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Onset and Dynamics of a Subaqueous Dune Field in a Tideless Erosional Deltaic Shoreface: an Analog for the Initial Development of Sand Ridges

AuthorsGuerrero, Queralt ; Guillén, Jorge ; Durán, Ruth ; Urgeles, Roger
Issue Date13-Dec-2016
PublisherAmerican Geophysical Union
Citation2016 AGU Fall Meeting (2016)
AbstractA subaqueous dune field located over a retreating deltaic lobe in the Ebro delta (NW Mediterranean) is morphodynamically characterized by analyzing three sets of co-located, multibeam bathymetric data acquired in 2004, 2013 and 2015, measurements of near-bottom currents and suspended sediment concentrations, high-resolution seismic profiles and aerial photographs. The dunes, made of fine sand, extend from 5 to 15 m water depth, have straight crestlines and maximum heights and wavelengths of 2.5 and 350 m, respectively (Fig. 1). Results suggest that the onset of dune field development is closely related to the contemporary evolution of the Ebro delta. A change in the main river channel in the 1940s led to the progressive abandonment of the former river mouth, severe coastal retreatment (~37 m·y-1) and increased sediment availability. The characteristic NW winds of the region induce near-bottom currents flowing towards the SE which are able to rework and transport these sediments. The dune field developed over the shoreface of the abandoned river mouth and is currently active with mean SE migration rates of ~10 m·y-1, most likely when high-energetic currents occur. The morphology of the dune field and crestline obliquity to shoreline orientation agree well with that observed in sand ridges of continental shelves worldwide. Mid-outer shelf sand ridges have been interpreted as sedimentary bodies formed in coastal waters and detached from the coast during sea level rise. The studied dune field could therefore be an example of the initial stages of sand ridges development when large amounts of sand are suddenly available. The field developed when the river mouth switched, favored by a pre-existing seafloor irregularity. Despite the time-scale for the genesis and evolution of shoreface sand ridges has been set in time-scales of hundreds/thousands of years, this study shows that shoreface sand ridges can develop during shorter time-scales (tens of years). Furthermore, it is discussed that, in absence of a rapid sea level rise, these sand ridges probably will vanish as a consequence of sediment scarcity and wave reworking
DescriptionAmerican Geophysical Union Fall Meeting, 12-16 December 2016, San Francisco
Publisher version (URL)https://agu.confex.com/agu/fm16/meetingapp.cgi/Paper/156918
Appears in Collections:(ICM) Comunicaciones congresos
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