Geology Lecture
Outline
Introduction
–
Classifying Coastlines – Primary versus Secondary
Primary Coastlines – Rugged, Irregular, and Rocky
Secondary
Coastlines – All Shapes and Sizes
Beaches – Where Surf Meets the Sand
Estuaries
and Deltas – Where Rivers Meet the Sea
Reefs and Atolls –
Other
Coastal Features – From
Humans Assault on Shorelines - Mother
Nature Knows Best
II. Introduction
A. Coastlines are Long, Narrow Geographic
Features
1. Occur wherever ocean and land meet at or
near sea level
·
Margins of
continents
·
Edges of
inner-continental seaways
·
Island rims
2. Typically are only up to a kilometer or two wide
·
The term coastline or coastal zone has a much broader meaning
than shoreline and includes many other habitats and ecosystems associated with
terrestrial and marine processes
·
The coastal zone includes beaches, wave-cut terraces,
offshore bars, bluffs, back beach dunes, deltas, estuaries, lagoons, swamps,
and marshes
·
A shoreline is more limited to the beach, or littoral
zone
3.
shoreline.
·
Equals 1 1/2
times the distance to the Moon
B.
Shorelines are the Most Dynamic Regions on Earth
1. Comprises a special geography where
atmosphere, land and ocean meet at
a
triple interface
2. A geographic region affected by many
natural agents
·
Wind
·
Surf
·
Tides
·
Tsunami
·
Storms
·
Flooding
·
Sea level
fluctuation
·
Glaciation
·
Biologic forces
·
Earthquakes
·
Volcanism
·
Tectonics-
Uplift/Subsidence
·
Human
interference
3. The location and shape of coastlines
are always changing
·
Location controlled by two factors:
ü Tectonics and
ü Ocean volume
·
Shape is controlled by several factors:
ü Uplift
ü Subsidence
ü Eustatic sea level fluctuations
ü Erosion
ü Deposition
ü Volcanism
C.
Much of World's Population Lives At/Near the Coast
1. Coastal
dwellers are exposed to similar dynamic agents that shapes the
coast
2. Coastal dwellers have responded to dynamic change
along coastlines by
attempting to stabilize coastal features
·
Jetties,
seawalls, dikes, breakwater, groins, etc.
III. Classifying Shorelines
A.
Classification Schemes for Coastlines are Based on the
Dynamic Factors that
Shape Them
1. Common geotectonic origin
·
Leading edge
coasts - active coasts
ü Plate boundary coastlines
ü Tectonically active
ü Active magmatism
·
Trailing edge
coasts - passive coasts
ü Innerplate coastlines
ü Little to no tectonic or magmatic activity
2. Eustatic (worldwide) sea level fluctuations
·
Variation in
total ocean water volume
·
Variation in
ocean basin volume
·
Variation in
water column density
3.
Local changes in local sea level
·
Tectonic uplift
or subsidence
·
Isostatic adjustment
·
Local ocean
surface fluctuations
o
Storm surges
o
Waves
o
Tsunami
o
El Nino and La
Nina
4. Coastlines are classified into two
distinctive types, based on the source of
dominate
influence(s)
·
Primary - Dominated by Terrestrial Influences
·
Secondary
- Dominated by Marine Influences
C. Primary Coastlines
1. Primary coasts typically have the following character:
·
Rugged
Relief
·
Irregular
·
Rocky
2. Primary coasts are
dominated by one or several terrestrial influences –
agents
of change
·
River
erosion - downcutting of river valleys
·
River
deposition at river mouths - deltas
·
Regional
crustal movement - mountain building
·
Volcanism
·
Glacial erosion
and deposition - fiords
3. Three general types
of primary coastal zones
·
Land
erosion coasts
o Example: Coast of
·
Depositional
build-out coasts
o Example: Coast of
·
Tectonic/Faulting
coasts
o Examples:
·
Volcanic coasts
o
Example:
4. In many cases, a primary
coast may be a hybrid of the above three general
types
·
Example:
D.
