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GEOL200 > Week 9: Coastlines and barrier islands > Flashcards

Week 9: Coastlines and barrier islands Flashcards

1
Q

What are barrier islands?

A

Variable lengths and widths
Mobile strip of land
Parallel to coast
Separated from mainland by lagoons, marshes and estuaries
Dynamic environment (migrates towards land)

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2
Q

Where are barrier islands?

A

Form near river deltas in areas w low tectonic (passive margins) activity and flat coastal terrain

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3
Q

Why do barrier islands matter?

A

Protect mainland against wave attack
Line of defence against sea level rise
Imp ecological communities

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4
Q

Features of barrier islands

A

Distinctive depositional zones
Lagoon, marsh and tidal flat, barrier flat, dunes, beach
Affected by longshore currents, waves, storms and tidal activity

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5
Q

Barrier islands- humans

A

As humans populate these islands they are becoming more immobile
**due to concrete and pavement, no sand to pick up

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6
Q

Overwash

A

Process by which water and sediment flow over the crest of a barrier island or dune; result of storm surge

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7
Q

Washover

A

Actual sediment deposited inland of a beach by overwash
**sediment moves inland

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8
Q

Beach heather

A

Anchor sand into places in dunes
Used in restoration of beach dunes

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9
Q

Importance of dunes

A

Protect homes during hurricane/storm surge
BUT they are removed when people build seaside homes

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10
Q

Beach nourishment

A

Addition of sand by humans to increase sand width or volume
*sand added either directly on beach or as underwater mounds

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11
Q

Impacts of beach nourishment

A

Increased turbidity
Increases cloudiness of water and affects sunlight reaching water which impacts photosynthesis and therefore food chains
Change in sand grain size can impact organisms that live btwn them
Smothers coral in sediment
High concentrations of silts and clays may suffocate infauna by clogging their gills
Environmental costs

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12
Q

What shapes the coastlines?

A

Erosion
Deposition
Transportation
Accretion (adding material in non-natural way)

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13
Q

Sediment movement on a beach

A
  1. Dune erosion during storms
  2. Offshore loss through rips especially during storms
  3. Wind erosion or wave washover off the beach
  4. Longshore transport out of area
  5. Longshore transport into system
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14
Q

Dunes

A

Mounds/ridges of sand deposited by the wind immediately landward of the beach
**erosion during high-energy events

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15
Q

What makes up longshore transport?

A
  1. Longshore current
  2. Longshore drift (net movement of sand particles)
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16
Q

Longshore transport

A

Occurs in foreshore and nearshore
Sediment transport by longshore current and by swash and backwash
**moves parallel to coastline
It is why you float away from friends on the beach

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17
Q

How does longshore transport occur?

A

Waves approach shore at an angle
Change in velocity as part of wave enters shallow water while the deeper part keeps moving
Slower at shore and faster deeper

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18
Q

Longshore transport part 2

A

Part of wave’s energy is directed perpendicular to shore and part of it is directed parallel to shore
Parallel direction generates longshore current

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19
Q

Swash

A

Water moving onto beach, carries sediment onshore, increases beach slope

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20
Q

Backwash

A

Water returning to ocean, can also transport sediment
**travels perpendicular to beach
Lease energy expenditure possible

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21
Q

Can coasts have both depositional and erosional features?

A

Yes

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22
Q

Erosional coasts- weathering and erosion

A

Weathering- breaking down rock
Erosion- Broken pieces removed by wave action and currents

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23
Q

How can erosion occur?

A

Precipitation
Heat
Freezing
Wind
Waves

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24
Q

What causes weathering and erosion?

A
  1. Abrasion
  2. Attrition
  3. Corrosion
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25
Q

Abrasion

A

Wave picks up sediment, throw it against cliffs and it wears down cliffs

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26
Q

Attrition

A

Sediment hits each other, become smaller and smoother

27
Q

Corrosion

A

Breaking down of rock naturally by chemical reaction

28
Q

Hydraulic action

A

Breaking wave compressing air into a crack

29
Q

Salt weathering

A

Salt deposited as saline solutions, solution evaporates and salt crystals left behind
Salt crystals expand w addition of water, temp changes
**creates destructive pressures

30
Q

Rate of weathering and erosion

A

Depends on…
- Hardness and rock strength
- Wave energy
- Tidal range

31
Q

What percentage of present day coasts are rocky?

