Ria

The drowning of river valleys along a stretch of coast and formation of rias results in an extremely irregular and indented coastline.

The result is often a very large estuary at the mouth of a relatively insignificant river (or else sediments would quickly fill the ria).

As originally defined, the term was restricted to drowned river valleys cut parallel to the structure of the country rock that was at right angles to the coastline.

These are long narrow inlets with steep sides or cliffs, created in a valley carved by glacial activity.

In the 21st century, however, the preferred usage of ria by geologists and geomorphologists is to refer solely to drowned unglaciated river valleys.