Coastal Environments Flashcards
(92 cards)
1
Q
How does a wave form?
A
Wind blowing over the sea surface (fetch)
2
Q
What are examples of wave inputs?
A
Sediment/ human activity
3
Q
What 3 things determine the energy go the wave?
A
Strength of the wind
Duration of the wind
The distance (fetch)
4
Q
What is the wave frequency?
A
The number of waves per minute past a fixed point
5
Q
What is the wave period?
A
The time it takes to get from crest to crest- complete cycle
6
Q
What results from an increase in wave height
A
More energy
7
Q
What causes waves to break?
A
Friction
8
Q
Draw a cross profile of a wave.
A
Crest Wave length Wave height Amplitude Orbit Trough Sea Level Friction
9
Q
Whats the difference between constructive and destructive waves?
A
Constructive:
Create beaches, low energy
created by gentle, short duration winds with a small fetch.
They have a long (elliptical) cross profile
Very long- up to 100meters in length
Low frequency- 6-8 waves per minute
Wave energy is proportionally lower due to wave height
Not steep, low (less than 1 meter)
Swash is much stronger than backwash as the material is carried up the beach and deposited
The wave energy spreads over a large area, resulting in a weak backwash.
Destructive:
High (More than 1 meter) and steep
Short (Less than 20 meters)
More frequent (11-15 waves per minute)
Wave energy is proportionally high due to the higher wave height
Swash is weaker than backwash as material is removed from the beach
Energy concentrated on a small area
10
Q
What is a coastal System?
A
Where land meets sea
11
Q
What are coastal sediment cells?
A
Sections of the coast where sediment transport is present,
a sediment cell is a closed system where no sediment is transported from one cell to another
Boundaries are determined by the shape of the coastline and topography (arrangement of natural and artificial physical features)
It is difficult to retain sediment in a single cell due to the change in wind direction and tidal currents. There are also sub-cells within major cells
12
Q
What are tides?
A
The periodic rise and fall of the ocean surface, caused by the gravitational pull of the sun and moon
Tides affect where waves break
High tide- Waves break higher up the shore
13
Q
What is the inter-tidal range?
A
The point between maximum high tide and minimum low tide, where landforms are created and destroyed
14
Q
What is subaerial weathering?
A
Processes not linked to the actions of the sea causing the gradual breakdown of material
15
Q
What is Through flow?
A
The flow of water through something e.g cliffs
16
Q
What is Runoff?
A
The flow of water over land
17
Q
What is mass movement?
A
Movement of material downhill due to gravity e.g landslides, slumping and rockfall
18
Q
What is a WAVE CASE STUDY?
A
Nazare- West coast of Portugal
78ft tall
Long fetch across Atlantic ocean
Strong winds over several weeks
19
Q
Draw a diagram of wave refraction.
A
Litteral currents
Orthogonal
Energy is focused at the headland as its the first point the waves hit. Headland has stronger rock and holds shallower water, they start to bend/refract as they mirror the shape of the coastline.
20
Q
What is a spring tide?
A
Forms when the sun, earth and moon are aligned causing, the gravitational pull to be at its greatest
Results in a highest high tide and a lowest low tide
They cause stronger tidal currents
occurs when new moon/full moon is present
21
Q
What is a neap tide?
A
Happens when the sun and moon are at right angles to the earth. The gravitational pull the sun partially balances the effect of the moons pull, creating a lowest high tide and a highest low tide
Low tidal range creating weaker tidal currents than normal
22
Q
What is Macrotidal?
A
Applied to the coastline when the tidal range in the excess of 4 meters
23
Q
What is Mesotidal?
A
Applied to the coastline when the tidal range is 2-4 meters
24
Q
What is Microtidal?
A
applied to the coastline when the tidal range is less than 2 meters
25
What is Coriolis Force?
The direction of Earth Movement
26
True or False: Near higher mass, the tidal range is higher
True, anything with mass has a gravitational pull
27
What else affects tidal range?
Narrow necks of water, concentrated into a narrow area
| Moons orbit not completely circular around the Earth, the further away the moon is, the lower the gravitational pull
28
What are some examples of sediment sources?
Erosion of cliffs
Currents input material from the sea bed
Rivers bringing sediment from downstream
Sediment can also be moved to a sand dune
29
What are the 2 types of sediment?
Clastic: From rock weathering + Erosion
Biogenic: Sediments are shells and skeletons of Marine Organisms
30
What is a UK Tidal storm surge Case study?
