A 6th-century landslide near Lake Geneva may have triggered an 8m tsunami, confirmed by a 250 million cubic meter mud layer at the lake's bottom.
Simulation of ancient landslide event
A simulation of a landslide that occurred in 563 AD on Lake Geneva suggests that a wave reached the tip of the lake 70 minutes after the start of the event, which may have been caused by the collapse of a mountain section near the mouth of the Rhône.Freshwater tsunami on a lake
The event, described as a freshwater tsunami, is surprising for a lake. A tsunami is a wave created by the sudden movement of a large mass, such as sediments sliding underwater, and not necessarily from an underwater earthquake.Lake Geneva's size and historical event
Lake Geneva, the largest lake in Western Europe, is large enough to have experienced such an event. A landslide in 563 AD triggered an 8-meter wave in Geneva, leaving a trace in the form of a layer of mud at the bottom of the lake.Historical accounts and carbon dating
Two bishops, Marius of Avenches and Gregory of Tours, recorded the event in their writings, describing a wave that destroyed villages, mills, and the bridge of Geneva, killing people and livestock. Carbon-14 dating places the event between 381 and 612 AD, aligning with the bishops' accounts.Geologists' study of the lakebed
Three geologists from the University of Geneva explored the bottom of Lake Geneva and found a huge layer of mud measuring 250 million cubic meters. This deposit is much larger than ordinary lake sedimentation and suggests an extraordinary event.Carbon dating and historical alignment
Carbon-14 dating of biological materials from the layer places the event between 381 and 612 AD. The year 563 is the only major event known in that period, aligning with the accounts of the two bishops.Landslide mechanism and wave origin
According to the geologists' explanation, the rocks may have fallen on the Rhône delta, destabilizing it and causing a slide into the lake. This slide, rather than the fall of the blocks, may have lifted the water, creating the wave.Wave propagation simulation
A numerical model simulates the wave's propagation, showing a 13-meter wave hitting the shore of Lausanne after 15 minutes. The wave weakens as it moves up the narrow tip of the lake, reaching 8 meters in Geneva 70 minutes after the start of the slide.Modern population and risk
Today, at least 1 million people live along Lake Geneva, compared to a much smaller population in the sixth century. The same shores now host entire cities, increasing the potential impact of a similar event.Historical slides and future risk
A 2015 study indicates that Lake Geneva has experienced several major slides in the past, including the one in 563 AD. However, the risk of a new episode has not been quantified by the authors of the 2012 study.
