Tauredunum event

The Tauredunum event (German: Tauredunum-Ereignis) of 563 AD was a tsunami on Lake Geneva (then under the Frankish territory of the Kingdom of Orleans), triggered by a massive landslide which caused widespread devastation and loss of life along the lakeshore.

A study published in October 2012 suggests that the Tauredunum landslide triggered the collapse of sediments that had accumulated at the point where the River Rhône flows into Lake Geneva.

Here a curious bellowing sound was heard for more than sixty days: then the whole hillside was split open and separated from the mountain nearest to it, and it fell into the river, carrying with it men, churches, property and houses.

A second time the inhabitants were taken unawares, and as the accumulated water forced its way through again it drowned those who lived there, just as it had done higher up, destroying their houses, killing their cattle, and carrying away and overwhelming with its violent and unexpected inundation everything which stood on its banks as far as the city of Geneva.

The danger is recognised by Switzerland's Federal Office for Civil Protection, which takes the risk of landslide-caused tsunamis into account in its disaster planning.

[6] A study by a team from the University of Geneva, led by Stéphanie Girardclos and Guy Simpson, has found that the tsunami of 563 may not have been directly caused by the landslide, but by the collapse of sediments on the lake bed.

The team found a giant fan of turbidite – a mixture of sand and mud deposited by a rapid flow of water – spread across the lake bed.

[7][8] It is hypothesised that the impact of the Tauredunum landslide destabilised sedimentary deposits at the mouth of the Rhône, causing their collapse and triggering a large tsunami.

[9] The team also found evidence of four older layers of turbidite, suggesting that such collapses have been a recurrent event since Lake Geneva formed at the end of the last ice age some 19,000 years ago.