A coastal landform characterized by a drowned or submerged river valley in an unglaciated region is known as a:

💡 Solution & Explanation

A Ria coast develops when sea levels rise and submerge an unglaciated river valley system, creating branching estuaries and distinctive V-shaped coastal inlets. This submergence occurs along coastal regions where mountain ridges run perpendicular to the shoreline, leaving only the peaks exposed as headlands or islands. Fjords share a similar drowned valley origin but are formed by the glacial excavation of U-shaped troughs in high-latitude regions. Ria coastlines offer excellent natural harbors for maritime shipping and port development.