Prodeltaic Undulations and Hyperpycnal Flows (I): Morphological Observations

Fields of submarine undulations occurring over prodeltaic slopes may be caused in some circumstances by the imprint of high-density sediment flows (i.e. hyperpycnal flows). This is the case of numerous Mediterranean settings, where marked seasonal climates and abrupt inshore physiography are conducive to the generation of these flows. In this contribution we examine the morphological patterns of undulations that are compatible with such an origin. Prodeltaic undulations occur off the offlap breaks on relatively low slopes (1°–2°) and show dominance of landward-directed forms. Morphological parameters of undulations such as heights, widths and lengths exhibit distinctive dimensions and tend to follow consistent patterns around nearby river mouths. In particular, height distributions tend to follow symmetric patterns, and vertical form indexes are lower than those of other sediment waves with a different genesis. These observations are compatible with geological processes under the influence of high-density sediment flows, such as different deposition rates due to enhanced bedload transport. Lateral changes of river mouths involving modifications of sediment flows are also imprinted in the geomorphological parameters of this kind of undulation.