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Advanced Geomorphology > MIDTERM CHPT 9 > Flashcards

MIDTERM CHPT 9 Flashcards

1
Q
  1. Describe the geomorphology of the deep ocean basins.
A

There is very little sediment in deep ocean environments. Sediment that IS there is fine grained and occurs as thin horizontal beds. This sediment blankets the ocean floor.

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2
Q
  1. How are wind generated waves created on the ocean?
A

Waves are a disturbance of the surface of a body of water caused by air moving over its surface.

Energy of the moving air is transferred into the water to create a wave.

(wind speed and wind direction are both factors that control the formation of a wave.)

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3
Q
  1. FETCH
A

This is the body of water the wind blows over.

Bigger fetch, bigger wave.

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4
Q
  1. What are the three factors that control the formation of a wave?
A

Wind speed
Wind direction
Fetch

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5
Q
  1. Using a diagram describe the features of a wave (i.e wave height) including the pattern of circulation beneath a wave crest.
A

(SEE DIAGRAM)

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6
Q
  1. What is wave interference?
A

This happens when different wave patterns meet and combine.

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7
Q
  1. Briefly explain (wave interference) using one example.
A

Two waves that are in phase combine or interfere in such a way that the crest is twice as tall (the two crests add) and the trough is twice as deep (the two troughs add)

This is positive or constructive interference.

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8
Q
  1. What is wave reflection?
A

This occurs when a wave bounces off an object.
Often the only thing that is changed is wave direction.
(see diagram)

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9
Q
  1. What is wave refraction? (DIAGRAM)
A

This happens when a wave bends around an object.

  • (A) As a wave approaches an object, they slow down and bunch up (wavelength is reduced)
  • (B) the waves move on without any change due to the object
  • As a result, the wave bends or refract around the island. Wave energy is focused on the part of the island that faces the waves and erosion increases.
  • In the sheltered lee side of the island, at (C), there is a drop in water energy as turbulence increases. More deposition takes place here.
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10
Q
  1. Briefly explain how a wave becomes more parallel to a shoreline as it approaches the shoreline (DIAGRAM)
A
  • As the part of the wave at (A) enters shallow water it contacts the bottom and slows down.
  • At (B) the wave continues at it’s original speed.
  • As a result, the entire wave bends in such a way that it becomes parallel to the coast.
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11
Q
  1. Briefly explain how a long shore current is generated by waves at a shoreline. (DIAGRAM)
A

A (A), the waves strike the shoreline at an angle as it breaks. Water rushes up on shore and goes to zero velocity.

At (B), the water returns straight back offshore.

At (C) the returning water is redirected back on shore by the next incoming wave

The water returns back offshore again and the process repeats itself over and over.

The result is a longshore current - the flow of water parallel to the shoreline.

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12
Q
  1. Plunging Wave (diagram)
A

The top falls over. These waves happen most often on steep beaches.

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13
Q
  1. Surging Wave (diagram)
A

Entire wave front advances as it breaks. These waves happen most often on steep beaches.

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14
Q
  1. Spilling Wave (diagram)
A

Top falls down the front. Waves tend to occur on a beach with a shallow gradient.

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15
Q
  1. What is a beach?
A

A sedimentary deposit at a coastline created by waves.

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16
Q
  1. What is the difference between a winter beach profile and a summer beach profile? SUMMER
A

In summer, the movement of water onshore carries sediment onto the beach. However, because summer waves are smaller, the return flow is weak and sediment is not carried back offshore.

It remains at the high water mark to create the summer profile.

17
Q
  1. How do multiple bars form in the breaker zone?
A

You get different waves breaking at different times.
Off shore bars are deposited by the action of breaking waves.

When waves break at different places and times (because they are different) they can produce more than one bar.

On gently sloping shorelines the same wave can break more than once as it breaks, reforms and breaks again resulting in multiple bars.

18
Q
  1. BAR
A

A bar is a ridge of sediment that is created as a result of breaking waves.

19
Q
  1. What is an Edge Wave? How does it form?
A

An edge wave is a wave that travels parallel to the shoreline.
The crest of an edge wave is perpendicular to the shoreline.