A

75-80%

32
Q

Features of erosional coasts

A

Blowhole
Headland
Sea stack
Sea cave
Sea cliffs
Exposed beach
Sea arch
Stumps

33
Q

Wave-cut platforms

A

Flat area, base of sea cliff
Cliff receedes overtime

34
Q

Irregular shorelines

A

Headlands and bays/coves
Result of wave refraction

35
Q

What are depositional coasts shaped by?

A

Longshore drift
Wind generates a longshore current moving left to right

36
Q

Features of depositional coasts

A

Beach
Spit
Tombolo
Delta
Bay barrier, bay mouth bar
Barrier island

37
Q

What is a beach?

A

Accumulation of unconsolidated sand or gravel that extends from average low tide to uppermost exent of wave impact

38
Q

Types of beach sediment?

A
  1. Volcanic source
  2. Rounded glass fragments (old garbage dump)
  3. Mix of terrestrial and biological particles
39
Q

Seasonal beaches

A

More storms in winter, increase in wave energy moving material onshore and carrying material offshore

40
Q

Fined grained sediment

A

Water easily and quickly runs down beach slope
More sediment carried away by backwash
Broader flatter surface

41
Q

Coarse grain sediment

A

Water moves easily downward through sediment
Backwash carries less sediment back into ocean
Steeper beach

42
Q

Beach in winter vs summer

A

Winter= steeply dipping, narrow berm, sand stored offshore, coaser grains
Summer= Shallow dipping, wide berm, sand stored on beach, finer grains

43
Q

Spits

A

Linear accumulation of sediment attached to land at one end

44
Q

Tombolo

A

Strip of sediment accumulating btwn an offshore island or sea stack and main shoreline
*forms by change of velocity of longshore current

45
Q

Baymouth bar/ bar barrier

A

Spit grows across a bay

46
Q

Delta

A

Deposition of sediment at river’s mouth

47
Q

River-dominated delta

A

Weak wave activity, low tidal range, RIVER INPUT
EX. missisipi river delta (birds foot)

48
Q

Tide-dominated delta

A

Strong tidal influence
Lone narrow sand bodies separated by tidal channels
Parallels tide direction
ex. Ganges river (largest delta in world)

49
Q

Wave-dominated delta

A

Wave erosion controls shape
Straight shorelines and well-developed beaches oriented parallel to coast
ex. Nile delta

50
Q

What is an estuary?

A

Bodies of water and associated coastal habitats found where rivers meet ocean
Saline water mixies w freshwater (brackish water)
One of the most productive ecosystems on earth
**bullsharks

51
Q

Ecosystem services of estuaries

A

Water filtration, habitat and shoreline protection, buffer zones

52
Q

Classifying estuaries

A

Either based on geologic origin or based on salinity and mixing patterns

53
Q

Estuaries origin

A
  1. Drowned river mouth
  2. Fjord
  3. Bar-built
  4. Tectonic
54
Q

Drowned river mouth- coastal plain

A

Shallow w fluvial sediment input from rivers
ex. East coast of North America
*submergent coast

55
Q

Fjord (drowned glacial valley)

A

Formed in deep, U shaped basins carved by glaciers
Steep sides, rock bottoms, underwater sills (underwater ridge of sediment)
*submergent coast

56
Q

Tectonic

A

Result of tectonic movements
Faulting causes some sections of crust to subside
*primary coastline

57
Q

Bar-built (restricted mouth)

A

Barrier btwn mainland and ocean
Water that remains behind the barrier is partially cut off from ocean
ex. along passive margins (Atlantic coast)
*depositional coastline

58
Q

Estuaries salinity and mixing

A
  1. Salt wedge
  2. Partially mixed
  3. Well mixed
  4. Fjord
59
Q

Salt wedge

A

Least mixed (most stratified)
Freshwater on top, saltwater on bottom
ex. St. Lawrence river

60
Q

How is sediment brought to beaches?

A

Wave activity, river deposition, cliff/dune erosion

61
Q

How does sediment withdraw from beaches?

A

Transport down submarine canyons

62
Q

Coastal cells

A

Break coastline up into a number of coastal cells
Complete cycle of sedimentation including source areas, transport paths and sediment sinks

63
Q

How can we prevent too much deposition?

A

Build dams
Build jetty

64
Q

Starved beaches

A

Not enough sediment being supplied to beaches in coastal cell
Coastline moves inland
Increases effects of sea level rise and storms

GEOL200 (10 decks)

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