17. The Galician Rías. NW Coast of Spain

The rías on the coast of Galicia make up a series of deep sea inlets along the entire 1720 km long coastline. They are also associated with a complex variety of sedimentary environments, such as bays, intertidal plains, deltas, marshlands, beaches and sand dunes. In plant view, their morphology is cone or funnel-shaped and features two distinct sectors: the first makes up the larger cone, which corresponds to the ría itself, and the second is the smaller cone corresponding to the river channel which discharges into the headwaters. Rías can be classified as drowned river valleys that were flooded by seawater after the last transgression, with rivers at their headwaters, all of which bring about conditions more typically seen in estuaries. Unlike in estuaries, wave action in rías constitutes one of the main processes that control the dynamics of the greater part of this environment. On the contrary, in estuaries, forcing mechanisms are fluvial discharge at the head and daily variations in sea level at the mouth. These differences are what bring about a different distribution of sediments on the bottoms. Over one complete sea-level cycle (sea-level fall to subsequent highstand) two main sedimentary sequences can be differentiated: the ría central basin and the estuarine zone.