What Is a Ria?

Answer:

Bay of Kotor

A ria is a landform, often referred to as a drowned river valley. Rias are almost always estuaries. Rias form where sea levels rise relative to the land either as a result of eustatic sea level change (where the global sea levels rise), or isostatic sea level change (where the local land sinks). When this happens valleys which were previously at sea level become submerged. The result is often a very large estuary at the mouth of a relatively insignificant river (or else sediments would quickly fill the ria). The Kingsbridge Estuary is an extreme example of a ria forming an estuary disproportionate to the size of its river; no significant river flows into it at all, only a number of small streams.

Rias are sometimes confused with fjords. Although both are formed in drowned valleys, fjords are created not by rivers but by glaciers. For instance, a ria north of Rovinj on the western coast of Istria, Croatia, the Lim Bay (Limski kanal in Croatian) is often called "Lim fjord", although it was not actually formed by glacial erosion but by the river Pazincica.

The word ria comes from Galician language, as rias are present all along the Galician coast. It relates to the word rio (river). The 19 Galician rias are divided in three main groups: Rias Altas (Upper Rias), Rias Medias (Middle Rias) and Rias Baixas (Lower Rias).