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Coasts Flashcards

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1
Q

What affects wave energy

A

-the strength of the wind-determined by the pressure gradient
-the duration of the wind
-the fetch

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2
Q

How are waves formed

A

As air moves across the water, frictional drag disturbs the surface and forms ripples or waves. In the open sea, there is little horizontal movement of water. Instead, there is an orbital motion of the water particles. Close to the coast, horizontal movement of water does occur as waves are driven onshore to break on the beach

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3
Q

Two main types of waves

A

Constructive and destructive

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4
Q

Constructive wave

A

-low, surging waves with a long wave length
-strong seas, weak backswash
-beach gain
-usually associated with a gentle beach profile

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5
Q

Destructive waves

A

-local storms responsible
-high, plunging waves with a short wavelength
-weak swath, string backwash
-beach loss
-steep beach profile

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6
Q

What is a tide

A

Tides are changes in the water level of seas and oceans caused by the gravitational pull of the moon, and to a lesser extent, thr Sun

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7
Q

How many tides does Uk have a day

A

Two high and two low tides each day

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8
Q

What is tidal range

A

The relative difference in height between high and low tides each

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9
Q

What is a rip current

A

A series of plunging waves causes a temporary build up of water at the top of the beach. Met with resistance from the breaking waves, water returning down the beach ( backwash ) is forced just below the surface following troughs and small undulations. Fast flowing offshore surge of water can drown ppl

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10
Q

What are high energy environments

A

Where the rate of erosion exceeds the rate of deposition. Erosional landforms e.g rocky coasts

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11
Q

Low energy env

A

-deposition exceeds erosion
-depositional landforms found

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12
Q

What is wave refraction

A

Eave refraction causes energy to be concentrated at headlands and dissipated in bays.

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13
Q

Where does sediment come from

A

-rivers
Cliff erosion
Longshore drift
Wind
Glaciers
Offshore

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14
Q

What’s a sediment cell

A

A stretch of coastline , usually bordered by two prominent headlands, where the movement of sediment is more or less contained.

Inputs: river and coastal erosion
Flows: long shore drift and rip currents
Stores: beach,. Sand dune spit

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15
Q

What’s a sediment budget

A

Losses and gains of sediment. Losses = deposition in sediment sink whereas gains tend to involve coastal erosion pr sediment brought in from river. Dynamic equilibrium, balance upset by storms

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16
Q

What is weathering

A

The break down of rock in situ

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17
Q

What is freeze thaw

A

Occurs when water enters cracks when it rains and then freezes. When water freezes, it expands which exerts pressure on the rock causing the crack to widen. Fragements of rock break away and collect at base as scree

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18
Q

What is salt crystallisation

A

When salt water avporates, it leaves behind salt crystals which grow over time and exert pressure on rock.

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19
Q

What is biological weathering

A

The breakdown of rocks by organic activity
E.g plants grow into small cracks in a cliff face which widen and breaks up the rock

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20
Q
A
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21
Q

What is chemical weathering

A

Carbonation - rainwater absorbs co2 from the air to form a weak carbonic acid which reacts with calcium carbonate in rocks to form calcium bi carbonate which is easily dissolvable.

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22
Q

Mass movement

A

The downhill movement of material under the influence of gravity is known as mass movement

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23
Q

Mudflows

A

Involves earth and mud flowing downhill, usually over unconsolidated or weak bedrock such as clay, often after heavy rainfall. Water gets trapped within the rock, increasing pore water pressure, which forces rock particles apart leading to slope failure,

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24
Q

Landslide

A

A block of rock moving very rapidly downhill;;. When the slip surface become lubricated and friction is reduced.

