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Oceanography > Coastal water and estuaries - 10 > Flashcards

Coastal water and estuaries - 10 Flashcards

1
Q

What does it mean when waves ‘shoal’?

A

When waves touch the bottom of the floor

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2
Q

What is wave set up?

A

A process whereby waves pile water against the short

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3
Q

What are longshore currents?

A

Currents generated by a pressure gradient (the sea surface slopes from areas of larger waves down to areas of smaller waves) that runs parallel to the shore

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4
Q

What are rip tides?

A

A swift, narrow, sea ward flow perpendicular to the coastline generated by the convergence of longshore currents

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5
Q

What the angle of wave approach?

A

The acute angle between the wave crest and the beach (it’s rarely larger than 10º)

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6
Q

How is sediment moved on the beach and the nearshore?

A

Currents and breakers

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7
Q

How can you divide the beach up?

A
  • Offshore

- Nearshore

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8
Q

What is offshore?

A

The area seaward of where waves first being to break

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9
Q

What is nearshore?

A

The area from offshore to where waves wash back and forth across the beach … it can be divided into the breaker zone, the surf zone, the swash zone and the backshore

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10
Q

What is the breaker zone?

A

Where waves begin to break on the nearshore

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11
Q

What is the surf zone?

A

Where the waves expend most of their energy

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12
Q

What is the swash zone?

A

Where waves wash back and forth

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13
Q

What is the back shore?

A

The land that adjoins the nearshore

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14
Q

Zones of the beach change with high and low tide. How?

A

At high tide, zones advance landward. At low tide, zones advance seaward

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15
Q

What is a beach profile?

A

A cross section of a beach taken perpendicular to the shoreline that can be compared at different times to see if the beach is expanding or eroding

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16
Q

What 2 different types of beach profile exist?

A

A swell profile and a storm profile

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17
Q

What are the characteristics of a swell profile?

A
  • wide, broad berm
  • steep intertidal beach face
  • develops during the summer
  • enlarges the volume of the beach
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18
Q

What are the characteristics of a storm profile?

A
  • erosion of the berm
  • broad, flat intertidal beach face
  • develop during winter
  • coarse sediment left on the beach
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19
Q

What is the sand budget?

A

The balance between sediment added to and sediment eroded from the beach

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20
Q

Where does beach sediment input come from?

A

River, sea-cliff erosion and onshore sediment transport

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21
Q

How is beach sediment removed?

A

Longshore currents, offshore transport and wind erosion

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22
Q

How are coastal cells formed?

A

When sand transported by long shore drift is permanently lost in submarine canyons

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23
Q

What are the best conditions for sand dune formation?

A
  • Abundant sand
  • Strong persistent onshore winds
  • Large tidal range
  • Beach is wide and gently sloping
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24
Q

How far inland can sand dunes extend?

A

Up to 10km

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25
Q

What are blowouts?

A

Wind-scoured breaks in the dune or depressions in the dune ridge, commonly caused by destruction of vegetation

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26
Q

What is dune migration?

A

The movement of dunes. Sand salutes (bounces) up the windward side of the dune, collects in the wind-shadow and periodically slides down the leeward face of the dune

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27
Q

What impact does wave erosion have on sand dunes?

A

Creates a steep scarp at the base of the dune which then reflects wave energy, reducing erosion

28
Q

What are barrier islands?

A

Landforms composed of sediment that parallel the coast and form where sand supply is abundant and a broad seafloor slopes gently seaward

29
Q

What environments develop on barrier islands?

A

Nearshore zone, dune fields, back-island flats, forests and salt marshes

30
Q

How are barrier islands created?

A
  • Sand ridges on the coastal plain that become isolated due to sea level rise
  • Sand spits that become breached during a storm and remained separate by a tidal inlet
  • Vertical growth and emergence of longshore sand bars
31
Q

What is rollover?

A

The migration of barrier islands landward due to sea level rise, which causes the washover of sediments from the seaward died to the landward side

32
Q

How are sea cliffs eroded?

A
  • Waves slam into cliffs … water compressed inside cracks … expands violently when the wave recedes … shatters the rock
  • Sea water can dissolve some types of rock
  • Evaporation leaving behind salt crystals in faults … chemically breaks down rocks
33
Q

What does cliff recession depend on?

