Own Knowledge - Coasts Flashcards
define fetch
the distance over which the wind has been blowing - stronger winds = longer fetch = more powerful winds
destructive waves
- formed from strong winds over long fetches
- cause coastal erosion
- break at a high frequency = 11-15 waves a minute
- backwash stronger then swash = erosion
- forms narrow + steep beaches
constructive waves
- light winds + short fetches
- deposition
- low in height
- break at a low frequency = 6-9 waves break/ crests per minute
- swash stronger than backwash
- forms wide + shallow beaches
discordant coastline
bands of resistant and less resistant rock type run at right angles / perpendicular to the coastline
- forms headlands + bays
concordant coastline
- bands of rock run parallel to coastline
headlands
- discordant coastline = eroding at different rates depending on rock type
- the harder rocks eg. CHALK = less resistant to erosion
- these areas stand out as prominent rocky headlands
bays
- discordant coastline
- softer rocks eg. MUDSTONE erode more quickly
- erode back to form a bay eg SWANAGE BAY
what is a cove
a circular area of water with a narrow entrance from the sea
- formed from harder rock being breaches through lines of weakness such as faults and joints
- soft rock exposed = soft rock is eroded
where do caves stacks and arches usually form
headlands
how is a cave formed
- a destructive wave breaks against headlands attacking joins + cracks
- these waves erode the rock through hydraulic action and abrasion
- erosion will widen the crack = eventually form a cave
how is an arch formed
- waves continually attack cabe through HYDRAULIC ACTION + ABRASION
- when a waves breaks it blocks off entrance + traps air
- the trapped air is compressed increasing pressure
- pressure from waves caused back of cave to be eroded through
- forming an arch
how is a stack formed
- continues erosion by the sea widens arch
- as the sea undercuts base = more pressure on top of arch
- weakened roof of arch collapsed = stack
- stack = pinnacle of rock separated from mainland
how is a stump formed
continued weathering and erosion of the stack
how is a cliff + wave cut platform formed
- destructive waves attack the land between HIGH AND LOW WATER MARKS
- through hydraulic action + abrasion, the waves undercut the cliff causing a WAVE CUT NOTCH
- as the notch gets deeper, the overhanging cliff is unsupported and collapses
- repeat = retreat
- a gently sloping rocky area is left at the bottom of a retreating cliff = WAVE CUT PLATFORM
- covered at high tide but exposed at low tide
types of mass movement
rock falls - happen suddenly when a piece of rock falls from a cliff that has been weathered or undercut
slumping - occurs after long periods of rain. the rain seeps through soil and permeable rocks eg. SANDSTONE. at the junction when impermeable meets permeable , the saturated rock slumps in a rotational manner
sliding - occurs along a flat surface eg. bedding plane
direction of prevailing winds in UK
south-westerly
long shore drift
- process of transportation that moves sand and pebbles along the coast
- the swash carries the sand up the beach at the same angle as the prevailing winds
- the backwash then draws the sediment back down the beach at RIGHT ANGLES
- zigzag movement
how are beaches formed
- when eroded material is transported and deposited by constructive waves along the coastline
what did the bar in slapton create
a lagoon - Slapton Leys
how does a spit form
- long and narrow ridge of sand or shingle - one side attached to land
- material is transported along a beach due to longshore drift
- when the coastline bends round, the sediment is deposited on the seabed
- gradually more and more is deposited - forming a ridge that extends into sea
- as the ridge extends, the tip is affected by winds as waves approach from different directions
- causes the spit to curve
how does a bar form
a bar is a ridge of sand or shingle across the entrance to a bay or river mouth
- material is transported along the beach via LSD
- deposition continues in a straight line, directly across entrance to bay
- fresh or slightly salty water is trapped behind to form a LAGOON
human causes of coastal changes
settlements tourism - groynes to maintain tourist beaches = increases erosion further down coast infrastructure - hard engineering construction agriculture
effects of sea level rise
- cliffs will continue to retreat
- areas of ‘soft coastline’, may erode more often/ at a faster rate
what is integrated coastal zone management
a way to manage the coast and the land behind it sustainably, by involving everyone who uses it
types of coastal management
no intervention
hold the line - maintain the existing shoreline by building defences
managed / strategic realignment - allow the shoreline to change naturally, but manage and direct the process
advance the line - build new defences on the seaward side
hard engineering
- groynes
- sea walls
soft engineering
- beach replenishment
- slope stabilisation
what do hard engineering strategies aim to do
deflect or absorb the waves energy by building barriers
what is managed retreat
- a shoreline is allowed to retreat but actions taken to minimise the impact
advantages and disadvantages of rock armour
advantage
- cheap
disadvantage
- ugly
- undermined by shingle and sand
advantages and disadvantages of sea wall
advantages
- protects base of cliffs
- made of resistant concrete
- if ‘recurved’ it reflects energy
disadvantages
- expensive
- restricts beach acess
- ugly
advantages and disadvantages of groynes
advantages
- builds a wide beach
- attracts tourists
disadvantage
- high maintenance = wood rots
- sand prevented from moving so can cause erosion further along
advantages and disadvantages of beach replenishment
artificially adding to the amount of material on a beach to protect the back of a beach or cliff from wave attack
advantages
- looks natural
- beach attracts tourists
- chepa
disadvantages
- replacement of sediment needed regularly
advantages and disadvantages of slope stabilisation
a useful soft engineering strategy to employ on cliffs that are prone to mass movement processes = technique used to prevent slumping and erosion .
drains are installed at the the top low the cliff to remove groundwater, preventing rocks from becoming saturated
advantages
- prevents mass movement
- keeps cliff in place
- safer for people on the beach
disadvantages
- difficult to install
- expensive
