C -> 3.1 - 3.4 Flashcards
Glass Beach, California
- tourist attraction, 1-2000 people a day
- gradually diminishing
- a need for replenishment
traction
sediment rolls along
suspension
its carried along, making the water all muddy
saltation
it bounces along 2-10cm above the beach
solution
its dissolved, but it doesn’t happen very much
sediment cells
- stretches of coastline where the movement of material is mainly self contained
- closed systems of inputs (erosion), transport, outputs (deposition)
- the key question: is sediment transferred from one cell to another
dynamic equilibrium
- negative - when erosion leads to block fall mass movement, collapsed debris act as barrier protecting base, lowering erosion. Or when major erosion of sand dunes could lead to excessive deposition offshore, creating offshore bar that reduces energy, allowing dunes time to recover.
Positive - when wind erosion of dune section during high velocity storms may remove stabilising vegetation.
Longshore drift
(drift aligned beach)
swash comes in at an angle 30 is the most efficient because of the wind
backwash out perpendicular 90o because gravity
are they closed or open systems
- closed: large natural barriers might stop sediment being moved between, or out of cells - e.g. Thames Estuary, Start Point Headland.
- semi closed: small material could make it out of cells, or between sub-cells, e.g. Christchurch Harbour
- Open: Wind, tides, or tidal currents might remove material
deposition into stores
- when waves no longer have sufficient energy to continue to transport material
- gravity settling (energy is too low), or Flocculation (small clay particles attracted, clump together)
- might be beach, eg. Slapton sands, or offshore, e.g. Dolphin Bank
Inputs
- from cliffs, headlands, rivers, lagoons by coastal erosion processes (HA, Att, Ab, Cor)
- OR: deposited by rivers in coastal environments
transport
by littoral drift/ currents / wind
Real example - Christchurch Bay
source 1 - cliff erosion, e.g. Highcliffe Barton Sands/ Barton clay
Sink 2 (Source 3) - Offshore bars, e.g. Dolphin Bank
point of open cell - double spit (Christchurch Harbour) - sediment can skip over
sink 1 - Hurst Spit
closed cell - river disrupts longshore drift at Hurst Narrows
transport processes - longshore drift, west to east
what is a sediment cell?
littoral cell - linked system of sources/ inputs, transfers and sinks/ outputs of sediment along a section of a coastline
- 11 sediment cells within UK and Wales, boundaries are formed by major headlands or estuaries
examples of inputs + what is it
were sediment is generated from eg. cliff erosion, onshore currents, river transport, aeolian sediment, sub aerial processes
cliff erosion
unconsolidated material after mass movement
river transport
saltation, traction, suspension, solution
aeolian sediment
wind blown sediment
transfers
sediment is moved along shore through longshore drift and offshore currents
sinks
locations where dominant process is deposition and depositional landforms are created, eg. spits and offshore bars
swash aligned
directly faces prevailing wind, wave fronts approach it aligned parallel to the coast, swash aligned beaches often exhibit well defined berms
drift aligned
aligned at an angle to prevailing wind direction, wave fronts approach coast at an angle, so there is transport by LSD. May exhibit some sorting of sediment with smaller more rounded at furthest end
interference
transport of material is stopped or changed, eg river flow, wind
wave refraction
energy levels of the waves are changed/ reduced direction material transport is probably changed
distance decay/ gravity settling
wave energy is reduced, larger material deposited, smaller material is deposited later/ transported further
offshore bars
- ridges of sand or shingle running parallel to coast in offshore zone
- form from sediment eroded by destructive waves and carried seawards by backwash.
- Sediment deposited at boundary of the offshore and nearshore zone
Spit - eg, Spurn Head on the Holderness coast
- ridges of sand or shingle beach stretching into sea beyond a turn in coastline, but connected to land on one end.
- Usually form on drift aligned coastline, where at the turn, LSD continues in the original direction, but its energy is dispersed, lost as wave refracts and current spreads, leading to deposition on the seabed.
- Overtime, sufficient sediment deposited, extending beach into sea as a spit. Length of spit determined by existence of secondary currents causing erosion like flow of river.
- the length of a spit is determined by the existence of secondary currents causing erosion, either the flow of river or a wave action which limits its length
Bayhead Beach - eg, Lulworth Cove, Dorset
- a swash aligned feature, where waves break at 90o to the shoreline and move sediment into a bay where a beach forms
- curved beaches found at the back of a bay, common on swash aligned coastlines, where wave refraction dispereses wave energy around bay perimeter. Waves break at 90o to shoreline and move sediment into a bay, where a beach forms. Through wave refraction, erosion is concentrate at headlands and bay is an area of deposition
tombolo - eg, St Ninian’s tombolo
- bar of sand and shingle connecting offshore island to coastline of the mainland
- form on drift aligned coastlines when LSD builds spit out from land until contacts with offshore island.
- Or on swash aligned coasts when there is wave refraction around both island, causes of collision of wave fronts on the landward side, cancelling each other out and producing zone of calm deposition water, in which case the depositional feature is similar to a spit, e.g. st Ninians tomobolo
barrier beach/ bar - eg, Chesil Beach, Dorset
- sand or shingle beach connecting two areas of land with a shallow water lagoon behind
- Can form on drift aligned coastlines when LSD extends a spit across entire width of bay
- e.g. 9km Barrie beach that extends across start bay in Devon, with slapton Ley lagoon trapped behin
hooked/ recurved spit - eg, Hurst Castle spit, Hampshire
- spit whose end is curved landwards, into a bay
- may form at the end of a spit, as wave refraction around distal end transports and deposits sediment for short distance in landward direction.
what is a cuspate foreland
- Low lying triangular shaped headlands, extending out from a shoreline, formed from deposited sediment
- forms when LSD currents from opposing directions converge at boundary of two sediment cells.
- e.g DUNGENESS in Kent, extends for 11km in SE direction, W-E LSD meets N-S LSD
what causes a cuspate foreland
- main contribute is littoral drift, when constructive waves wash up onto the coast and push the sediment along the shoreline
- is an area of vegetation along the coast, this can cause the transported material to build up and over time this where a spit or cuspate foreland can be formed
what is tombolo
A tombolo is a spit connecting an island to the mainland. An example of a tombolo is Chesil Beach, which connects the Isle of Portland to the mainland of the Dorset coast.
Beach formation
accumulations of sand and /or shingle found in foreshore and back shore zones, produced by material deposited by constructive waves, swash has enough strength to carry material up beach, but backwash doesn’t.
Double spit
- when two spits extend out in opposite directions from both sides of bay towards middle.
- Form where LSD is operating in different directions on opposite sides of the bay
- e.g in Poole harbour, main LSD is SW-NE driven around Studland bay by the prevailing wind, = spit from the south.
- However, wave refraction around durlston head produces wave fronts from NE-SW along = spit from the north.
Positive feedback at sediment cells
when wind erosion of dune during high velocity storms may remove stabilising veg. Then further wind erosion would not occur in low velocity wind conditions.
Mass movement creates distinctive landforms:
- rotational scars - after rotational slumping, a fresh curved upweathered and unvegetated rock surface on the cliff face
- talus scree slopes: blockfall debris accumulate at the cliff foot to form talus scree slopes - a fan shaped mound of material with angle 34-40
