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geography > Unit 7: Coastal Environments > Flashcards

Unit 7: Coastal Environments Flashcards

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1
Q

Coast

A

The part of the land adjoining or near the sea

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2
Q

Coastline

A

The boundary of a coast where land meets water

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3
Q

Coastal environments

A

The landforms and habitats that make up the area

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4
Q

Lithology

A

Hard rocks like granite and basalt give rugged landscapes (Northern Ireland) whereas soft rocks like sand and gravels produce low, flat landscape (Nile delta)

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5
Q

Geological structure

A

Concordant coastlines occur where the geological strata lie parallel to the coastline (South Ireland) whereas discordant coastlines occur where the geological strata ate at 90 degrees to the shoreline (South west Ireland)

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6
Q

Processes

A

Erosional landscapes contain rapidly retreating cliffs (East England) whereas areas of rapid deposition contain many sand dunes and coastal flats (Netherlands)

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7
Q

Human impacts

A

Some coasts are extensively modified (Florida) whereas others are more natural ( Iceland)

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8
Q

Ecosystem types

A

Mangrove, coral, sand dune, saltmarsh and rocky shore add further variety to the coastline

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9
Q

Coastal zones

A

Include a wider area than coasts or coastlines
Spread from 320 km offshore up to 60 km in land beyond political jurisdiction
These areas interact and influence each other through sediment supply, pollution, weather and climate
Dynamic and complex. Can experience rapid changes as inputs and processes on land, sea and the atmosphere mix

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10
Q

Wave generation

A

Waves result from friction between wind and sea surface

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11
Q

Waves of oscillation

A

Occurring in the deep ocean sea consisting of forward surges of energy but circulating water particles

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12
Q

Breaker waves

A

Waves that reach and then break onto the shore

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13
Q

Crest

A

Highest point on a wave

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14
Q

Trough

A

Lowest point on a wave

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15
Q

Height

A

Vertical distance between crest and trough

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16
Q

Wavelength

A

Horizontal distance between 2 identical points on a wave

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17
Q

Period

A

Time taken for a wave to travel 1 wavelength

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18
Q

Velocity

A

Speed of a wave

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19
Q

Frequency

A

Number of waves that break per second

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20
Q

Steepness

A

If greater than 1:7, it will break due to wave height / wavelength

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21
Q

Energy

A

Related to wave height
Small increase in height produces a large energy increase due to square relationship
Energy is released when the wave breaks

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22
Q

Orbit

A

The shape of a wave either circular or elliptical. Size of orbit decreases with depth

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23
Q

Base

A

The point at which water movement is no longer influenced by wind. Usually equal to the wavelength of the waves above

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24
Q

Wave height

A

Indicates the amount of energy a wave has
Determined by wind strength, fetch and depth of sea
Fetch is the distance of open water a wave travels over
The greater the fetch the larger the wave

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25
Q

Swell vs storm waves

A

Waves can be up to 15m high in the open ocean
When these aves travel long distances form where they were created (generation area) and reach far away shores they are swell waves. Have a lower height and longer wavelength. Will occur no matter what the local weather
Storm waves occur because of more local extreme weather conditions and are characterised by shorter wavelengths, greater heights and higher frequency

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26
Q

Wave shoaling

A

When wavelengths are reduced and wave height increases as a wave enters shallower water. At this point it is a breaker wave

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27
Q

Spilling breakers

A

Associated with gentle beach gradients and steep waves. Characterised by a gradual peaking of the wave until the crest becomes unstable causing a gentle spilling forward of the crest

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28
Q

Plunging breakers

A

Occur on steeper beaches with waves of intermediate steepness. Distinguished by the shoreward face of the wave becoming vertical, curling over and plunging forward and downward as an intact mass of water

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29
Q

Surging breakers

A

Found on steep beaches with low steepness waves. The front face and crest remain relatively smooth and the wave slides directly up the beach without breaking. A large proportion of the wave energy is reflected at the beach

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30
Q

Waves of translation

A

Once a wave breaks and travels onshore it is a wave of translation
-Constructive
-Destructive
Both have a swash and backwash

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31
Q

Constructive waves

A

Tend to occur when wave frequency is low (6-8) per minute especially when these waves advance over a gently shelving sea floor. Have been generated far offshore. The gentle offshore slope creates a gradual increase in friction which will cause a gradual steepening of the wave front. A spilling breaker is formed where water movement is elliptical. As the breaker collapses the powerful swash surges up the gentle gradient. Due to low frequency the backwash has time to return to he sea before the next wave breaks. The swash os not impeded and retains maximum energy

32
Q

Destructive waves

A

Are the result of locally generated winds which create waves of high frequency (12-14 per minute). Rapid approach of waves especially if moving onshore up a steady shelving coastline creates a rapid increase in friction and a very steep, plunging breaker where water movement is circular. Due to rapid steepening and curling of wave breaker, the wave energy is transmitted down the beach on breaker collapse accelerated by the steeper gradient so the waves becomes destructive, breaking down beach material

