Geomorphology, processes and geohazards of giant submarine landslides and tsunami generation capacity, as recorded in the sedimentary record of the only historic slide of this kind: the 1929 Grand Banks landslide of the Canadian Atlantic continental margin - Cruise No. MSM47 - September 30 - October 30, 2015 - St. John's (Canada) - Ponta Delgada, Azores (Portugal)

On November 18, 1929, a M7.2 earthquake occurred beneath the Laurentian Channel off the coast of Newfoundland. Nearly simultaneously, 12 undersea trans-Atlantic communication cables were severed and within two hours, a devastating tsunami struck the south coast of Newfoundland, claiming 28 lives. Only in 1952, it was understood that a slump-generated turbidity current caused the sequential severance of the cables and likely generated the tsunami. The 1929 Grand Banks events were pivotal, as they led to the first unequivocal recognition of a turbidity current and landslide-triggered tsunami. The landslide site was visited numerous times as underwater survey technologies evolved. No major head scarp related to the event is recognized. The landslide appears to have affected shallow sediments (top 5–100 m) and was laterally extensive. In order to test the hypothesis that a distributed, laterally extensive, shallow submarine mass failure event caused the tsunami, we collected ~ 1500 km of seismic lines in combination with a dense net of hydroacoustic data. A total of ~130 m of gravity cores were recovered at 30 stations. Giant box cores were taken at 15 stations. Three CPT (free-fall cone penetrating testing) transects were collected across landslide scarps. The data in the failure area show abundant small scarps and several young landslide deposits. The existing bathymetric data were slightly expanded to the shelf break but no obvious major scarp was discovered. The combined interpretation of existing and new data will allow estimating the volume of the failed material, which is an important input parameter for tsunami modelling. Another important aspect will be to assess the activity of listric faults in the failure area with special emphasis on their role for the failure dynamics and the triggering of the tsunami. The deposits of the related turbidity current were investigated in a complex channel area downslope of the failure area. Several coring transects will allow to reconstruct the flow lines of the 1929 turbidity current from bypass dominated to depositional areas. Very coarse gravel was sampled up to 150 m above the canyon thalweg. First estimates suggest high concentrations of sediments in the flow, which was able to run out over 1000s of kilometers.

MARIA S. MERIAN-Berichte MSM47. DFG-Senatskommission für Ozeanographie, p. 55