On the Timing and Nature of the Multiple Phases of Slope Instability on Eastern Rockall Bank, Northeast Atlantic

• Published in: Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2019-02, Vol.20 (2), p.594-613
• Main Authors: Georgiopoulou, A., Krastel, S., Finch, N., Zehn, K., McCarron, S., Huvenne, V. A. I., Haughton, P. D. W., Shannon, P. M.
• Format: Article
• Language: English
• Subjects: Bathymetric data; bottom currents; British Irish Ice Sheet; debrite; Deep sea; Escarpments; flow transformation; Instability; Lakes; Landslides; Landslides & mudslides; multiphase slope collapse; Oceans; Offshore; Profiles; Resolution; Risk assessment; Rockall Bank Slide Complex; Seismic profiles; Seismology; Slope stability; Slopes; Swimming pools; Underwater
• ISSN: 1525-2027; 1525-2027
• DOI: 10.1029/2018GC007674

One of the most challenging tasks when studying large submarine landslides is determining whether the landslide was initiated as a single large event, a chain of events closely spaced in time or multiple events separated by long periods of time as all have implications in risk assessments. In this study we combine new multichannel seismic profiles and new sediment cores with bathymetric data to test whether the Rockall Bank Slide Complex, offshore western Ireland, is the composite of multiple slope collapse events and, if so, to differentiate them. We conclude that there have been at least three voluminous episodes of slope collapse separated by long periods of slope stability, a fourth, less voluminous event, and possibly a fifth more localized event. The oldest event, Slide A (200 km3), is estimated to be several hundred thousand years old. The second event, Slide B (125 km3), took place at the same location as slide A, reactivating the same scar, nearly 200 ka ago, possibly through retrogression of the scarp. Slide C (400 km3) took place 22 ka ago and occurred further north from the other slides. Slide D was a much smaller event that happened 10 ka ago, while the most recent event, albeit very small scale, took place within the last 1,000 years. This study highlights the need to thoroughly investigate large slide complexes to evaluate event sequencing, as seismic studies may hide multiple small‐scale events. This work also reveals that the same slide scarps can be reactivated and generate slides with different flow behaviors. Plain Language Summary When studying large underwater landslides, determining whether what we see in our data was created by one large landslide event or several smaller events is very difficult due to the inaccessibility of the deep sea. But, being able to distinguish between different events and their frequency allows for more accurate risk assessments. Forty years ago, a large landslide was discovered in the northeast Atlantic, on the flank of an underwater plateau offshore of western Ireland. Studies since its discovery have interpreted it as one large event. With present‐day technology and a higher resolution data set, we have discovered that it is composed of several landslides. The most recent, but very small and localized event, happened in the last 1,000 years. The one before is happened 10,000 years ago, and it was the size of 680,000 Olympic‐size swimming pools. Around 22,000 years ago, a landslide 250 times bigger slid