Chapter 10
COASTAL GEOGRAPHY AND WATERS
I. General Coastal Geography
A. shore: zone between high water mark and the lowest line where land has been
exposed; includes water and land territory
1. offshore: zone beyond breakers; open ocean
2. nearshore: zone between low tide mark and breaker line
3. foreshore [intertidal zone]: zone between high and low tide
4. backshore: division of shore only touched by water during storms or
abnormally high water; extends from high tide mark
5. shoreline (water’s edge): boundary between water and land
B.
C.
D.
E.
F.
G.
H.
I.
6. breaker line: line where the farthest breakers touch bottom
coast: extends from high shore boundary to any land still affected by marine
processes
1. coastline: boundary between coast and shore
beach: entire active area of sediments affected by breakers; a sediment deposit in
the shore area
1. variables that affect erosion:
a. degree of exposure to ocean
b. tidal range
c. composition of coastal bedrock
concordant coast: bands of differing rock types run parallel to coast
discordant coast: bands of differing rock types run perpendicular to coast; leads to
development of headlands and bays
eustatic change: global change in sea level caused by a change in the volume of
water present in the ocean or the ocean’s capacity
1. sea level is lower during ice ages
2. a mid-ocean ridge changes the ocean’s capacity
isostatic change: change in sea level relative to land caused by a tectonic activity
in the continental crust that raises or lowers it
wintertime beach: beach with a thin berm, gently-sloped beach face, and welldefined longshore bar; swash does not soak into the beach due to heavy wave
activity, so more backwash carries sediment down the slope
summertime beach: beach with wide berm, steep beach face, and no longshore
bar; swash soaks into the sand due to light wave activity, so there is not much
backwash to erode beach sand
II. Headlands and Bays
A. headland: a piece of land extending from the shore surrounded by water on three
sides; found only on discordant coastlines; wave energy is concentrated on
headlands due to refraction, which leads to the features seen below
1. headlands are caused by erosion of the rock along the ocean; weaker rock,
such as sands and clays, are eroded by the sea and form bays and the stronger
rock is not eroded nearly as much and becomes a headland
B. headland features (caused by wave refraction):
1. sea caves: caves dug in the side of headlands due to concentrated wave energy
2. sea arches: form when caves are drilled all the way through a headland and
openings are made on both sides
3. sea stacks: vertical, tall, slender rocks formed by erosion of sea arches
a. sea stump: short sea stack
C. types of headlands include:
1. peninsula: large headland
2. cape: headland disruptive to a current
3. promontory: long, narrow, and high headland
D. bay: body of water with land on three sides; wave energy is reduced here due to
refraction
1. pocket beach: beach formed between two headlands; doesn’t experience
longshore drift with other beach sections
2. gulf: a large bay
3. bight: a shallow bay
III. Beach Flow
A. longshore currents: due to waves coming onto the beach at an angle, water moves
parallel to the beach; this leads to longshore drift, the transport of sediments
parallel to the shore in the surf zone; can travel at 4 km/hr; most flow south along
US coasts; these components lead to longshore currents/drift by vector addition:
1. swash: the water from breaking waves that travels up the beach parallel to
wave motion
2. backwash: the water that travels directly down the beach slope due to gravity
a. sheet flow: laminar movement of water away from the beach along the
bottom starting as backwash
b. undertow: strong pull of water along the bottom away from shore due to
backwash
B. beach flow types
1. swash-aligned: waves arrive perpendicular to shore and don’t transport
sediment
2. drift-aligned: waves arrive at an angle and transport sediment parallel to shore
C. rip currents: strong, thin currents perpendicular to the shore caused by the
concentrated diversion of longshore currents at certain spots on the shore; usually
not very long, have smaller waves, and look turbulent; speed can exceed 8 km/hr
and is increased by:
1. greater beach slope
2. greater angle of breakers with beach
3. greater wave height
4. shorter wave period
IV. Primary and Secondary Coasts (Francis P. Shephard)
A. primary coast: formed by non-marine processes; usually are young; include:
1. volcanic coast: contains igneous rock
2. tectonically-formed coast
3. alluvial plain: area around the mouth of a river, including the delta
