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Incoastal geography, aconcordant,longitudinal, orPacific type coastline occurs wherebeds, or layers, of differingrock types arefolded intoridges that run parallel to thecoast.[1] The outer hard rock (for example,granite) provides a protective barrier toerosion of the softer rocks (for example,clays) further inland. Sometimes the outer hard rock is punctured, allowing the sea to erode the softer rocks behind. This creates acove, a circular area of water with a relatively narrow entrance from the sea.
Lulworth Cove inDorset is situated on a concordant coastline. The outer hard rock isPortland limestone. The sea has broken through this barrier and easily eroded the clays behind it. Achalk cliff face at the back of the cove slows further erosion. Erosion is just starting to the west, where the sea has again broken through thePortland limestone barrier atStair Hole.
The concordant coast may take one of two landform types. The Dalmatian type, named fromDalmatia on theAdriatic Sea, features long offshore islands and coastal inlets that are parallel to the coastline. The Adriatic Sea itself is a concordant landform, consisting of a body of water between parallel ranges. These Dalmatian types normally occur in high energy environments from where there is eustatic or isostatic change creating a submerging coastline. The second landform is the Haff type as in the Haffs, or lagoons, of the southern shore of theBaltic Sea, which are enclosed by long spits of sand parallel to the low coast.[2]
The converse of concordant coastline is adiscordant coastline.
