coasts Flashcards
what is a system?
a set of interrelated objects comprising of components (stores) and processes (links) that are connected together to form a working unit or unified whole
types of energy in a coastal landscape system?
kinetic
potential
thermal
are coastal landscape systems open or closed?
what does this mean w/ example
OPEN
energy and matter can be transferred form neighbouring systems as an input and transferred to neighbouring systems as an output
e.g. input of fluvial sediment from river
inputs to a coastal landscape system
fluvial (river) sediment
KE from wind and waves
thermal energy from heat of sun
marine sediment deposited by the waves
weathered material from cliffs
outputs of coastal landscape systems
evaporation of water
marine sediment eroded by waves
sediment eroded/taken away by wind
stores of coastal landscape systems
beach
sand dunes
offshore bars
flows/transfers of coastal landscape systems
movement of sediment along beach by LSD
wave movement on and off beach
wind blowing sediment
what is equilibrium?
a long-term balance between inputs and outputs in a system
example of equilibrium on a beach
happens when rate at which sediment is being added to the beach is equal to the rate at which sediment is being removed from the beach, so the beach remains the same size
what happens when equilibrium is disturbed?
what is this known as?
system undergoes self-regulation and changes its form in order to restore the equilibrium
this is known as dynamic equilibrium, as the stem produces its own response to the disturbance; an example of negative feedback
what is negative feedback?
an automatic response to a change in a system that restores equilibrium
sediment cell definition
a stretch of coastline and its associated nearshore area within which the movement of coarse sediment, sand and shingle is largely self-contained
is a sediment cell an open or closed system?
what does this suggest?
CLOSED
no sediment is transferred between cells
how many sediment cells are in England and Wales
boundaries of these?
11
determined by topography and shape of coastline: large physical features e.g. lands end act as natural barriers that prevent transfer of sediment
what affects the shape of coastlines?
geology
waves
wind
ocean currents
tides
are sediment cells completely closed systems? why?
unlikely: variations in wind direction and presence of tidal currents mean it is inevitable that some sediment is transferred between neighbouring cells. input fluvial sediment too
depends on scale, since the major 11 cells contain many smaller sub-cells
swell waves:
formed where?
wavelength/wave period?
formed in open oceans and can travel huge distances from where they are generated.
tend to have long wavelength and a wave period of up to 20 seconds
storm waves:
formed where?
wavelength, height and wave period?
locally generated
typically have shorter wavelength, greater height and shorter wave period
constructive waves charcteristics
low-energy wave
strong swash travels far up gradually sloping beach
lower height and frequency
pushes sand up shoreline, building up material and increasing the gradient
longer wavelength
summer months
destructive waves characteristics
higher energy wave
stronger backwash- pulling material away from shoreline by erosion
greater height and frequency
removes material from top of beach and decreases gradient
moves sand to offshore zone
shorter wavelength
winter months
significance of waves affecting coastal landscapes?
controls whether deposition/erosion dominate
changes diurnally and seasonally
small scale
controlled by wind
aeolian effects on coastal landscapes
wave energy is produced through frictional drag of wind across ocean’s surface
higher windspeed and lower fetch lead to larger waves which possess more energy
onshore winds drive waves to the coast
wind blowing at oblique angle leads to waves approaching obliquely, leading to LSD
wind is a moving force so carries out erosion, transportation and deposition
significance in wind affecting coastal landforms?
not that significant
key=wind determines waves
significance changed form day to day
in exposed places, wind has more significance than in sheltered places
small scale
tidal impacts on coastline
generated by gravitational pull of the moon
tidal ranges are low in enclosed areas of sea (e.g. mediterranean)
smaller tidal ranges lead to more erosion bc waves are hammering smaller area more often and with more force
in areas with larger tidal ranges, deposition is dominant, so forms estuaries (e.g. Severn Estuary has large 14m tidal range bc water is funnelled)
significance of tidal ranges on coastal landscapes?
account for lots of erosion over long time period
determine whether erosive/ depositional landforms dominate
larger scale
ocean currents impact on coastlines?
generated by Earth’s rotation and convection, and transfer heat energy
change temp of water and air so affect weathering processes (increase sediment input)
also affect input of sediment to a coastal system (dep. landforms/ sed. budget/ equilibrium affected)
rip current caused by tidal motion or waves breaking and right angles to shore can form cusps (small scale)
significance of ocean currents on coastlines?
large scale
esp. significant in Western facing coastal landscapes bc driven by onshore winds
cold ocean currents have less effect on landscapes bc they are driven by offshore winds
affects sub-aerial processes, but not than significant
what is lithology?
physical and chemical composition of rocks
weak lithology with example
e.g. clay
little resistance to erosion, weathering and mass movements
weak chemical bonds between rock’s particles
strong lithology with example
e.g. basalt
highly resistant, therefore more likely to form cliffs and headlands
strong chemical bonds between rock’s particles
mineral composition of rocks and chemical weathering
rocks e.g. chalk and limestone have mineral composition which is soluble in weak acids so is easily weathered chemically e.g. by carbonation
subtopics of geology structure
joints, cracks, faults
rock permeability
discordant vs concordant
angle of dip
what are joints, faults and cracks and how do they affect the shape of a coastline?
joints= fractures in rocks created without displacement
some rocks e.g. limestone and chalk form with many joints and cracks, so erode at faster rates. this is apparent during differential erosion
rocks with faults and cracks are easier for waves to erode because the wave energy can exploit these weaker points in the rock so lead to rapid erosion
e.g. evolution of cave to stump
what is rock permeability and how does it affect the shape of a coastline?
primary permeability= in porous rock e.g. chalk, tiny air spaces separate mineral particles. these pores can absorb and store water
secondary permeability= Carboniferous limestone is permeable because water seeps into it because of its joints, which are enlarged by solution
permeable rocks are less resistant to weathering
how does discordance affect the shape of a coastline?
discordant= when rock strata lie at right angles to the coastline discordant planforms are created, which tend to have an alternating pattern of indented bays and projecting headlands due to the alternating bands of soft and hard rock
how does concordance affect the shape of a coastline?
concordant= when rock starts that is uniform or runs parallel to coast
tend to produce straight coastlines or small bays
some have long narrow, islands parallel to the coastline
how are angles of dip formed?
what do they affect?
tectonic processes
strength and steepness of cliff an likelihood of slipping. stronger=steeper
describe each angle of dip.
HORIZONTAL= near-vertical profile with notches where rock is less resistant, so is exposed at the wave cut platform
SEAWARD DIP=areas of overhanging rock, vulnerable to landslides, rock slides and sloping
LANDWARD DIP= steep 70-80 degrees, very stable cliff, less rock falls
significance of geology impacting coastal landscapes?
very significant on small scale
determines shape of coastline and the landforms present
long term
3 main sources of sediment
terrestrial (from the land)
offshore (from the sea)
human (deliberate)
examples of terrestrial sediment
fluvial (rivers)
cliffs
examples of offshore sediment
offshore bars
ocean currents
longshore drift
examples of human sediment sources
beach nourishment/replenishment
rain bowing
(adding sediment to beaches that are in sediment deficit)
terrestrial sediment source: fluvial
where?
when?
how much?
rivers are major sources of sediment into the coastal sediment budget (particularly true of coasts with a steep gradient where rivers directly deposit their material at the coast)
sediment delivery to the shoreline can be irregular/intermittent, mostly occurring during floods
in some locations, 80% of sediment is fluvial
terrestrial sediment source:
cliffs
how and when?
how much?
origin of sediment is the erosion of inland areas by water, wind, ice and sub-aerial weathering
wave erosion is also the source of lots of sediment
cliff erosion is increased by rising sea levels and is amplified by storm surges (can contribute 70% of overall material; although typically less), can be large rocks if directly from collapse of cliffs
offshore sediment source:
wave transport
constructive waves bring sediment to the shore from offshore locations and deposit it (marine deposition), adding to the sediment budget. tides and current do the same.
terrestrial sediment source:
aeolian processes
what type of sediment and where?
