ABSTRACT

Fernandez, G.B.; Figueiredo, M.S.; Rocha. T.B.; Maluf, V.B.; Martins, C., and Moulton, M.B.A., 2016. Foredunes Morphological Changes by Offshore Winds Revealed By Ground-Penetrating Radar: Massambaba Beach – Rio de Janeiro, Brazil. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 278–282. Coconut Creek (Florida), ISSN 0749-0208.

Foredunes are usually formed under particular conditions, more common from onshore winds and available medium to fine sediments coming from the beach, with the vegetation playing an important role fixing this material. In some specific conditions, foredunes can be observed in areas with prevalent offshore winds. Massambaba beach is 54 km long and orientated in east-west direction. This beach is under action of prevalent northeast winds (offshore) and storm surges frequently formed by south to southwest winds and high-energy waves. At the east side of Massambaba beach, storm surges are responsible for overwash processes that deposit sediments in the back dunes. These deposits are reworked by offshore winds and represent the main sediment source for the foredunes. In these specific environmental conditions, the objective of this work is investigate morphological aspects and sedimentary architecture of the foredunes at east Massambaba beach. For this purpose, 3D morphological representations were made using DGPS and sedimentary architecture was identified by use of ground-penetrating radar. The 3D morphological representations revealed susceptible areas to washover processes and aeolian morphological impact. The sedimentary architecture observed shows six radarfacies. The following structures stood out: an onshore structure (f1c – avalanche deposits) associated with storm conditions, an offshore structure (f1d – aeolian cross-bedding) associated with the action of offshore winds and another offshore structure at the top of one of the radar profiles (f1e – parabolic migration deposits) that reveals recent movement of sediments. The applied methods allowed the identification of morphologic characteristics and similarities and differences in the sedimentary architecture.

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