In coastal geography, a concordant, longitudinal, or Pacific type coastline occurs where beds, or layers, of differing rock types are folded into

ridge A ridge is a long, narrow, elevated geomorphologic landform, structural feature, or a combination of both separated from the surrounding terrain by steep sides. The sides of a ridge slope away from a narrow top, the crest or ridgecrest, wi ...

s that run parallel to the

coast A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, su ...

. The outer hard rock (for example,

granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...

) provides a protective barrier to

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

of the softer rocks (for example,

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

s) further inland. Sometimes the outer hard rock is punctured, allowing the sea to erode the softer rocks behind. This creates a

cove A cove is a small bay or coastal inlet. They usually have narrow, restricted entrances, are often circular or oval, and are often situated within a larger bay. Small, narrow, sheltered bays, inlets, creek (tidal), creeks, or recesses in a coast ...

, a circular area of water with a relatively narrow entrance from the sea. Lulworth Cove in

Dorset Dorset ( ; Archaism, archaically: Dorsetshire , ) is a Ceremonial counties of England, ceremonial county in South West England. It is bordered by Somerset to the north-west, Wiltshire to the north and the north-east, Hampshire to the east, t ...

is situated on a concordant coastline. The outer hard rock is Portland limestone. The sea has broken through this barrier and easily eroded the clays behind it. A

chalk Chalk is a soft, white, porous, sedimentary carbonate rock. It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor. Ch ...

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 the Portland limestone barrier at Stair Hole. The concordant coast may take one of two landform types. The Dalmatian type, named from

Dalmatia Dalmatia (; ; ) is a historical region located in modern-day Croatia and Montenegro, on the eastern shore of the Adriatic Sea. Through time it formed part of several historical states, most notably the Roman Empire, the Kingdom of Croatia (925 ...

on the

Adriatic Sea The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkans, Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Se ...

, 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 the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...

, which are enclosed by long spits of sand parallel to the low coast. The converse of concordant coastline is a discordant coastline.

References

{{coastal geography Coastal geography

See also

References