Secondary Coastlines
1. Secondary coasts are
highly variable in character:
·
Can
be rugged, irregular and rocky
o Example: Coast of
·
Can by low-lying,
straight, and sandy
o
Example:
2. Secondary coasts
have been significantly altered by marine processes,
including
the following:
·
Wave and surf
action
·
Longshore currents
·
Ocean dissolution
·
Tidal action
·
Salt weathering
3. Wave action is the
dominant agent of change
·
Most intense on
high-energy coasts
·
Particularly
during storm events
4. Land erosion forces
also contribute to changing a primary coast to a
secondary
coast
·
Stream erosion
·
Wind abrasion
·
Mass wasting
·
Plant and animal
activities
5. Typical features of
secondary coasts include:
·
Sea cliffs
·
Sea caves
·
Sea stacks
·
Sea arches
·
Wave-cut
platforms
·
Barrier islands
·
Sand spits and tombolos
·
Bay mouth bars
·
Beaches
6. Ocean wave and
current action over time will ultimately straighten the
shoreline
·
Wave
refraction intensifies energy at headlands
·
Wave
refraction dissipates energy in bays
·
See
figure 12.13 (page 298)
·
Overall effect of
shoreline straightening
o Wear away headlands
o Fill in the bays
o
Build up and
accumulate beaches
A.
Beaches Defined
1. The beach is a zone of unconsolidated sediment that
covers all or part of the
shoreline
·
Beaches extend
from beyond the breaker zone to the landward edge of the coastal zone
·
Consists of sand
and/or pebbles and/or cobbles
·
Another term for
the beach is the littoral zone
2. Beaches can
be divided into three regions:
·
Offshore – the area seaward from where waves first begin to
break, breaker zone
·
Nearshore – the area
from the offshore to where waves wash back and forth across the beach
o
Near shore can be
divided into the:
§
Breaker
zone – where the waves begin to break
§
Surf
zone – where the waves expend most
of their energy
§
Swash
zone – where waves wash back-and-forth
across the beach face
·
Backshore – the land that adjoins the near shore
o
Also termed the backbeach
3. Position of
the divisions of the beach varies with the tides, advancing
landward with high tide and retreating seaward with low tide
B.
Beach Profile and Anatomy
1.
A beach profile is a cross section of the beach along a line that is
perpendicular to
the shoreline
·
By comparing a
series of beach profiles along the same line made at different times, it is
possible to tell if the beach is
expanding or eroding
·
Beaches display
seasonal cycles of expansion and contraction related to wave size
·
There is a
general relationship between beach material
composition and beach slope angle
o More gradual - the finer the sediment
o More steeper - the coarser the
sediment
o
See Table 12.1
(p. 299) for comparing
·
Study text figure
showing a beach profile
2. A swell profile is
concave upward with a wide, broad berm
(relatively flat
backshore) and
steep intertidal beach face
·
This profile
typically develops during summer when the weather is fair and the dominant waves
are flat swells, which transport sediment shoreward and enlarge the beach.
3.
A storm profile displays erosion of the berm into a beach scarp and
a broad
flat intertidal
beach face
·
This profile
typically develops during winter when the weather is more unsettled and the
dominant waves are high, steep, and erosive
·
Finer sediment is
transported seaward, leaving coarser sediment behind on the beach
·
Some of the
sediment transported seaward forms sets of longshore bars and
troughs, which later migrates landward as the swell profile begins to
redevelop
C.
Ocean Breakers and Currents
1. Ocean waves that meet the shoreline will break
·
Breaking waves,
or breakers, and the resultant white water is termed surf
·
The size of surf is
dependent on swell size, coastline shape, and bottom conditions
·
The shape of the
breaking waves is dependent mainly on bottom conditions
2. Breaking waves turn swell energy into translational
kinetic energy –
shoreward-moving turbulent water termed "white
water"
3. Surf energy goes to work in several ways:
·
Generates
longshore currents
·
Generates
rip currents
·
Moves
beach material perpendicular to shore
o Combination of saltation
and suspension
·
Erodes
bedrock base - creates wave-cut platform
·
Erodes and
undermines sea cliffs
4. Waves that
approach the shore at an angle will break at an angle to the
beach and result in a peeling wave
·
Angled breakers
have a translational (white water) component that is parallel to shore
·
The
shoreline-parallel component of white water over time
generates a nearshore current called a longshore current
·
Longshore (parallel-to-shore) currents move in the direction
opposite that of
the direction the swell arrives from
o
Northerly swells
generate a southward-bound longshore
current along a
west or east-facing beach
o
Southerly swells
generate a northward-bound longshore
current along a
west or east-facing beach
·
Beach material
moved by a longshore current is termed
longshore
transport or drift
·
Study Text Figure
for longshore transport
5. Waves approaching the shore at an angle will
disturb the bottom sediment
prior to breaking
·
Sediment will be
moved in similar direction to the longshorecurrent
·
This is termed offshore transport
6. Longshore currents cause
transport (drift) of beach material in the direction
of the current
·
The dominant longshore
current and transport direction is south, due to the predominant northerly
swell directions of winter swell
7. White water that piles up along a section of
beach must find
a means to exit
back out to sea
to maintain a water mass balance along the seashore –
gravity
maintained
·
This is commonly
accomplished by the generation of narrow seaward-bound currents running
perpendicular to shore
o
These currents
are called rip currents
8.