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25
Rockfall
The sudden collapse or breaking away of individual rock fragments at a cliff face. A rockfall is triggered by mechanical weathering like freeze thaw. Rocks fall or bounce down the slope to from scree.
26
What is coastal erosion
Removing debris from the foot of cliffs and providing an input into sediment cells
27
Hydraulic action
Air compressed in cracks which expands when the wave retreats. Also called cavitation
28
Wave quarrying
Dig at the bottom and scoop
29
Corrosion
When waves advance, they pick up sand and pebbles from the seabed. When they break at the base of the cliff, the transported material is hurled at the cliff foot.
30
Abrasion
Sandpapering effect as sediment is dragged up and down or across the shoreline, eroding and smoothing rock surface,.
31
Solution
Weak acids dissolved alkaline rock,
32
What affects erosion
Waves Rock type Geological structure Beach Subaerial processes Coastal management
33
Traction
The rolling of coarse sediment along the sea bed that is too heavy to be picked up and carried by the sea Sal
34
Saltation
Sediment is bounced along the sea bed, light enough to be picked up or dislodged but too heavy to remain within the flow of water
35
Suspension
Smaller lighter seudnebr picked up and carried within the flow of water
36
Solution
Carbonation
37
Longshore drift
Most waves approach beach at an angle, generally in the same direction as prevailing wind. The backwash then pul;s material down the beach at right angle to the shore. Zig zag movement .
38
Deposition
Deposition takes place when the velocity of the water falls below a critical value for a particular size of particle and can no longer be tranpisertd,
39
Wave cut platforms
When waves break against the foot cliff, erosion creates a wave cut notch. As the notch gets bigger, the cliff is undercut and the rock above it becomes unstable, eventually collapsing. NEGATIVE FEEDBACK - cliff retreats and so does platform. Wave cut platforms will rarely extend massively because waves will break earlier and its energy will be dissipated before it reaches the cliff, reducing further erosion
40
Caves arches, stacks
-erosion of chalk exploits cracks -caves created and join or eroded through to form arch -top of arch collapses leaving stack
41
Beach
A despositioanl landforms extending from highest high tide to lowest low tide. Beach accretion will tale place during a prolonged period pf constructive waves. Destructive waves excavate beach
42
Swash aligned beach
Waves arrive parallel to shore
43
Drift aligned beach
Form where the waves approach the coast at an angle. Longshore drift
44
Beach forms
Berms, cusps and runnels.
45
Why are larger pebbles at stop
Constructive waves will carry a range of sediment sizes up a beach due to a strong swash but, due to water percolating into the beach, the weaker backswash will only be able to drag bag smaller pebbles, Smaller pebbles more rounded due to attrition
46
Spit
Long narrow feature, made of sand that extends from land into the sea.
47
Tombolo
Spit joined to island
48
Offshore bars
Destructive waves erode sand from the beach with their strong backwash and deposit it offshore. They can absorb wave energy thereby reducing impacts off wave d
49
Barrier beaches ( bars )
Where a spit extends across a bay to join two headlands. Lagoons behind them. Barrier beaches and bars on the south coast of England are believed to have been deposited following a rise in sea level after the last glacial period. Sediment deposited by meltwater was bulldozed onshore to form barrier beaches. Longshore drift has added more matererial and has reworked the sediment, where a beach becomes separated from toe mainland, it is referred to as a barrier island.
50
Sand dune
Need: Large quantities of available sand, washed onshore by constructive waves Large tidal range, creating a large exposure of sand that can dry out at low tide Dominant onshore winds that will blow dried sand to the back of beach
51
What happens on sand dunes
Vegetation succession
52
Estuarine mudflats and salt marshes
River estuaries are important sediment stores where huge quantities of river sediment is deposited in water close to the edges of the river. Most of the sediment that accumulates here is mud - mudflats can develop into saltamrshes
53
Salt marshes
Areas of flat, silty sediments that accumulate around estuaries or lagoons . They develop in sheltered areas ( behind spit ) and where there are no strong tides or currents to prevent deposits
54
Process of salt marsh development
To begging with, mud is deposited close to the high tide line, dropping out of the water in flocculationn. This involves the tiny individual particles of mud sticking together such that the combined mass enables them to sink to the seabed. Succession occurs in tidal range
55
Ecstatic change
When the sea level itself rises or falls
56
Isostatic change
When the land rises or falls, relative to the sea
57
Eustatic change
Eustatic change is global. In cold glacial periods, precipitation falls as snow and forms huge ice sheets that store water that is usually held in the oceans. As a result, sea levels fall. As temperatures rise at the end pf the glacial periods, the ice sheets begin to melt and retreat. Their stored water then flows into the rivers and the sea, and sea levels rise.
58
Isostatic change
Isostatic change occurs locally. During glacial periods, the enormous weight of the ice sheets makes the land sink known as Isostatic subsidence. As the ice begins to melt at the end of a glacial periods, the reduce weight of the ice causes the land to rise - Isostatic recovery.
59
Emergent coastal landforms
As the land rose as a result of Isostatic recovery, former wave cut platforms and their beaches were raised above the present sea level. Raised beaches - common in west Scotland;ands where the remains of eroded cliff lines can be found on the raised beach’s
60
Submergent coastal land forms
- submergence results im the flooding of coastlines. Rias form when the valley in a dissected upland area are flooded. Fjords are formed when deep glacial troughs are flooded by a rise in sea levels. They are long and steep sided with a U shaped cross section . Dalmatian coasts form in a landscape where valleys run parallel to the coast. When the sea levels rise, the valleys flood, although the tops of the ridges remain exposed.
61
62
Traditional coastal approaches
Hard engineering
63
Groynes
Rock structures built at right angles to the coast. They trap sediment being moved along the coast by Longshore drift. However, this starves the beaches further along the coast of fresh sediment.
64
Sea walls
Stone or concrete walls at the foot of a cliff. They usually have a curved face to reflect waves back into the sea. However, they reflect wave energy rather than absorbing it. Very expensive and unnatural
65
RIP rap
Large rocks placed at the foot of a cliff, forming a permeable barrier to the sea and breaking up the waves
66
Revetments
Sloping concrete or wood structured at foot of cliff which break up waves energy. Intrusive and unnatural
67
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Coasts (1 decks)

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