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Geography > Coastal > Flashcards

Coastal Flashcards

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1
Q

What factors affect the coastal environment?

A
  • offshore water depth
  • fetch
    -currents + tides
  • sea level change
  • wave type
  • storms/weather conditions
  • building e.g houses/ human activity
  • coastal ecosystems e.g. sand dunes
  • prevailing winds
  • geology
  • weathering + mass movement
  • coastal management
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2
Q

Is the coast an open or closed system?

A

Open

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3
Q

What are some inputs into the coast?

A

-energy (waves, wind, tides, currents)
-unconsolidated sediment from beach and sea bed
- sediment beyond the backshore
- sediment from cliffs

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4
Q

What are some flows/transfers within the coast.

A

-erosion
- deposition
-transport (longshore drift/ wind)

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5
Q

What are some stores/ components within a coast?

A

-cliffs
- erosional landforms e.g. stack
- depositional landforms e.g. spit
- beach

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6
Q

What are some outputs within a coast?

A

-lost energy
- sediment lost beyond the limits of the sediment cell

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7
Q

Characteristics of a constructive wave?

A

-low wave height but long wave length
- low frequency of around 6-8/min
- strong slash, weak backwash
- material slowly but constantly moved to the beach - leading to formation of ridges

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8
Q

What are the characteristics of a destructive wave?

A
  • high wave, steep form + high frequency
  • powerful backwash as little forward movement of water
  • very little material moved up beach, backwash pulls material back down the beach
  • commonly associated with steeper beach profiles
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9
Q

What are the impacts of waves and sediment on beach morphology?

A
  • constructive waves build up beach leading to a steeper beach profile
  • encourages waves to become more destructive
  • destructive waves move material back towards the sea reducing the beach angle encouraging more constructive waves
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10
Q

What is neap tide?

A

Lowest monthly tidal range (small bulges of water)

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11
Q

What is spring tide?

A

highest monthly tidal range (large bulges of water)

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12
Q

What is the tidal range?

A

Difference in height of the sea water of high and low tide

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13
Q

What are currents?

A

Permanent or seasonal movement of surface water in the seas and oceans e.g. longshore currents, rip currents, upwelling

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14
Q

High energy coast characteristics?

A
  • a coastline where strong, steady prevailing winds create high energy waves and the rate of erosion is greater than the rate of deposition
  • typical landforms include headlands, cliffs and wave -cut platforms
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15
Q

Low energy coast characteristics?

A
  • a coastline where wave energy is low and the rate of deposition often exceeds the rate of erosion of sediment
  • typical landforms include beaches and spits
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16
Q

How are waves formed?

A

By winds on the surface of the sea - can be combination of waves derived from local + distant winds

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17
Q

What is the equation for wave strength?

A

Wind velocity + duration + fetch

18
Q

What is meant by the term fetch?

A

Refers to the distance of open water over which a wind blows uninterrupted by major land obstacles

19
Q

What is the wave energy equation?

A

Energy ♾️ wavelength x waveheight’2

(♾️ equal or proportional to)

20
Q

How does the wave change shape as it approaches the shore?

A

The wave becomes increasingly elliptical. Friction with sea bed increases - crest rises - waves are steep u til wave height to wavelength ratio of 1:7 (break point)

21
Q

What is wave refraction?

A

Refraction is the change in direction of waves as they move between materials with different properties. Water waves are refracted as they move from deep water to shallow water. Water waves travel faster in deep water than in shallow water.

22
Q

How is river discharge a sediment source?

A

The sediment that is washed down rivers = weather + eroded materials (mountains, floodplains, river banks etc…). Brings nutrients

23
Q

How are ocean current a sediment source?

A

Bring sediment from other areas of coast or offshore

24
Q

How is seabed disturbance a sediment source?

A

When the sea bed is disturbed - picking up sediment from the bottom. Brings nutrients

25
Q

How is cliff and shore disintegration a sediment source?

A

Weathering, erosion, mass movement

26
Q

What is a sediment/ littoral cell?

A

A linked system of sources/inputs, transfers and sinks (outputs of sediment) along a section of a a coastline
Closed system

27
Q

What is the sediment budget?

A

The inputs - the outputs
(The difference between them)

28
Q

How can human activities interfere with sediment cells?

A

Coastal management e.g. sea walls, groynes - can prevent cliff erosion - reduces/ halts sediment supply to sink region

29
Q

Example: South Downs sediment cell?