wind also blows sediment from other locations, including exposed sand bars, dunes and beaches elsewhere along the coast. this aeolian material is generally fine sand, as wind has less energy than water and so cannot transport very large particles
terrestrial sediment source: longshore drift
supplies sediment from one coastal area by moving it along the coast to adjacent areas
human sediment source: beach nourishment and rainbowing
how?
why?
has been adopted all over the world in order to preserve and protect the coastal environment
sediment can be brought in by lorry and dumped on the beach before being spread out by bulldozers.
alternatively, sand and water can be pumped onshore by pipeline from offshore sources. low bunds hold the mixture in place while the water drains away, leaving the sediment behind
how to work out if the sediment budget is in surplus, deficit or equilibrium
wind, waves and LSD can remove sediment from the budget. by subtracting the amount of sediment lost from the sediment gained, it can be determined if the oddment budget is in equilibrium, surplus or deficit
what could affect the relative significance of different sources of sediment?
resistance of coastal rock types & fluvial sediment (geology)
how sheltered/exposed the beach is and its geographical location
wind strength
presence of a river
wave strength
key processes in a costal environment with an example
mass movement events e.g. landslides
sub-aerial weathering e.g. freeze thaw
transportation e.g. LSD
deposition e.g. waves lose energy and drop material
erosion e.g. abrasion
flows of energy in a coastal landscape
kinetic energy of wind and waves
thermal energy e.g. sun dries out sand so its easier to transport and drives currents&winds
GPE causes mass movement and backwash
flows of material in a coastal landscape
aeolian flows can move sediment from beach to sand dune
fluvial provide lots of sediment so depositional features often dominant around river mouths
LSD moves sediment along beach and between beaches
mass movement events e.g. rockfalls and landslides
what percentage of sediment comes from rivers in a coastal landscape?
70-80%
direction of LSD in the UK
N to S in NE UK
W to E in SW UK
difference between erosion and sub aerial weathering?
erosion= wearing away and/or removal of rock/other material by a moving force
sub-aerial weathering= a collective term for weathering(breakdown of material in situ) & mass movement processes
under what 5 conditions does deposition occur?
when rate of sediment accumulation exceeds the rate of removal
when waves slow down immediately after breaking
at top of swash, where water is no longer moving for a brief moment
during backwash when water percolates into the beach material
in low-energy environments, sheltered from wind and waves e.g. estuaries
what is the settling velocity?
the velocity at which sediment particles are deposited
what is a mass movement event?
occurs when forces acting downwards on slope material (mainly resultant force of gravity) exceed the forces trying to keep the material on the slope (predominantly friction)
what are the most significant mass movement events in a a coastal landscape?
those acting on cliffs
lead to addition of material to sediment budget by transferring rocks & regolith onto shore below
what is flocculation?
a process buy which salt causes the aggregation of minute particles (e.g. clay) into larger masses that are too heavy to remain suspended in the water, so are deposited
where does flocculation occur?
where fresh and salt water occur e.g. river mouths/ estuaries
freeze thaw weathering description
water enters cracks/joints and expands by 10% when it freezes
in confined spaces this exerts pressure on the rock, causing it to split/ pieces break off
even occurs in resistant rocks
solution weathering description
some salts are soluble in water. other minerals (e.g. iron) are only soluble in very acidic water (pH3)
any process by which a mineral dissolves in water is known as solution, although mineral specific processes (e.g. carbonation) can be identified
tree root weathering description
tree roots grow into cracks or joints in rocks and exert pressure outward
(operates in a similar way and with similar effects to freeze-thaw)
when trees topple, their root can also exert leverage on the rock/soil, bringing them to the surface and exposing them to further weathering
burrowing animals may also have the same effect
particularly significant on cliff tops/ cliff faces
abrasion description
when waves armed with rock particles scour the coastline; rock rubbing against rock
attrition description
when rock particles, transported by wave action, collide with each other and with coastal rocks and progressively become worn away
they become smoother, smaller and rounder, eventually producing sand
hydraulic action description
when waves break against a cliff face, and air and water trapped in cracks and crevices becomes compressed.
as the wave recedes, the pressure is released the air and water suddenly expands and the crack is widened
pounding description
when the mass of a breaking wave exerts pressure on the rock, causing it to weaken.
forces as much as 30 tonnes per m^2 can be exerted by high-energy waves
force exerted by high-energy waves?
as much as 30 tonnes per m^2
corrosion/ solution (erosion) description
involves dissolving minerals (e.g. MgCO3) in coastal rock.
however, because pH of seawater is around 7 or 8, this process is usually less significant (unless water is locally polluted or acidic. even then, only coastal rocks containing significant amounts of soluble materials are likely to be affected by this)
suspension description
small particles of sand, silt and clay can be carried by currents (accounts for brown/muddy appearance of some sea water)
larger particles can also be carried in this way (esp. during storm events)
traction description
largest particles in the loads may be pushed along the sea floor by the force of the flow
(can be called rolling but movement is seldom continuous)
large boulders may undertake a partial rotation before coming to rest again
saltation description
a series of irregular movements of material which is too heavy to be carried in suspension continuously
turbulent flow may enable sand-sized particles to be picked up (entrained) and carried for a short distance then dropped back down again
similarly, other particles may be dislodged by the impact, allowing water to get beneath them and cause entrainment.
solution transportation description
minerals that have been dissolved into the mass of moving water.
this type of load is invisible and the minerals will remain in solution until water is evaporated and they precipitate out of the solution
what are aeolian processes?
erosional, transportation and depositional processes by the wind
aeolian erosion description
wind picks up sand particles and moves them by deflation.
40km/h
erosive force increases with wind velocity
attrition is more effective than in water because there is no protection
aeolian transportation description
particles are entrained, carried, saltated or moved by surface creep.
40km/h
smallest grains are carried in suspension
aeolian deposition description
material is deposited when wind speed falls, usually due to surface friction inland where friction increases due to vegetation and surface irregularities-> forms sand dunes
what sort of sand is transported most easily by aeolian processes?
dry sand bc its much easier for wind to pick up than wet sand bc moisture increases cohesion between particles so they stick together
smaller grains can be carried in suspension, but most cannot so this limits erosion to about 1m high (limits effects on rocky cliffs/coastlines)
when does longshore drift occur?
describe process of LSD
when waves approach the coast at an angle due to the direction of the prevailing wind
when the waves have broken the swash carries particles diagonally up the beach
under the influence of gravity, the backwash moves them perpendicularly back down the beach. if this movement is repeated, the net result is a movement of material down the beach
also leads to attrition of beach sediment so particles become smaller w/ increasing distance along the beach
rockfall description
where are they common?
what are they triggered by?
sudden collapse or breaking away of individual rock fragments or a block of rock at a cliff face. these rocks fall or bounce down slope to form scree (temp. store)
steep/vertical cliffs in heavily jointed & resistant rock
mechanical weathering e.g. freeze-thaw or an earthquake
mudflow description
what type of bedrock?
sudden and fast-flowing earth and mud flowing downhill, often after heavy rainfall. water gets trapped in rock, increasing pore water pressure, so rock particles are forced apart and slope failure is caused
unconsolidated/weak bedrock e.g. clay
what is pore water pressure?
a form of energy within the slope system
is v important factor in determining slope instability
landslide description
what are they often triggered by?
a block of rock moving v. rapidly downhill along a planar surface, often a bedding plane that is parallel to the ground surface. this block remains largely intact
triggered by earthquakes and v. heavy rainfall bc slip surface becomes lubricated and friction is reduced
landslip/ slump description
occurs in which rock types?
what are they characterised by?
rock moving downhill rapidly along a curved slide surface
weak and unconsolidated clays and sands, often where permeable rock overlies impermeable rock, causing a buildup of pore water pressure
a sharp break of slope and the formation of a scar. multiple car result in terraced appearance on cliff face
soil creep description
movement direction?
charcateristics?
extremely slow movement of individual soil particles downhill. often involves particles rising towards surface due to wetting/freezing, then returning vertically to surface in response to gravity as soil dries/thaws
zigzag movement
forms shallow terracettes, builds up soil on the upslope side of walls and bending of tree trunks
solifluction description
specific to which environments?