Rip currents are narrow river-like channels of ocean water that move
seaward through
the nearshore surf zone and into the offshore region
of
the beach where
they dissipate
·
Rip currents
typically have an extended mushroom-like shape (from a
"bird's eye" view), and are often accentuated by rough,
foamy water
·
Rip currents form
by a combination of two phenomena at specific locations along a beach:
o
Convergence zones
of inbound white water energy
o
Inshore-bound
waters especially accumulate along
low-standing
channels along the beach bottom
·
Swimmers and
surfers caught in outgoing rip currents escape them by swimming or paddling
parallel to shore
D.
Seasonal Beach Changes
1. Beaches undergo seasonal changes
due to differences in marine weather
·
Times of the year
with persistent large stormy surf results in excessive beach erosion
o
Winter- and Spring
along the
o
Sand is moved
offshore into longshore bars beneath the waves
o
Beaches become
lower, narrower and steeper
o
Beach sediment
size becomes coarser
·
Times of the year
with persistently calm conditions
results in excess beach deposition
o
Summer and Fall
along the
o
Sand is moved
shoreward back onto the exposed beach
o
Beaches become
higher, wider and flatter
o
Beach sediment
size becomes finer
E.
Coastal Beach Cells
1.
Beach-lined coastlines are broken into separate unique segments called
coastal cells
2. Each coastal cell acts like a river of sand
·
Driven primarily
by longshore currents
·
"Upstream
and "downstream" ends of a cell
3.
Each coastal cell has a sand budget
·
The sand budget
is the balance between sediment added
to and sediment removed from the cell
4. Major input sources of sediment for beach cells:
·
Rivers
·
Coastal cliffs
5. The boundary between coastal cells is marked
by a coastal geographic
barrier that
diverts or terminates longshore transport
·
Typically the
barrier is a submarine canyon or extensive
headland
6. Longshore and offshore currents transport beach material
both parallel to
the shoreline
·
Parallel sand
movement is termed longshore transport
·
Sediment input to
the beach comes from rivers, sea cliff erosion, and on-shore sediment transport
·
Beach sediment is
removed by longshore current, off-short transport,
and wind erosion
·
A balance between
sediment gains and loss results in a stead-state condition
·
If sediment loss
is greater than sediment gain, a negative sand budget exists and the beach will
begin to erode
·
If sediment loss
is less than sediment gain, a positive sand
budget exists and the beach will begin to expand
7.
The typical final output destination for sediment in a coastal sand cell is an
underwater
(submarine) canyon
·
Sand is funneled
down these underwater ravines via turbidity currents
·
Sand is
permanently removed from the coastal cell
V. Estuaries and Deltas
A. Estuaries
1. Defined:
·
Estuaries are
semi-enclosed bodies of water wherefresh water from
the land mixes with sea water
2. Estuaries
originate as:
§
Drowned
river valleys – with the rise in sea
level, the lower portions of river valleys have flooded
§
Fjords – as glaciers have retreated and sea level risen, the
lower portions of glacial valleys have flooded
¨
Fjords are
typically long, narrow, and deep with steep
cliff-like sides
¨
The bottom of
fjords frequently are partially blocked byglacial
moraines (ridges of sediment deposited at the front of the glacier) which inhibit
current flow and can produce hypoxic to anoxic conditions at the bottom.
·
Bar-built
estuaries – spits and sand bars may
partially block the entrance of an embayment, thereby restricting tidal flow.
·
Tectonic
estuaries – uplift associated with plate
tectonics can partially block the entrance to an embayment.
