Chapter 11

Geology 1301 with Jacobs at Southern Methodist University

About this deck

By: Samantha Leder
Textbook:

Essentials of Oceanography
Created: 2011-11-14
Size: 42 flashcards
Views: 24

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Coasts

World oceans bounded by 440,000 km of coastline.

Coasts are temporary changing features around the shoreline.

Shore

Where ocean meets land.

Erosional Coasts

Erosive processes exceed depositional ones (depends on sea level)

Dominated by processes that remove material

Depositional Coasts

Deposited sediments exceed erosive ones (depends on sea level)

Steady or growing because of sediment accumulation or biological build up

How can the average sea level change at the coast?

Eustatic sea level change (measured all over the world)

1. Amount of water in the ocean can vary (global glaciations)

2. Ocean basin size can vary (mid-ocean ridges displace seawater)

3. Temperature changes can expand or contract sea water

Local sea level changes

4. Tectonic activity at the coast changes height and shape

5. Temporarily wind and current can force water against coast or draw it away

Waves Effect on Sea Level

Waves are the single most influential agent in changing the shore.

Waves erode shore through solution, abrasion, and hydraulic action.

Sea Cliffs

Wave action on erosional beaches produce sea cliffs.

Sea Caves

Sea caves are cut by waves at zone of weakness in rocks, sometimes resulting in blowholes.

Wave-Cut Platforms

Wave-cut platforms mark submerged limit of rapid marine erosion

Arches and Stacks

Offshore erosional remenants

Beaches

Steep, narrow rocky beaches are found in high areas of high wave energy.

The flatter the beach the finer the sand, and the smaller the waves affecting it.

Coastal Erosion

Eventually produces a smooth shore line.

Wave Refraction

Focuses wave energy onto headlands, causing erosion.

Sediments eroded from the headlands accumulates in tranquil bays eventually smoothing the shore contours.

Volcanoes

Also shape coats, ex. Isla Encantada, Mexico

Glacier

Formed, Ex. Tracy Arm Fjord, Alaska

Beaches Dominate Depositional Coasts

Erosional shorelines evolve in depositional shorelines.

Runs parallel to shore and marks normal limit of sand deposition by waves.

Berm Crest

Usually highest point on beach, marking most recent high tide

Backshore

Relatively inactive landward limit of sand deposition

Foreshore

Active zone seaward of berm crest, from base of berm (where scarp (downward part after berm) forms from wave erosion) to low tide mark.

Offshore Zone

Begins at low tide mark.

Erosional Longshore Troughs and Depositional Longshore Bars (sand bars)

Erosional Longshore Troughs- deep parts between longshore bars

Longshore Bars- like sand bars

Found parallel to shore.

Waves transport sediment on beaches

Beaches are usually cut to lower level in winter than summer because higher waves accompany winter storms

Longshore Drift

Movement of sediment along coast, driven by wave action

Longshore Current

Waves breaking at an angle distribute a potion of their energy away from their direction of approach, forming a longshore current.

Sand input and outflow are balanced in coastal cells

New sand on a coast is brought in by rivers.

Longshore drift moves sand parallel to beach in submarine canyon

Gravity transports sand down canyon

The sand is deposited in a submarine fan

Sand Spits

Longshore currents slow as a bay is approached and sand is deposited

Bay Mouth Bar

When a sand spit closes off a bay by growing to the opposite headlands

Barrier Islands

Sediments in island parallel to shore.

Mark the site where coastal sand dunes formed during the last low stand of sea level.

Flooded by the rise in sea level producing islands

Lagoons

Shallow water formed behind barrier islands

Tombolo

Bridge of sediment connecting sea island

Estuary

A body of water partially surrounded by land where fresh water from rivers and ocean water mix

Types of Estuaries:

Classified by origin:

- Drowned river mouths

- fjords

- bar-built

- tectonic

Estuaries are characterized by their circulation pattern

3 Factors control this:

1. Shape of estuary

2. Volume of river flow

3. Range of tides

Types of mixing estuaries:

a. Salt wedge- high river, low tide

b. Well-Mixed- low river, hide tide

c. Partially mixed

d. Fjord

e. Reverse-evaporation

Pacific Coast

1. Actively rising margin

2. Beaches interrupted by headlands or submarine canyons

3. Sand movement to south

4. No deltas formed

Atlantic Coast

1. Passive margin-- tectonically calm

2. Subsidence of coast 0.3 meters per 100 years

3. Flooded river valley estuaries

4. Sand trapped in estuaries with small southern movement

5. Deep sediment layers offshore

6. Glaciers shaped the northern coast (moraines)

Gulf Coast

1. Passive margin-- tectonically calm

2. Smaller tidal range

3. Smaller wave size except hurricanes

4. Subsidence rate high (ex. galveston, tx = 2/3 meters in 100 years)

Human Interference in coastal processes

At least 20% of the beach-bounded coastline of the US is in danger of serious or catastrophic alteration

Breakwater

An artificial structure that interrupts the progression of waves to shore

Groins

Short extensions of rock or other material placed at right angles to the shoreline (jetties)

Seawalls

Walls built to protect coasts

Increase erosion by deflecting wave energy and sand around them

Importing sand

to combat beach erosion

often taken from dunes which is finer grained and erodes more rapidly

About this deck

By: Samantha Leder
Textbook:

Essentials of Oceanography
Created: 2011-11-14
Size: 42 flashcards
Views: 24

About StudyBlue

“Simply amazing. The flash cards are smooth, there are many different types of studying tools, and there is a great search engine. I praise you on the awesomeness.”
Dennis