Alpine landslide into a Swiss lake suggests that perhaps they should. Landlocked tsunamis are possible if lakes get hit by large enough landslides or volcanic collapses, for example. Live Science’s Charles Q. Choi describes one ancient scenario in which this catastrophe played out:

In 563 A.D., a rock fall took place in the mountains more than 45 miles (70 kilometers) from Geneva, according to two historical accounts — one from St. Gregory of Tours, the other from Marius, bishop of Avenches. The rock fall, known as the Tauredunum event after a nearby fort, brought down boulders near where the Rhone River enters Lake Geneva. The falling boulders destroyed several villages.

The disaster then went on to generate a tsunami in Lake Geneva that drenched everything on the lake’s shore, devastated villages, demolished the Geneva bridge and mills, and even crashed over the city walls of Geneva, killing several people inside.

To arrive at these conclusions, researchers took seismic surveys of Lake Geneva’s depths. They found sediment deposits more than 6 miles long and 3 miles wide. Core samples suggested that the giant deposit wound up in the lake between 381 and 612 A.D., which lines up temporally with the Tauredunum rock fall. The researchers guess that the rock fall’s impact on soft sediments near the lakeshore caused part of the delta to collapse, which triggered a tsunami. Under this scenario, a wave about 25 feet high traveling at around 45 miles per hour could have reached Geneva approximately 70 minutes following the original impact.

“Tsunamis have happened in Lake Geneva in the past, and in all likelihood, will probably happen at some stage in the future,” the investigators told Choi.

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