3. Salinity
typically grades from normal marine salinity at the tidal inlet of fresh
water at the mouth of the river.
§
In some
estuaries, the water is well stratified with a strong halocline separating the
dense saline water below from the fresh
water above
4. Tidal flow
provides the energy for mixing the fresh and saltwater masses.
§
If tidal flow is
strong, stratification is weak.
5. Estuaries
can be subdivided into three types based upon the relative
importance of river inflow and tidal mixing.
.
§
Salt-wedge
estuaries
§
Partially-mixed
estuaries
§
Well-mixed
estuaries
6. Salt-wedge estuaries are dominated by the outflow from
rivers
§
The outflow from
rivers is much greater than the inflowfrom the tides
§
The water column
is highly stratified with a well-defined, strong halocline that inhibits mixing
§
Salt water forms
a wedge that extends landward below the fresh water wedge that extends seaward
§
Strong turbulent
currents in the fresh water flow across the halocline and generate internal
waves
§
As the internal
waves steepen and break, they mix salt water into the fresh wand it is swept
seaward
§
The continual
loss of salt water into the fresh water generates a slow current that flows in
along the bottom and up along the underside of the fresh water wedge
§
The bottom
current is too weak to carry much sediment into the estuary from outside the
tidal inlet
§
Sediment distribution
in the estuary consists of river sand at the landward edge of the saltwater
wedge and mainly river clays and silts elsewhere
7. Partially-mixed estuaries are
dominated by neither river inflow nor tidal
mixing
§
Tidal currents
promote greater mixing and both stratification
and the
halocline are greatly weakened
§
As more saltwater
mixes into the fresh, a stronger bottom
current is
generated
·
The bottom of the
seaward end of the estuary is covered
with sediments from
the shelf, whereas the landward end
is dominated by river sediments
8. Well-mixed estuaries
are dominated by tidal turbulence which destroys the
halocline and water stratification
§
In wide
estuaries, Coriolis deflects river outflow to one
side and tidal inflow to the other
§
A salinity gradient extends across the
estuary, but not vertically within the water column
§
Seawater flows in
and fresh water flows out on opposite sides of the tidal inlet at all depths
9. Since river
discharge and tidal inflow vary, the type of estuary can change
10. The widely
fluctuating environmental conditions in estuaries make life
stressful for organisms
11. Estuaries
are extremely fertile because nutrients are brought in by rivers
and recycled
from the bottom because of the
turbulence (waves and tides)
§
Stressful
conditions and abundant nutrients result in low species diversity, but great
abundance of the species present
12. The benthic fauna strongly reflects the nature of
the substrate and most
fishes are juvenile forms living within the estuary until
they mature and
migrate to the ocean.
B.
River Deltas
1. Defined:
·
A delta is an
emergent accumulation of sediment deposited at the mouth of a river as it flows
into a standing body of water
2. The three major areas of a delta are:
·
Delta plain –
flat, low-lying area at or below sea level that is drained by a system of
distributaries
·
Delta front –
shoreline and broad submerged area of the delta that slopes gently seaward
·
Prodelta – far off shore area of the inner shelf that
receives fine sediment from the river
3. In cross sections, a delta’s deposits can be divided
into three sets of beds:
·
Topset beds – flat-lyign beds of
sand and mud of the delta plain deposited by the distributaries in their
channels and in the inter-channel areas
·
Foreset beds – thick silts and sands of the delta front that
slope gently seaward and form the bulk of the delta
·
Bottomset beds – flat-lying silts and clays of the prodelta that settle out of suspension far offshore
4.
As sediment accumulates the delta expands seaward with forest beds
burying bottomset beds and topset beds
covering foreset beds
5. Shape of the delta can be altered by tides,
waves, and river deposition
·
River
dominated deltas form in areas protected
from large waves and with a small tidal ranges
o
Delta displays
the ideal triangular form
o
Example: the
·
Wave
dominated deltas are so altered by wave
erosion and longshore drift that most of the delta
sediment is distributed along the coast and only a slight protrusion exists at
the mouth of the river
o
Delta displays
only a slight protrusion at the mouth of
the river
o
Example: the
·
Tide
dominated deltas are altered by the ebb
and flow of the tides and into the ocean
o
Delta displays
long linear submarine ridges
and
islands that radiate from the river’s mouth
o
Example: the
6.