forms what
in summer, surface layer of soil thaws and becomes v. saturated bc it lies on top of impermeable permafrost. known as the active layer, this soil w/ vegetation moves downhill by a combination of heave and flow
cold periglacial environments
solifluction lobes
significance of mass movement at the coast
add sediment to the system
rapidly changes coastline significantly
what is wave refraction?
when does it take place?
reorientation of wave fronts as they enter shallow water so that they are about parallel to the shoreline
when waves approach an irregularly shaped coastline (particularly on coastlines with bays and headlands- discordant)
description of how wave refraction takes place
as each wave nears the coastline, it is slowed by friction in the shallower water off the headland
at the same time, the part of the wave crest in the deeper water approaching the bay moves faster bc it is not being slowed by friction
wave bends/refracts around the headland and the orthagonals converge
wave energy and erosive power focused and concentrated on headland ->caves,arches,stacks,stumps
orthagonals diverge in bays and the energy is dissipated so deposition takes place
longshore movement of eroded material into bays bc waves break onto headland at an angle -> build-up of beach sediment
what are orthagonals?
imaginary lines perpendicular to wave fronts, representing transfer of energy as waves form towards coasts
where do swash aligned beaches form
which waves are here?
in low-energy environments e.g. bays which are affected by waves arriving roughly parallel to the shore
where do drift-aligned beaches form
what process affects the beach profile?
where waves approach the beach at an angle.
longshore drift moves sediment along the beach culminating in the formation of a spit
what landforms are associated to swash-aligned beaches
cusps, berms, ridges, runnels
bayhead beaches (curved beaches formed at the back of bays)
cave to stump formation on headlands of bay head beaches
what landforms are associated with drift-aligned beaches
spits, bars, tombolos
beaches that run parallel to the coast
example of a beach
Filey Bay, Yorkshire
5 miles wide
where do beaches form and what do they represent?
formed in bays where there are shallower waters and more sheltered conditions
represent accumulation of material deposited between lowest tides and highest storm waves
how do beaches form?
constructive waves have a stronger swash than backwash, so carry sediment up the beach and then deposit it, because they percolate or lose energy through friction
where do ripples form and why?
further down a beach from cusps,
develop in the sand due to the orbital movement of water in waves
how do longshore bars and runnels form on beaches?
at the lower edge of beaches, sand accumulates to form longshore bars parallel to the waves
material has been combed by plunging destructive waves
breaks in these ridges result from rip currents which form in the strong backlogs, inland of these runnels form
what are cusps?
how do they develop?
small, semi-circular depressions
temporary features formed by a collection of waves reaching the same point and when the swash and backwash have similar strength
the sides of the cusp channel incoming swash into the centre of the depression, producing a strong backwash, which drags material down the beach from the centre of the cusp, enlarging the depression
what are berms?
small ridges that develop at the position of the mean high tide mark, resulting from deposition at the top of the swash
how does a storm beach/storm ridge form?
storm waves hurl pebbles and cobbles to the back of the beach
swash aligned vs drift aligned beaches
swash aligned beaches are more influenced by constructive wave patterns, which are also important for building up large beaches
drift aligned coasts bring in waves at an angle to the shoreline and so therefore, the waves tend to transport sediment down the coast, keeping beaches relatively narrow
what sort of material do beaches contain and where does it come from?
material consists of sand, pebbles & cobbles from cliff erosion, offshore sources and rivers
what are spits and where do they form?
long, narrow beaches of sand or shingle that are attached to the land at one end and extend across a bay, estuary or indentation in the coastline
how do spits form?
when LSD occurs in one dominant direction & carries beach material to the end of the beach then beyond into the open water
storms build up larger material to make the spit a more permanent feature
end of spit often becomes recurved as a result of wave refraction around the end ion the spit or a 2nd wave direction
multiple recurves form over time and become extended
size is limited if the spit is across an estuary due to the flow of the river’s current
spit example
Orford Ness, East Anglia
10 miles long
what are onshore bars?
linear ridges of sand/shingle extending across a bay, connected to land on both sides
how do onshore bars form?
can develop if a spit continues to grow across an indentation e.g. bay, cove in the coastline until it joins onto the land at the other end
they trap a body of seawater behind them, forming a lagoon
what is flandrian transgression?
a period of rapid sea level rise where sediment is driven form offshore sources by waves so a ridge of sediment forms
can form onshore bars
onshore bars example
slapton sands, devon
4km long
what are tombolos?
beaches that connect the mainland to an offshore island
tombolo formation by spit extension
formed from spits that have continued to grow seaward until they reach and join an island
LSD occurs and waves push sediment at an angle so the beach builds up between the mainland and island
tombolo formation by wave refraction and diffraction
waves are slowed down as they enter shallower water around islands, so are refracted around the island, pick up sediment and then deposit it where the waves meet (on the side facing the coast)
this sediment builds up and a sand bar is created joining the island and beach
example of a tombolo
chesil beach dorset= spit extension
st ninians, orkneys= wave refraction 500m long
how are salt marshes formed?
as wave energy is reduces, deposition occurs in sheltered areas. this deposited material e.g. salt and mud builds up, and can result in the growth of salt-tolerant vegetation e.g. eelgrass. the roots of these plants traps sediment so increases the height of the marsh
flocculation aids formation
where do salt marshes form?
in estuaries and on the landward side of spits
what is flocculation
salt causes aggregation of small particles e.g. clay into larger particles (flocculation) which are too heavy to be carried in the river flow, so settle out of suspension and are deposited
daily changes in salt marshes?
subjected to inundation and exposure twice daily as tides rise and fall
example of salt marsh
Abel tasman, New Zealand
characteristics of a cliff
usually at a steep angle of over 40 degrees but may also be vertical or overhanging
often found on the coast with a shore platform below
how are cliffs created?
when destructive waves repetitively break on relatively steep sloping coastlines, undercutting can occur between the high and low tide levels, forming a wave cut notch
continued undercutting of the notch weakens support for the rock strata above, which eventually collapses and produces a steep profile and a cliff
the regular removal of material at the base of the cliff by waves means that the cliff profile remains steep and the cliff retreats inland parallel to the coast
how are cliff profiles affected by geology?
ANGLE OF DIP
chemical composition
how do cliff profiles vary with angle of dip?
HORIZONTAL= steep, almost vertical profile which follows the angle of the dipping strata, parallel to coast, at the base, a gentle sloping shore platform is cut into the solid rock (attacked by abrasion as debris is carried across the surface by wave action), when a rock platform is created due to the rocks being too large to be removed, friction on the platform slows down approaching waves so they break on the platform (rather than the cliff), so undercutting & erosion decreases
SEAWARD= undercutting removes basal support, vulnerable to rockslides, only one rock type facing the sea, lose material easier as it moves down the 45 degree slope into the sea as rock layers loosen in mass movements
LANDWARD= rocks loosened by weather and difficult to dislodge due to the gravitational force pulling them back into place, few rock falls due so the stable profile 70-80 degree slope,
processes contributing to cliff formation besides erosion (main one)
mass movement events e.g. rockfalls
weathering processes e.g. solution, freeze-thaw, salt crystallisation (depends on geology & climate)
when platform is exposed at low tide, marine organisms e.g. algae increase weathering because they release CO2 at night (no p/s can take place), which mixes with seawater, making it more acidic and increasing chemical weathering
where do rock pools form?
shore platform with a slope of 0-3 degrees which are covered at high tide
marine animals e.g. crabs get trapped so don’t return back to sea
how do wave cut platforms form?
rock debris eroded from cliffs (collapsing) which is too large to be carried away by wave action often accumulates on the shore platform
eventually the platform becomes so wide that it produces shallow water and small waves
friction from the platform slows down approaching waves sufficiently for them to break on the platform rather than at the base of the cliffs (platform acts as a wave break and absorbs all the energy from the sea processes)
undercutting slows and eventually ceases
what must the geology be for a shore platform to form?
horizontally strataed
what is cliff recession/shore platform formation an example of?
negative feedback
where do bays and headlands form?