4. sediment deposition coast: contains sediment from land
5. land erosion coasts
6. river delta: rivers (land features) deposit sediment on the coast
B. secondary coast: formed by marine processes; usually are old; include:
1. wave erosion coast (US Pacific Coast): beaches with higher wave activity tend
to have coarser/larger sediments
a. armored beach: contains large rocks, which form lag deposits, which are
there because the beach is highly eroded; eventually, the large rocks
protect the beach from further erosion
2. marine deposition coast (US Atlantic Coast): sandy beaches and spits
3. biological (less common): mangrove coasts, coral reefs, marshes
V. depositional features: caused by the accretion and transport of sediment
A. spit: linear ridge of sand attached at one end to land; the other end points in
direction of longshore drift; open end usually curves into a bay; formed by
longshore drift
B. bay barrier: a spit may grow until it links up with land and completely encloses a
bay
C. tombolo: a ridge of sand that connects an island to the mainland or an island to
another island; caused by wave refraction, which diverts sediment deposition
D. barrier islands: long offshore deposits of sand lying parallel to the coast; common
along US Atlantic coast; can be thin or wide; barrier islands along the US Atlantic
coast are migrating landward due to relative sea level rise
1. dunes: hills of sand on the shore formed by wind blowing dry sands; stabilized
by grasses
2. barrier flat: flat area landward of the dunes
3. salt marsh: biologically-productive area along the lagoon side of a barrier
island
4. lagoon: water separating a barrier island from the mainland
E. key [cay]: a small, low, sandy island formed on or around a coral reef in tropical
regions
F. moraine: deposit of sediment from a glacier that once reached the edge of the
continent, then left sediment after it melted
G. river delta: flat, fertile area of sediment deposited by a river at its mouth
1. distributary: small branching channel of water that distributes sediment onto a
delta
VI. Coastline Classification Based on Sea Level Change: sea level has risen 120 m since
the last ice age (18,000 years ago)
A. Emergent Coast: coasts of this type have visible features that were previously
underwater; caused by the rising of a continent and/or a drop in sea level;
characteristic of US Pacific coast due to thermal expansion of land
1. causes
a. subduction of oceanic crust under continental crust
b. glacial rebound: weight of ice is removed
2. marine terraces: series of adjacent beach berms, platforms, or benches on a
beach caused by the relative sea level changing (due to tectonic, seasonal, or
tidal processes), which results in erosion and deposition to be concentrated at
different heights on the beach; change in sea level exposes or submerges these
terraces
3. wave-cut notch and wave-cut platform [bench]: water erodes part of a cliff
and a notch forms at sea level; when the weight of the rock in the upper part
of the cliff cannot be supported, it falls down and only a flat platform is left
4. stranded beach deposit: deposit of sediment well above sea level
B. Submergent [Drowned] Coast: coasts that were once high up, but are now closer
to sea level or below sea level due to a relative rise in sea level; characteristic of
US Atlantic coast due to thermal contraction of land
1. cause: tectonic activity
2. relict beach: an area underwater that was once a beach
3. estuaries (fjords, rias, coastal plain estuaries)
VII. Beach: system of sand set in motion by waves up to a depth of 10 meters off a
coast; can be created or enlarged by deposition of sediments suspended in the ocean
A. features
1. berm: raised section of gently-sloping sand just above the shoreline; formed
by deposition from waves
a. crest: a slight ridge running parallel to the shoreline; marks edge of berm
b. face: slope leading from berm crest down to the ocean or to another berm
2. scarp: steep-sloped bank on the beach at the high tide water level where wave
action erodes sand; occurs at the seaward edge of a berm
3. trough: depression separating a sand bar from the beach face
4. longshore bar [sand bar]: slightly raised embankment formed below water
where waves first start to break; caused by deposition from wave action
underwater
5. drift line: high point of where materials are deposited by waves on a beach
6. beach cusps: sorted deposits of different-sized sediment along the shore in
arcs
B. beach slope
1. gentle slope: fine-grained sand; occurs because swash cannot deposit sand
easily among densely-packed fine-grained sand particles already there
