Rias: Global distribution and causes

Rias are the drowned mouths of unglaciated valleys, usually bordered by steep slopes rising to mountains, hills, or plateaux. They are formed on rocky coasts. This paper examines many of the features of rias and ria coastlines, discussing their definition, their distribution (which is greater than previously thought), their morphologies, and some of the potential controls on their distribution, including tectonic history and tidal range. Notable clusters occur in Australia, south east Asia, East Asia, Oceania, eastern Africa, Oman, parts of South America (Argentina, Colombia, Brazil and Venezuela), Crimea, and the Mediterranean and Black Sea basins. The finest examples occur in areas with high tidal ranges.