adjacent to each other
on discordant coastlines (rock lying parallel to coastline)
rocks have differing resistance to erosion
how do bays and headlands form on discordant coastlines?
less resistant rocks are eroded more rapidly to form bays while the more resistant rocks remain between bays as headlands
WAVE REFRACTION leads to increased rates of differential erosion
what determines the width of bays?
what determines the depth of bays?
the width of the band of weaker rock
the differential rates of erosion between more/less resistant rocks
how do bays and headlands form on concordant coastlines?
if the more resistant rock lies on the seaward side, it protects any weaker rocks inland from erosion
the resultant coastline is quite straight/even, but small bays or coves may occasionally be eroded ar points of weakness e.g. fault lines
flows of energy and materials in formation of bays and headlands
energy: kinetic energy of waves and wind (bay waves have lower energy and headland wave shave higher energy)
material: lower energy bay waves (constructive) deposit sand onto section of the beach, sediment is eroded off headlands by high energy waves (destructive)
why is there not a huge difference between the headland and bay?
sediment eroded from the headland is deposited in the bay (NEGATIVE FEEDBACK)
what is a geo?
an inlet, a gully or a narrow, deep cleft in the face of a cliff with steep sides
width of a geo?
a few feet to hundreds of feet wide
usually only 10-20m wide
what are geos created by? (brief)
wave driven erosion along faults and bedding planes in rock in the face of a cliff
what is a blowhole?
a vertical fault which has been widened by wave attack
between a tunnel-like cave and the cliff top
requirements for a geo to form?
the faults must be 70 degrees to 90 degrees to the coastline
example of a geo
huntsman’s head geo, Pembroke, Wales
4m at its smallest and 40m at its widest
often used for rock climbing and thrill seekers who jump over it
flows of energy in evolved in forming a geo/blowhole
KE of waves and wind eroding the cliff face
GPE eroding the fault from above, causing the roof to collapse
once the blowhole collapses, KE is lost (wave power is lost so not enough energy left to erode) so the geo won’t get much bigger; will only widen slightly due to weathering
what is the main form of erosion that takes place in the formation of geos/blowholes?
hydraulic action as the high pressure from the rapid wave action targets the mega fault, making it weaker
also forces air/water into the fault, further weakening the rock strata
processes involved in the formation of a geo/blowhole
erosion of fault/mega fault by HA, abrasion, solution, pounding
weathering on top of the cliff e.g. freeze thaw, helping to erode the fault from above
these processes take place over a long time weakening the fault, but a particularly strong storm could cause the roof to collapse
evolution of a geo?
fault erodes to cave
if part of the roof collapses along the joint, forming a vertical shaft, a blowhole is formed
if the WHOLE roof collapses it forms a geo
geology affecting a geo
rock type?
strata?
discordance/concordance?
the rock face is usually hard resistant rock e.g. limestone, which has a mega fault that causes its line of weakness
the rock face could have bedding planes (horizontal layers) within the rock as cracks and faults are commonly found in these
discordant/concordant planforms do not affect geos
how does a geo actually form?
rock face has lines of weakness e.g. joints/faults
these weak points are eroded more rapidly by wave action than the more resistant rock around them
HA is particularly important in forcing air and water into the joints and weakening the rock strata
sometimes initially form as tunnel-like caves at 90 degrees to cliff line, which become enlarged by continuing erosion, and roof collapse forms a geo
if only PART of the roof collapses, forming a vertical shaft that reaches the cliff top, a blowhole id formed
what may geos be associated with in Cornwall and what are they called?
zawns
associated with old tin mining shafts
blowholes characteristics in storms
large waves may force spray out of blowhole as plumes of white, aerated water during storms
requirements for caves/arches/stacks/stumps to form?
discordance (creates the headland)
high energy waves for erosion (high flows of energy are required)
rocks with joints/faults/cracks so differential erosion can take place e.g. limestone or chalk
refraction of waves
why is wave refraction required for the formation of caves/arches/stacks/stumps?
focusses energy around the headland
differential erosion of the headland can occur because there is enough erosive power, so the lines of weakness are exploited more
examples of cave/arch/stack/stump evolution
Old Harry Rocks, near Swanage
Ko Tapu
where do caves form on the headland?
where the wave attack is focussed; between high and low tide levels
where there are points of weakness
step by step formation of cave/arch/stack/stump
due to wave refraction, energy is focussed on side of headland
points of weakness are exploited by erosion processes
small cave may develop on one or both sides of headland between high and low tide levels
if a cave enlarges so that it extends through to the other side of the headland, an arch is formed
erosion widens the arch and weakens its support, along with weathering processes
arch may collapse, leaving an isolated stack separated from the headland
further erosion at the base of the stack may eventually cause further collapse leaving a small, flat portion of the stack as a stump (may only be visible at low tide)
case study of a high energy coastline??
flamborough head to saltburn, NE England
physical factors influencing the landforms between flamborough head and saltburn
geology
wave energy
sediment supply
rate of erosion in chalk and limestone
0.1m/year
rate of erosion in Lias and shale?
0.8m/year
wave direction/direction of prevailing wind at flamborough head to saltburn coastline
northerly winds
length of fetch at flamborough head to saltburn coastline?
1500km
direction of LSD on flamborough head to saltburn coastline
north to south
name of river on flamborough head to saltburn coastline and its sediment input? why?
river Ask
minimal sediment input because it is a heavily managed river
how is geology linked to stacks/stumps
discordant coastlines create layers of hard and soft rocks
this means that headlands stick out (harder rock)
over time, these can be eroded by high energy waves refracting and creating stacks and stumps e.g. Green Stack at Flamborough Head
how is wave energy linked to stacks/stumps
high energy waves from North (1500km fetch) erodes stacks
how is wave energy linked to shore platforms
high energy waves from North erodes the softer rock in the shore platform e.g. Robin Hood’s Bay
how are shore platforms linked to cliffs
shore platforms act as wave breaks for cliffs so slow the rate of erosion
shore platform forms as cliff erodes where there are horizontally bedded layers of hard/soft rock
how are cliffs related to bays flamborough head to saltburn
cliffs made of LIAS rocks erode at 0.8m/year so supply the most sediment to bays
how are rivers linked to bays flamborough head to saltburn
not many rivers so less sediment input
therefore there are small bays or beaches
how are headlands linked to bays flamborough head to saltburn
as bay retreats, headland acts as a wave break and energy is focussed on headland due to wave refraction
therefore less energy in the bay so deposition takes place
e.g. Filey Brigg/Filey Bay
examples of cliffs on flamborough head to saltburn coastline
cliffs at flamborough
cliffs at robin hoods bay and saltburn
example of shore platform on flamborough head to saltburn coastline
shore platform at robin hoods bay
example of beach on flamborough head to saltburn coastline
saltburn beach
example of arch on flamborough head to saltburn coastline
arch at selwick bay
examples of bays on flamborough head to saltburn coastline
robin hoods bay
Filey bay
example of headland flamborough head to saltburn
rock type
formation
flamborough head= large chalk headland
cliffs have till on top, a superficial deposit left behind by glaciers during the Devensian glacial period
cliffs at flamborough:
rock type, height, angle
change over time?
chalk; strong
20-30m high
vertical but the top of the cliffs (composed of till) are lowered by mass movement so have an angle of 40 degrees
lower part= strong rock w/ tightly bonded material so is slow to erode via marine processes
cliff collapse is most likely but this will be a slow process (probably in storm)
upper half is weaker so prone to biological weathering and mass movement (slumping, slipping). erosion here more extensively in winter than summer
cliffs at Robin Hood’s Bay
geology
change over time?
stepped profile due to more varied geology. steeper areas= sandstone and limestone
horizontal bedding planes here (stronger rocks interspersed by weaker rocks); weaker rocks subject to more weathering & erosion so slumping is more common.
therefore angle of cliff not as steep
will retreat more quickly than flamborough head cliffs
erosion more extensive in winter than summer
shore platform at robin hoods bay
angle, width, when was it formed?
change over time?
