Coasts Flashcards
1
Q
how can coasts be classified?
A
- formation processes (e.g. primary coasts are formed by land based processes such as river deposition whilst secondary coasts are formed by marine based processes such as wave action)
- balance between erosion and deposition creation varying landforms
- sea level changes produce submerging or emergent coastlines
- level of energy (high or low)
- geology (rock type, lithology and structure) this can influence if it is discordant of concordant or even if its rocky cliffed plains or coastal (sandy/estuarine) planes.
2
Q
what is the order of the littoral zone?
A
- (going out into the sea) back shore, foreshore, nearshore, offshore
- backshore and foreshore is where the greatest human activity occurs and so they experience the most change
3
Q
what are the inputs (external factors) to coastal landscapes?
A
- marine (waves, tides and storm surges)
- atmospheric (weather, climate)
- terrestrial (geology, tectonics)
- people (economic activity and coastal management)
4
Q
what are the processes to coastal landscapes?
A
- weathering
- mass movement
- erosion
- transportation
- deposition
5
Q
what are the outputs (outcomes) of coastal landscapes?
A
- erosional landforms
- depositional landforms
- different types of coasts
6
Q
what are submerging and emergent coastlines?
A
- emergent coastlines are those which have risen relative to the sea level
- submergent coastlines are those which have dropped and become drowned or flooded by the sea
7
Q
geological structure
A
how the rock is arranged on a macro scale, it looks at the arrangement of different rock types in relation to each other
8
Q
how do headlands and bay form at discordant coastlines?
A
- bands of alternating rock strata facing perpendicular to the coast
- wave action erodes the less resistant rock quicker due to hydraulic action and abrasion to produce bays. this becomes a sheltered low energy environment where wave energy is dissipated leading to deposition and beaches
- more resistant rock is less easily eroded so is left sticking out as a headland.
- this causes incoming waves to refract as water becomes shallower (wave refraction with a pincer like movement)
- wave energy is now concentration on the headlands, with waves becoming higher and steeper increasing the erosive power on the headland
- they will then eventually be eroded into a stack/stump
- in theory this may mean the process starts again as the coastline evens out
9
Q
what are the types of tidal change?
A
- microtidal coasts (range of 0-4m)
- mesotidal coasts (range of 2-4m)
- macrotidal coasts (range greater than 4m)
10
Q
what are the different wave energy environments?
A
- low energy sheltered coasts have limited fetches and low and speeds resulting in small waves
- high energy exposed coasts often face prevailing winds with long fetches creating powerful waves.
11
Q
how do coves form?
A
- at concordant coastlines rock strata is arranged in alternating bands parallel to the coastline
- initially, the outer layer of the coastline was a band of more resistant rock such as limestone
- as wave action was continually concentrated on the rock it weakened leading to faults and joints through processes like hydraulic action and abrasion
- as wave action forces it way through this more resistant rock which is easier to erode (e.g. clay) there is rapid erosion in all directions forming a cove.
- eventually erosion slows as more resistant rock layers have been reached
- this sheltered environment allows for deposition and the creation of beaches via constructive waves
12
Q
how do Dalmatian coasts form?
A
- type of submerging coastline
- tectonic activity folded limestone layers so that ridges (anticlines) and valleys (synclines) formed parallel to the coast
- sea levels rose following the end of the ice age and drowned the valleys (submerging coast)
- the ridges remain as islands running parallel to the coastline
- the best example of this is the Creation Dalmatian coast
- ice on land that melts causes sea levels to rise but ice in the water that melts doesn’t
13
Q
how do half coasts form?
