1 Wave action and longshore drift
2 Atmospheric processes
3 Biological processes
4 Physical processes
8 See also 9 Notes 10 References 11 External links
Wave action and longshore drift
Port Campbell in southern Australia is a high-energy shoreline.
The waves of different strengths that constantly hit against the shoreline are the primary movers and shapers of the coastline. Despite the simplicity of this process, the differences between waves and the rocks they hit result in hugely varying shapes. The effect that waves have depends on their strength. Strong waves, also called destructive waves, occur on high-energy beaches and are typical of winter. They reduce the quantity of sediment present on the beach by carrying it out to bars under the sea. Constructive, weak waves are typical of low-energy beaches and occur most during summer. They do the opposite to destructive waves and increase the size of the beach by piling sediment up onto the berm. One of the most important transport mechanisms results from wave refraction. Since waves rarely break onto a shore at right angles, the upward movement of water onto the beach (swash) occurs at an oblique angle. However, the return of water (backwash) is at right angles to the beach, resulting in the net movement of beach material laterally. This movement is known as beach drift (Figure 3). The endless cycle of swash and backwash and resulting beach drift can be observed on all beaches. This may differ between coasts.
Rhossili in Wales is a low-energy shoreline.
Probably the most important effect is longshore drift (LSD)(Also known
as Littoral Drift), the process by which sediment is continuously
moved along beaches by wave action. LSD occurs because waves hit the
shore at an angle, pick up sediment (sand) on the shore and carry it
down the beach at an angle (this is called swash). Due to gravity, the
water then falls back perpendicular to the beach, dropping its
sediment as it loses energy (this is called backwash). The sediment is
then picked up by the next wave and pushed slightly further down the
beach, resulting in a continual movement of sediment in one direction.
This is the reason why long strips of coast are covered in sediment,
not just the areas around river mouths, which are the main sources of
beach sediment. LSD is reliant on a constant supply of sediment from
rivers and if sediment supply is stopped or sediment falls into a
submarine canals at any point along a beach, this can lead to bare
beaches further along the shore.
LSD helps create many landforms including barrier islands, bay beaches
and spits. In general LSD action serves to straighten the coast
because the creation of barriers cuts off bays from the sea while
sediment usually builds up in bays because the waves there are weaker
(due to wave refraction), while sediment is carried away from the
exposed headlands. The lack of sediment on headlands removes the
protection of waves from them and makes them more vulnerable to
weathering while the gathering of sediment in bays (where longshore
drift is unable to remove it) protects the bays from further erosion
and makes them pleasant recreational beaches.
Onshore winds blowing "up" the beach, pick up sand and move it up the beach to form sand dunes. Rain hits the shore and erodes rocks, and carries weathered material to the shoreline to form beaches. Warm weather can encourage biological processes to occur more rapidly. In tropical areas some plants and animals protect stones from weathering, while other plants and animals actually eat away at the rocks. Temperatures that vary from below to above freezing point result in frost weathering, whereas weather more than a few degrees below freezing point creates sea ice.
In tropical regions in particular, plants and animals not only affect
the weathering of rocks but are a source of sediment themselves. The
shells and skeletons of many organisms are of calcium carbonate and
when this is broken down it forms sediment, limestone and clay.
The main physical
Chesil Beach, a tombolo in Dorset, United Kingdom.
If the coast suddenly changes direction, especially around an estuary,
spits are likely to form.
Long shore drift
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Codrington, Stephen. Planet Geography 3rd Edition (02-Dec-2006) Chapter 8 
Glossary of terms used in coastal geography Coastal science terms and definitions
v t e
v t e
Anchialine pool Archipelago Atoll Avulsion Ayre Barrier island Bay Baymouth bar Bight Bodden Brackish marsh Cape Channel Cliff Coast Coastal plain Coastal waterfall Continental margin Continental shelf Coral reef Cove Dune
Blowhole Cliffed coast Coastal biogeomorphology Coastal erosion Concordant coastline Current Cuspate foreland Discordant coastline Emergent coastline Feeder bluff Fetch Flat coast Graded shoreline Headlands and bays Ingression coast Large-scale coastal behaviour Longshore drift Marine regression Marine transgression Raised shoreline Rip current Rocky shore Sea cave Sea foam Shoal Steep coast Submergent coastline Surf break Surf zone Surge channel Swash Undertow Volcanic arc Wave-cut platform Wave shoaling Wind wave Wrack zone
Accretion Coastal management Integrated coastal zone management Submersion
Bulkhead line Grain size
boulder clay cobble granule pebble sand shingle silt
Intertidal zone Littoral zone Physical oceanography Region of freshwater influence
v t e
Airy wave theory Ballantine scale Benjamin–Feir instability Boussinesq approximation Breaking wave Clapotis Cnoidal wave Cross sea Dispersion Edge wave Equatorial waves Fetch Gravity wave Green's law Infragravity wave Internal wave Iribarren number Kelvin wave Kinematic wave Longshore drift Luke's variational principle Mild-slope equation Radiation stress Rogue wave Rossby wave Rossby-gravity waves Sea state Seiche Significant wave height Soliton Stokes boundary layer Stokes drift Stokes wave Swell Trochoidal wave Tsunami
Undertow Ursell number Wave action Wave base Wave height Wave power Wave radar Wave setup Wave shoaling Wave turbulence Wave–current interaction Waves and shallow water
one-dimensional Saint-Venant equations shallow water equations
Craik–Leibovich vortex force
El Niño–Southern Oscillation
General circulation model
Head of tide
Perigean spring tide
Rule of twelfths
Abyssal fan Abyssal plain Atoll Bathymetric chart Coastal geography Cold seep Continental margin Continental rise Continental shelf Contourite Guyot Hydrography Oceanic basin Oceanic plateau Oceanic trench Passive margin Seabed Seamount Submarine canyon Submarine volcano
Convergent boundary Divergent boundary Fracture zone Hydrothermal vent Marine geology Mid-ocean ridge Mohorovičić discontinuity Vine–Matthews–Morley hypothesis Oceanic crust Outer trench swell Ridge push Seafloor spreading Slab pull Slab suction Slab window Subduction Transform fault Volcanic arc
Benthic Deep ocean water Deep sea Littoral Mesopelagic Oceanic Pelagic Photic Surf Swash
Deep-ocean Assessment and Reporting of Tsunamis
Future sea level
Global Sea Level Observing System
North West Shelf Operational Oceanographic System
Deep scattering layer
Color of water
National Oceanographic Data Center