1 degree
max. width of 500m
formed within last 6000 years
as shore platform grows, it acts as its own breakwater so waves will erode shore notch making platform bigger at a slower rate
therefore shore platform does not grow as quickly, unless sea levels rise so waves can reach base of cliffs more regularly
Filey bay
geology
change over time?
eroded in to weak kimmeridge clay
more resistant limestone and chalk either side forming the headlands
bay accumulates sediment during summer constructive waves and loses sediment in winter months due to storms/destructive waves
dynamic equilibrium exists to keep beach roughly the same size
beach at saltburn
sediment levels
accumulation of sediment?
change over time?
net increase of sediment of 9245m3 between 2008 and 2011
rare example along this coastline as waves usually erode sediment before accretion (accumulation can take place)
loses sediment in winter months due to storms and destructive waves
green stacks pinnacle and arch at selwick bay
formation
rock type
change over time?
as a result of wave refraction, wave energy becomes v concentrated I flamborough head; has left stack isolated at the end where HA has opened up a joint and an arch next to it
chalk
over time, it will collapse to form a stump; probably during a winter storm after years of erosion
arch will eventually collapse to form a stack
robin hoods bay
rock type
change over time?
eroded into lower Lias shales
stronger bands of sandstone to north (ness point) and south (ravenscar) forming the 2 headlands
bay accumulates sediment during summer constructive waves and loses sediment in winter months due to storms/destructive waves
dynamic equilibrium exists to keep beach roughly the same size
example of stack on flamborough head to saltburn coastline
Green Stacks Pinnacle
points in question:
‘explain the role of flows of energy in the formation of stumps(8)’
form on discordant coastlines bc headland sticks out as more resistant rock.
destructive waves necessary
wave refraction= energy conc. on sides of headlands
wave exploit weaknesses e.g. joints and faults (more common in chalk/limestone) and erode into a cave
waves erode through headland, opening up cave into an arch
HA and abrasion from high-energy waves (flow of energy) along with freeze thaw and biological weathering of top of arch causes it to collapse (GPE pulls it down) to form a stack
destructive waves form wave cut notch in stack at base, which collapses to form a stump when support is lost (1/3 of height of cliff)
changes to these landforms will change v quickly after a storm/high energy event
points in question:
‘explain the roles if flows of energy in the formation of geos(8)’
geo= an inlet/gully/narrow & deep cleft in face of a cliff
between a metre and 100s of feet wide
can recede up to 50m back
formed in resistant rock (e.g. limestone)
cracks and faults common due to horizontal bedding planes
cave= formed where there is a fault/megafault at 70-90 degrees to cliff bc rock is weaker so can be eroded by waves & HA/abrasion
freeze-thaw weathering & biological weathering erode top of cliff, causing part of the roof of cave to collapse and form a blowhole
if KE from waves continues to weakens and erode rock, whole roof collapses to form geo
points in question:
‘explain the roles of flows of energy in the formation of shore platforms(8)’
shore platforms= horizontal/gently sloped rock (0-3 degrees) at base of cliffs (usually cliffs are at steep angel of >40 degrees but may be vertical/overhanging)
required horizontally bedded rocks
high KE of wind and waves form destructive waves, which repeatedly hit steep coastline, forming a wave cut notch between high and low tide levels over a long period of time.
notch increases in size, decreasing stability of cliffs bc undercutting weakens rock strata
cliff collapses due to GPE and retreats
high energy waves remove material from base of cliff, leaving profile parallel to coast
over time, this process repeats, building up forming a wave cut platform in the areas of cliff recession
NEGATIVE FEEDBACK LOOP- as platform grows, it acts as a wave break which slows down rate of growth of platform
points in question:
‘explain the impact of geology on coastal landscapes(8)’
lithology/structure: discordance/concordance, where differential erosion affects the shape of the coastline
discordant coasts (e.g. st davids bay, Pembroke), have alternation pattern of bays/headlands due to bands of hard/soft rock. concordant coasts (e.g. lulworth cove) lie parallel to trend of geology, so from bays and coves and form straight coastlines
joints(found in chalk/limestone)= easier for waves to erode due to waves easily exploiting weaker points->differential erosion. therefore evolution of cave->stump and, where there is a megafault, blowhole and geo
angle of dip: horizontal=weak strata exposed so eroded so wave cut notch & platform form
seaward= vulnerable to rockslides bc bonds between strata are weak
landward= v. stable w/reduced rock falls
points in question:
‘formation of bays and headlands(8)’
headlands formed when waves erode discordant coastline
alternating bands= differential erosion e.g. HA and abrasion of high-energy, destructive waves (KE)
harder rock juts out so wave refraction occurs, which acts as a negative feedback loop as it speeds up rate of erosion of headland and encourages deposition in bays
width of Nile delta and what type of delta is it?
population?
240km wide
arcuate delta
majority of Egyptian population lives here
Nile distributaries names
Rosetta and Damietta
Nile delta examples of:
spit
bar
lagoon
sand dune
crescentic bar
Damietta spit
Rosetta onshore bar
Manzala and Burullus lagoons
Gamsa sand dunes
Crescentic bars at Alexandria
Nile delta direction of LSD
West to East
example of hard engineering in Nile Delta
why?
at Alexandria
there was a spit forming here but significant hard engineering strategies have been employed to control the rates of deposition & erosion in the coastal system
due to the high value land in the area
key historic reasons for Nile delta’s morphology
sediment supply
coastal processes
historic sediment supply causing Nile deltas morphology
delta formation needs consistent sediment supply
Nile=longest river in world: 120 million tonnes of sediment was transported annually
river traditionally flooded annually, and these floods deposited vast amounts of sediment on the delta flood plains -> fertile soils
sediment not deposited on plains reached mediterranean and was deposited bc of flocculation -> deposition focussed around mouths of distributares
depth of fertile soils around Cairo
up to 9.6m
why is the mediterranean a low energy environment?
short fetch of waves
lack of tidal range
storms are rare (high-energy coastal events are rare too)
dominant wind direction Nile delta
from West/North-West 55-60% of the time
coastal processes leading to Nile delta morphology
low-energy environment->deposition
prevailing wind direction not perp. to coast
LSD reworks sediment eastwards, creating spits which eventually become bars, behind which lagoons form
coastal processes+ deposition= traditionally delta has grown & extended out into the Med
lagoons have gradually been getting filled by sediment (no longer reworked by LSD)
causes of future change to Nile delta landscape?
building of Azwan high dam
consistent wave & wind energy
climate change
when was the Azwan Dam built?
1964
purpose of Azwan Dam?
to ensure a water supply for the growing population of Egypt
produce HEP
effect of Azwan Dam construction on coastal system
particular areas?
massively reduced water and sediment supply downstream
virtually no sediment flows
delta erodes/retreats by up to 148m/year
areas most affected=by mouths of distributaries due to lack of sediment supply
however E end of bars still growing due to LSD
Rosetta Mouth eroded at 24m/year
Damietta Mouth eroded at 36m/year
effect of Azwan Dam construction on environment and population?
degraded agricultural land bc soils are less rich/fertile due to decreased flooding
forces movement of people from farming to fishing in lagoons-> pressure exerted on fragile ecosystems
if bars protecting lagoons are eroded, ecosystems will be lost along with the fish farming and economic potential
(unsustainable approach bc landforms will be fully eroded in time)
future issues of dam construction in Ethiopia for Nile delta
Ethiopia planning construction of large dam to store water for its industry, HEP and growing pop.
political issues as this would inhibit sediment and water supply even further
future nile delta landscape changes caused by consistent wind & wave energy
dom. winds (NW in summer and NE in winter) so sediment steadily reworked by LSD to increase size of onshore bars and spits
seasonal wind direction difference will cancel out some of the LSD
wind energy also moves sand from Burullus sand bar landward, decreasing size of lagoon
future nile delta landscape change due to development on coast
drying of sand caused and more people to dunes bc vegetation which holds dunes together removed
wind able to erode dunes more easily
future changes of Nile delta due to climate change
sea level rise expected to be between 18 and 64cm by 2100
increased risk of flooding and delta inundated with saltwater, leading to in-farmable land->economic impact
up to 60% loss of farmland by 2100
rate of coastal retreat will increase, reducing land available for human activity
future changes of Nile delta due to climate change
sea level rise expected to be between 45 and 90cm by 2100
increased risk of flooding and delta inundated with saltwater, leading to in-farmable land->economic impact
up to 60% loss of farmland by 2100
rate of coastal retreat will increase, reducing land available for human activity
drinking water supplies and aquifers threatened
breaching of bars and spits (especially at W end)->lagoons exposed to seawater
GRADUAL change
how have Damietta spit and Rosetta onshore bar formed?
sediment carried by distributor is deposited at mouth due to flocculation
due to low-energy environment(short fetch and lack of tidal range), sediment accumulates
prevailing wind direction is NW 55-60% of times so sediment is reworked East by LSD, forming a spit, which grows until it extends to reach the coast and forms a bar, trapping a lagoon behind it of brackish water
how will Damietta spit and Rosetta onshore bar change over time?