East Anglia- 6th December 2013
31
What were the causes of the East Anglia surge?
- Area of low pressure passing the North coast of the UK, causing the sea level to rise
- Southward blowing wind causing large waves to build, leading to flooding at high tide
32
What were the Impacts of the East Anglia storm surge?
-2 people dead
-7 cliff top homes collapsed in Hemsby , Norfolk
-800,000 homes had been protected by flood defences
-400 homes in Humber were affected by flood water
-500 homes evacuated in Kent
In Boston, 200 people spent the night in evacuation centres
33
What is a storm surge?
Changes in sea level due to variations in atmospheric pressure and associated winds, also occurs at high tide
one millibar change in pressure gives one CM change in sea level
Strong winds which contribute towards surges also produce high storm waves
34
Whats the difference between positive and negative storm surges?
Negative- Wind direction blows water away from the coast causing sea level in that area to drop, less dangerous than positive surges
35
Why are storm surges a growing threat?
Global warming- sea level rise
Increasing number of human modifications on the coast
Socioeconomic changes, more people moving towards the coast
36
How does air rise?
The water is heated by the sun, so it rises, then the cool air moves in
37
What is marine erosion?
processes associated with the action of waves`
38
What are examples of marine erosion?
Hydrualic action, Abrasion, Attrition and solution
39
How does solution occurs as carbonic acid?
CO2 reacts with the water to form weak carbonic acids which erode the rock (limestone)
40
What is subaerial weathering?
The decomposition of rocks in their fixed place
41
What are the 3 types of sub aerial weathering?
Mechanical/Physical- rock breakdown by physical processes (freeze thaw)
Biological-Rock breakdown by plants/animals (tree roots/animals burrowing)
Chemical-Rock breakdown by chemical changes (Carbonation)
42
Sort the types of mass movement in order of speed.
Rockfall- radio but rare movements, produce debris slopes at the bottom of the cliff as the material diintergrates after collapse
Earth/mudflows- Mud which is saturated and falls down a slope due to gravity
Slides and Slumps- Soft rock fills with water and weight causes it to fall down the slope
Solifluction- Ground freezes and as the water melts, it also moves the soil
Soil creep- Raindrops splatter on the mud and slowly move it downslope
43
What are the hard and soft rock present at Swanage Bay?
Hard rock= Chalk
| Soft rock= Clay
44
What is a cove?
An example of a concordant coastline, the cracks of limestone break revealing clay, this continues to repeat itself.
45
How can a fault form in a headland?
Tectonic plates crumpling together
46
Difference between high and low energy coastlines
High energy= Long fetch, strong winds creating a large wave height as they are concentrated in a small area
Low energy= Low wave energy, wave spread out energy over a large area
British isles- high energy waves towards the west coast
47
Why did slumping occur at Holbeck Hall, scarborough and she did it occur?
Summer 1993
Long period without rainfall followed by a period of heavy rainfall, the water is able to penetrate through the sand/gravel making up the cliff, causing it to become saturated.
The rainfall reached 140mm in 2 Months before the slumping occurred, this acted as a lubricant, making the material more slippery and prone to collapse.
The rock material of the cliff was soft and therefore unable to support itself, containing a mixture of sandy/silty clay. This means the rock resistance is very weak as the fragments are free to slide over each other.
The pore water pressure build up- pressure caused the force between the particles and surface to reduce as it filled with water, therefore reducing the overall resistance
48
What is Longshore Drift?
The transportation of sediment along a stretch of coastline caused by waves approaching at an angle.
49
What is backwash?
The retreat of a wave back out to sea, vertically travels down, the path of the least energy 90 degrees to the beach due to gravity
50
Describe and explain the formation of headlands and Bays with an example.
Headlands and Bays form along a discordant coastline with the bands of hard and soft rock perpendicular to the coastline. Headlands are sections of hard rock which jut out into sea whereas, bays are inlets of softer rock, commonly producing a beach.
An example of this would be at Swanage bay, where an inlet of softer clay is more prone to erosion as opposed to the neighboring chalk and limestone (taking a longer time yo erode), as a result this causes differential rates of erosion means the coastline is shaped accordingly.
51
Explain the 4 stages of cove formation at Concordant coastlines.
Give an example.
