Concordant coastline
Encyclopedia
A concordant, longitudinal, or Pacific type coastline occurs where beds, or layers, of differing rock
types are folded into ridges that run parallel to the coast
. The outer hard rock (for example, granite
) provides a protective barrier to erosion of the softer rocks (for example, clay
s) further inland. Sometimes the outer hard rock is punctured, allowing the sea to erode the softer rocks behind. This creates a cove
, a circular area of water with a relatively narrow entrance from the sea.
Lulworth Cove
in Dorset
is situated on a concordant coastline. The outer hard rock is Portland limestone. The sea has broken through this barrier and easily eroded the clay
s behind it. A chalk
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
on the Adriatic 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. The second landform is the Haff type as in the Haffs, or lagoons, of the southern shore of the Baltic Sea
, which are enclosed by long spits of sand parallel to the low coast.
The converse of concordant coastline is a discordant coastline
.
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...
types are folded into ridges that run parallel to the coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
. The outer hard rock (for example, granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
) provides a protective barrier to erosion of the softer rocks (for example, clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
s) further inland. Sometimes the outer hard rock is punctured, allowing the sea to erode the softer rocks behind. This creates a cove
Cove
A cove is a small type of bay or coastal inlet. They usually have narrow, restricted entrances, are often circular or oval, and are often inside a larger bay. Small, narrow, sheltered bays, inlets, creeks, or recesses in a coast are often considered coves...
, a circular area of water with a relatively narrow entrance from the sea.
Lulworth Cove
Lulworth Cove
Lulworth Cove is a cove near the village of West Lulworth, on the Jurassic Coast World Heritage Site in Dorset, southern England. The cove is one of the world's finest examples of such a landform, and is a tourist location with over 1 million visitors a year...
in Dorset
Dorset
Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...
is situated on a concordant coastline. The outer hard rock is Portland limestone. The sea has broken through this barrier and easily eroded the clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
s behind it. A chalk
Chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
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
Stair Hole
Stair Hole is a cove that is forming just to the west of Lulworth Cove in Dorset, southern England. In a few hundred thousand years it may be as large as nearby Lulworth Cove. The folded limestone strata known as the Lulworth crumple are particularly visible at Stair Hole. Stair hole featured in...
.
The concordant coast may take one of two landform types. The Dalmatian type, named from Dalmatia
Dalmatia
Dalmatia is a historical region on the eastern coast of the Adriatic Sea. It stretches from the island of Rab in the northwest to the Bay of Kotor in the southeast. The hinterland, the Dalmatian Zagora, ranges from fifty kilometers in width in the north to just a few kilometers in the south....
on the Adriatic Sea
Adriatic Sea
The Adriatic Sea is a body of water separating the Italian Peninsula from the Balkan peninsula, and the system of the Apennine Mountains from that of the Dinaric Alps and adjacent ranges...
, 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. The second landform is the Haff type as in the Haffs, or lagoons, of the southern shore of the Baltic Sea
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
, which are enclosed by long spits of sand parallel to the low coast.
The converse of concordant coastline is a discordant coastline
Discordant coastline
A discordant coastline occurs where bands of differing rock type run perpendicular to the coast.The differing resistance to erosion leads to the formation of headlands and bays...
.