33
Q

Wave dominated processes and landforms

A

Shore platforms
Cliffs
Beaches
Splits, tombolos
Deltas
High energy

34
Q

Tide dominated processes and landforms

A

Mudflats
Sandflats
Saltmarshes
Mangroves
Deltas
Low energy

35
Q

Wind dominated processes and landforms

A

Sand dunes
High energy

36
Q

Tides

A

Regular movements in the seas surface caused by the gravitational pull of the moon and sun on the oceans
The moon accounts for most of the pull

37
Q

Low spring tide

A

Occur just after a new moon

38
Q

High spring tide

A

Occur after a full moon when the sun and moon are aligned

39
Q

Neap tides

A

Occurs when the sun and moon are at right angles to the earth

40
Q

Influences on tide sizes

A

Size and shape of ocean basins
Characteristics of shoreline
Coriolis force caused by the spinning on the earth
Meteorological conditions
Tides are greatest in bays and funnel shaped coastlines
In the NH flows of water are directed to the right. In the SH to the left
During low pressure systems water will rise by 10 cm of every decrease of 10 millibars of pressure

41
Q

Tidal range

A

The difference between high and low tide
This can vary
Classified as
-microtidal ( less than 2m)
-mesotidal (2-4m)
-macrotidal ( over 4m)

42
Q

Amphidromic point

A

The place where there is no tidal range. Tides may increase with distance from the point

43
Q

Tidal range influences on coastal processes

A

Controls the vertical range of erosion and deposition
Weathering and biological activity is affected by the time between tides
Velocity of tidal currents impact levels of erosion

44
Q

Tidal bores

A

A large wave or bore caused by the constriction of the spring tide as it enters a long, narrow, shallow inlet

45
Q

Rip currents

A

An intermittent strong surface current flowing seaward from the shore
Can be caused by a combination of tides and the uneven breaking of waves along a shoreline
Once formed they modify the beach creating cusps which makes the current more likely to occur again in the future

46
Q

Storm surges

A

An abnormal rise in sea level accompanying a hurricane or intense storm significantly above astronomical tide. Can cause extreme flooding in coasts

47
Q

Causes of storm surges

A

Low atmospheric pressure
Strong winds
Wave action
Coastal topography
Tides

48
Q

Impacts of storm surges

A

Loss of life
Property damage
Displacement
Environmental damage
Economic costs

49
Q

Preparation and mitigation of storm surges

A

Early warning systems
Infrastructure improvements
Community preparedness
Environmental management

50
Q

Hydraulic action

A

Occurs as waves break onto cliffs. As they break against the cliff face any air trapped in cracks, joints and bedding planes is put under great pressure. As the wave retreats the pressure is released with explosive force. This is cavitation. Stress weakens the coherence of the rock aiding erosion. Particularly obvious in well bedded and jointed rocks like limestones, sandstones, granite and chalk as well as rocks poorly consolidated like clay and glacial deposits. Also notable during storm wave activity

51
Q

Abrasion

A

Where a breaking wave can hurl pebbles and shingle against a coast

52
Q

Attrition

A

Occurs as other forms of erosion continue. The eroded material is worn down by attrition explaining the variety of sizes of beach material

53
Q

Solution

A

Is a form of chemical erosion. With calcareous rock waves remove material by acidic water. The source of acidity is from organisms. These make the water more acidic especially in rock pools at low tide

54
Q

Waves affecting rate of erosion (energy)

A

Wave steepness: Steep destructive waves formed locally have more erosive power than less steep constructive waves
Wave breaking point: Waves breaking at a cliff base cause maximum erosion whereas waves breaking off shore lose energy

55
Q

Tides affecting rate of erosion (energy)

A

Neap and spring tides vary the zone of wave attack. Strong tidal currents can scaur estuary channels

56
Q

Currents affecting rate of erosion (energy)

A

Longshore and rip currents can move large quantities of material

57
Q

Winds affecting rate of erosion (energy)

A

Onshore winds erode rine beach sane to form dunes
Offshore winds may erode dunes and nourish the beach
The longer the fetch the greater the wave energy potential

58
Q

Sediment supply affecting rate of erosion (material)

A

Continual supply is necessary for abrasion whereas an oversupply can protect the coast

59
Q

Beach/rock platform width affecting rate of erosion (material)

A

Beaches/rock platforms influence wave energy by absorbing waves before they can attack cliffs

60
Q

Rock resistance affecting rate of erosion (material)

A

Rock type influences the rate of erosion. Granites are very resistant whereas unconsolidated volcanic ash has little resistance to wave attack. Erosion is rapid where rocks of different resistance overlie one another

61
Q

Rock structure and dip affecting rate of erosion (material)

A

Well jointed or faulted rocks are very susceptible to erosion
Horizontal or vertical structures produce steep cliffs
Rocks dipping away from the sea produce gentle cliffs

62
Q

Offshore topography affecting rate of erosion (slope geometry)

A

A teep seabed creates higher and steeper waves than one with a gentle gradient
Longshore bars cause waves to break offshore and lose energy