Aswan Dam has decreased sediment supply so Damietta mouth erodes at 36m/year and Rosetta mouth at 24m/year (short term change, significant)
E ends still growing steadily due to LSD/migrating SE (consistent wave/wind direction and energy)
bar may be breached due to sea level rise caused by climate change in W end
wave refraction recurves spit due to wave energy in deeper water
smaller due to no new sediment
Manzala and Burullus Lagoon formation
spit extends to meet coast due to LSD, trapping sea behind it (encloses bay), forming a bar and lagoon of brackish water
Manzala and Burullus Lagoon future change
being drained for farming so drying out
agricultural waste filling it up is decreasing lagoon size
wind energy moving sand into lagoon form bar= decreased size
people forced to move form arable farming to fishing= pressure on fragile ecosystems
bars eroded/breached due to lack of sediment supply and sea level rise, so no more shelter for lagoons and they are exposed to seawater
Gamsa sand dunes formation
result form large back shore area
onshore winds allow for aeolian processes (saltation, deposition) to take place
warm, dry conditions and thermal energy dry sand out, making it easier for the wind to transport
size and location of Gamsa sand dunes
30km across
between the 2 lagoons
future change of Gamsa sand dunes
dunes migrate and move South with wind
highway developed along coast so more people to area, meaning vegetation holding dunes together is eroded more easily
CC=warmer so drier sand, which is eroded more easily
decreased sediment supply means eroded sediment is less likely to be replaces
formation of crescentic bars at Alexandria
formed by rip currents and onshore water with little LSD
Sabkahs (salt flats) formation
have formed behind Manzala and Burullus lagoons, where older lagoons have dried out leaving flat salt plains
water evaporates, minerals concentrate until only salt remains
future change of Sabkahs
climate change= increased temps= increased evaporation of water in lagoons so increased Sabah formation
lagoon drained for farming so more sabkahs form
physical factors affecting nile delta landscape
wave energy
wind energy
sediment supply
how does wave energy affect landscape Nile delta
specific landforms due to this?
prevailing wind direction = NW so LSD creates spits/bars and drift aligned beaches bc sediment is transported along coast
waves are low energy/constructive and have small tidal range so deposition is more dominant so there is less erosion-> depositional landforms
how significant is wave energy in affecting the Nile Delta landscape?
varies seasonally (NW summer, NE winter) so may reverse effects, but 55-60% from NW
sig. in transporting seidment
requires constant input of sediment
slow/long term change
how does wind energy affect landscape in Nile delta?
specific landforms affected?
powers wave direction and LSD
forms sand dunes through aeolian processes
short fetch in Med so decreased wind energy
dom. wind direction =W->E in summer
fairly consistent strength
sand dunes affected (saltation, transportation)
LSD: spits/bars by determing wave direction
how significant is wind energy in affecting the Nile Delta landscape?
similar to waves (controls them)
varies seasonally (NW summer, NE winter) and diurnally
forms sand dunes but relies on big beaches/ sediment supply being continuous
how does sediment supply affect landscape in Nile delta?
specific landforms affected?
HISTORICALLY
provided 120million tonnes of sediment for formation of spits/bars/dunes through LSD/aeolian processes
sediment inputted to system
positive sediment budget
PRESENT
azwan dam, 1964 so virtually 0 sediment input to system from river
delta eroding/retreating by up to 148m/year
how significant is sediment supply in affecting the Nile Delta landscape?
rising sea levels and decreasing sediment supply due to Aswan dam means coastline retretaing and flooding, bars breaching e.t.c.
used to be v. sig providing sediment for depositional landforms
how are Damietta spit and rosetta bar interrelated?
rosetta bar affects Damietta spit bc LSD reworks sediment from the bar eastwards to the spit
eustatic change definition
global change in sea level
isostatic change definition
regional change in land level
describe eustatic change
last 18000 years= interglacial (gone from glacial to warm period)
120m s.l rise on average so submerging landforms
caused massive input of sediment ‘rolled onshore’ by rising sea levels (flandrian transgression)
last 6000 years= stable temps & climate, which allowed progression of civilisation
describe isostatic change
happens due to glaciers melting & land ‘rebounding’ back up or due to tectonic activity
e.g. in Scotland and Scandinavia
areas with large isostatic change= less worried about sea level rise flooding them bc isostatic changes are not caught up by eustatic change
examples of submergent landforms
rias
fjords
shingle beach
examples of emergent landforms
relict cliff
marine terrace
raised beach
briefly, what is a fjord?
a submerged glacial valley with steep, cliff-like valley sides
characteristics of fjords
uniformly deep water (often over 1000m)
not very wide (2-4km)
U-shaped cross section (reflects shape of original glacial valley)
threshold at the end of the valley is the shallowest part
straighter than rias
steep, cliff-like valley sides
over what period of time did fjords form?
last ice age wouldn’t have solely caused the formation of fjords/formed over last hundreds of thousands of years
describe the formation of fjords
originally, valleys were secured by glaciers through plucking and abrasion, creating up to 3km deep U-shaped valleys
glaciers melted in last warm period, increasing sea level and flooding glacial valleys
glacial valleys are narrow, deep, 2km high and steep sided
have threshold at end near mouth where glacier didn’t erode and deposited terminal moraines
cruise ships and submarines easily frequent
what are lochs and when do they form?
when glaciers melt and sea level rises, flooding glacial valley
if valley is only partially flooded and not joined to the sea it is called a loch (e.g. in Scotland)
examples of fjords
Sognefjord in Norway
Milford Sound in New Zealand
current geomorphic processes acting on fjords?
coastal erosion at sea level, very slowly widening the fjord (v. slow bc rock type is usually hard so this is insignificant). notches may form.
eustatic s.l. rise deepens the fjord
freeze-thaw and biological weathering cause the steep sides to become less steep as material is weathered away (scree)
mass movement events: steep valley sides are prone to rock fall after weathering/heavy rainfall
characteristics of fjord on a map
straight path
steep valley sides
not very wide
briefly, what is a ria?
a funnel shaped estuary that occurs at a river mouth.
formed by submergence of lower portion of river valley.
flooded river valley.
describe the formation of a ria
throughout lowland coastal areas, rivers form floodplains and deltas= flat and wide, made of weak alluvial deposits (silts, clays deposited due to flocculation)
when sea level rises, these floodplains get flooded, creating bodies of water which are wide but shallow, with one deeper section where the river used to be
often have multiple tributaries which were river tributaries which have all flooded.
common on south coast of UK, and due to large tidal range theyb often leas to inlets which are only navigable by boats at high tide: creates large mud flats whihc are good for wildlife (e.g. wading birds)
current geomorphic processes affecting rias?
coastal erosion processes at sea level at the mouth can form notches
rivers depositing at the river mouth due to flocculation of river sediments silt up the ria and fill it in
sea level rise due to climate change (continuing eustatic change) will deepen ria (better for shipping)
why are human settlements often found in rias?
what impacts can humans have on rias?
sheltered coastal locations
may dredge the areas for shipping, develop sea defences to alter the processes to protect human settlements
why do rias cause an exaggerated tidal effect?
