675000 676000 677000 67800 202000 203000 204000 205000 Prozesse Unterwasserrutschungen / Ufer- und Deltaabbrüche Gefahrenpotential Flutwellen schwache Intensität mittlere Intensität starke Intensität Notfallplanung Erdbeben - Grundlagen Flutwellen renpotential Flutwellen arte EHQ - Teil Ost 10'000 tung herung, Riedenmatt 1, 6371 Stans ölkerungsschutz, Wilstrasse 1, 6371 Stans-Oberdorf gie, Stansstaderstrasse 59, 6371 Stans trasse 1, 6371 Stans r AG, Lerchenweg 2, 4303 Kaiseraugst Quartärgeologie und Paläoklimatologie Institut für Geologie Universität Bern Baltzerstrasse 1+3 3012 Bern lt Visum Plan-Nr. Format slopes have already given way. Objects dating back to the Stone Age were discovered in Lake Constance. Anselmetti is spearheading the work. Scientists can now pinpoint “loaded” underwater slopes. These analyses are ongoing, he says. The results will be incorporated into hazard maps. But how could people be warned if there were another tsunami? Advanced buoy-and-siren warning systems are a challenge to deploy, given the rarity of such an event and the short warning times involved, the geologist says. Yet simply being knowledgeable of the danger can itself make a difference, as it would anywhere around the world. If you are near a flat shoreline during an earthquake, it is advisable to get away from that area. “A tsunami is most likely coming.” The crucial point is this: when all the water at a specific point rises up from the bottom like a column, the energy is intense – generating a tsunami wave that travels quietly but barely loses any strength. If a massive chunk of rock fell into the lake, this would cause a different kind of wave, Anselmetti says. The surge may well be even greater than a tsunami wave to begin with, but would weaken very quickly. The transfer of energy would be relatively modest, because most of it would be restricted to the surface of the lake without large masses of water being displaced. Several risk factors But what about the current tsunami risk on Switzerland’s lakes? According to Anselmetti, two exacerbating factors come into play: firstly, “susceptible” underwater slopes packed with mud, and secondly, flat shorelines. The flatter the land, the further a wave can penetrate. Buochs has both these ingredients. However, most of the underwater slopes in Lake Lucerne expelled so much sediment in the 1601 earthquake that it will still take centuries before similar deposits build up to a critical level again, he says. An underwater slope is “susceptible” if it has a gradient of around 10 to 25 degrees, he continues. Any steeper, and barely any sediment would settle. Any flatter, and no big slippages would occur. Lakes Geneva, Thun and Zug all have underwater slopes that could collapse and trigger a tsunami after an earthquake. Surrounded by steep mountains, lakes Oeschinen, Walen, Lungern and Brienz are examples of lakes where rockfall-induced wave surges are to be expected, he explains. Some Swiss cantons are in the process of mapping tsunami risk. Nidwalden, which bore the brunt in 1601, is the first canton to have done so already – given that there are insurance considerations to take into account, among other things. Wave surges like the one in 1601 would still cause significant damage today. Earthquake? Get away from the shore Thanks to modern multibeam sonar systems, it is now possible to map lake floors with centimetre accuracy and reveal structures and patterns that were unknown until recently. Lake Zurich shows sections where Lake Lucerne in a state of tumult – this visualisation shows how far the 1601 tsunami penetrated into Ennetbürgen (left) and Buochs. Visualisation: provided/ Flavio Anselmetti The canton of Nidwalden has produced a map showing which areas of shoreline would be flooded in the event of a tsunami. Map: provided/canton of Nidwalden Swiss Review / October 2026 / No. 4 23
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