Coastal Classification
I.
First
Order Influences
A.
Most important factor is Plate Tectonics--formation of new sea floor at
spreading centers
and subduction of old material along
trenches. How
coasts related
to spreading centers
determines classification.
B.
Major
types--Trailing Edge and Collision Coasts
1.
Collision Coasts--where
plates collide
Examples--West coasts of N.
& S. America
Characteristics
a.
High Mountains near coast
b.
Volcanism and earthquakes along coast
c.
Straight coasts and narrow shelves
d.
Mountains provide major sediment source but narrow shelf
means sediments
lost to deep ocean
2.
Trailing edge coasts--Coasts
which face a spreading center (ocean
ridge)
a.
Neo-Trailing Edge--Coasts
faces new spreading center--Red
Sea, Gulf
of Aden
(1) No
continental shelf (no time for sediments to accumulate
(2) Cliffs/plateaus adjacent to coast
(3) Volcanism/seismicity may be present
b.
Amero-Trailing Edge--Coast
faces spreading center and
opposite side
of
continent is collision coast--East
coast of N / S
America
(1) Wide shelf, thick underlying
sediment wedge
(2) Coast
backed by wide relatively
(3)
Coasts consists of many
depositional features such as barrier
islands, deltas, marshes, tidal flats
(4)
Tectonically inactive
c.
Afro-Trailing Edge-
Coast faces spreading center and opposite
side
of continent
faces one too-- E / W Africa
(1) Moderate to wide shelf
(2) Coast is backed by hills or lowlands
(3) Tectonically inactive
(4) Not as much deposition along this type of coast
3.
Marginal Sea Coasts-
Semi-protected – Gulf of Mexico, Eastern Asian
coasts
a.
Sheltered by land masses, island arcs, pack ice
(1) Wide shelf
(2) Hilly low-lying regions back coast
(3) Tectonically inactive
II.
Second Order Influences--influences a smaller coastal segment within a particular
setting
A.
Sediment Supply--Related
to tectonics
1.
Along Amero- trailing coasts lots of
sediments delivered to coast
2.
Most barrier islands and
deltas found
B.
Glaciation--Different in N / S
latitudes
1.
Direct effects
a.
Brings sediment to coast
b.
Carved out river valleys-fiords
2.
Indirect effects
a.
Lowering
of sea level and subsequent rise
b.
River valleys widened during this time
c.
Subsequent rise during deglaciation floods valleys and forms
Chesapeake, Delaware
Bays
C.
Climate--Influences
biologic activity, weathering, and storm processes.
1.
Biologic Activity
a.
In
warm climates mangroves develop in low
energy environments
b.
Coral
reef development is temperature dependent
2.
Production of Sea Ice
a.
In cold climates sea forms and is pushed
toward or onshore and may either
protect or erode beach
4.
Weathering--Temperature
and Precipitation control vegetation,
river
discharge and chemical
weathering (mud formation)
5.
Storm processes--
a.
Where tropical storm occur
b.
Where majority of gales occur
c.
Generally West facing coasts are more energetic
D.
Hydrographic Regime--Influence
of wave versus tidal energy
1.
Wave processes-
a.
Move sediment along the shoreline
b.
At inlets move sediment landward
2.
Tidal processes-
a.
Tidal currents move sediment perpendicular to shoreline
b.
At inlets and rivers sediment moves on/off shoreline
3.
Hydrographic Regime Controls occurrence of barriers, inlets,
tidal deltas, salt marshes
and type of river deltas, and hence
major depositional
feature
A.
F. P. Shepard proposed a
scheme based on the dominant “process”
shaping
the coast
1.
Distinguished two broad categories
a.
Terrestrial--Primary coasts shaped by rivers, glaciers,
volcanoes
b.
Marine--Secondary
coasts shaped by waves, tides,
organisms
B.
Primary-Terrestrial Types
1.
Stream (erosion) coasts where streams have cut valleys
and are now flooded
by the sea
(estuary)
a.
Rias—steep-sided valley now flooded
2.
Glacial—ice-carved huge “U” shaped valleys, mouths
now filled with sea
fiords—high
relief valleys, Maine
coast is low relief
a.
Other ice-related coasts are not related to erosion
but rather deposition. Vast
amounts of materia
from outwash as glacier melts . . . Mass. Martha’s
Vineyard. Hampton’s/Long
Island
3.
Landslide
coasts—Mass wasting common along active
coasts, on permafrost coasts (ice in soil) & where soils
contain a lot of water.
4.
Karst—where
limestone is found. Limestone
dissolved by rain/
groundwater, South Fla., Barbados, “Yugoslavia.”
5.
Delta
(River) – large volumes of sediment accumulates faster
than waves can redistribute it down coast.
a.
Delta shape varies depending upon how much sediment,
how much wave energy and what is the tide range.
6.
Volcanic –
several kinds, recognized on basis of material that
comprises the cone or landscape, two types of lava that is
extruded onto earth’s surface
a.
Fluid lava—produces basalt
Little explosiveness
CC5
Relatively quiet
Builds shield-like volcanoes
b. Pasty
lava—produces andesite
Highly explosive
Steep sided
Composite cones/strato-volcano
Major catastrophic events, Atlantis, and Krakotoa,
Tomboro, etc.
c.
Both contain
lava and pyroclastics
(ash-bombs) fluid—lava, pasty—lot of ash
C.
Secondary Coasts—Marine processes CC6
Climate is very important.
Determines wave height and frequency.
Determines kinds of organisms, if any.
1.
Storm coasts—wave eroded rugged cliffs,
spectacular
landforms notch at base of cliffs
Waves cut at base
Of cliff and remove
Cliff Face
rock that has fallen.
2-500 M high
Rocks move to/fro
across platform.
Notch
Materials
Extends
Platform
transported
Landwards
2-3 KM wide
off platform
Cliff retreats as face falls
2.
Marine Depositional—swell coasts CC7
deposition
due to waves, swell refers to very long low
waves that travel great distances, as much as 2000 KM.
Wrightsville Beach, much of S.E. USA
3.
Tropical
Coasts (organic)
Organisms assume dominant role at 20 degrees N/S
of equator and on western sides of ocean basins.
a.
Coral Reefs—protect area behind
b.
Mangroves—help trap sediment/extend shoreline,
found in bays, estuaries, some open ocean shorelines.