sediment transportation & depositional landforms (2B.5A/B)

Question 1

the four transportation processes

Answer 1

traction (where large, heavy load items are rolled along the sea bed)
saltation (where lighter sediment bounces along)
suspension (where very light sediment is carried aloft within a body of water or air)
solution (where sediment is carried dissolved within the water)

Question 2

swash vs drift aligned

Answer 2

1. swash aligned coasts: waves break in line (parallel with the coast) which equals production of smoothly curved, concave beach
2. drift aligned coats: waves break at angle to the coast (swash occurs at angle but backwash runs perpendicular) which as a result is transported along beach via longshore drift.

Question 3

longshore drift

Answer 3

• waves approach beach at an angle from a direction similar to that of the prevailing wind.
• the incoming swash transports sediment up the beach at an angle
• gravitational backwash then transports sediment back down the beach at 90’ to the coastline.
• the net effect of this movement is a lateral shift as material moves in a zig-zag fashion along the beach with each incoming wave.
• where the removal of sediment is greater than the supply, the beach is eroded

Question 4

tides and currents

Answer 4

tides= periodic rise and fall of the seas surface and are produced by the gravitational pull of the moon and to a lesser extent, the sun.
the relative difference in height between a high and low tide= tidal range.
- a high tidal range create powerful tidal currents as tides rise and fall. these currents are particularly strong and fast in estuaries and narrow channels and are important in transporting sediment

Question 5

why and how does deposition occur?

Answer 5

occurs when the energy of transporting water becomes too low to move sediment. Large sediment will be deposited first, followed by smaller sediment (pebbles -> sand -> silt)

this loss of energy might be due to:

• the wind dropping, removing an energy source
• resistance by obstruction, e.g. a groyne or headland
• dissipation of energy through refraction
• friction from extended transport across shallow angled nearshore and foreshore zone

side note! (flocculation is a depositional process that is important for very small particles, such as clay, which are so small that they will remain suspended in water. Clay particles clump together through electrical or chemical attraction, and become large enough to sink. )

Question 6

types of spit

Answer 6

1. spit= long narrow feature made of sand/ shingle extending from mainland out to sea.
   formed on drift aligned beaches.
   longshore drift occurs moving material. if there is a sudden change in coastline (eg headland) longshore drift will continue to transport in same direction rather than following shape of coastline. eventually material is deposited and builds up as strength of drift weakens.
2. recurved spit
   formed when end of spit curves around as a result of wave refraction. area behind curve is sheltered from waves often forming salt marshes behind them.
3. double spit= two spits in opposing directions.
   often as a result of two directions of prevailing winds (longshore drift is operating in different directions) on opposite sides of the bay. and most commonly found across mouth of an estuary (EG Poole Harbour)

Question 7

barrier beaches (bars) and islands

Answer 7

1. where a beach/ spit extends forming a ridge of material that is connected at both ends to mainland. it is located above sea level and often traps water behind forming lagoons. EG Loe Bar in Cornwall
2. when a beach becomes separated from the mainland= an island. they form parallel to a flat coastline and only under certain conditions (low tidal ranges and gently sloping coastlines) EG Americas Eastern Sea Board, 300 islands.

Question 8

tombolo’s and cuspate forelands

Answer 8

1. ridge of material that has formed between small island and mainland.
   can either occur on drift aligned coastlines, when longshore drift builds a spit out from land until it contacts with an offshore island (deposition occurs, wave lose energy, tombolo builds up EG Lindisfarne)
   OR
   on swash aligned coasts when there is wave refraction around both sides of the island.
2. triangular shaped headland that extends out from the main coastline
   - occurs where coast is exposed to longshore drift from opposite directions. sediment is deposited where the 2 meet forming a natural triangle
   - vegetation begins to grow stabilizing the cuspate and protecting it from erosion.

cuspate can be small or large (extending out 3 miles)

EG Burgerness, Kent; slowly built up. multiple lighthouses replaced as point of land continues to grow