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Chapter 12 - Coasts, Beaches, Estuaries
The Oregon coast – Pacific Ocean
Coasts – areas where the land meet the ocean
Coast: land area affected by marine processes - tides, winds, waves.
Coastal area, coastal zone: land + water areas.
Shore: outer limit of wave action along the bottom to limit of waves’
direct influence on land.
Beach: area of accumulation of sediments (sand) that occupies part of
the shore.
Different types depending on oceanic and atmospheric processes
affecting the area, as well as tectonic processes
The coast of South Africa – Cape of Good Hope: meeting of
Atlantic and Indian Oceans
Types of Coasts - I
They are classified according to processes and according to shapes.
We can summarize all of that as follows:
(1) a. erosional - lose sediments
b. depositional - gain sediments
(2) a. due to land-air processes
b. due to marine processes
And further:
A. Primary Coasts
B. Secondary Coasts
1. erosion of land
1. erosion by waves
2. deposit of sediments
2. deposit of sediment by waves
3. volcanic activities
3. alteration of marine plants and
4. uplift and subsidence
animals
Primary Coast – Fjord in New Zealand
Types of Coasts - II
And further yet:
A. Primary Coasts
B. Secondary Coasts
fjords
sea stacks
moraine
bars - barrier islands
drowned valley/ria coasts
sand spits and hooks
delta - alluvial plain
reef coasts
dune coasts
salt marshes
lave coasts - cratered coasts
faulty bay
Secondary Coasts
Cliffed coast in New Zealand
Sea stacks in northern
California
Anatomy of a Beach
Beach Dynamics:
Summer: gentler waves move sand shoreward
Winter: large storm waves remove sand to offshore
bars
Longshore Transport of Sand
Spit Formation
Rip Currents
Primary Coast – Drowned river valley in
Delaware and Chesapeake Bays
The Chesapeake
Bay is also one
of the largest
estuaries in US
Estuaries
•Estuaries are found anywhere freshwater interacts with
saltwater in a protected area.
•These are some of the most productive ecosystems on
earth
•Estuaries are more common on passive margins than active
margins
•Many have been greatly disturbed by human influence (i.e.
Hudson River/NYC)
Estuaries
They are mainly classified according to the physical processes
that are important in these water bodies, namely according to net
circulation and vertical distribution of salinity.
Four types:
1. Salt wedge type
2. Well-mixed
3. Partially-mixed
4. Fjord-type
Four types of Estuaries
1. Salt wedge type
* mixing by entrainment and controlled by rate of river discharge
2. Well-mixed
* mixing due to tidal influence,
* unidirectional flow toward the sea,
* 1 layer circulation,
* weakly stratified
3. Partially-mixed estuary
* 2 layer flow: strong surface flow toward the sea, strong bottom flow toward river
entrance,
* approximately 2 layer circulation,
* tidal current, turbulence entrainment and river flow all contribute to mixing but
river flow DOES NOT dominate,
* rapid exchange between estuary and ocean, turbulent mixing important but also
very important is mixing by advection.
4. Fjord-type estuary
* smaller area but very deep
* moderate to high river input + little tidal mixing
* common around glaciated coasts
* advection provides salt at depth
* river flow tends to stay in a thin surface layer
* stagnation leading to hypoxia and anoxia
* slow, very sluggish bottom flow
Processes that control and affect the degree of vertical mixing in
estuaries:
* strength of oscillatory tidal currents
* rate of freshwater addition (so, what happens in spring?!)
* roughness of bottom topography
* average depth of estuary
The energy for mixing comes from tides and winds mainly.
Seasonal variation of stratification (why should this happen?!)
Finally, please note that the Chesapeake Bay estuary is better
characterized as a partially-mixed type of estuary, NOT a well-mixed
type as it is stated in the textbook.