Edge waves are wind generated waves.

20
Q
  1. Edge Wave Travel
A

Edge waves are wind generated waves.

They travel parallel to the coast because that was the direction the wind was blowing. They may also travel parallel to the coast because of wave refraction.

21
Q
  1. What is a beach cusp?
A

A beach cusp is a regular pattern of sediment distribution in the swash zone that includes a raised “horn” and low “embayment.

22
Q
  1. How does a beach cusp form?
A

Along a coastline there can be two patterns of waves. At C these two wave crests meet to make one larger crest (positive interference).
At D, two wave troughs meet to make one lower trough (positive interference).

A- larger waves breaking further on shore
B- smaller waves breaking lower on the shoreline

As a result of wave interference there is an alternating pattern of larger (A) and smaller waves (B) breaking on the shoreline.

The larger waves create the low embayments composed of finer sand and the combination of return flow from the embayment and the smaller waves create the horns and the corse sediment in them.

23
Q
  1. What is a spit?
A

An extension of the coast and beach into deeper, offshore water.

24
Q
  1. How does a spit form?
A

A a longshore current moves sediment along the coast to form a beach. Where the coast changes direction the long shore current may continue to into deeper, offshore water. Sediment continues to be deposited as current velocity decreases. The result is a spit.

25
Q
  1. What is a barrier island?
A

A barrier island is a linear ridge of sediment parallel to the coast that is some distance offshore.

26
Q
  1. How does a barrier island form?
A
  • Form is a spit becomes detached from the coast.
  • Form is an offshore berm grows in size and is exposed above sea level.

when: can happen during a storm.

27
Q
  1. What is a beach step and how does it form?
A

On a shoreline the upward motion as a wave breaks (I) meets the return flow from the swash zone (II)
As a result of this mixing of water, coarse sediment is concentrated and a depositional feature called a step is formed.

28
Q

Plunging Wave

A

These two waves happen most often on steep beaches.

29
Q

Plunging Wave

A

These waves happen most often on steep beaches.

30
Q

Surging Wave

A

Entire wave front advances as it breaks.

31
Q

Wavelength

A

The distance between adjacent crests or adjacent troughs

32
Q

Wave Height

A

This is the difference between a crest and a trough

33
Q

Circulation under a wave crest.

A

Beneath a wave is a series of stack orbits. They decrease in size with depth to a maximum depth of half the wavelength.

34
Q

Landforms that form in the breaker zone

A

In the breaker zone, the water is shallow and getting shallower. The water is also turbulent and there can be abundant sand moving as bedload. The water also moves back and forth (two directions.) The end result is the formation of ripple bedding.

35
Q

Landforms that form in the swash zone

A

In the swash zone (2) the typical landform is horizontal bedding (tilted towards the ocean) created by the thin layer of fast moving water created by the final breaking of the wave.

36
Q

Landforms that form in dune areas

A

These consist of piles of sand controlled by wind action.

37
Q
  1. Briefly explain the process of a wave breaking at a shoreline. (DIAGRAM)
A
  1. The waves move toward the shoreline
  2. As the wave moves into shallower water, the orbits touch bottom, the waves slow down and begin to break.
  3. The waves bunch up and wavelength decreases
    Wave height increases as water is forced upward.
    Wave orbits flatten as the wave runs out of room.
    Instead of the orbital motion, there is a distinct back and forth motion to the water beneath the wave.
  4. The wave reaches a height and speed where it is no longer stable and it falls over.
  5. Final wave energy is expended as the water rushes up the swash zone. This is often as a thin, fast moving layer of water.
  6. The water reaches zero velocity and stops. Some water infiltrates into the shoreline.
  7. water that remains on the surface returns back off shore as a bottom current.
38
Q

Ripple bedding. (breaker zone)

A

As waves begin to brake, the orbits compress and increasingly produce a back and forth water motion.

Beneath a crest (a) there is a stronger onshore motion while beneath the trough(b) there is a weaker offshore motion.

This two way motion helps to create asymmetrical ripples.

Advanced Geomorphology (10 decks)

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