A
- concordant coastlines (e.g. the south of the Baltic Sea)
- they are long sediment ridges (sand and mud) topped by sand dunes that run parallel to the coast
- the build up of these sand dunes have created lagoons (haffs) between them and the shore
- form in low energy environments due to deposition by onshore winds and low energy constructive waves
14
Q
meso structures
A
smaller stretches of cliff and their layers/ lithology
15
Q
micro structures
A
one cliff profile and its features
16
Q
coastal morphology
A
the shape and form of a coastal landscape and their features
17
Q
bedding planes
A
natural breaks in the strata caused by gaps in time during periods of rock formation
18
Q
folds
A
formed by pressure from tectonic activity which causes rocks to buckle and crumple
19
Q
dip
A
the angle at which rock strata lies (horizontal or vertical, island or outland)
20
Q
joints and faults
A
- joints (vertical cracks) are fractures caused either by contraction as sediment drys out or by earth movements during uplift
- faults form when the pressure or stress to which a rock is subjected exceeds its internal strength, it then slips or moves along fault planes
21
Q
what happens in rock dips towards the sea?
A
- if a rock layer dips towards the sea, it will be possible for blocks of rock to slide under there influence of gravity (mass movement). the steeper it is the softer the bade of the profile is and so this speeds up recession
- slight not so steep dipping, joints are often opened by weathering and pressure release
- if rock dips inland stable cliff profiles are creates yet if there are well developed faults and joints perpendicular to bedding planes they can act as slide planes
22
Q
what is the influence of horizontal strata?
A
this can lead to layers of differing resistances and therefore protrusions and indentations as well as small features such as caves, blowholes and geos
-if the layers of less resistant rock are at the base of the cliff it is likely to lead to caves and an overhand yet if it is at the top more so indentations due to weathering.
23
Q
how does mineral composition of the rock (micro) affect the rate of recession?
A
- in limestone there are reactive minerals such as calcite which are easily broken down by chemical weathering speeding up erosion. it is soluble in rainwater becoming dilute carbonic acid after having absorbed carbon dioxide from the air. this can create small pits and pinnacle
- yet in geology like sandstone there are more inert minerals such as quartz which weather and erode more slowly
- both are sedimentary so have the same inadvertent resistance yet other factors affect rate of recession
- this can make is subject to weathering such as carbonation or hydrolysis
24
Q
lithology
A
refers to the physical characteristics of the rock. this varies for igneous, sedimentary, metamorphic and unconsolidated rock.
25
Q
igneous rock
A
- crystalline structure of interlocking crystals
- this makes sediment better connected with strong chemical bonding and therefore is less permeable and susceptible to erosion
- they have few points of weakness
- tend to form rocky coastlines with steep profile cliffs that erode very slowly
- rocks like granite in ‘Lands End’ Cornwall
- recede slowest at 0.1-0.3 cm/yr
26
Q
metamorphic rock
A
- formed boy the recrystallisation of sedimentary and igneous rock under immense heat and pressure
- resistant due to crystalline structure yet less resistant than igneous as crystals are often orientated in the same direction (foliation) making them weaker than the interlocking crystals of igneous rock
- often heavily folded and faulted
- often recede slowly at about 0.5-1cm per year
27
Q
resistant sedimentary rock
A
- strata is clastic and so made up of unconsolidated sediment particles making them subject to fissures
- strata is more porous as particles are less tightly compacted leading to air spaces between layers
- this means geology becomes more easily saturated lessening its ability to retain its structure
- limestone and chalk
28
Q
less resistant sedimentary rock
A
- same structure as resistant sedimentary rock but with further reduced stability due to unconsolidated sediment which hasn’t been cemented together by pressure
- e.g. boulder clay
29
Q
differential erosion
A
different sections of a cliff eroding at different rates
30
Q
how can the arrangement of rocks lead to differential erosion?
A
- if there is a porous rock above an impermeable rock water collects in the upper layer saturating it and usually leading to slumping and mass movement
- resistant rock creates a bench feature at the base leading to surface run off
31
Q
what are pioneer species?
A
- marram grass (xerophyte) in a sand dune
- glasswort and cord grass (halophyte, resistant to salt) in a salt marsh
- they colonise an area meaning a plat community develops overtime helping to stabilise the cliff
- adds organic matter to the sand helping soil to develop which is less vulnerable to wind erosion
32
Q
what does marram grass do?