Coves are formed when bands of rock are horizontal to the coastline. Facing the sea is a band of hard rock (Limestone at the perbeck coastline) and behind is the softer rock (clay). 1) The force of the waves create faults in the hard rock through hydraulic action and abrasion until the wave reach the softer rock behind. [Stair Hole] 2) The erosion processes of the waves erode the softer rock at a faster rate (differential erosion) leaving a circular cove with a narrow entrance to sea. The waves spread out and widen the cove due to diffraction. [Lulworth Cove] 3) Another cove forms beside through the same process and meets the original cove, although a section of rock is left free standing [Man-o-war]. In stage 4 the free standing rock continues to get undercut by erosional solution until it collapses leaving a larger cove.
An example would be Lulworth Cove on the Purbeck Coastline.
52
Draw a diagram of wave refraction
include:
- Headlands
- Bays
- Othogonals
- Wave crests
- Energy
- Convergence of wave energy
- Divergence of Wave energy
- Littoral currents
53
How do the following influence tidal range?
- Proximity of land
- Moons Orbit
- Narrow neck of water
Proximity of land: the larger the land mass, the greater the gravitational pull
Moons orbit: Not completely circular around the Earth, the further the distance between the moon and oceans, the weaker the gravitational pull
Narrow neck of water: Higher tidal range as the water is compact into a confined area
54
What is a swash?
Prevailing winds approach the beach and break at an angle, depositing sediment.
55
```
Sketch the per beck coastline Include:
Concordant/Discordant coastline
Actual rock types
Studland Bay
Old harry rocks
Durlston Head
Lulworth cove
Man-o-War
The foreland
```
```
see notes
Rock types are:
Chalk (hard)
Clay/Sands (soft)
Limestone (hard)
```
56
Draw a fully labelled diagram of a wave cut platform
see notes
57
Draw a labelled diagram showing the evolution of a headland
see notes
58
Explain the formation of a spit
LSD moves sediment along the coast , as the coast changes direction, sediment continues to accumulate at sea.
Continual accumulation leads to sediment breaching surface and producing a finger like protrusion out at sea
The dominant wind direction may lead to a curved end (recurved end)
As waves return to their original direction, several recurred ends are abandoned
Finally, the area behind the spit offers low energy as its sheltered from the wind, therefore sediment is deposited forming a salt marsh
River stops sediment from going all the way along the mouth
59
What is a beach?
A beach is a coastal landform caused by deposition consisting of pebbles/sand from high tide to low tide marks
60
What is the back shore?
Highest point on the beach
| Not usually entrenched by waves in the absence of a storm. Sand dunes, cliffs, golf courses and buildings are found here
61
What is the foreshore?
Located closest to the back shore
| Sediment transport takes place here due to the breaking of waves, much of the waves energy is dissipated
62
What is near shore?
Similar to foreshore but only functions at low tide. activities such as quarrying and coastal defences are here
63
What are berms?
Berms are a terrace on the backshore of a beach above the water level at high tide
Nearly horizontal portion of the beach formed by deposition of sediment from receeding waves marking high tides
64
What are ridges?
A wave swept/deposited ridge running parallel to the shoreline
65
What are runnels?
A through that runs parallel to the beach, often trapping water
66
What are cusps?
Semi-circular shaped depressions created as swash and backwash are strong and/or waves break directly on the beach
67
Why is the largest sediment found within the backshore?
The sediment is introduced by mass movement e.g. Rockfall from a cliff. As the waves energy dissipates further inshore, it's carrying capacity diminishes and its unable to lift heavier rocks back out to sea
68
Salt marshes, Stage 1:
Where do salt marshes form?
Under what conditions do they form?
What depositional features help create salt marshes?
What input is needed for a salt marsh to develop?
Where does this input come from?
```
Behind a spit
Form under low energy/sheltered environments
Spits help form salt marshes
A large input of sediment is needed
The input comes from a tidal flat/river
```
69
Salt marsh stage 2:
What is coastal accretion?
What are pioneer plants? Give an example
What are halophytic plants?
The accumulation of sediment/mud, allowing plants to grow
Plants which first colonise e.g. Cord grass/glass wort
Halophytic plats are those that love salt and are stay under water for a long period of time.
70
Salt marshes stage 3:
What happens as time goes on?
What helps trap more sediment? Give examples of plants that grow in this stage
As time goes on, more plants colonise higher up the salt marsh due to more sediment
Long blades of cord and roots help trap sediment
Examples of plants: marrow grass, red fescue
71
Salt Marshes stage 4:
When does this stage of the marsh get covered by sea water?
How much vegetation is now on the marsh?
Examples?