A

Sediment cell 4, subcell 4d on the Sussex coast of England
- between cliff headlands of Selsey Bill + bealhy head
-the shoreline management plan will further split cell in half east to west of Brighton Marina - forming two subcells
- of the 22km of cliff in cell, 8km is protected
- rottingham, saltden, seaford have become seriously depleted + have been critically replenished
- where rivers enter the sea it blocks the eastward movements of longshore drift

30
Q

What are some inputs into a sediment cell?

A

Cliff erosion, river transport, marine organisms, wind blown (aeolian) sediment from, land, offshore currents

31
Q

What are some transfers within a sediment cell?

A

Longshore drift, swash/backwash, tidal currents, sea (ocean currents + wind)

32
Q

What are some outputs of a sediment cell?

A

Sand dune, beaches, bars barrier islands

33
Q

What are the six main ways waves erode the coastline?

A
  1. Corrasion(abrasion) - bits of rock and sediment transported by the waves smash and grind against rocks and cliffs, breaking bits off and smoothing surfaces
  2. Hydraulic action - air in cracks in cliffs is compressed when waves crash in. The pressure exerted by the compressed air breaks off rock pieces
  3. Cavitation - as waves recede, the compressed air expands violently, again exerting pressure on the rock and causing pieces to break off
  4. Wave quarrying - the energy of a wave as it breaks against a cliff is enough to detach bits of rock
  5. Solution (corrosion) - soluble rocks (e.g. limestone, chalk) get gradually dissolved by the seawater
  6. Attrition - bits of rock in the water smash against each other and break into smaller bits
34
Q

What are the four main processes of transportation?

A
  1. Solution - substances that can dissolve are carried along in the water e.g. limestone is dissolved into water that’s slightly acidic
  2. Saltation - larger particles, such as pebbles or gravel, are too heavy to be carried in suspension. Instead, the force of the water causes them to bounce along the sea bed.
  3. Suspension - very fine material, such as silt and clay particles, is whipped up by turbulence (erratic swirling of the water) and carried along in the water. Most eroded material is transported in this way.
  4. Traction - very large particles e.g. boulders, are pushed along the sea bed by the force of the water
35
Q

What is longshore drift?

A
  1. Swash carries sediment up the beach, parallel to the prevailing wind. Backwash carries sediment back down the beach, at right angles to the shoreline
  2. When there’s an angle between the prevailing and the shoreline, a few rounds of swash and backwash move the sediment along the shoreline
36
Q

What is deposition?

A
  1. Deposition is when material being transported is dropped on the coast
    - marine deposition is when sediment carried by seawater is deposited
    - aeolian deposition is when sediment carried by wind is deposited
  2. Both marine and aeolian deposition happen when the sediment load exceeds the ability of water or wind to carry it. This can be because sediment load increases (e.g. if there is a landslide), or because wind or water flows slows down (so it has less energy). Wind and water slow down for similar reasons
    - friction increases - if waves enter shallow water or wind reaches land, friction between the water/ wind and ground surface increases, which slows down the water or wind
    - flows become turbulent - if water or wind encounters an obstacle (e,g, a current moving in the opposite direction, or an area of vegetation) flow becomes rougher and overall speed decreases
  3. If the wind drops, wave height, speed and energy will decrease as well
37
Q

What are the types of weathering that affects coast?

A
  1. Salt weathering - salt weathering is caused by saline (salty) water - this saline water enters pores or cracks in rocks at high tide - as the tide goes out the rocks dry and the water evaporates, forming salt crystals. As the salt crystals form they expand, exerting pressure on the rock - this causes pieces to fall of.
  2. Freeze - thaw weathering - it occurs in areas where temperatures fluctuate above and below freezing - water enters the joints and crevices in rocks - if the temperature drops below 0, the water in the cracks freezes and expands - over time, related freeze-thaw action weakens the rocks and causes pieces to fall off
  3. Wetting and drying - some rocks contain clay - when clay gets wet, it expands and the pressure caused by this breaks fragments off the rock
  4. Chemical weathering - it is the breakdown of rock by changing its chemical composition - for example, carbon dioxide in the atmosphere dissolved in rainwater, forming a weak carbonic acid. This acid reacts with rock that contains calcium carbonate, e.g. Carboniferous limestone, so the rocks are gradually dissolved
38
Q

What is mass movement and what are the different types?

A
  1. Mass movement is the shifting of material downhill due to gravity. In coastal areas, it is most likely to occur when cliffs are undercut by wave action - this causes an unsupported overhang, which is likely to collapse
  2. Slides - material shifts in a straight line
    Slumps - material shifts with a rotation
    Rockfalls - material breaks up and falls
    Mudflows - material flows downslope
    Can also move gradually downhill by soil creep
  3. Unconsolidated rocks e.g. clay are prone to collapse as there’s little friction between particles to hold them together
  4. Heavy rain can saturate unconsolidated rock, further reducing friction and making it more likely to collapse
  5. Runoff (the flow of water over the land) can erode fine particles (e.g. sand and silt) and transport them downslope
39
Q

Coastal landforms caused by erosion?