Reduction in the supply of sediment to a delta results in delta erosion and
subsidence as the
sediments of the delta compact
·
Erosion and
Subsidence
VII. Reefs,
A.
Coral Reefs Defined
1. A coral reef is an organically constructed,
wave-resistant, rock-like structure
created by carbonate-secreting organisms
·
Most of the reef
is composed of loose to well-cemented
organic debris
of carbonate shells and skeletons
·
The living part
of the reef is just a thin veneer on the
surface
·
Corals belong to
the Animal Order Cnidaris
Ř The animal is the coral polyp
Ř The body of the polyp resembles a sac with the open
end surrounded
with tentacles
Ř The corralite is the
exoskeleton formed by the polyp.
Its interior is divided by septa,
vertical partitions.
2.
Corals share a symbiotic relationship (mutually
beneficial) with
the algae called zooxanthallae which live
within the skin of
the polyp and can comprise up to 75%
of the polyp’s
body weight
·
The coral
provides protection for the algae and supplies
them with nutrients and carbon dioxide from the polyps
metabolic wastes
·
The algae supply
the coral with oxygen and food
·
Recycling of
nutrients between the polyp and the algae
allows the corals
to thrive in the nutrient-poor tropical seas
3.
Corals cannot survive in fresh, brackish water or highly
turbid water
4. Corals do best in nutrient poor water because
they are
easily out-competed
by benthic filter feeders in nutrient-
rich water where
phytoplankton are abundant
B.
Evolution of Coral Reef Systems
1. As a result of corals growing continuously
upward
towards the
sunlight as sea level rises and/or land
subsides and, coral
reefs pass through three stages of
reef
development
·
Fringe reefs
·
Barrier reefs
·
Atolls
2. Fringe reefs
form limestone shorelines around islands
or along
continents
·
Represents
the earliest stage of reef development
·
Form
in areas with low rainfall runoff
·
Leeward
side of islands
·
Many Hawaiian
reefs are this type
3. Over time, islands do two important things
·
Slowly subside
with the underlying ocean crust
·
Slowly wear down
to sea level by wave erosion
4.
Upwards reef growth keep ups with sinking island
·
Reefs grow upward
at up to 1 cm/year
5.
As the land is progressively submerged and the coral
grows upward, an
expanding shallow lagoon begins to
separate the
fringe reef from the shoreline and the reef is
called a barrier reef (second stage)
·
Barrier reefs
occur at lower latitudes than fringe reefs
·
6. In the final stage, the
land vanishes below the sea and
the reef forms an island ring or ring or islands, called an
atoll, around a shallow
lagoon (final stage)
7. See Figure 12.27 in text (page 307)
C.
Atolls and Guyouts are Modified Oceanic Islands
1.
only
the growing reef able to maintain at sea level
·
This stage of an
island is termed an atoll
2. Eventually reef growth lags behind rate of
atoll
subsidence, and
entire atoll structure becomes
permanently submerged
·
The submerged
atoll is termed a guyout
3.
See Figure 12.27 in text (page 307)
V. Other Geographic Features of Coastlines
A.
Coastal Bluffs and Cliffs
1. Defined:
·
A sea cliff is an
abrupt rise of the land from sea level
2.
A sea cliff is most vulnerable to erosion at its base
because:
·
As waves slam
against the cliff, air is compressed inside
cracks and then
expands violently as the wave recedes
o
This can
eventually shatter the rock
·
Sediment is
hurled against the cliff by the waves
·
Sea water can
dissolve some rock types
·
When sufficient
rock at the base of the cliff has been
removed, the upper
part of the cliff collapses
3. Collapsed material protects the base of the
sea cliff from
additional erosion
until it is destroyed and removed
4.
The rate at which the cliff recedes is dependent upon:
·
Composition and
durability of the cliff material
·
Joints,
fractures, faults and other weaknesses in the
cliff material
·
Amount of
precipitation
·
Steepness of the
cliff
5. The wave-cut
platform is the gentle sloping area in front
of the sea cliff that was produced by sea-cliff retreat
B. Coastal
Dunes
1. Sand dunes
are formed by onshore winds blowing sand
landward from the dry part of the beach
2. Well developed dunes typically have a
sinusoidal profile
with the primary
dune at the landward edge of the beach
and possible secondary
dunes located farther inland
·
Dunes can extend
up to 10 km into the interior
·
The area between
adjacent dunes is called a valley or swale
·
Small, irregular foredunes commonly occur a the upper
edge of the
beach
2.
