The history of mass-movements in Trondheimsfjorden, central Norway, has been investigated from high resolution seismic data, swath bathymetry, deep boreholes and short cores. A comprehensive radiocarbon-dating program has also been carried out. Numerous slides, debris flows and turbidites have been recorded. They show a spread in ages from the last deglaciation to the present, although periods of increased mass-movement activity are evident. Major events with mass movement occurred at several localities around 400 cal. BP, 3500 cal. BP and 8000 cal. BP, while periods of large mass-movement activity are recognized at 3000-4000 cal. BP, 5500-6000 cal. BP, and before 9000 cal. BP. Several slides have occurred over the past 100-200 years in the harbour area of Trondheim and in Orkdalsfjorden, e.g. a major event took place in Orkdalsfjorden in 1930 with movement of up to 60 million m3 of sediment by sliding, debris flow and turbidity currents. Other recent slides and debris flows have occurred north of Midtfjordsgrunnen and in inner Trondheimsfjorden. A ca. 3500 cal. BP slide in central Trondheimsfjorden involved the transport of more than 30 million m3 of sediment. This slide might have caused a tsunami that generated strong currents along the seafloor resulting in local erosion and deposition of a silty clay layer evident in cores and seismic data.
Holocene mass-movement processes in Trondheimsfjorden, Central Norway