they have a widening funnel shape which steadily increase in depth
when did rias form?
during interglacial period
last 18000 years
rias cross section
V-shaped
example of rias
Kingsbridge Estuary on South Devon coast
6 miles long
1 mile wide near mouth a Salcombe
2 large drowned tributaires extend form east side of ria
briefly, what is a shingle beach?
long beaches with a large quantity of sediment (glacial in origin) which is greater than would have been provided from cliff erosion
material found on beach= between 2 and 200mm and often rounded
source of sediment for shingle beach
sediment would have been rolled up from offshore as sea levels rose during the Flandrian Transgression, hence causing wave action to to push the sediment onshore
sediment was originally deposited by glaciers or form periglacial processes during glacial periods
example of shingle beach
Chesil Beach, Dorset
29km long
constructive waves have moved it inland
has formed a tombolo, connecting the Isle of Purbeck to the mainland, and a lagoon behind it called the Fleet has formed
barrier shingle beach
no longer growing bc all of sediment transported from offshore, leaving beach as a relict feature
LSD re-works sediment south east
effects of current geomorphic processes on shingle beaches
LSD can rework sediments, creating a beach with an asymmetric profile or sediment that is more rounded at one end than another
constructive waves creating larger beaches
destructive waves removing sediment
human action impacts on shingle beach?
groynes slow sediment transfer due to LSD
8 MARKER HOW HAVE SEA LEVEL RISE AND CURRENT GEOMORPHIC PROCESSES INFLUENCED FORMATION OF SHINGLE BEACHES
single beaches= large beaches w/ large quantity of sediment which is greater than could have been provided by cliff erosion. ‘shingle’:2-200mm rounded sediment
eustatic change is responsible. initially, s.l falls due to fall in global temp so glaciers advance.
in most recent interglacial, glaciers retreated and deposited outwash plains containing lots of reworked glacial sediment.
10000 to 6000 y ago, Flandrian Transgressiom reworked this sediment onshore by constructive wave action w/ s.l rise to form shingle beaches
CHESIL BEACH EXAMPLE
in future, eustatic rise due to CC may flood single beaches through higher/stronger destructive waves eroding them.
current geomorphic processes= LSD: reworking sediment to create asymmetric profile or beach w/ more angular sediment at one end or can recurve spit to form barrier beach/tombolo
constructive waves can build up beach w/ material eroded from cliffs/fluvial inputs.
human interventions can alter impacts e.g. groynes
NO LONGER REPLENISHED BC RELICT INPUT SO NEGATIVE SEDIMENT BUDGET
how to answer 8 marker of emergent/submergent landforms
describe it
draw a diagram
role of eustatic change: explain this
role of current geomorphic processes: coastal, weathering, continuing eustatic change, rivers depositing,
what are drowned forest?
after glaciers retreated, vegetation and forests pioneered the glacial outwash and boulders clay left behind.
however, as sea levels subsequently rose, these forests were drowned by the sea
examples of drowned forests
bexhill in East Sussex
why are emergent landforms forming?
isostatic rebound (land level rising): previous glaciers pushed down/compressed land. when the glaciers melted, the land rebounded (about 15,000 years ago)
historical eustatic change (sea level falling)
where are emergent landforms forming?
Scotland, NW UK, California, Scandinavia
effects of current geomorphic processes on relict cliffs
biological weathering loosening material @ top so leading to mass movement events, decreasing steepness of the cliffs
current eustatic change leads to cliff becoming active/drowned
effects of geomorphic processes on raised beach
biological weathering and colonisation by vegetation
current eustatic change leads to beach becoming active
how are marine terraces different to raised beaches?
(used to be shore platform)
STEPPED: 2 periods of isostatic/eustatic change
case study of a coastal landscape that is being managed intentionally?
West Somerset Coastline: Minehead
what does ‘intentional’ mean in terms of activity on a coastline?
planned, deliberate action taken in order to protect it e.g. from floods, erosion, coastal retreat, mass movement, threshold events
what is the shoreline management plan?
sustainable strategy for flood and coastal defences
how to manage entire coastline, recognising budgeting limitations
management strategy at Porlock Bay
justification
Managed realignment in short and long term
low-value land, low-pop. density, so there are less negative consequences
removes pressure off Minehead
management strategy at seaworthy cliffs
justification
do nothing
resistant rock type (quartzite) so a were erosion rate. decreased likelihood of retreat and provides own defence
low population density
management strategy at minehead
justification
hold the line by maintaining and improving defences
high-value land and high pop. density
mudstones in the bay= less resistant rock type so is more prone to erosion and retreat. therefore it requires human intervention to protect the land behind
management strategy at the warren golf course
justification
ST: protection, hold the line. LT: managed realignment as protection becomes unsustainable
lower value land so will be sacrificed as sea level rises
next to Minehead (so is currently worth protecting)
reasons to protect Minehead?
high population density and high value land
low-lying (around 7m)
socio-economic profile of minehead relies on butlins, where the beach is the key attraction. therefore the coastal protection increases tourism, causing PME, tourists bring money to Minehead and creates lots of jobs.
how has butlins decreased seaosonality of tourism?
popular all year round due to xmas themes, stag/hen dos
advantages of using OS maps
has scale: can compare distances and measure
land use and land height are clearly displayed
spatially and proportionally accurate features
easy to read
‘layers’ of information
physical geo and human land use
disadvantages of using OS maps
no temporal change: displays an area in an instant: ‘snapshot’ so could be outdated over time
doesn’t show seasonal variation in beach e.g. height and width
advantages of using aerial photos
visually east to see land use (physical and human)
easy to understand/access
easy to do re-photography
disadvantages of using aerial photos
doesn’t show scale, height (contours), tidal change
lack of labels/information: cannot necessarily tell what they are
no compass points
coastal processes at Minehead coast
sediment eroded form cliffs at seaworthy= SMALL input
LSD inputs sediment from West
historic inputs of sediment due to sea level rise 6000 years ago
flow of LSD and constructive waves transporting sediments
output of LSD and destructive waves, especially during a strom
description of curved sea wall
deflects waves and reduces overtopping
recurved face rotates the wave backwards so that some of the energy is reflected back at sea, which impedes the next wave reducing its energy, and thus its erosive power.
nature of all prevents all but extreme coastal flooding
how do curved sea walls impact the system/ processes/ landforms at mine head?
has curved front to deflect waves and reduces overtopping. reflects wave energy back out to sea. BUT increases strength of backwash so erodes beach (waves won’t break in front of it so is less effective)
shouldn’t be sued alone
landward side faced with attractive local red sandstone, increasing visual amenity
although ti was expensive, it is effective at decreasing erosion
wide walkway with seating so popular with toursits
how high is mine heads curved sea wall?
0.6m
how do rock groynes impact the system/processes /landforms at mine head
work with physical flow: interlink of human and physical
traps sediment being moved bay LSD (flow) to build up beach (store): absorbs wave energy and decreases flood risk in mine head. has caused beach to grow up to 80m in width, increasing tourism and providing shelter from wind too
good for fishing
terminal groyne to E starves area in front of golf course of sediment, increasing rate of erosion and vulnerability to floods. in the next 50-100 years, predictions of up to 100m in coastal retreat
what does rip-rap do?
how does rip-rap impact the system/ processes/ landforms?
at base of sea-wall to dissipate some of the wave energy, so decreases flood risk and rate of erosion
expensive but low maintenance and cost of upkeep
rocs chosen blend in with local landscape, increasing visual amenity
can have short lifespan but effective at preventing erosion
fishing and wildlife can benefit bc habitats are created
beach nourishment impacts on system/ processes/ landforms
sand used to build up beach by 2m in height, forcing waves to break further outs to sea, decreasing energy focused on sea wall
sandy beach formed for tourists, increasing tourism (which is vital for mineheads econ. profile)
medium capital costs and maintenance costs bc it is eroded so must be replaced annually (not v. sustainable)
what is the best form of coastal defence?
beach: natural defence
absorbs wave energy so decreases energy reaching the sea wall
less likelihood of erosion of hard engineering strategies, so less cost of upkeep
easier and cheaper to replace than hard engineering
positive or negative sediment budget at mine head?