A
- colonise the bare surface (sand) and reduce wind and water erosion
- long roots up to 3m long but also creeping stems called Rhizomes extend sideways below the surface creating a ladder like structure. This helps to bind sediment together to stop it being washed or blown away
- one the surface wind speeds are reduced as the vegetation acts like a wind break preventing sand from being blown away
- thrives in arid conditions on free draining sand preventing unnecessary water loss (e.g. waxy leaves are rolled inwards to prevent surface evaporation)
33
Q
what does glasswort do?
A
- helps to trap and secure muds and slits to develop salt marshes
- when submerged plants provide a protective layer so that sediment isn’t directly exposed to action from the tide
- succluent stem to store water
- adds organic matter helping to develop soil which is less vulnerable to erosion
34
Q
what is succession?
A
the changing structure of a plant community overtime as an initially base surface is colonised by pioneer species and continues to develop
-they typically occur at coastlines where deposition is taking place in low energy sheltered environments
35
Q
first four stages of sand dune succession
A
- psammosphere
- there is plentiful supply of sand, a large areas for sand to dry out and onshore winds that blow sand landwards. sand accumulates to form an embryo dune
- pioneer species like marram grass colonise the dune stabilising it and helping it to trap more sand
- a fore dune develops when enough sand has been trapped and the dune becomes more stable
- with soil now developed on the dune, it becomes a yellow dune. this is permanent and the conditions are suited to a greater variety of species including gorse and heather
36
Q
last four stages of sand dune succession
A
- now an established dune will become more vegetated by marram grass. it provides dead organise matter to the sand and soil start to develop, improving conditions for other species. this is now a grey dune
- between dunes dune slack develops. wind erosion can deepen them and they ma be water logged in high tide conditions
- further inland is the climax community mature dunes. Here the soil is fully developed, the dune is fully stabilised and species diversity is at its highest. (e.g. trees can grow here)
37
Q
first three stages of plant succession on a salt marsh
A
- form in low energy environments on estuaries, sheltered bays and behind spits
- river brings fine muds and slits and tidal conditions bring other sediments, all of which are deposited
- tiny sediment particles combine in a process called flocculation which increases deposition due to the weight. the area is colonised by algae which have to survive being submerged twice a day
38
Q
last three stages of plant succession on a salt marsh
A
- the vegetation helps to trap more sediment and builds the height of the marsh, making more suitable for other species
- sediment becomes more stable and vegetation adds dead organic matter, making conditions better for more species to grow. conditions become less salty as the marsh is now only occasionally submerged
- at the inland end of the marsh, soil has developed and the climax community is established
39
Q
structure of a salt marsh
A
- upper part is raised above regular inundation and may be dissected by small channels and creeks.
- this can help sustain less salt tolerant plants
- the lower part of the salt marsh is under water for longer periods and only hardy halophytic plants grow here
40
Q
what are rocky coastlines and costal plains
A
Rocky coasts (high and low relief) result from resistant geology (to the erosive forces of sea, rain and wind), often in a high-energy environment -whereas coastal plain landscapes (sandy and estuarine coasts) are found near areas of low relief and result from supply of sediment from direct terrestrial and offshore sources, often in a low-energy environment
41
Q
coastal plains
A
- Coastal plain landscapes are relatively flat, low relief areas adjacent to the sea.
- They often contain freshwater wetlands and marshes due to the poor drainage of the flat landscape.
- Their littoral zone is composed of sand dunes, beaches, mud flats and salt marshes
42
Q
examples of coastal plains
A
- sandy coasts, composed of sands, shingles and cobbles.
