Mass movement‐induced fold‐and‐thrust belt structures in unconsolidated sediments in Lake Lucerne (Switzerland)

High‐resolution seismic imaging and piston coring in Lake Lucerne, Switzerland, have revealed surprising deformation structures in flat‐lying, unconsolidated sediment at the foot of subaqueous slopes. These deformation structures appear beneath wedges of massflow deposits and resemble fold‐and‐thrust belts with basal décollement surfaces. The deformation is interpreted as the result of gravity spreading induced by loading of the slope‐adjacent lake floor during massflow deposition. This study investigated four earthquake‐triggered lateral mass‐movement deposits in Lake Lucerne affecting four sections of the lake floor with areas ranging from 0·25 to 6·5 km2 in area. Up to 6 m thick sediment packages draping the subaqueous slopes slid along the acoustic basement. The resulting failure scars typically lie in water depths of >30 m on slopes characterized by downward steepening and inclinations of >10°. From the base‐of‐slope to several hundred metres out onto the flat plains, the wedges of massflow deposits overlie deeply (10–20 m) deformed basin‐plain sediment characterized by soft sediment fold‐and‐thrust belts with arcuate strikes and pronounced frontal thrusts. The intensity of deformation decreases towards the more external parts of the massflow wedges. Beyond the frontal thrust, the overridden lake floor remains mostly undisturbed. Geometrical relationships between massflow deposits and the deformed basin‐plain sediment indicate that deformation occurred mainly during massflow deposition. Gravity spreading induced by the successive collapse of the growing slope‐adjacent massflow wedge is proposed as the driving mechanism for the deformation. The geometry of fjord‐type lakes with sharp lower slope breaks favours the deposition of thick, basin‐marginal massflow wedges, that effectively load and deform the underlying sediment. In the centre of the basins, the two largest massflow deposits described are directly overlain by thick contained (mega‐)turbidites, interpreted as combined products of the suspension clouds set up by subaqueous mass movements and related tsunami and seiche waves.

[1]  K. Kelts,et al.  The limnogeology-ETH coring system , 1986, Swiss journal of hydrology.

[2]  K. Hsü,et al.  Swiss lakes as a geological laboratory , 1985, Naturwissenschaften.

[3]  K. Hsü,et al.  Swiss lakes as a geological laboratory , 1985, Naturwissenschaften.

[4]  M. Schnellmann.  Late quaternary mass-movements in a perialpine lake (Lake Lucerne, Switzerland) , 2004 .

[5]  M. Canals,et al.  The Gebra Slide: a submarine slide on the Trinity Peninsula Margin, Antarctica , 2003 .

[6]  Donat Fäh,et al.  Earthquake Catalogue of Switzerland (ECOS) and the Related Macroseismic Database , 2003 .

[7]  D. Giardini,et al.  The earthquake in Unterwalden on September 18, 1601: A historico-critical macroseismic evaluation , 2003 .

[8]  D. Giardini,et al.  Prehistoric earthquake history revealed by lacustrine slump deposits , 2002 .

[9]  J. Locat,et al.  The Saguenay Fjord, Quebec, Canada: integrating marine geotechnical and geophysical data for spatial seismic slope stability and hazard assessment , 2002 .

[10]  J. Locat,et al.  Submarine landslides: advances and challenges , 2002 .

[11]  N. Mitchell,et al.  Passage of debris flows and turbidity currents through a topographic constriction: seafloor erosion and deflection of flow pathways , 2001 .

[12]  D. Schultz-Ela.  Excursus on gravity gliding and gravity spreading , 2001 .

[13]  M. De Batist,et al.  The late Quaternary sedimentary infill of Lake Annecy (northwestern Alps): an overview from two seismic-reflection surveys , 2001 .

[14]  Y. Kanai,et al.  Sedimentary features of seismoturbidites triggered by the 1983 and older historical earthquakes in the eastern margin of the Japan Sea , 2000 .

[15]  J. Halfman,et al.  Seismic stratigraphy of Waterton Lake, a sediment-starved glaciated basin in the Rocky Mountains of Alberta, Canada and Montana, USA , 2000 .

