Abstract
Submarine landslides can generate sediment-laden flows whose scale is impressive. Individual flow deposits have been mapped that extend for 1,500 km offshore from northwest Africa1,2,3,4,5,6,7. These are the longest run-out sediment density flow deposits yet documented on Earth. This contribution analyses one of these deposits, which contains ten times the mass of sediment transported annually by all of the world’s rivers8. Understanding how this type of submarine flow evolves is a significant problem, because they are extremely difficult to monitor directly9. Previous work has shown how progressive disintegration of landslide blocks can generate debris flow, the deposit of which extends downslope from the original landslide10,11,12,13. We provide evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide, encased within deposits of a more dilute flow type called turbidity current. Very little sediment was deposited across the intervening large expanse of sea floor, where the flow was locally very erosive. Sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea-floor gradient from 0.05° to 0.01°. This debris flow was probably generated by flow transformation from the decelerating turbidity current. The alternative is that non-channelized debris flow left almost no trace of its passage across one hundred kilometres of flat (0.2° to 0.05°) sea floor. Our work shows that initially well-mixed and highly erosive submarine flows can produce extensive debris flow deposits beyond subtle slope breaks located far out in the deep ocean.
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Acknowledgements
We thank the officers and crew of RSS Charles Darwin and Shipboard Scientific Party and Coring Technical Team on cruise CD166. This work was supported by the UK Natural Environment Research Council, ConocoPhillips, BHP Billiton, ExxonMobil and Shell.
Author Contributions P.J.T. wrote the manuscript, incorporating comments from all co-authors. R.B.W. led the research project and was chief scientist on cruise CD166. B.T.C. was co-chief scientist during cruise CD166. P.J.T., D.G.M., M.F., A.M.A., S.D.-T., A.G. and C.Z. participated in data collection during this cruise. P.J.T., R.B.W. and D.G.M. visually described cores. M.F. completed grain size analyses. R.S. analysed benthic foraminifera assemblages. A.M.A. processed bathymetric and shallow seismic data. S.D.-T., assisted by C.Z., quantified sediment composition and imaged sedimentary structures. S.B., P.P.E.W. and A.G. analysed coccolith assemblages. L.A.A. contributed to data interpretation. R.B.W., P.J.T. and B.T.C. obtained industry funding.
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The file contains Supplementary Figures 1-5 and Legends, Supplementary Methods, Supplementary Discussion and additional references. This file contains Supplementary Discussion and additional references related to previous studies of debris flow, evidence that this is a debris flow deposit, and alternative mechanisms for debris flow formation. Supplementary Figures show correlation of flow deposits, evidence for erosion in the lower canyon, and composition and shape of Bed 5. (PDF 867 kb)
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Talling, P., Wynn, R., Masson, D. et al. Onset of submarine debris flow deposition far from original giant landslide. Nature 450, 541–544 (2007). https://doi.org/10.1038/nature06313
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DOI: https://doi.org/10.1038/nature06313
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