Submarine mass movements and trigger mechanisms in Byfjorden, western Norway
Presented by Dr. Berit Oline HJELSTUEN on 24 Sep 2013 from 09:30 to 09:45
Type: Oral presentation, full-paper
Session: 05: Fjords & High Latitudes
Track: Oral presentations
High-resolution TOPAS seismic profiles, bathymetric records and gravity cores from Byfjorden, surrounding the city of Bergen on the west coast of Norway, have been analysed in order to identify mass failures and their trigger mechanisms during the last 15,000 years. The seismic profiles show that Byfjorden comprises four 20-50 m deep sediment basins. These basins are characterised by glacimarine and hemipelagic acoustically laminated successions and acoustically transparent lens-shaped features, interpreted to be slide debrites. The gravity cores, taken from the sediment basin close to Bergen Harbour, penetrate the upper 2.4 m of the sediment infill in Byfjorden and reveal a 1.5 m thick turbidite above a larger-scale slide debrite. The turbidite is radiocarbon dated to c. 1180 cal yrs BP, noting that such an age also has been assigned as a minimum age for a turbidite identified in the neighbouring Fensfjorden system. These turbidites are considerably younger than turbidites found in other western Norwegian fjord systems, which commonly cluster around 8200, 2800 and 2100 cal yrs BP. We suggest an earthquake as trigger mechanism for the 1180 cal yrs BP event, whereas the larger-sized slide debrites identified may be related to changes in depositional environments due to the last withdrawal of the Fennoscandian Ice Sheet in the Weichselian.