Types of Coasts
Types of Coasts and Beaches
The damage by storms, surges, and tsunamis depends in part of the type of coast.
There are many different types, and many different ways to classify coasts.
The geological setting is important. The Office of Naval
Research web page on Coasts divides
coasts into two categories:
- Primary Coasts, which were created by non-marine processes. The
processes include erosion, deposition, and tectonic activity. River
deltas are an important example
- Secondary Coasts, which were formed by marine action. The processes
include deposition of sand by waves and currents, and growth of
reefs by corals. Barrier islands are an important example.
of a rocky coast (From US
Office of Naval Research).
A barrier island (From J
How would you classify the Texas coast?
The tectonic setting influences the geology of the coast. Inman
and Nordstrom (1971) classify coasts based on plate tectonics.
- Collisional Coasts, such as the Pacific Coast of North
America, characterized by steep, fault-guided cliff lines fronted by
narrow continental shelves, and
- Trailing-edge Coasts, such as the east
coast of the US, characterized by flat topography, lagoons, and wide
The Wikipedia has a page that illustrates various types
of coastal landforms.
The Texas coast has:
- Barrier Islands "Elongate, narrow accumulations
of sediment which have formed in the shallow coastal zone and are separated
from the mainland by some combination of coastal bays and marshes.
They are typically several times longer than their width and are
interrupted by tidal inlets." From Barrier
- Lagoons "A lagoon is a body of comparatively
shallow salt or brackish water separated from the deeper sea by a shallow
or exposed sandbank, coral reef, or similar feature." From Lagoon.
- River Deltas A feature at the mouth of a
river caused by deposition of sediment. In Texas, the dominant delta is made
by the Brazos River. On the Gulf Coast, the biggest delta is made by the
The beach type along the coast is also important.
A beach is a section of the
seashore where unconsolidated sediment, or grains of worn-down
rock, has collected. Unconsolidated sediment is a sediment in which
the individual grains are clearly separated and can move freely,
like grains of rice. In contrast, consolidated sediment is a sediment
in which the individual grains cling together, like particles of
moist flour or mud. Most beaches are composed primarily of sand
(grains of quartz and other hard minerals between 0.063 mm/0.025
in. and 2 mm/0.08 in. in size), although some are composed primarily
of pebbles or fragments of seashells. The unconsolidated and small
sediments that make up a beach are easily moved by the action of
waves and wind. Consequently, the shape of a beach is constantly
changing as sand is removed from or deposited along the shoreline.
Some geologists consider a
beach to be merely a shoreline feature of deposited material, but
Willard Bascom (1980) has argued that a beach is the entire system
of sand set in motion by waves to a depth of ten meters (30+ feet)
or more off ocean coasts. Submerged, longshore bars are therefore
also part of the beach.
The beach extends from the seaward limit of wave influence
to the landward limit of wave influence. See Dr.
Beaches are dynamic landforms
altered by wind and waves in a continual process of creation and
erosion. Seasonal cycles of sand deposition and loss dramatically
affect the appearance of beaches from summer to winter. Wide and
gently sloping in summer, they become steep-fronted and narrow
in winter, and can vanish overnight, stripped of sand by violent
storm waves. Most of the sand removed from winter beaches is deposited
in offshore sandbars and is returned to the beach during the mild
summer months by gentle swells that push the sand to the exposed
shore. River sediments are the source of 80 to 90 per cent of beach
sand; some beaches are built to great widths by sediments washed
to the sea by episodic floods, gradually eroding until the next
major flood replenishes the sand.
Coastal Resources Guide.
Important features of a beach. From Dr
For more information on beaches, read the California
Coastal Resources Guide.
Fairbridge (2004 uses three processes to classify coasts:
The simplest description of a given coast
requires a minimum of three terms, embracing the following: (1) material
(hard/soft; soluble or otherwise); (2) agencies (erosive/constructive;
physical, chemical, biological, and geographic setting [latitude,
exposure, fetch]), and (3) historical factors (time scale: geotectonic,
glacioisostatic, eustatic, steric, anthropic)..."
Classifications based on perceived "relative" relationships
such as submergence or emergence are useful as generalizations, but
only when provided with the time scale. Similar constraints apply to
subsidence and uplift, and always subject to the three fundamental
Inman, D.L., and Nordstrom, C.E., l97l. On the tectonic
and morpho- logic classification of coasts. Journal of Geology, 79: 1–21.
3 August, 2009