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The study of mass movements in lake sediments provides insights into past natural hazards at historic and prehistoric timescales. Sediments from the deep basin of Lake Geneva reveal a succession of six large-scale (volumes of 22 x 10^6 to 250 x 10^6 m^3) mass-transport deposits, associated with five mass movement events within 2600 years (4000 cal BP to 563 AD). The mass-transport deposits result from: (i) lateral slope failures (mass-transport deposit B at 3895 ± 225 cal BP and mass-transport deposits A and C at 3683 ± 128 cal BP); and (ii) Rhône delta collapses (mass-transport deposits D to G dated at 2650 ± 150 cal BP, 2185 ± 85 cal BP, 1920 ± 120 cal BP and 563 AD, respectively). Mass-transport deposits A and C were most probably triggered by an earthquake, whereas the Rhône delta collapses were likely to be due to sediment overload with a rockfall as the external trigger (mass-transport deposit G, the Tauredunum event in 563 AD known from historical records), an earthquake(mass-transport deposit E) or unknown external triggers (mass-transport deposits D and F). Independent of their origin and trigger mechanisms, numerical simulations show that all of these recorded mass-transport deposits are large enough to have generated at least metre-scale tsunamis during mass movement initiation. Since the Tauredunum event in 563 AD, two small-scale (volumes of 1 to 2x10^6 m^3) mass-transport deposits (H and I) are present in the seismic record, both of which are associated with small lateral slope failures. Mass-transport deposits H and I might be related to earthquakes in Lausanne/Geneva (possibly) 1322 AD and Aigle 1584 AD, respectively. The sedimentary record of the deep basin of Lake Geneva, in combination with the historical record, show that during the past 3695 years, at least six tsunamis were generated by mass movements, indicating that the tsunami hazard in the Lake Geneva region should not be neglected, although such events are not frequent with a recurrence time of 0.0016 yr-1

a b s t r a c tSubaquatic canyons are an important pathway for sediment transport into oceanic and lacustrine basins. Understanding the mechanisms governing their geomorphological evolution is a key to predict the sediment distribution patterns through these sediment conduits as well as to implement geo-hazard assessments. Submerged channels developed in large lacustrine basins offer a small-scale natural laboratory to understand the sedimentological processes operating in submarine channels. For this reason, a multidisciplinary research initiative -including time-lapse, high-resolution bathymetric surveys, innovative coring using submersibles, in situ geotechnical tests, and geophysical and sedimentological analyses-was applied to unravel the factors controlling the geomorphological evolution of the Rhone delta channels in Lake Geneva during the last decades. The morphology of the lacustrine Rhone Delta consists of a freshwater delta system deeply incised by nine canyons (C1eC9). Geotechnical measurements in proximal areas and sediment cores retrieved in the distal fans at the end of each canyon revealed complex sediment dynamics. No turbidity current events have occurred in the easternmost canyons (C1eC4) during the last decades while the western canyons sediment record (C5eC9) indicated repeated flushing events during the 20 th century. The main "active" canyon C8 has been dominated by turbidite activity on the canyon floor with frequent overspill events along the levees. A large 6.2 Â 10 6 m 3 Mass-Transport Deposit (MTD) that resembles a debrite in its upper section was found in the distal area of the active channel. The MTD was dated at 1998e2000 CE and most likely originated from proximal delta areas affected by frequent slope failures of the steep channel walls. In situ geotechnical tests on the modern proximal channel floor showed an unconsolidated soft top-layer that might have served as a low-friction surface favouring the MTD long run-out distance to the distal part of the channel. The MTD has had a major effect morphological evolution of the distal channel by filling the existing conduit, indirectly promoting the formation of a new channel. The role of MTD emplacement in subaquatic channels has important implications for hydrocarbon exploration as they control channel avulsion processes and the location of sand-prone deposits. This study gives a detailed insight on poorly investigated short-term sedimentological dynamics that affect the long-term evolution of turbidite systems and channel migration processes. This detailed model of a river-dominated deep-lacustrine depositional system can be used as an analog for similar modern and ancient deep-water systems.