why?
due to hard engineering, there is a negative sediment budget
most sediment on the beach is relict from the last sea level rise (there are a few inputs e.g. cliff erosion, LSD but these are small)
cliffs to W= hard rock so have little erosion
sea wall increases strength of backwash and therefore increases outputs, especially during storms
why will managed retreat strategy be adopted at golf course in the future?
increased risk for flooding is significant
retreat of 110m in next 50 years
low-value land
what is the concern with allowing managed retreat at the golf course?
flanking (sea eroding and flooding the unprotected east and then flooding into mine head)
scale of natural/human factors influencing coastline at mine head?
human= small scale, varies place to place, only small area is protected
natural= large scale: sea level rise=global, LSD=fairly large scale but varies slightly dependent on angle of becah or wind direction
timeframe of natural vs human factors influencing coastline at minehead?
human= short term: due to costal retreat, s,l rise, must be replaced
natural= long term s.l rise and sediment inputs. minimised impacts in short term by human activity
natural vs human factors influencing coastline in LIDC vs AC
ACs can afford coastal protection schemes more readily
therefore natural factors impact coastlines in LIDCs more in short AND long term and on small AND large scale
case study of unintentional impact of coastal management?
mangawahi-pakiri coast, new zealand
historical background of pakiri sand mining
on 8 Feb 1994, the minister of conservation granted commercial sand extractors five coastal permits under the RMS to dredge sand from the nearshore seabed at Mangawhai and Pakiri.
the permits allow a total of up to 165,000m3 of sand to be won annually for 10 years
why is sand being mined at Pakiri/
sand fro glass, fill, concrete/bricks, beach nourishment
beach nourishment using sand form pakir?
sand from pakiri used to re nourish ailing beaches , esp. in popular places where the cost can be justified economically by visitors. e.g. in Auckland
cost of 1m3 of sand in NZ
$40 in 2000
why is the sand being mined for glass/concrete/bricks?
construction of buildings in Auckland
how much sand is mined weekly in pakiri?
1500 tonnes
how does pakiri’s location make it attractive for sand mining?
high-quality sand resource occurs in the nearshore zone here
sand is suitable for construction industry
5km north of Auckland: NZ’s largest region, which is home to 1/3 of its population and is growing rapidly. therefore, demand for sand for construction is growing
overview of past/current sand mining in pakiri
nearshore sand dredging on the coastline has operated for over 70 years
between 1994 and 2004, 165000m3/year
mining ended at mangawhai in 2005, but has continued at pakiri
current rates= 75000m3/year until 2020
here was sediment at pakiri beach originally sourced from?
deposited during Holocene (past 9000 years)
sand=non-renewable resource on this coastline
few sizeable rivers in the area and most sand is derived from offshore
what sort of landform is pakiri beach?
shingle beach
emergent landform
sediment budget and system at pakiri beach?
CLOSED SYSTEM
outputs of sand through nearshore mining are not replaced by current inputs
NEGATIVES SEDIMENT BUDGET
ratio of inputs to outputs at pakiri beach?
1:5
what impacts is the mining having on the coastal landforms at pakiri?
beach starve dog sediment so is narrowe and flatter, less effective at absorbing wave energy
increased wave energy erodes the beaches, so dunes and spits are more vulnerable
foredune ridges are undercut by wave action to form steep, seaward-facing scarps (cliffs)
loss of vegetation make the dunes susceptible to wind erosion
impacts of storm at pakiri in 1978?
what did humans do in response?
28m breach 2 base of mangawhai spit & a 2nd breach altered tidal currents, causing sedimentation of mangawhai’s harbour
therefore, water in the harbour was made shallower, and the waterfront community was threatened by flooding
the harbour was therefore dredged and groynes were constructed on the spit, restoring some equilibrium
statistics for coastal retreat in future at pakiri
LT retreat by 2100 is estimated at 35m
width of coastal zone susceptible to erosion varies from 48 to 11m (higher than any of the Auckland region’s other 123 beaches)
why are rates of coastal erosion going to retreat in the future at pakirir?
Auckland regional council studies suggest increased rates of erosion with decreased natural protection from extreme storm events
costal retreat is attributed partly to sand extraction, though this is complicated by climate change and sea level rise
dredging at pakiri depth?
occurring at 8-10m depth= active
sediment form here is usually moved by constructive waves onto the beach.
THEREFORE sediment budget= negative
IF sediment was taken from deeper (18-25m), it wouldn’t impact the coastal system bc waves are not breaking here so this sediment is not being used to replenish the beach
which area of pakiri will lose sediment first
why?
the southern end due to LSD reworking sediment north
impacts of manmade pine forest on pakiri beach system?
as the trees grow, they lift the sea wind off the beach, impairing the beach’s self repair mechanism
with the sea wind reduced, the beach sand would not dry as quickly and once dried, would nnot eb blown into the dunes.
lakc of sand reaching the beach means sand dunes are starved of a key source of sediment, so are becoming lower and narrower, reducing the resilience of the coastline to flooding. dunes are in process of retreat, leaving steep banks behind
local conservation society fighting for the end of sand mining?
successfully fought to stop it off the spit in 2004
BUT dredges still operate to the south off pakiri: starving sediment supply and spit is in precarious situation.
will have greater consequences on sediment budget and tourism in area
future concern for pakiri?
at some point, a large, infrequent winter storm will cause a breach significant enough to permanently change the morphology of the landscape and create a new equilibrium state
how could New Zealand government reduce future concern for pakiri beach?
confine sand mining to a depth where sediment is not being moved within the surf zone
to what extent do unintentional impacts influence coastal landforms and processes?
human actions make coastal system less resilient to natural processes so the physical factors have increased risk
the equilibrium was disturbed by human action, creating a negative sediemnt budget
points to make in question: to whaty extent are long term changes mire influential on coastal landscape systems than short term changes?
SHORT TERM PARA
ST: e.g. of flamborough case study. take place over seconds
mass movements drastically change shape: difficult to adapt to/predict: social impacts e.g. Holbeck Hall Hotel. inputs of sediment so provide material for dep. landforms. cliff collapse in heavily-jointed rocks. many of these ST slowly form shore platform over LT
happen infrequently e.g. collapse of arch to stack. SMALL SCALE, harder rock. add sediment to system, contributing to LT changes to shape
human management impacts flows of energy & sediment e.g. Azwan Dam. will have LT impacts of coastal retreat. breaching can occur due to groynes, flooding homes or ecosystems (porlock)
threshold events, irreversible change to new state. move away form equilibrium
SMALLER SCALE SO SEEN AS LESS INFLUENTIAL
SHORTER TIME PERIODS
STEPPING STONES TO LT CHANGE
points to make in question: to whaty extent are long term changes mire influential on coastal landscape systems than short term changes?
LONG TERM PARA
take places over 100,000s of years: gradual and long-lasting
sea level rise due to climate change= GLOBAL SCALE. continuous impact. causes ST events, e.g. bar breaching. historic inputs of sediment: Flandrian= used for formation of dep. landforms e.g. tombolos.
CC also causing floods e.g. Nile Delta retreat
warming ocean temps & acidification change ocean currents and sediment supply, erosion by solution
changes to rainfall affect weathering of cliff tops, and more extreme weather will increase chance of ST mass movement events.
dev. of beach/spit/bar= built up by constructive waves
ST cliff collapses cause formation of shore platforms= negative feedbakc loop
HUGE SOCIAL IMPACTS OF FLOODS GOBALLY
large spatial impacts
impacts size/shape of coastline, so impact potential for dev. and land use.
harder to protect against/adapt to due to ongoing nature: challenge for LIDCs
points to make in question: to whaty extent are long term changes mire influential on coastal landscape systems than short term changes?
CONCLUSION
LT more sig. in low energy coastline
dependence between LT and ST changes: complex interrelationship
global scale and future impacts presented by CC which is accelerated by human action will present socioeconomic challenges, esp. in LIDCs
change position and shape of coastal profiles, affecting where wave energy hits and where ST changes happen
