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1 Cardiff University of Wales, Department of Earth Sciences, PO Box 914, Cardiff CF1 3YE, UK
Département de Géologie et Océanographie, CNRS URA 197, Université de Bordeaux I, Avenue des Facultés, 33405 Talence Cedex, France
2 IFREMER, Géosciences Marines, BP 70, 29280 Plouzané, France
3 Geological Survey of Canada-Atlantic, PO Box 1006, Dartmouth, Nova Scotia, B2Y 4A2, Canada
4 Institute of Arctic & Alpine Research, University of Colorado at Boulder, 1560 30th Street, Campus Box 450, Boulder, CO 80309-0450, USA
The Var system extends off Nice in the Western Mediterranean. It comprises a river, a delta and a submarine valley leading to a deep-sea fan that together have been in operation since the Early Pliocene. The Var system is an area experiencing active sediment transport, where at least three major types of sediment transfer process are identified: hyperpycnal turbid plumes, surge-like turbidity currents generated by shallow failures induced by excess pore pressure during river flood periods, and by large earthquake-triggered slides. The last two processes might generate higher-density turbidity currents, but at different return intervals. Hydrological data, direct observations of the sea floor, geotechnical testing and numerical modelling confirm the very high frequency of these sediment transfer events. Some of the processes have catastrophic surge behaviour, others are continuous during periods of river flooding. In the latter case, all the sediment supplied to the vicinity of the river mouth is transferred seaward without or with only brief periods of deposition. The geological record of such continuous activity remains difficult to identify. The palaeo-events identified in sedimentary series are often widespread, high-magnitude events with return periods close to a millennium, i.e. usually beyond historical records. Normal background processes provide only thin deposits that are not interpretable in the geological record.
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