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Chapter 13

The Restless Ocean

I. Ocean water movement

A. Surface currents

1. Huge, slowly moving gyres ( jir )

2. Generated by wind

3. Related to atmospheric circulation

4. Deflected by the Coriolis effect

a. To the right in the Northern Hemisphere

b. To the left in the Southern Hemisphere

5. Importance of surface currents

a. Navigation

b. Influence climates

 

B. Upwelling

1. Vertical water movement

2. Along eastern shores of oceans

3. Caused by

a. Coriolis effect

b. Surface water moving from the shore

 

C. Deep-water circulation

1. Governed by gravity

2. Driven by density differences

3. Factors creating a dense mass of water

a. Temperature - cold water is dense

b. Salinity - density increases with increasing salinity

4. Called thermohaline circulation

5. Dense water masses are created in

a. Arctic regions

b. Antarctic regions

 

D. Tides

1. Changes in elevation of the ocean surface

2. Caused by the gravitational forces of the

a. Moon, and to a lesser extent the

b. sun

3. Tidal heights

a. Spring tide

1. During new and full moons

2. Gravitational forces added together

3. Especially high and low tides

4. Large daily tidal range

 

Tidal heights continued

b. Neap tide

1. First and third quarters of the moon

2. Gravitational forces are offset

3. Daily tidal range is least

4. Other influencing factors

a. Shape of the coastline

b. Configuration of the ocean basin

 

Types of tides

A. Semidiurnal tide

B. Diurnal tide

C. Mixed tide

 

A. Semidiurnal tide

1. Two high and two low tides each tidal day

2. Little difference in the high and low water heights

3. Occur along the Atlantic coast of the U.S.

 

B. Diurnal tide

1. A single high and low water height each tidal day

2. Occur along the northern shore of the Gulf of Mexico

 

C. Mixed tide

1. Two high and two low waters each day

2. Large inequality in high water heights, low water heights, or both

3. Prevalent along the Pacific coast of the U.S.

 

6. TIDAL CURRENTS

A. Horizontal flow accompanying tides

b. Types of tidal currents

1. Flood current - advances into the coastal zone

2. Ebb current - seaward-moving water

 

E. Wind-generated waves

1. Derive their energy and motion from wind

2. Parts

a. Crest

b. Trough

3. Measurements of a wave

a. Wave height-the distance between a trough and a crest

b. Wavelength-the horizontal distance between crests

c. Wave period-the time interval between crests

 

Wave measurements continued

4. Height. Length, and period depend upon

a. Wind speed

b. Length of time wind blows

c. Fetch-the distance wind travels

5. Types of waves

a. Wave of oscillation

1. In open sea

2. Shape moves forward

b. Wave of translation

1. Wave breaks along the shore

2. Water advances up the shore

3. Forms surf

 

Wind-generated waves continued

6. Wave erosion is caused by

a. Wave impact and pressure

b. Abrasion by rock fragments

7. Wave refraction

a. Bending of a wave along a coast

b. Wave arrives parallel to shore

c. Results

1. Wave energy directed against headland

2. Wave erosion straightens an irregular shoreline

 

Wind-generated waves continued

8. Moving sand along the beach

a. Beach drift - sediment moves in a zigzag pattern

b. Longshore current

1. Current in surf zone

2. Flows parallel to coast

 

II. Shoreline features

A. Features caused by wave erosion

1. Wave-cut cliff

2. Wave-cut platform

3. Associated with headlands

a. Sea arch

b. Sea stack

 

B. Related to beach drift and longshore currents

1. Spit - a ridge of sand extending from the land into a bay with an end that often hooks landward

2. Baymouth bar - a sand bar that completely crosses a bay

3. Tombolo - connects an island to the mainland.

 

C. Barrier island

1. Mainly along the Atlantic and Gulf coasts

2. Parallels the cost

3. 3 to 30 kilometers offshore

4. Originates in several ways

 

D. Results of shoreline erosion and deposition is to eventually produce a straighter coast

III. Shoreline erosion problems

A. Influenced by the local factors

1. Proximity to sediment-laden rivers

2. Degree of tectonic activity

3. Topography and composition of the land

4. Prevailing wind and weather patterns

5. Configuration of the coastline

 

B. Three basic responses to erosion problems

1. Building structures

a. Types of structures

1. Groin

a. Barrier built at a right angle to the beach

b. Traps sand

2. Breakwater

a. Barrier built offshore and parallel to the coast

b. Protects boats from the force of large breaking waves

3. Seawall

a. Barrier parallel to shore

b. Stops waves from reaching the beach areas behind the wall

b. Often not effective

 

Continuation erosion problems

2. Addition of sand to replenish the beaches

a. Called beach nourishment

b. Not a permanent solution

3. Relocation of buildings away from beach

 

C. Atlantic and Pacific Coasts

1. Shoreline erosion problems are different along the opposite coasts

2. Atlantic Coast

a. Broad, gently sloping coastal plains

b. Development occurs mainly on the barrier islands

1. Face open ocean

2. Receive full force of storms

 

3. Pacific Coast

a. Relatively narrow beaches backed by steep cliffs and mountains

b. Major problem is the narrowing of the beaches

1. Sediment for beaches is interrupted by dams and reservoirs

2. Rapid erosion along beaches

 

IV. Emergent and submergent coasts

A. Emergent coast

1. Caused by

a. Uplift of an area, or

b. A drop in sea level

2. Features of an emergent coast

a. Wave-cut cliffs

b. Wave -cut platforms

 

B. Submergent coast

1. Caused by

a. Land adjacent to sea subsides, or

b. Sea level rises

2. Features of a submergent coast

a. Highly irregular shoreline

b. Estuaries-drowned river mouths

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