Geological work of Sea
Sea coast:- The meeting place of land and sea is called “coast”. Sea coasts may have many kinds of shape. Chief type of sea coasts are:-
- Steep rocky cliffs
- Broad low beaches
- Small bays alternating with rocky headlands
- Sandy tidal flats
Shorelines:- A shoreline is the line along which the water meets the land the shorelines are classified into three group
- Shorelines of emergence
- Shorelines of submergence
- Compound shorelines
Shorelines may be uplifted or it may subside with respect to sea level. In some cases uplift and subsidence may operate simultaneously in different parts of the same region.
- Shorelines of emergence:- These shorelines are formed when sea coasts are uplifted or the sea level is lowered. The shorelines of emergence are characterized by a relatively straight shoreline raised beaches and elevated shore feature like sea cliffs, sea caves etc.
- Shorelines of submergence:- These shoreline are formed when either the coastal lands have subsided relative to the sea level or the sea level has risen with respect to the coastal lands. Such shorelines are generally very irregular with drowned valleys deep bays, headlands and islands. Fiords are formed in the glaciated areas.
- Compound shorelines:- The shoreline having a complex history of up and down movements relative to sea level are called compound shorelines.
Shorelines erosional features
Common types shorelines erosional features develop to work of sea water are:-
- Wave cut cliff:- The sea waves dash against the rocky shore and cut it actively . Due to continuous erosion at the base of coastal land, a cliff is formed. This cliff called wave cut cliff.
- Wave cut bench:-The sea waves undercut the cliffs and produce a notch at the base. This causes the overhanging rock to fall into the water. In this way the cliff gradually retreats towards land leaving a submerged rocky platform which is called wave cut bench.
- Sea arch and sea stack:-At first cave like features are produced at the base of the cliff which are called sea caves. When two on opposite side of a headland unite a gateway like structure is formed. Such a structure is called sea arch. When the arch falls a pillar like structure of rocks is left standing in the sea. Such a remnant pillar of rock is called sea stack.
Depositional features of sea:–
where beach drift and long shore currents are active, several depositional features may develop along the shore. The principal depositional features are as follows.
- Beach: – A beach is the flat mass of sand and gravel that is deposited on sea shores. The sediments of the beach is derived from erosion of adjacent cliffs and from alluvium contributed by rivers.
- Wave cut terrace:– under suitable conditions a part of the sediment is carried beyond the rock bench and is deposited there. In this way a flat platform like feature which is called wave built terrace. Towards shore it merges with the beach.
- Spits:- where a straight shoreline takes a sharp turn the long shore current are not able to flow parallel to it. Such a shore directs the currents into water of increasing depth where deposition takes place. This results in the formation of a submerged bar one end of which is attached to the main land. This bar is called spit. The end of the spit often becomes curved landward in response to the wave action. Such a spit us called hooked spit or hook.
- Sand bar:- sand bar are the low offshore ridges of sand which extend parallel to the coast. They commonly enclose a lagoon.
- Tombolo:- in the lee side of islands spit are often formed. If such a ridge connects an island to the main land or joins two islands together it is called a tombolo.