The incident, called the Tauredunum event (as that’s where the tsunami originated) was known only from historical sources. That’s until 2012 when geologists reported findings that added weight to the eyewitness accounts. The scientists discovered a layer of sediment that seemed to have been left by a single event, likely the giant rockfall. They were able to pinpoint the incident to between AD 381 and AD 621.
“[The tsunami] certainly happened before and I think we can expect that it will probably happen again sometime,” Guy Simpson, a geologist at the University of Geneva, explained.
Fears are now that if a similar incident occurs then the 200,000 plus inhabitants of the Lake Geneva region could be at risk.
Tsunamis, or tidal waves, are most often thought to occur in oceans, but they have been known to happen in closed lakes. In 2010, a huge chunk of Peru’s Hualcan glacier collapsed, sending a 23-metre high wave across the lake below. While in the Great Lakes of North America, high wind speeds have whipped up waves of up to nine metres in the past.
The Tauredunum event is not the only tsunami to have struck Switzerland. In 1601, an earthquake triggered a landslide into Lake Lucerne, which sent a wave cascading into the town, killing eight people. The scientists believe that at least four other tsunamis have occurred on Lake Geneva during the last 4,000 years. Tauredunum was likely the highest of the five, reaching eight meters high when it crashed into Geneva.
Earthquakes are a relatively common occurrence in Switzerland, but they are usually more on the tremor-side of the Richter scale. But with enough magnitude, they could dislodge enough earth to cause giant waves in several of Switzerland’s lakes. In 2016, there were 31 earthquakes with magnitudes of 2.5 or greater in and around Switzerland, an unusually high number. According to the Swiss Seismological Service there are an average of 23 earthquakes above 2.5 every year.
To assess exactly how much of a risk is posed, scientists launched a project earlier this year to try and understand this phenomenon and take steps to “quantify this underestimated natural danger.” Local councils are also accepting the risk of tsunamis in their disaster planning, a sure sign that we shouldn’t be too surprised to see a tsunami crashing on to the shores of Switzerland’s lakes in the near future.