The awareness of geohazards in the subaqueous environment has steadily increased in the past years and there is an increased need to assess these hazards in a quantitative sense. Prime examples are subaqueous landslides, which can be triggered by a number of processes including earthquakes or human activities, and which may impact offshore and onshore infrastructure and communities. In the literature, a plenitude of subaqueous landslide events are related to historical earthquakes, including cases from lakes in Switzerland. Here, we present an approach for a basin-wide earthquake-triggered subaquatic landslide hazard assessment for Lake Zurich, which is surrounded by a densely populated shoreline. Our analysis is based on high-resolution sediment-mechanical and geophysical input data. Slope stabilities are calculated with a grid-based limit equilibrium model on an infinite slope, which uses Monte Carlo sampled input data from a sedimentmechanical stratigraphy of the lateral slopes. Combined with probabilistic ground-shaking forecasts from a recent national seismic hazard analysis, subaquatic earthquake-triggered landslide hazard maps are constructed for different mean return periods, ranging from 475 to 9975 years. Our results provide a first quantitative landslide hazard estimation for the lateral slopes in Lake Zurich. Furthermore, a back-analysis of a case-study site indicates that pseudostatic accelerations in the range between 0.04 and 0.08 g were needed to trigger a well-investigated subaqueous landslide, dated to *2210 cal. years B.P.

High-resolution seismic and sediment core data from the ‘Grand Lac' basin of Lake Geneva reveal traces of repeated slope instabilities with one main slide-evolved mass-flow (minimum volume 0.13 km3) that originated from the northern lateral slope of the lake near the city of Lausanne. Radiocarbon dating of organic remains sampled from the top of the main deposit gives an age interval of 1865–1608 BC. This date coincides with the age interval for a mass movement event described in the ‘Petit Lac' basin of Lake Geneva (1872–1622 BC). Because multiple mass movements took place at the same time in different parts of the lake, we consider the most likely trigger mechanism to be a strong earthquake (Mw 6) that occurred in the period between 1872 and 1608 BC. Based on numerical simulations, we show the major deposit near Lausanne would have generated a tsunami with local wave heights of up to 6 m. The combined effects of the earthquake and the following tsunami provide a possible explanation for a gap in lake dwellers occupation along the shores of Lake Geneva revealed by dendrochronological dating of two palafitte archaeological site

BackgroundIn aerodynamic levitation, solids and liquids are floated in a vertical gas stream. In combination with CO2-laser heating, containerless melting at high temperature of oxides and silicates is possible. We apply aerodynamic levitation to bulk rocks in preparation for microchemical analyses, and for evaporation and reduction experiments.ResultsLiquid silicate droplets (~2 mm) were maintained stable in levitation using a nozzle with a 0.8 mm bore and an opening angle of 60°. The gas flow was ~250 ml min-1. Rock powders were melted and homogenized for microchemcial analyses. Laser melting produced chemically homogeneous glass spheres. Only highly (e.g. H2O) and moderately volatile components (Na, K) were partially lost. The composition of evaporated materials was determined by directly combining levitation and inductively coupled plasma mass spectrometry. It is shown that the evaporated material is composed of Na > K >> Si. Levitation of metal oxide-rich material in a mixture of H2 and Ar resulted in the exsolution of liquid metal.ConclusionsLevitation melting is a rapid technique or for the preparation of bulk rock powders for major, minor and trace element analysis. With exception of moderately volatile elements Na and K, bulk rock analyses can be performed with an uncertainty of ± 5% relative. The technique has great potential for the quantitative determination of evaporated materials from silicate melts. Reduction of oxides to metal is a means for the extraction and analysis of siderophile elements from silicates and can be used to better understand the origin of chondritic metal.

Submarine landslides are major agents of sediment mass transfer from the shallow to deep sea. Due to their rapid emplacement and tsunamigenic potential, such landslides are significant geohazards for society and offand on-shore infrastructure. The relationship between climate change and the occurrence of submarine landslides is widely debated. However, there is a lack of continuous long-term submarine landslide records with which to comprehensively understand the relationship between climate-driven forces and submarine landslide occurrence. Here, using oxygen isotope stratigraphy in combination with tephrochronology, we date a 1 Myr continuous record of six landslide deposits (at 13.0-14.2, 323-339, 372-384, 394-413, 508-521, and 857-867 ka) recorded in a slope basin of the Nankai Trough subduction zone, off-shore Japan, which represents the major outcome of this study. The ages of the six landslides coincide mostly with interglacial periods. Thus, we propose that climate forcing might act as a preconditioning factor for slope instability in this active tectonic region.