Vegetation on the dunes traps windblown sand on their
downwind side and
promotes dune growth and stability
3. Blowouts are wind-scoured breaks In the dune or
depressions in the
dune ridge and commonly occur if
vegetation is
destroyed
·
With time blowout
can enlarge and destroy the dune
4. Dunes are best developed in the following
conditions:
·
Sand is abundant
·
Onshore winds are
strong and persistent
·
The tidal range
is large
·
The beach is wide
and gently sloping
5.
Wave erosion of sand dunes transports sand offshore
and creates a steep
scarp at the base of the dune
·
The scarp
reflects the wave energy and lessens additional
erosion of the
dune by the breakers
7. Dunes act as a natural barrier and prevent
inland
flooding
8. Human activity that damages vegetation leads
to dune
destruction by
blowouts and washover by storm waves
·
Washover forms a washover fan on the
landward side of
the dune
C.
1. Barrier islands are islands composed of sediment
that
parallel the
coast and form where sand supply is
abundant and a broad sea floor slopes gently seaward
2.
The islands are separated from the mainland by shallow
bodies of water
which are connected to the ocean
through tidal
inlets
3. A series of distinct environments develop
across the
island parallel to
the beach and include the nearshore
zone, dune field,
back-island flats, and salt marshes
·
The back island
flats are washover fans deposited during
storms as water
flooded across the lower parts of the island
·
Salt mashes are
protected areas on the back side of the
island where mud
collects
4.
Barrier islands are created in many ways including:
·
Sand ridges on
the coastal plain which paralleled the coast
and were later
isolated as lowlands were submerged by
rising sea level
·
Sand spits that
were breached during a storm and remained
separated from
the mainland by a tidal inlet
·
Vertical growth
and emergence of alongshore sand bars
·
As sea level
rises, barrier islands migrate landward as
washover
transports sediments from the seaward side
of the island to
the landward side
D. Sand spits
1. Sand spit defined:
·
linear feature made up of unconsolidated sediment that
grows downcurrent of the longshore current
2. Sand spits are anchored
to coast off of natural or man-
made projections,
such as sea stacks or jetties
3. Usually, the youngest
end of the spit is wide and/or
hook-shaped
E. Tombolos
1. Tombolo
defined:
·
A sand spit that grows from the shore to an offshore
landmass
2. Tombolos
are common features of sandy shorelines that
have
abundant seastacks
and islands in close proximity
to shore
F. Bay Mouth Bars
1. Bay mouth bar defined:
§
Form when spits grow across and block the entrance to a bay
2. If waves and tides are
strong enough, the bar will be
breached. Otherwise, a lagoon will develop
G.
Lagoons
1.
Lagoons defined:
·
Lagoons are
isolated to semi-enclosed, shallow, coastal
bodies of water that receive little if any fresh water
inflow
2. Some lagoons are now polluted; were once
productive,
now are wastelands
H.
Salt Marshes
1. Salt marshes defined:
·
Salt marshes are
intertidal flats covered by grassy vegetation
2. Mashes are most commonly found in protected
areas
with a moderate
tidal range, such as the landward side of
barrier islands
3.
Marshes flood daily at high tide and then drain through a
series of channels
with the ebb tide
4.
They are one of the most productive environments,
despite harsh
conditions
5. Marshes can be divided into two parts:
·
Low salt marshes
– extend from the low tide mark to neap
high tide
o
Along the
Atlantic and
dominated by a knee-high
cordgrass
o
Low marshes are
the more productive area with
productivity of
800-2600 gm C/m2/yr
o
Nitrate is
commonly the limiting nutrient
o
Plants die in
autumn, partially decompose and supply
abundant detritus
which becomes food for the
detritivores
or accumulates and eventually forms peat
·
High salt marshes
–extend form neap high tide to highest
spring tide
o
This area is
flooded only at the highest spring tide or
during a storm
surge
o
It is more
terrestrial than marine in nature and has a
more diverse
fauna and flora
§
Distribution and
density of organisms in salt marshes strongly
reflects
availability of food, need for protection, and frequency
of flooding
§
Salt marshes
serve as nursery and shelter for juvenile organisms
§
Many salt marshes
damaged by man – filled in
I.
