Depositional Landforms

Question 1

Beaches

Answer 1

• Accumulation of material deposited between the lowest tides & highest storm waves

Sand, pebbles & cobble SOURCES:

• Cliff erosion
• Offshore
• Sea beds & rivers

Question 2

Beaches are DYNAMIC

Answer 2

Profile changes over time as wind strength and wave energy changes

EQUILIBRIUM PROFILE ~ balance between erosion and deposition

DESTRUCTIVE WAVES ~

• high-energy
• remove sediment offshore
• create flatter beach profiles
• shallow water
• more friction
• reduction in wave energy

CONSTRUCTIVE WAVES ~

• low-energy
• transfer sediment onshore
• create steeper profiles
• deeper water
• less friction
• increase in wave energy

Question 3

Sand Beaches

Answer 3

• Gentle gradient

COMPACT when wet ~ little percolation during backwash

LESS FRICTION ~ no absorption of energy

STRONGER BACKWASH ~ material carried back down beach rather than deposited

• Development of RIDGES & RUNNELS

Question 4

Shingle Beaches

Answer 4

• Steeper gradient
• Pebbles & medium sized cobbles

RAPID PERCOLATION:

• larger air spaces
• little backwash
• greater deposition
• Development of BERMS and CUSPS

Question 5

Swash aligned beaches

Answer 5

• 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.

Question 6

Drift aligned beaches

Answer 6

• Dominated by waves approaching at an OBLIQUE angle
• Waves move sediment by LONGSHORE DRIFT

OPEN SYSTEM ~ material is moved to other systems.

Question 7

Berms

Answer 7

• Small ridges
• Develop at the position of the mean HIGH TIDE MARK
• Result from deposition at the top of the swash
• Created by SMALLER WAVES that have less energy and carry smaller material.

Question 8

Cusps

Answer 8

• 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.
• STRONG BACKWASH drags material down the beach from the centre of the cusp

Question 9

Runnels / Ripples

Answer 9

• Wave energy SPREADS across a wide area of beach
• Form due to the ORBITAL movement of water in waves
• Aligned PARALLEL to the shore

Question 10

Tombolo

Answer 10

CONTROVERSY over the exact formation:
- some formed by drift aligned features
- others through sea level rise

PREVAILING WINDS ~ determine direction and power of waves that would create conditions suitable
for deposition

WAVE REFRACTION ~ around an off-shore island causing a wave-energy shadow where increased deposition occurs on the landward side

LONGSHORE DRIFT ~ caused by waves
causing movement of sediment through energy absorbed by winds

SPIT ~ starts to form growing seawards until they reach and adjoin an offshore island

• The resulting beaches may be covered during high tide e.g. Lindisfarne, Northumberland or St
  Agnes, Scilly Isles

CHESIL BEACH, DORSET:
- a tombolo formed in a more complex manner
- Most likely the beach developed as a barrier island and moved
onshore during the Flandrian Transgression as sea levels rose, enabling waves to move
material onshore

Question 11

Spits

Answer 11

• Long, narrow beaches of sand & shingle
• attached to land at one end & extend across a bay or estuary

LONGSHORE DRIFT:
- occurs in one dominant direction
- carries sand & shingle to end of beach
- coastline changes direction
- material carried out into open water

STORMY CONDITIONS ~ larger material make feature more substantial & permanent

WAVE REFRACTION ~ end of spit becomes recurved

SILT & MUD ~ deposited in sheltered area behind spit

COLONISATION ~ salt-tolerant vegetation, leads to formation of saltmarsh

Question 12

Bars

Answer 12

• Formation of spit
• ongoing sediment supply & longshore drift
• spit grows across bay
• spit joins opposite headland forming a CONTINUOUS bar
• water trapped behind, creating sheltered low-energy LAGOON

Question 13

Saltmarshes

Answer 13

• form in areas such as behind spits or in estuaries where wave energy is very low

DESPOSITION:
- Fine materials, e.g silt and clay
- rivers lose energy as enter sea
- flocculation of clay particles ~ become larger & heavier

• Formation of MUDFLATS
  Accumulated sediment builds up to create intertidal mudflats that are regularly exposed at low tide.

SALT-TOLERANT PLANT SPECIES:
- trap sediment
- e.g eelgrass
- help increase height of marsh

• Plant stems slow water flow and trap additional sediment, increasing deposition.

LOW MARSH:
- seaward sie
- high salinity
- turbid water
- long periods of submergence
- poor species diversity

Question 14

Structures that are found due to the formation of a saltmarsh

• low cliff
• creeks

Answer 14

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.

Question 15

Structures that are found due to the formation of a saltmarsh

• salt pans
• flocs

Answer 15

SALTPANS ~
- found between creeks
- shallow depressions
- trap water when the tide falls and lack any vegetation.

FLOCS ~
- formed by flocculation of clay particles
- tiny particles carry an electrical charge & attracted to each other in salty water
- clump together to form flocs
- large & heavy so deposited

Question 16

Deltas ~ FORMATION

Answer 16

• Sediment deposited by rivers & tidal currents

DEPOSITION by rivers & tidal currents > REMOVAL by waves & tides

• river enters sea carrying large sediment loads
• lose energy & velocity
• FLOCCULATIO of clay particles
• a broad shelf at river mouth acts as platform for sediment accumulation
• low tidal range
• extensive network of distributaries formed
• many channels with reduced energy levels encourage further deposition

Question 17

Deltas ~ 3 DISTINCTIVE COMPONENTS

Answer 17

UPPER DELTA PLAIN:
- furthest inland
- beyond reach of tides
- composition ~ river deposits

LOWER DELTA PLAIN:
- inter-tidal zone
- regularly submerged
- composition ~ river & marine deposits

SUBMERGED DELTA PLAIN:
- lies below mean low water mark
- composition ~ marine sediments

Question 18

3 different types of deltas

Answer 18

CUSPATE:
- pointed extension to coastline
- Occurs when sediment accumulates
- gentle currents from opposite directions
- Has few distributaries

ARCUATE:
- Sufficient sediment supply causes the delta to grow seawards
- Strong wave action smooths & trims 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

Question 19

Dunes

Answer 19

• Winds blow from the sea
• Dry sand is moved up the beach by SALTATION
• Sand becomes trapped by obstacles on the berm or the point of the highest spring tides
• Build up and become colonised by plants, e.g Marram grass
• Grasses trap more sand , forming an
  embryo dune which grow to form a RIDGE
• covered by areas of brackish (salty), saltwater marshes