[16]  G. G. Back,et al.  Gradual downslope change in high-resolution acoustic characters and geometry of large-scale submarine debris lobes in Ulleung Basin, East Sea (Sea of Japan), Korea , 1999 .

[17]  M. Batist,et al.  High-resolution seismic stratigraphy of glacial to interglacial fill of a deep glacigenic lake: Lake Le Bourget, Northwestern Alps, France , 1999 .

[18]  M. Pourchet,et al.  1822 earthquake‐triggered homogenite in Lake Le Bourget (NW Alps) , 1999 .

[19]  Pierre Cochonat,et al.  The sequence of events around the epicentre of the 1929 Grand Banks earthquake: initiation of debris flows and turbidity current inferred from sidescan sonar , 1999 .

[20]  J. Syvitski,et al.  Evidence for an earthquake-triggered basin collapse in Saguenay Fjord, Canada , 1996 .

[21]  T. Mulder,et al.  Classification of Offshore Mass Movements , 1996 .

[22]  M. Batist,et al.  Lacustrine sedimentary records of brutal events in Lake Le Bourget (Northwestern Alps-Southern Jura) [ Enregistrements d'événements brutaux dans la sédimentation lacustre du Lac du Bourget (Alpes occidentales-Jura méridional).] , 1996 .

[23]  Kelin X. Whipple,et al.  Hydroplaning of subaqueous debris flows , 1995 .

[24]  David C. Mosher,et al.  Late Quaternary sediment, sediment mass flow processes and slope stability on the Scotian Slope, Canada , 1994 .

[25]  J. Clague,et al.  Documentation of earthquake-induced disturbance of lake sediments using subbottom acoustic profiling , 1992 .

[26]  N. Eyles,et al.  High-Resolution Seismic Stratigraphy of Lake Mcdonald, Glacier National Park, Montana, U.S.A. , 1991 .

[27]  P. Carlson,et al.  Development of large submarine canyons in the Bering Sea, indicated by morphologic, seismic, and sedimentologic characteristics , 1988 .

[28]  A. Bouma.  Megaturbidite: An acceptable term? , 1987 .

[29]  Su-min Wang,et al.  Earthquake and seiche deposits in Lake Lucerne, Switzerland , 1987 .

[30]  N. Kenyon.  Mass-wasting features on the continental slope of Northwest Europe , 1987 .

[31]  S. Pedersen.  Comparative studies of gravity tectonics in Quaternary sediments and sedimentary rocks related to fold belts , 1987, Geological Society, London, Special Publications.

[32]  Brian D. Edwards,et al.  Regional Method to Assess Offshore Slope Stability , 1986 .

[33]  D. B. Prior,et al.  Depositional Characteristics of a Submarine Debris Flow , 1984, The Journal of Geology.

[34]  A. Lambert,et al.  Seismic stratigraphy and bedrock forms in perialpine lakes , 1984 .

[35]  K. Kastens,et al.  Tsunami-induced sediment transport in the abyssal Mediterranean Sea , 1981 .

[36]  D. B. Prior,et al.  Submarine slope processes on a fan delta, Howe Sound, British Columbia , 1981 .

[37]  F. Hein,et al.  A Review of Mass Movement Processes Sediment and Acoustic Characteristics, and Contrasts in Slope and Base-of-Slope Systems Versus Canyon-Fan-Basin Floor Systems , 1979 .

[38]  James M. Coleman,et al.  Disintegrating retrogressive landslides on very-low-angle subaqueous slopes, Mississippi delta , 1978 .

[39]  K. Kelts.  Geological and sedimentary evolution of Lakes Zurich and Zug, Switzerland , 1978 .

[40]  S Hayashi,et al.  ESTIMATION OF LIQUEFACTION POTENTIAL OF SANDY SOILS , 1972 .

[41]  P. Komar.  Hydraulic Jumps in Turbidity Currents , 1971 .

[42]  Submarine Landslides , 1929, Science.