There are many different types of coasts; beaches are just one type.
Coasts are divided into two categories: primary coasts, which were created by non-marine processes, and secondary coasts, which were formed by marine action. Primary coasts happen because of changes in the land, such as river deltas or lava flows. Secondary coasts are caused by changes in the ocean, such as the creation of barrier islands or coral reefs.
Primary coasts are created by erosion
(the wearing away of soil or rock), deposition
(the buildup of sediment or sand) or tectonic
activity (changes in the structure of the rock and soil because
of earthquakes). Many of these coastlines were formed as the sea
level rose during the last 18,000 years, submerging river and glacial
valleys to form bays and fjords (a type of estuary).
River deltas are an example of a primary
coast. They form where a river deposits soil and other material
as it enters the sea. River deltas are divided into three groups:
the river-dominated delta, the tide-dominated
delta and the wave-dominated delta.
A Rocky Coast
River-dominated deltas, such as the Mississippi
or Nile river deltas, are formed when there are large amounts of material
in the water, and tidal action is relatively low. Tide-dominated deltas,
which are found where the daily tidal range
is more than a meter, have many branching channels and long narrow
islands formed as the tide and river flow in different directions.
Wave-dominated deltas are little more than a bulge on the shoreline
since there is so much wave activity that all the sediment is spread
evenly along the coast and does not accumulate at the river's end.
Primary coasts are divided into two categories: submergent
coasts and emergent coasts. Submergent
coastlines result from a general sea-level rise and crustal
subsidence (a lot of heavy sediment on top of the bedrock
is forcing the bedrock deeper into the earth). Most of the eastern
United States has submergent coastlines. One example is the Chesapeake
Bay. Emergent coastlines result from the land being lifted, either
by tectonic activity or rebound from the weight of heavy glaciers,
which exposes the former sea bottom bit by bit forming continuously
new shoreline. A characteristic feature of emergent coasts are marine
terraces, formed as tectonic uplift moves the land upward
in short bursts, which are then worn by wave action into relatively
flat surfaces, somewhat like a large staircase. Beach
ridges can be formed by rebound, and are composed of cobblestones
piled at the surfline by storm activity, which is slowly lifted
higher over time.
Secondary coasts are caused by the action of the sea
or by creatures that live in it. Sea cliffs, barrier islands, mud
flats, coral reefs, mangrove coasts and salt marshes are all examples
of secondary coastlines. While most of the eastern United States is
considered submergent, a great deal of the coastline formed between
submergent features is secondary, such as marshes, mangroves, sand
beaches and islands. Large portions of the US Pacific coast are secondary
as well, with eroded headlands and wave terraces.