- estuarine (alluvial) coasts composed of mud (clays and silts
43
Q
movement of waves
A
- the force of the breaking wave pushes up the beach creating a swash at 45 degrees
- after reaching its furthest point on the beach, the wave runs back down at 90 degrees due to gravity. this is the backwash
44
Q
destructive waves
A
- larger amplitude, smaller wavelength
- swash is bigger than backwash
- plunging breaker
- causes cliff retreat, flat beaches and degradation
- 13/15 per minute
- long fetch
- high energy
45
Q
constructive waves
A
- smaller amplitude, longer wavelength
- backwash is bigger than swash
- spilling breaker
- steep beaches, scoured beaches, steep beaches
- aggrades beaches
- swash builds up the beach creating berms
- low wave energy
- short fetch
46
Q
swell waves
A
- some waves originate in mid-ocean and maintain their energy for thousands of miles
- these mid ocean waves appear as larger waves amongst smaller locally degenerated waves (swell waves)
- swell is an ocean wave system not raised by the local wind blowing at the time of observation but rather raised some distance away. they continue to travel in the direction of the winds that originally formed
- may travel for thousands of miles before dying down
- as it advances, its crest becomes flattened and rounded, its surface smooth
- they are usually characterised by a relatively long and regular period
47
Q
why are coastal landscapes different?
A
- east and west Britain have very different landscapes (rocky cliffed coasts v coastal plains)
- the affect of geological structure on a macro scale on coastal landforms (concordant and discordant coastlines)
- lithology
- vegetation
48
Q
how are waves formed?
A
- as wind blows over the ocean, fiction occurs and energy is transferred to the water creating a wave
- the stronger the wind, the greater the wave power and size
- wind strength and wave strength and controlled by fetch (the distance over which the wind has blown)
- Cornwall and Devon face the longest fetches (Atlantic Ocean)
49
Q
how do waves move across the ocean?
A
- waves move across the open ocean in a circular motion as ocean swell
- as they reach shallower water, the fictional drag on the seabed slows down the base of the wave causing the wavelength to reduce and the wave height to increase
- eventually the wave breaks as the top of the wave is moving faster than the base.
- the circular movement of the wave acts in an increasingly elliptical orbit
50
Q
types of erosion
A
-abrasion
-attrition
-hydraulic action
solution
-during winter marine erosion is often at its highest as winter storms produce more destructive waves
51
Q
hydraulic action
A
- air trapped in cracks and fissures is compressed by the force of the waves crashing against the cliff face. when the wave retreats, pressure is released explosively (cavitation)
- this can widen cracks and dislodge particles/ rocks
52
Q
how do headlands and bays form?
A
- bands of less resistant rock are more easily eroded and so form bays
- the chalk headland absorbs some of the wave energy causing them to refract around its curvature in a pincer like movement, growing in height and steepness
- this means wave energy becomes concentrated on certain parts of the cliff and fissures are attacked through abrasion and hydraulic action (caviation)
- this widens cracks into crevices and caves
- this continues in particular during winter storms
- these can be eroded to form blowholes and eventually when overlying rock becomes unstable due to continual undercutting and arch and then stack/stump
53
Q
how do blowholes form?
A
- caves can partially collapse to produce a hole in the cliff
- waves hitting the base of the cliff can be force through and spout water at the top
- this can cause the top of the cave to collapse
- also known s marine geysers
54
Q
what do cliffs dominated by marine erosion form?
A
-active undercutting, steep faces and limited cliff base debris
55
Q
what do cliffs dominated by sub Ariel processes form?
A
-leads to curved slop profiles, lower angle faces and accumulated debris
56
Q
how to form wave cut notches and platforms?
A
- wave action at the base of the cliff means that hydraulic action and abrasion undercuts the cliff to form a wave cut notch
- this continues and the cliff above the notch is left unsupported and eventually collapses
- the cliff retreats leaving a wave cut platform which is now the base of the cliff left. This maintains a steep cliff profile
- happens when there is less resistant rock at the base of the cliff
- e.g. dancing ledge purbeck Dorset
57
Q
beach morphology
A
beach form and shape
- beaches consists of loose material and their morphology alters as wave change
- this leads to seasonal variations that create summer and winter gradients (e.g. sediment is dragged offshore by destructive waves during winter and returned by constructive waves in summer)
58
Q
how does material on a beach vary due to constructive waves?