63
Q

Coastal orientation affecting rate of erosion (slope geometry)

A

Headlands with vertical cliffs tend to concentrate wave energy by refraction
Degree of exposure to waves influence erosion rates

64
Q

Direction of fetch affecting rate of erosion (slope geometry)

A

The longer the fetch the greater the potential for erosion by waves

65
Q

Formation of wave cut platforms

A

Wave action works between HWM and LWM so causes undercutting of a cliff face forming a notch and overhang. Breaking waves especially during storms and spring tides can erode the coast above HWM. As the undercutting continues the notch becomes deeper and the overhang more pronounced. The overhand will collapse causing the cliff line to retreat. The base of the cliff will be left behind as a broadening platform often covered with deposited material with the coarsest near the cliff base gradually becoming smaller towards the open sea

66
Q

Weathering in sub ariel processes

A

Salt is where sodium and magnesium compounds expand in joints and cracks weakening rock structures
Freeze-thaw is where water freezes expands and degrades jointed rocks
Biological is carried out by molluscs, sponges and sea urchins
Solution is the chemical weathering of calcium by acidic water which occurs in rock pools due to the presence of organisms secreting organic acids
Slaking is where materials disintegrate when exposed to water by hydration cycles
Mass movements like slumping and rockfalls are also important in coasts

67
Q

Marine transportation and deposition

A

Sediment sources vary. They include reworked beach deposits, offshore marine deposits, river deposits, glacial deposits, material from cliff mass movements, wind blown deposits and artificial beach nourishment. SOme beaches are formed of volcanic ash and others are formed of shingle. Shingle beaches are of glacial and periglacial deposits. Sandy beaches are the result of river sediment reworked by waves. Others are artificial and use sand from elsewhere

68
Q

Bedload sediment transport

A

Grains transported by bedload are moved in continuous contact or discontinuous contact. In traction gains slide or roll. Weak currents may transport sand and strong currents transport pebbles and boulders. In saltation grains hop along the seabed. Moderate currents transport sand and strong transport pebbles

69
Q

Suspended load sediment transport

A

Grains carried by turbulent flow and help up by water. Suspension occurs in moderate currents transporting silts or strong transporting sand. Grains transported as wash leads are always in suspension consisting of clay and dissolved material. Deposition is governed by sediment size and shape and may flocculate

70
Q

Sediment cells

A

The coastal or littoral cell system examines coastal processes and patterns. It ranges from a single bay to regional. Each littoral cell is self contained where inputs and outputs are balanced. Dynamic equilibrium states that the littoral cell is the result of the inputs and processes operating in it. Change to 1 input has a knock on effect on processes and a change in landform. The balance changes so dynamic equilibrium

71
Q

Longshore drift

A

Leads to sediment moving gradually along the shore. The swash moves sediment up the beach in direction of prevailing wind while backwash moves straight down the beach in direction of steepest gradient. Net movement is downdrift

72
Q

Wave refraction

A

As a wave front approaches the shore, speed falls. Due to the interaction between onshore wind and direction and trend of coast wave fronts approach obliquely. This causes wavefront to bend and swing to break parallel to the shore. The speed and distortion change of the wavefront is wave refraction. If completed the fronts break parallel to the shore. Due to coastline shapes, refraction is not always totally achieved causing longshore drift which is a major transport of material. Refraction also distributes energy along a coast. Along a complex transverse coast with alternating headlands and bays, wave refraction concentrates wave energy and so erosional activity on headlands while energy is dispersed in bays as deposition. If refraction isn’t complete, longshore drift occurs

73
Q

Formation of caves

A

Begins with the erosion of weak points in coastal cliffs often at the base where the sea exerts the most force. Marine erosion involves hydraulic action, abrasion and corrosion. Over time these processes enlarge cracks into small cavities. As erosion continues the cavities grow into substantial recesses or caves. The initial formation if heavily influenced by rock type and structure. Sedimentary rocks with bedding planes and joints are especially susceptible to cave formation

74
Q

Formation of arches

A

As caves deepened they can penetrate through a headland. Happens when the sea erodes both sides of a headland where waves developed. Continuous wave action and sub aerial processes like weathering contribute to the enlargement and eventual meeting of opposite caves. Arches are further sculpted by marine and sub aerial erosion. The top of the arch is subjected to weathering like freeze-thaw and biological. This weakens the rock above the arch so is more susceptible to collapse

75
Q

Formation of stacks

A

When the arch is too unstable to support its weight it collapses leaving an isolated pillar of rock. Characterised by vertical form, standing alone due to the seas erosive power. Erosion continues on the stack particularly at its base where most wave energy is concentrated. Abrasion and hydraulic action are key eroding the base. This leads to further weakening and collapse of the stack into a smaller more stable form

76
Q

Formation of stumps

A

As the base of a stack is undercut by wave action the structure becomes unstable and collapses. The remaining base of the eroded stack only just visible at high tide is a stump. Stumps are the last remnants of the original cliff and are often submerged in high tide

77
Q
A

geography (23 decks)

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