2. steep slope: coarse sand; occurs because swash can deposit coarse sand easily
C. beach starvation: narrowing of beach due to erosion and disruption by man-made
structures
D. beach replenishment/nourishment: addition of sand to a beach to replace lost
sediment
E. beach sediment
1. pink sand: Bahamas; comes from foraminiferans
2. black sand: made of basalt, which comes from volcanoes
3. quartz is the most common mineral composition of sand
F. Ninety Mile Beach, Australia (94 mi, 151 km): longest unbroken beach
VIII. Coastal Waters
A. Characteristics
1. Salinity is lower due to greater runoff and river input; however, this is slightly
counteracted by the dry winds passing over the continent and then evaporating
large quantities of water on the coast, which raises salinity
2. Pollution concentrations are higher because pollutants are in water runoff
3. Seasonal temperature change is greatest in the mid-latitudes
4. Local geostrophic currents are on coasts and travel in the opposite direction
of the main currents; caused by the runoff veering right (in Northern
Hemisphere) due to Coriolis effect; Davidson current is a big one on US
Pacific coast
B. Coastal Lagoon: water separated from the ocean by a barrier island or spit; can be
diluted by freshwater or hypersaline due to high evaporation
1. Laguna Madre: hypersaline lagoon on the coast of Texas
C. Estuary: semi-enclosed coastal body of water in which the ocean water is diluted
by freshwater from a river or runoff; the water is given the term brackish because
it is brown and diluted; have high ecological productivity; bays, inlets, gulfs,
lagoons, and sounds can be considered estuaries; most exist because of rising sea
levels from glaciers melting in the past 18,000 yrs; water is generally isothermal
in estuaries and near coasts
1. Origin-Based Classifications
a. coastal plain estuary [drowned river valley, ria] (Chesapeake Bay): formed
by ocean invading a river valley; wider distribution than fjords
i. Chesapeake Bay: largest estuary in the US
b. fjord [drowned glacial valley] (Puget Sound): U-shaped, steep-walled
valley formed by glacial erosion that is filled with water; found in northern
regions
c. bar-built estuary (Pamlico Sound): shallow estuary in a lagoon separated
from the open ocean by a barrier island or other structure (spit, tombolo,
bay barrier); these are common along the US Gulf and east coasts
d. tectonic estuary (San Francisco Bay): produced by faulting or folding of
lithosphere; it is a depression in the land where ocean and river water mix
2. Water-Mixing Classifications
a. vertically mixed [well mixed]: vertically isohaline, shallow, low-volume
estuary; uniform salinity from top to bottom; salinity gradient is horizontal
from head to mouth
b. slightly stratified: moderately shallow estuary containing two layers, the
upper, less saline water from the river and the lower, salty water from the
ocean; mixing still exists and a horizontal salinity gradient from head to
mouth still exists
c. highly stratified: deep estuary in which the lower layer maintains a
relatively constant ocean salinity from mouth to head, relatively undiluted
by river input; the upper layer has a horizontal gradient from head to
mouth; prominent halocline exists
d. salt wedge (Mississippi Estuary): forms near deep, large-volume rivers in
which ocean water intrudes below the river water; prominent halocline
near mouth; upper layer is evenly-mixed and fresh
3. entrainment: process of freshwater getting more salty as it mixes with ocean
water
4. estuarine circulation pattern: net flow in stratified estuaries of low-salinity
surface water toward ocean and high-salinity subsurface water toward shore
5. sill: underwater ridge of sediment in a fjord that partially blocks water flow in
the estuary; forms by deposition from a glacier and is called a moraine above
ground
D. Marginal Seas: large bodies of water connected to the ocean
1. Mediterranean Sea: remnant of the ancient Tethys Sea separating Laurasia and
Gondwanaland
a. Mediterranean circulation: flow of ocean water into a marginal sea due to
high evaporation within the sea; the water gets salty and goes back to the
ocean as subsurface flow; this is the opposite of estuarine flow
b. about 6 million years ago, the Mediterranean dried up, but then took 100
years to fill back up with water at a later time
c. connects to the Atlantic Ocean by the Strait of Gibraltar; connects to the
Black Sea by Bosporus Strait; Suez canal connects it to the Red Sea
d. Adriatic Sea: part of Mediterranean that is east of Italy
e. Aegean Sea: part of Mediterranean that is between Greece and Turkey
2.
3.
