Ria
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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 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.
The southcoast of England is a submergent coastline, and contains many rias, including Portsmouth Harbour, Langstone Harbour, Chichester Harbour, Pagham Harbour, Southampton Water, Poole Harbour, the estuaries of the Exe, Teign and Dart, the Kingsbridge Estuary, and Plymouth Sound in Devon, and the estuaries of the River Fowey and River Fal in Cornwall. Milford Haven in Pembrokeshire, Wales is also a ria.
The east coast of Australia features several rias around Sydney, including Georges River, Port Hacking and Sydney Harbour itself.
The Marlborough Sounds are a large network of rias at the northern tip New Zealand's South Island.
Chesapeake Bay and Delaware Bay, on the east coast of the United States, and San Francisco Bay, on the Pacific coast, are rias. The phenomenon is also common in South America.
The rias in northern Brittany are called Abers; Aber Wrac'h (), Aber Benoît (), Aber Ildut ().
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 Pazinčica.
[edit] The rias of Portugal and Galicia
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The word "ria" is of Hebrew origin. Rias can be found in Australia and Oceania.
Starting along the Asturian coast and traveling counter clockwise, two "rias" are found on the western coast of Las Asturias, named the "Ria de Villaviciosa" and the "Ria de Navia". Continuing CCW along the northern coast of Galicia which fronts the Cantabrian Sea, are found the Rias Altas which comprise the Ria de Ribadeo, Ria de Foz, Ria del Barqueiro, Ria de Viveiro, and the Ria de Ortigueira. Continuing along the north west coast of Galicia are found the Rias Gallegos with the Ria de Cedeira, Ria de Ferrol, Ria de Betanzos, Ria da Coruña, Ria de Corme e Laxe, and the Ria de Camariñas. Continuing south along the western coast of Galicia are found the Rías Baixas with the "Ria de Muros e Noia, Ria de Arousa, Ria de Pontevedra, and the Ria de Vigo. On the western coast of Portugal near the city of Aveiro is found the "Ria de Aveiro".
The rias have shaped the development of Galicia as the population tended to cluster near their banks. The cities of A Coruña, Pontevedra, and Vigo are major ports on deep-water rias from which large vessels can operate. Fishing, and the production of shellfish on platforms (bateas) in the rias, are well-developed. The Rias region is one of high rainfall and moderate temperatures—between 0°C and 30°C. The variety of scenery and the beaches along these calm, relatively warm waters, attract tourists to such resorts as Sanxenxo and A Toxa.
