Disruption of the Feni sediment drift by debris flows from Rockall Bank

Slumping on the eastern margin of Rockall Bank (eastern North Atlantic) 15,000-16,000 years before present, produced a series of debris flows and turbidity currents which have disrupted the Feni Drift around 56°N 13°W. Near-bottom investigations with a deeply towed instrument package show that a large area of slightly irregular hyperbolic echoes (11,000 km²) on the Feni Drift reflects the presence of a large debris flow. Sediment cores indicate that associated turbidity-current deposits are present over a larger area. The irregular topography of the debris-flow deposit results from large blocks of relatively undisturbed sediments protruding from the surface of the flow on the shallower, erosional portion of the flow. The topography on the deeper, depositional region of the flow is due to folded sediments. The debris flow obliterated part of a field of sediment waves, the northern portion of which now forms its northern boundary. Near-bottom investigations indicate that these sediment-wave troughs have been rapidly filling in during most of the last 73,000 years, suggesting that a large sediment input to the trough preceded slumping. Possibly an influx of sediment during the last glacial period, combined with increased wave activity during lower sea-level stands, overloaded these sediment slopes and made them more susceptible to failure.