4.
5.
6.
7.
8.
9.
f. sill: underwater depositional ridge that separates parts of the
Mediterranean
Gulf of Mexico
Gulf of California: fed by rivers; opens toward south
Bering Sea: located in the north Atlantic between Alaska, Russia, and the
Aleutian islands
Red Sea: located by Indian Ocean between Asia and Africa; unusually salty
(maximum: 42.5 ppt)
Arabian Sea: extension of Indian Ocean between India and Africa
Bay of Bengal: located between India and other islands
Weddell Sea: just above a section of Antarctica
Black Sea: has anoxic water below 200 m due to a lack of mixing
IX. Ice
A. sea ice: permanent or nearly permanent ice covering high latitude waters due to
low temperatures; newly formed ice traps brine, which trickles out as the ice ages,
because of saltwater exclusion (salt does not freeze in ice)
1. pancake ice: small discs of ice
2. ice floes: sheets of ice on the open sea
3. pack ice: free-drifting ice not attached to the coast
4. fast ice: ice fastened to the coast; >2 m thick
a. ice shelf (fast ice): thick sheets of ice over the ocean extending from
continental glaciers, mostly in the Antarctic
i. Ross ice shelf: largest
ii. Larsen B ice shelf: disintegrated earlier in this century
B. icebergs: pieces of continental glaciers that have calved, or broken off, into the
water; majority of their mass is submerged; RMS Titanic hit an iceberg and sank
in 1912; Maxim Gorky, a soviet cruise ship, hit an iceberg in 1989, but nobody
died
1. castle berg: tall and thin
2. tabular berg: large and flat
C. in the Arctic ocean, ice covers 3 to 6 million square miles (7 to 15 million square
km) from summer to winter
D. polynyas: pools of water formed on ice sheets due to melting; create a positive
feedback loop that amplifies the effects of global warming because their albedo is
lower than that of ice
E. ice color
1. white: has air bubbles trapped in the structure
2. blue: densely packed ice that is mostly pure water
X. Other
A. fishing: 95% of fish is caught within 320 km (200 mi) of shore
B. beach compartment: collective region including a river, beach, and submarine
canyon
C. coastal counties, accounting for 17% of the area of the continental US, have 53%
of the population
D. Law of the Sea
1. United Nations Conference on the Law of the Sea (Geneva, Switzerland):
international meeting first held in Geneva, Switzerland; marine law was
decided at this meeting; the most controversial policies are related to mineral
mining rights
2. territorial sea: 12 mile wide zone around a country
3. exclusive economic zone [EEZ]: 200-nautical-mile wide zone around a
country where the country has jurisdiction over marine resource use
4. 42% of the oceans are controlled by individual nations
E. Amazon river: largest-volume river in the world; drains into South Atlantic from
South America
F. coastal defenses
1. flooding defense: dams and tidal barriers are built to prevent flooding
a. Deltaworks: Netherlands’ series of engineering projects built to protect the
country from sea flooding
2. soft stabilization
a. dredging [beach nourishment]: the movement of large masses of sand onto
the beach by humans, must be done to counteract erosion
b. dune stabilization: grasses prevent erosion
3. hard stabilization: manmade structures built to prevent local erosion on the
coast, but are actually harmful to natural sediment deposition processes, which
leads to severe erosion on other parts of shore
a. jetty: barrier constructed to protect a harbor entrance; very harmful to
natural sediment deposition processes
b. breakwater: a barrier or structure constructed near or on the shore to
decrease energy of oncoming waves; protects harbors against strong
waves; not excessively harmful, but may result in growth of the beach,
which will require dredging if a calm area is still desired
i. tethered-float breakwater: floating buoy devices that decrease wave
energy, but do not disrupt sediment transportation negatively
ii. rip-rap: rocks or other material used to armor and protect the shore
from erosion by absorbing the energy of wave impacts; typically made
of granite or concrete rubble
c. groins: barriers perpendicular to the beach that are spaced in intervals with
the goal of reducing local sediment loss by longshore drift; less destructive
than jetties
d. seawall: structure built parallel to shore to protect beachfront properties;
cause the most destruction of beaches because waves hitting the wall
cause turbulence that carries away excessive amounts of sand