The marsh gets entrenched at highest high tides of this stage
Very large amount of vegetation
Examples: sea lavender
72
What is a sand dune?
A lard or resulting from deposition, a dune is a mound/ridge of sand or other sediment formed by the surrounding wind.
73
What is the first event of psammoseral succession?
The wind carries the sand up the beach (AEOLIAN), depositing it at an obstacle of detritus/vegetation
74
What is an example of a sand dune?
Stud land bay, just North of Swannage
75
What are the first dunes to form and give information
Embryo dunes
They may disappear as quickly as formed but some are colonised by plants and stabilised
No more than 1 meter in height
Soil is loosely bounded due to the early stages, little humus and moisture
pH slightly over 8
Pioneer plants such as Lyme grass forms
76
What are the 2nd dunes to form and give information
Foredunes (yellow dunes)
5 meters in height
More roots and humus mean that the sediment is bound more strongly
Marram grass, Lyme grass
These plants are drought resistant and can withstand sand burial- halophytic plants
Marram grass adds humus to the sand adding moisture to the plants as they decay making the sediment more fertile
pH 7.5
Berms feature here
77
What are the 3rd dunes to form and give information
Grey dunes- more stable
8-10 meters in height
Soils further inland receive more organic material and have a high water retention
pH 6.5-7 with less influence of saline water
Plant types: lichens, mosses and flowering plants
78
What is the final stage of psamoseral succession?
Wasting dunes with blowouts (mature dune)
6-8 meters in height (reduction)
Being so far inland, only little quantities of sediment/sand are able to reach the mature dune
Dunes develop soils able to support trees and shrubs e.g. Oak trees
79
What is a wave?
Energy flowing through water
81
How would a spit become a bar?
When the spit travels across the sea through LSD until it joins a neighbouring headland, forming a lagoon behind
82
What is the difference between isostacy and eustacy?
Isostacy is the change in land level
| Eustacy is the change in sea level
83
Why does land rise or sink? Isostacy and eustacy
Isostatic rebound occurs as a result of an ice age. The build up of ice on land has caused an increasing weight to form reducing the level of land [negative isostacy], causing the sea level to rise [positive eustacy] (compression). As the ice melts at the end of an ice age, the land begins to rise again [positive isostacy] and sea level falls [negative eustacy] (decompression). Isostactic rebound is a very slow process and still taking place from the last ice age
In 20,000 years, the sea level has risen by 120mm
84
What is thermal expansion?
The influence of heat causes the water particles in the sea to expand, increasing their size and the sea level
85
What are fjords?
| Give an Example
Submerged glacial valley
Steep-cliff like sides
Formed when glaciers are eroded below sea level (glacial retreat)
Previous river forms a V-shaped valley, fills with ice which erodes and expands valley cracks
Norway
86
What are the factors of sea level change?
-global average temperatures have risen by 0.8 degrees C since 1880
Rapid melting of ice glaciers (positive eustacy)
Thermal expansion
Delivery of sediment into ocean bases
Tectonic movements
87
What is a ria?
| Give an Example
A V shaped valley that has been flooded by positive eustacy
Caused by a global rise in temperatures +0.8 degrees C since 1880 resulting in thermal expansion (gaps between water particles expand)
E.g. Poole Harbour
Cross profile= gentle + long, wide and deep at the mouth
Poole harbour = 48c, depth
88
How is a raised beach formed?
| Give an example
Emergent landforms
Positive isostacy during isostatic rebound
As the sediment on the beach rises, the lower section experiences marine erosion creating a small secondary cliff, therefore the former cliff at the top is no longer undercut by the sea, becoming clothed in bushes and shrubs
'Staircase effect'
E.g. Scotland
Apparent sediment heights are: 8m, 15m and 30 m above sea level
88
Economic uses of rias
Deep sheltered natural harbours, access for large vessels
Attractive scenery , habitats
Tourism
88
What is the prediction for future sea level rise? (By 2090)
Sea level will rise by 0.3-0.5m by 2090
| The rate has increased from 1/2mm a year to 4/5mm a year
89
Impacts of sea level rise on farmers?
Rising sea levels means that more sea water is able to mix and contaminate the freshwater creating silt and clay particles through flocculation, meaning farmers have less water to use
90
What is the effect of sea level rise on insurance?
Insurance costs nearer the coastline are high due to the risk of flooding, an effective way of encouraging people out of the area
91
Why does isostatic rebound occur on the west coast?
The area where the greatest weight of ice was in place before it melted doe to a rise in temperature