A
  1. Cliffs and wave-cut platforms
    - cliffs are common coastal landforms - they form as the sea erodes the land. Over time, cliffs retreat due to the action of waves and weathering
    - weathering and wave erosion cause a notch to form at the high water mark. This eventually develops into a cave
    - rock above the cave becomes unstable with nothing to support it, and it collapses
    - wave - cut platforms are flat surfaces left behind when a cliff is eroded
  2. Headlands and bays
    - they form where there are bands of alternating hard rock and soft rock at right angles to the shoreline
    - the soft rock is eroded quickly, forming a bay. The harder rock is eroded less and sticks out as a headland
  3. Caves, arches and stacks
    - some landforms are found in cliffs - these are called cliff profile features
    - weak areas in rock e.g. joints are eroded to form caves
    - caves on the opposite sides of a narrow headland may eventually join up to form an arch
    - when an arch collapses it forms a stack then a stump
40
Q

Coastal landforms caused by deposition?

A
  1. Beaches
    - they form when constructive waves deposit sediment on the shore - they are a store in the coastal system
    - shingle beaches are steep and narrow. They’re made up of larger particles, which pile up at steep angles. Sand beaches formed from smaller particles, are wide and flat
    - beaches have distinctive features. Berms are ridges of sand and pebbles (about 1-2 meters high) found at high tide marks. Runnels are grooves in the sand running parallel to the shore, formed by backwash draining to the sea. Cusps are crescent - shaped indentations that form on beaches of mixed sand and shingle.
  2. Spits - they tend to form where the coast suddenly changes direction e.g. across river mouths
    - longshore drift continues to deposit material across the river mouth, leaving a bank of sand and shingle sticking out into the sea. A straight spit that grows out roughly parallel to the coast is called a simple spit.
    - occasional changes to the dominant wind and wave direction may lead to a spit having a curved end
    - over time, several recurved ends may be abandoned as the waves return to their original direction. A spit that has multiple recurved ends resulting from several periods of growth is called a compound spit
    - the area behind the spit is sheltered from the waves and often develops into mudflats and salt marshes
  3. Offshore bars and tombolos
    - bars are formed when a spit joins two headlands together. This can occur across a bay or across a river mouth
    - a lagoon forms behind the bar
    - bars can also form off the coast when material moves towards the coast (normally as sea level rises). These may remain partly submerged by the sea - in this case they’re called offshore bars
    - a bar that connects the shore to an island (often a stack) is called a tombolo
    - e.g. St Ninian’s Isle in the Shetland islands is joined to a larger island by a tombolo
  4. Barrier islands
    - they are long narrow islands of sand or gravel that run parallel to the shore and are detached from it. They tend to form in areas where there’s a good supply of sediment, a gentle slope offshore, fairly powerful waves and a small tidal range
    - not clear exactly how they form but scientists think they probably formed after the last ice age ended, when ice melt caused rapid sea level rise. The rising waters flooded the land behind beaches and transported sand offshore, where it was deposited in shallow water, forming islands
    - another theory is that the islands were actually bars attached to the coast which were eroded in sections causing breaches in the bar
    - a lagoon or marsh often forms behind the barrier island where the coast is sheltered from wave action
    - barrier islands are found on many coastlines, including the east coast of the USA
  5. Sand dunes
    - they are formed when sand deposited by longshore drift is moved up the beach by wind
    - sand trapped by Driftwood, or berms is colonised by plants and grasses e.g. marram grass, the vegetation stabilises the sand and encourages more sand to accumulate there forming embryo dunes.
    - overtime, the oldest dunes migrate in land as newer, embryo dunes are formed. These mature dunes can reach heights of up to 10 m.
  6. Estuarine mudflats and salt marshes
    - Mudflats and salt, marshes form in sheltered low energy environments, e.g. river estuaries, or behind spits
    - as silt and mud are deposited by the river or the tide mudflats develop
    - the mudflats are colonised by vegetation that can survive the high salt levels and long periods of submergence by the tide
    - the plants trap more mud and silt, and gradually they build upwards to create an area of salt marsh that remains exposed for longer and longer between tides
    - erosion by tidal currents or streams forms channels in the surface of mudflats and salt marshes. these may be permanently flooded or dry at low tide.

Geography (6 decks)

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