Multistage Rock-Slope Failures Revealed in Lake Sediments in a Seismically Active Alpine Region (Lake Oeschinen, Switzerland)

Late Glacial and Holocene rock-slope failures occur often as multistage failures where paraglacial adjustment and stress adaptation are hypothesized to control phases of detachment. However, only limited data sets are available to decipher large multistage rock-slope failures in detail. Here we apply sedimentology, radiocarbon dating, and geophysics to reconstruct multistage rock-slope failure recorded in lake sediments. We present a unique inventory from Lake Oeschinen (Bernese Alps, Switzerland) covering ~2.5 kyr of rock-slope failure history. The lake sediments have been investigated using sediment-core analysis, radiocarbon dating, and seismic-to-core and core-to-core correlations, which were linked to (pre-) historic and meteorological records. The results imply that the lake in its present extent is significantly younger than the ~9.5-kyr-old Kandersteg rock avalanche in the close vicinity. Up to eleven rock-slope failure events could be identified and related to specific detachment scarps, which provided information for energy considerations. Four events likely coincided with (pre-) historic earthquakes. At least six events detached from the same area, potentially initiated by prehistoric seismicity and later from stress-relaxation processes. The data imply unexpected high recurrence rates (~1/300 years) and also help to understand the generation of a historical lake-outburst flood. Here we show how polymethodical analysis of lake sediments can help to decipher massive multistage rock-slope failures, which are often camouflaged in subaerial settings.