A
  • Composition and durability of cliff material
  • Presence of joints, faults and cracks
  • Amount of precipitation
  • Steepness of the cliff
  • Wave energy
34
Q

What is a wave-cut platform?

A

The gentle sloping area in front of the sea cliff that was produced by erosion and sea-cliff retreat

35
Q

What is a delta?

A

An emergent accumulation of sediment deposited at the mouth of a river

36
Q

What are the major areas of a delta?

A
  • Delta plain
  • Delta front
  • Prodelta
37
Q

What is the delta plain?

A

The flat, low-lying area at or below sea level that is drained by a system is distributaries

38
Q

What is the delta front?

A

The shoreline and broad submerged area of the delta that slopes gently seaward

39
Q

What is the pro delta?

A

The far offshore area of the inner shelf that receives fine sediment from the river

40
Q

How can we divide up a delta?

A
  • Topset bed
  • Forest bed
  • Bottomset bed
41
Q

What are topset beds?

A

Flat-lying beds of sand and mud of the delta plain and deposited by the distributaries in their channels

42
Q

What are foreset beds?

A

Thick silts and sands of the delta front that slope gently seaward and form the bulk of the delta

43
Q

What are bottomset beds?

A

Flat-lying silts and clays of the pro delta that settle out of suspension far offshore

44
Q

How does a delta expand?

A

Sediment accumulation (foreset beds bury bottomset beds and topset beds blanket foreset beds)

45
Q

What is the shape of a delta dependent on?

A

The relative power of tides, waves and rivers

46
Q

Where do river-dominated deltas form?

A
  • Areas protected from large waves

- Small tidal range

47
Q

What are the different types of delta?

A
  • River dominated
  • Wave dominated
  • Tide dominated
48
Q

What are wave dominated deltas altered by?

A

Wave erosion and longshore drift (most of the sediment if distributed along the coast and only a slight protrusion exists)

49
Q

What are tide-dominated deltas altered by?

A

The ebb and flow of the tides into long, linear submarine ridges and islands

50
Q

What are estuaries?

A

Semi-enclosed bodies of water where freshwater from the land mixes with sea water

51
Q

How are estuaries created?

A
  • Drowned river valleys (rise in sea level floods lower portions)
  • Fjords (glaciers retreat, sea level rises, lower portions flooded)
  • Bar built
  • Tectonic estuaries
52
Q

What is the typical salinity gradient in an estuary?

A

Normal marine salinity at the tidal inlet to freshwater at he river mouth

53
Q

What provides the energy for mixing of water in estuaries?

A

Tidal flow

54
Q

How are estuaries categorised?

A

Based upon the relative importance of river inflow and tidal mixing

55
Q

What are the three types of estuaries?

A
  • Salt-wedge
  • Partially mixed
  • Well imxed
56
Q

What is a salt wedge estuary?

A

An estuary dominated by the outflow from rivers (greater than inflow from tides)

57
Q

What are the characteristics of a salt-wedge estuary?

A
  • Well stratified
  • Sharp halocline
  • salt water form a wedge that lifts freshwater outflow off the bottom
  • internal waves propagate along the halocline
  • land-ward directed bottom current
  • sea ward directed surface current
58
Q

What is sediment like in a salt wedge estuary?

A

River sand near the landward edge and river clays and silts elsewhere

59
Q

What is a partially mixed estuary?

A

An estuary equally affected by river discharge and tidal mixing

60
Q

What are the characteristics of a partially mixed estuary?

A
  • Weaker halocline
  • strong landward directed bottom current due to upward mixing of seawater
  • beach and shelf sediment blanket the lower half of the estuary
  • river sand and mud blanket the upper landward half
61
Q

What is flocculation?

A

When clay particles stick together in sea water forming a larger aggregate which sinks more rapidly

62
Q

Where do mud shoals form?

A

Where currents are weak in the estuary

63
Q

What is a well mixed estuary?

A

When tidal turbulence destroys the halocline, meaning water does not change with water depth

64
Q

What effect does Coriolis have on wide estuaries?

A

Deflects river outflow to one side and tidal inflow to the other … creates a lateral salinity gradient

65
Q

What is sediment like in a well mixed estuary?

A

Abundant marine sediments that dominate throughout the estuary

Oceanography (13 decks)

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