Flash floods in Switzerland
Evidence of rock avalanches and landslides that triggered flash floods in Switzerland's history and prehistory has been found in many Swiss lakes, taking the form of chaotically mixed deposits that differ markedly from normal sediments. Since their age can be ascertained, they can be retrospectively attributed to a seismic event. The height of the flash flood wave can be calculated by numerical models and then compared with historical reports.
The following flash floods in Swiss lakes have been historically documented:
- In 563 A.D., a rock avalanche in the Rhone Valley triggered a submarine landslide in the river's delta. This slide in turn generated a wave up to 13 m high, which swept over the bank of Lake Geneva, flooding the old city of Geneva (Kremer et al., 2012).
- In 1584, an earthquake near Aigle destroyed villages and caused rockslides. A tsunami in Lake Geneva was observed (Fritsche et al., 2012).
- On 18 September 1601, an earthquake with a magnitude of 5.9 caused submarine landslides in Lake Lucerne, triggering a 4-m-high tsunami wave that engulfed the city of Lucerne (Schnellmann et al., 2002; Siegenthaler et al., 1987).
- On 23 September 1687, parts of the Muota delta slid into Lake Lucerne, triggering a wave 5 m high (Hilbe and Anselmetti, 2014).
- On 2 September 1806, the village of Goldau was destroyed by a rock avalanche that caused a 10-m-high tsunami wave in Lake Lauerz (Bussmann and Anselmetti, 2010).
- In 1996, the remains of a human body between 190 and 290 years old were found in Lake Brienz, freed from the mud by a smallish landslide in the Aare delta that triggered a wave 1 m high. This unusual movement of water was observed by employees of the company Aarekies (Girardclos et al., 2007).
These historical examples show how different the causes of lake tsunamis can be and suggest that the possibility of future flash floods in Swiss lakes cannot be ruled out. However, there is no way of predicting where or when these phenomena may occur or what form they might take.
Sources:
Bussmann, F., Anselmetti, F., 2010. Rossberg landslide history and flood chronology as recorded in Lake Lauerz sediments (Central Switzerland). Swiss J. Geosci. 103, 43-59.
Fritsche, S., Fäh, D., Schwarz-Zanetti, G., 2012. Historical intensity VIII earthquakes along the Rhone valley (Valais, Switzerland): primary and secondary effects. Swiss J. Geosci. 105, 1-18.
Girardclos, S., Schmidt, O.T., Sturm, M., Ariztegui, D., Pugin, A., Anselmetti, F.S., 2007. The 1996 AD delta collapse and large turbidite in Lake Brienz. Marine Geology 241, 137-154.
Hilbe, M., Anselmetti, F.S., 2014. Signatures of slope failures and river-delta collapses in a perialpine lake (Lake Lucerne, Switzerland). Sedimentology 61, 1883-1907.
Kremer, K., Simpson, G., Girardclos, S., 2012. Giant Lake Geneva tsunami in AD 563. Nat. Geosci. 5, 756-757.
Schnellmann, M., Anselmetti, F.S., Giardini, D., McKenzie, J.A., Ward, S.N., 2002. Prehistoric earthquake history revealed by lacustrine slump deposits. Geology 30, 1131-1134.
Siegenthaler, C., Finger, W., Kelts, K., Wang, S., 1987. Earthquake and seiche deposits in Lake Lucerne, Switzerland. Eclogae Geologicae Helvetiae 80, 241-260.