Depositional Landforms Flashcards
beaches
- Accumulation of material deposited such as sand , pebbles or cobbles.
- Main sources ~ cliff erosion , offshore from sea bed and rivers.
DYNAMIC :
- their profile changes over time as wind strength and wave energy changes.
- beaches respond to these changes by developing an equilibrium profile , with a balance between erosion and deposition.
HIGH ENERGY DESTRUCTIVE WAVES ~
- remove sediment offshore
- create flatter profiles
- shallow water
- more friction and reduction in wave energy
LOW ENERGY CONSTRUCTIVE WAVES~
- transfer sediment onshore
- create steeper profiles
-deeper water
- less friction and increase in wave energy
Sand beaches
VS
shingle beaches
Sand beaches :
- GENTLE gradient
- SMALL particle size
- LITTLE percolation ~ causes compact sand when wet.
- STRONG backwash due to less friction .
- material carried DOWN the beach
- causes the development of RIDGES and RUNNELS.
Shingle beaches:
- STEEP gradient
-MEDIUM particle size
- RAPID percolation ~ larger spaces between sediment
- STRONGER swash
- material left at the TOP of the beach
- causes the development of BERMS and CUSPS.
Swash aligned beaches
VS
Drift aligned beaches
swash aligned beaches ~
- STRAIGHT and lack longshore drift movement.
- waves approach at RIGHT ANGLES to the coastline and are FULLY REFRACTED.
- CLOSED SYSTEM ~ no net movement of sediment out of the system.
Drift -aligned beaches~
- Dominated by waves approaching at an OBLIQUE angle.
-Waves move sediment by LONGSHORE DRIFT.
-OPEN SYSTEM ~ material is moved to other systems.
Berms
- Small ridges
- Develop at the position of the mean HIGH TIDE MARK .
- Results from deposition at the top of the swash.
- Created by SMALLER WAVES that have less energy and carry smaller material.
- Found on SHINGLE BEACHES with small pebbles.
Runnels / Ripples
- created when the waves energy spreads out across a wide area of beach.
- Form due to the ORBITAL movement of water in waves.
- Aligned PARALLEL to the shore.
- Found on shallow , SANDY BEACHES.
Cusps
- Small , semi - circular depressions
- TEMPORARY features
- Formed by a collection of waves reaching the SAME POINT .
- When the SWASH and BACKWASH have similar strength.
- The sides of the cusp, channel the incoming swash into the depression.
- This produces a STRONG BACKWASH which drags material down the beach from the centre of the cusp.
- Found on beached with a MIX of sand and shingle.
Spits
-Long , narrow beaches of sand or shingle.
- They are attached to the land at one end and extend across a bay, estuary or indentation in a coastline.
- Occur when longshore drift carries sediment to the end of the beach and then beyond into open water.
-The feature becomes more substantial and permanent as storms build up more and larger material.
- The end of the spit may become RECURVED due to wave refraction , or change in wind / wave direction.
BEHIND:
- a network of small lagoons , sand bars and channels.
- salt marsh becomes vegetated with salt loving plants.
Bars
ONSHORE BAR:
- develops if a spit continues to grow across an indentation, such as a bay.
- Longshore drift continues to move material across the front of the bay
- Eventually it joins onto the land at the other side.
OFFSHORE BAR:
-develops parallel to the coastline
- sediment accumulation due to the weak back wash depositing material in the water.
- Eventually it may join with the mainland as it is moved by the wind and waves.
- this will block off an indentation , such as a bay.
Behind the bar a LAGOON is created where seawater has been trapped.
Eventually the lagoon is infilled by deposition from rivers and becomes a SALTMARSH.
Tombolo
- A beach that connects the mainland to an offshore island.
- They form when spits continue to grow seawards due to longshore drift until they reach and join an island.
Saltmarshes
Featured of low - energy environments , such as estuaries and behind bars.
- Vegetated areas of deposited slits and clays.
- Shallow gradient which slopes seawards.
- SALT -TOLLERANT PIONEER PLANTS help trap sediment swept in by tidal currents , gradually helping to stabilise and increase the height of the saltmarsh
Low marsh ~ high salinity (salt) , turbid water and long periods of submergence - species diversity is poor.
Further inland ~ salinity, turbidity and submergence is lower - greater variety of species.
Structures that are found due to the formation of a saltmarsh
LOW CLIFF ~ sometimes separates the saltmarsh from the unvegetated mudflats on the seaward side.
CREEKS ~
- Extensive network of small, steep-sided channels
- drain the marsh at low tide and provide routes for the sea to enter as the tide rises.
SALTPANS ~
- found between creeks
- shallow depressions
- trap water when the tide falls and lack any vegetation.
FLOCS ~
- formed through a process called flocculation.
- when tiny particles carry an electrical charge and are attracted to each other in salty water , they clump together to form flocs.
- These are heavier so cannot be carried by the river.
- usually occurs behind spits.
Deltas
Large areas of sediment found at the mouths of rivers where they discharge into the sea.
Formed when:
- the sediment is being deposited at a faster rate than waves and tides can remove it.
- tidal ranges are low
-a broad continental shelf exists at the river mouth to provide a platform for sediment accumulation.
Made up of 3 distinctive components:
UPPER DELTA PLAIN~ furthest inland and composed of river deposits only.
LOWER DELTA PLAIN ~inter-tidal zone , regularly submerged and composed of both marine and river deposits.
SUBMERGED DELTA PLAIN ~below water mark , composed of mainly marine sediment.
3 different types of deltas
CUSPATE:
- Wave dominated
- Occurs when sediment accumulates
- The sediment is shaped by regular, gentle currents from opposite directions
- Has few distributaries
- Pointed shape
ARCUATE:
- Hybrid ( wave / tide)
- Sediment causes the delta to grow seawards
- Wave action is strong , smoothing the leading edge.
- Has several distributaries.
- Triangular / fan shaped
BIRDS FOOT :
- Tide dominated
- Sediment supply exceeds the rate of removal by waves and tides.
- Has many distributaries
- Birds foot shaped