A
varies in size and type depending on the distance from the shoreline
- beach profiles are steeper in summer when constructive waves are more common. this means waves energy dissipates and deposits over a wider area (weakens backwash)
- the swash of a constructive wave deposits larger material at the top of a beach creating a berm
- as the berm builds up the backwash becomes weaker (draining by percolation rather than down the beach), only having enough energy to move smaller material. this means sediment becomes finer closer to the shoreline
59
Q
how does beach morphology vary due to destructive waves?
A
- in winter waves occur at a higher frequency
- berms are eroded by plunging waves and high energy swash
- strong backwash transports sediment offshore (depositing it as offshore bars)
- sometimes the backwash exerts a current known as a rip of undertow, dragging sediment as the next wave arrives over the top
60
Q
formations of beach morphology
A
- storm beaches result from high energy deposition of very coarse sediment during the most severe storms
- berms typically of shingle/gravel result from summer swell wave deposition
- the middle area of the beach is mostly sand but the sand is coarser where berms/ridges have been deposited than in channels and runnels
- offshore ridges/bar are formed by destructive wave erosion and subsequent deposition of sand and shingle offshore
61
Q
how is sediment transported
A
- sediment is constantly moving at the coast due to waves, tides and currents
- the main process is LSD
- sediment is transported in the same way as in the river (traction, salutation, suspension, solution)
62
Q
how does LSD transport sediment
A
- the prevailing wind and therefore the waves approach the coastline at an angle (SW)
- this means that the swash moves sediment up the beach at the same angle but backwash moves sediment straight down the beach under gravity
- waves carry large pebbles by rolling them (traction) small pebbles bouncing them (saltation) and finer particles line sand and silt by suspension
- as the process continues sediment is moved east and a drift aligned beach will form
63
Q
what happens to sediment as it is transported?
A
-sediment will experience attrition and abrasion during it s transportation causing ti to become smaller in size and smoother in surface
64
Q
swash aligned beaches
A
- waves approach the coastline perpendicular to the beach
- the swash and backwash move sediment up and down the beach forming a stable, straight beach
65
Q
drift aligned beaches
A
- waves approach at an angle and sediment is moved along by longshore drift
- this forms wide beaches but uneven in sediment
66
Q
sources of sediment
A
- rivers
- constructive waves
- cliffs
- LSD from one area to another through transportation
67
Q
why does deposition occur?
A
- deposition due to gravity settling occurs in low energy coastal environments. course dropped first, finer further away
- flocculation helps the process of depositing fine flay particles. this is because they are very light and so by clumping together in salt water they become heavier
- sediment is stabilised by vegetation (sand dune and salt marsh succession)
68
Q
how do spits form?
A
- sediment is moved along the coast by LSD
- when there is a change in the direction of the coastline (e.g. the river mouth) longshore drift continues
- the waves loose energy in the slacker water behind the headland and the largest sediment is deposited here first in the same direction (gravity settling)
- as deposition continues, a spit is formed.
- finer material is carried further along the spit before being deposited as its lighter. flocculation helps with finer clay
- the spit grows and may form a hook if wind direction changes
- in the slack water behind a spit move deposition takes place and a salt marsh may develop with halophytic plants helping to trap sediment and allowing new land to develop.
69
Q
why don’t spits form across an estuary?
A
- spits don’t grow across an estuary as the velocity of the river current prevents deposition
- in areas where there are no river currents to prevent LSD deposition in a straight line the spit can join with land to form a bar, damming water behind it forming a lagoon
- e.g. slapton sands, devon
70
Q
how do Tombolos form?
A
- an island joined to the mainland
- it develops when deposition occurs behind and island due to the low energy sheltered environment it creates
- eventually the island will connect to the mainland
- these can also form by long shore drift and a bar forming or if there is a change in wind direction
- e.g. st Michaels Mount Cornwall
