Preparing for the next Swiss tsunami

A tsunami on Lake Geneva? Well, one did happen over 1,400 years ago.

BERN  As difficult as it may be to imagine a tsunami in landlocked Switzerland, geophysical and climate scientists consider it their duty to adopt a long-term view of cataclysmic events to help mankind prepare preventive measures. Records show that a tsunami caused by an earthquake did strike Lake Geneva back in 563. It created 8-metre-high waves that not only killed untold numbers but also destroyed villages, with waves that rose as high as the walls of Geneva’s Old Town. The subject of tsunamis on Swiss lakes has continued to come up over the years in scientific circles, most recently at the European Geosciences Union General Assembly in Vienna (27 April – 2 May).

Flavio Anselmetti, a professor of geology and paleo-climatology at the University of Bern, addressed the conference about the latest research in sophisticated computer codes and simulations that monitor underwater lake movement, and realistic scenarios regarding which land areas might be affected. He said that much of their research is sponsored by insurance companies and local authorities, which need hazard maps for their communities.

Anselmetti agrees that it is difficult for the general population to imagine the hazards of a tsunami that might not happen for several generations. “A thousand years may seem long. But if it was decided to build a nuclear power plant on a lake shore, it would have to be safe for more than a thousand years. If a structure could not be made safe from an event for that length of time, we would recommend against building it.”

Anselmetti said that his tsunami research on Swiss lakes was underway long before the 2011 ocean surge that caused Japan’s Fukushima nuclear disaster. There was nevertheless much discussion in Vienna about the increasing dangers of catastrophic flooding throughout the world owing to climate change. In his History of the Franks in the sixth century, Grégoire de Tours gave this account of the event: “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. The banks of the river were blocked and the water flowed backwards.”

According to a 2012 study by Katrina Kremer of the University of Geneva, the 563 tsunami is believed to have occurred following a massive landslide on the mountain of Le Grammont, near Les Evouettes, at the point where the Rhône empties into the extreme eastern end of Lake Geneva. Such events are not uncommon in the Alps. The Kremer study cited reports of waves as high as 13 metres in Lausanne and eight meters in Geneva. City excavations indicate that waves washed over the walls of the Old Town. The lake’s shoreline is today populated by more than a million people, 200,000 of them in Geneva alone, which is most vulnerable because of its position at the far western end of the funnel-shaped lake, in a configuration that increases the height of the waves.

So would Anselmetti buy a house on the shores of Lake Geneva today? “I was asked that once and I said I don’t have the money, but if I did and knew that such waves occur only every thousand years or so, why not?” Anselmetti added that geologists must be able to imagine phenomena that have no historical equivalent, examining such rare events as the extinction of dinosaurs by meteorites 65 million years ago. “If we are not prepared for exceptional possibilities, questions could be asked of people like us, why didn’t you know about this and warn us?”

Pamela Taylor