6 - coastal processes and deposition with associated landforms Flashcards
what are the processes of transportation
SOLUTION - dissolved in sea water, carried in solution, not visible
SUSPENSION - small particles carried in water
SALTATION - load bounced along sea bed, currents cant keep larger and heavier sediment afloat for long times
TRACTION - pebbles/larger sediment rolled along sea bed
what is longshore drift
net movement of sediment along a coastline in zig zag form
waves move up beach in swash at direction of prevailing wind
waves drain back down beach as backwash at right angles to beach (gravity)
larger sediment needs more energy = slower pace of transport , smaller it is the faster it is
how does the coast influence LSD
irregularities in shape of coastline = refraction not always achieved
= longshore drift, major force in transport of material
what is gross and net littoral drift
GROSS littoral drift = total volume of sand transported both up and down coast
NET littoral drift = difference in upwardly and downwardly transported volumes of sand
what is coastal deposition
DEPOSITION in open water occurs when energy of transporting water is too low to transport sediment
= laying down/depositing of material
what is stokes law
stokes law defining sediment deposited by water = directly proportional to mass (size) of sediment being transported
larger material deposited first, smaller material transported further
what is flocculation
clay particles aggregate together, forming larger material = floc
process increases mass of particles, deposition speeds up
flocculation beds deposited in deltas as rivers enter coastal waters and lose energy
what is sediment storing
usually largest sediment deposited first, smaller further
however in shallow water, wave energy causes differential deposition and largest cobbles and boulders are thrown above high water mark by storm waves
what are beaches
depositional landform
made of loose, unconsolidated sands/pebbles
they are mobile and able to adjust dynamic equilibrium
how/when are beaches built up in UK
most beaches built up in summer months - long periods of stable, anticyclonic weather, constructive waves
lose mass in winter as depressions bring destructive waves
profiles change annually
what are the three main types of beaches and what are they influenced by
main influence on beach profile = wave energy. prevailing wind conditions and sediment supply result in 3 main types:
- SWASH-ALIGNED
- DRIFT-ALIGNED
- ZETA-FORMED
what is a swash aligned beach
- waves break parallel to shore
- little longshore drift
- sediment moving in onshore-offshore direction
what is a drift aligned beach
- wave arrive at oblique angle
- lots of LSD
- plenty of sediment available
- depending on morphology, spits forming down drift end of beach
what is a zeta formed beach
- form at oblique angle to dominant wave approach with LSD
- where headlands at each end cause wave refraction and block sediment movement
- at far end, sediment builds up in front of headland creating wider down drift
what is a BERM and where/how is it formed
ridges of deposited material
- formed at top of foreshore of beach
- formed by deposition from top of swash during high tide
what is a RIDGE/RUNNEL
raised bank of sand and trough forming runnel
- located on lower foreshore
- strong backwash on beach with low gradient = transported sand then deposited back to foreshore
what is a RIPPLE
small ridges
- located in lower beach at back of foreshore
- caused by repeated orbital movement of water in waves
how is a spit formed
- beach material transported by LSD in direction of prevailing wind
- change in direction of coastline transportation
- deposition of larger, heavier storm material
- further deposition making spit extend into estuary (spits can become narrow and breached if sediment supply interrupted)
- change in direction of prevailing wind causing spit to curve (hook)as direction of transportation altered
- silt deposited in sheltered area behind spit
- salt marsh develops and becomes vegetated
what is a bar
bars are elongated deposits of sand and shingle lying parallel to coast
laid down by constructive waves and separated from shore by lagoons varying in size
how is an offshore bar formed (7 steps)
- elongated ridges of sand/shingle parallel to coastline but unattached
- waves approach gently sloping coast, friction between waves and sea bed = waves break and deposition occurs
- more material builds up parallel to coast to form ridge of sand called offshore bar
- body of coastal water could be completely shut off from open sea - lagoon
- further deposition encouraged
- submerged bars exposed at low tide and barrier islands partially exposed even at high tide
- most material deposited onshore side of bar resulting in coastward migration
what is a barrier beach/island
at macro scale, bars known as barrier beaches/islands. occuring in sea with shallow offshore gradients, low tidal range yet high wave energy
unlike small bars, they arent submerged at high tide
eg Fresian Islands
what is a tombolo
TOMBOLO = complex features develop when LSD joins an island onto mainland or larger island. this island known as a tied island
some smaller tombolos formed when cuspate foreland linked up with islands
what is a cuspate foreland
CUSPATE FORELAND = triangular shaped projections with apex pointing out to sea
varying in scale
what causes a cuspate foreland to be formed
where sediment, moved by LSD, becomes trapped when equilibrium is reached between sediment inputs and there is energy available to move it
how is a cuspate foreland formed
- triangle shaped accretions of sand and shingle extend seaward
- change in direction of coastland
- LSD extending both directions due to two dominant wind directions
- sediment brought in from both directions, foreland developed
- possible joining of 2 spits, trapping sediment
- sedimentation enhanced by rivers bringing sediment to their mouths
how was dungeness formed (CP)
formed largely of shingle beach in form of cuspate foreland sheltering large area of low lying land called Romney Marsh
result of two directions of LSD
describe beach equilibrium, what is involved and changes
a beach is a dynamic geomorphic system that is a buffer against erosion that can respond to changes:
when rate of sediment being added to beach equals amount leaving the beach resulting in the beach remaining the same size
if something happens the break this equilibrium (human actions, natural variations) the system will undertake negative feedback to restore equilibrium and sedimentary budget so erosion doesn’t increase
