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.