Mangrove Swamps
1. Mangroves defined:
·
Mangroves are
large woody trees with a dense, complex
root system that
grows downward from the branches
2. Mangroves
are the dominant plant of the tropical and
subtropical
intertidal area
3. Distribution of the trees is largely
controlled by air
temperature,
exposure to wave and current attack, tidal
range, substrate,
and sea water chemistry
4. Detritus from the mangrove forms the base of the
food
chain
J.
Effects of Storm Surges on Coastline Features
1. Storm surge defined:
·
Storm surge is
the high water created by the accumulation
of wind-blow
water against the shore and the mound of
water generated
by the low atmospheric pressure of the
storm
2. The elevated water level allows waves to
reach much
farther inland
than usual, especially if the storm surge
coincides with
high tide
3. During a storm surge, ocean waves more easily breach
the island and
wash over lower areas
4.
New tidal channels may form during a storm surge
·
Most tidal inlets
are eroded from the landward side of the
barrier island
seaward
·
The bay becomes
swollen with rainwater, runoff, and inflow
from the sea
·
The onshore wind
piles the water against the mainland and
after the storm
has passed, a seiche can develop which
then raises the water level against the landward side of the
barrier island
·
Storm winds may
also reverse direction on the rear of the
storm and blow
offshore, piling additional water against
the barrier island
·
If water breaches
the island, its seaward flow may create a
new inlet
·
Most inlets are quickly
filed with sediment because of
longshore
drift
VI. Coastlines of
the
A.
Pacific Coastlines
1. Tectonically active coastline
·
Dominated
by uplift
2. Typically rugged and irregular
with abundant sea cliffs
3. Sediment sources from nearby granitic and volcanic
mountains via rivers far exceed local bluff
input
4. Deltas tend not to form due to high energy
shorelines
B.
Atlantic Coastlines
1. Tectonically inactive coastline
·
Dominated by
subsidence
2. Abundance of barrier islands and submerged river
valleys
3. Sediment sources are mainly from offshore deposits
4. Deltas are rare or absent
C.
1. Tectonically inactive coastline
·
Dominated by
extreme subsidence
2. Typically very low-lying and straight with abundant
broad beaches and barrier islands
3. Absence of large waves (except infrequent
hurricanes)
and submarine canyons
4. Formation of large deltas
·
Excessive
sediment input from rivers
VII. Humans Assault on Coastlines
A. Beaches are Systems that Exist in a
Natural Balance
Between
Erosion and Deposition
1. Natural input of material from rivers and
sea cliffs
2. Natural movement of material in longshore transport
3. Natural seasonal changes in beach sand
budget
B. Humans Build Structures That Oppose Coastal
Processes and Typically Cause Cell
Imbalances
1. Breakwaters
·
Eliminate or
reduce wave influence
·
Disrupt longshore current and transport
·
Sand piles up on beach
behind breakwater
2. Groins
·
Disrupts and
intersects longshore transport
·
Designed to trap
and hold sand on beach
·
Excess sand
buildup on "upstream" side of groin
·
Excess sand
erosion on "downstream" side of groin
3. Jetties
·
Disrupts and
intersects longshore transport
·
Excess sand
buildup on "upstream" side of jetty
·
Designed to
prevent sand from blocking harbor
channel
entrance
4. Seawalls
·
Blocks wave
erosion of sea cliff or bluff
·
Reflected wave
energy increases beach erosion in front
of seawall
·
Blocking of bluff
erosion reduces sediment input fro beach
replenishment
·
Designed to
protect bluff and/or structures behind seawall
XI. Coastline and Beaches Vocabulary - Chapter 12
Active coast
Atoll
Backshore
Backbeach
Backwash
Barrier reef
Bay Mouth Bar
Beach
Beach scarp
Berm
Berm crest
Breaker
Breakwater
Coast(line)
Coastal cell
Delta
Dissolution
Estuary
Eustatic sea level change
Fjord
Foreshore
Fringing reef
Groin
Guyout
High-energy coast
Lagoon
Longshore bar
Longshore current
Longshore transport (drift)
Low-energy coast
Primary coast
Reef
Rip current
Sand spit
Sea cave
Sea cliff
Seamount
Seawall
Secondary coast
Shore(line)
Submarine canyon
Surf
Swash
Tombolo
Turbidity current
Wave-cut platform