Marine Transportation + Deposition

Question 1

What are the different types of sediment sources?

Answer 1

• rivers
• cliff erosion
• wind
• glaciers
• offshore
• longshore drift

Question 2

Rivers as sediment sources

Answer 2

• most of the sediment in coastal zones is a result of an input of rivers
• sediment may be deposited in estuaries, the sediment is then transported throughout the coastal system by waves, tides + currents

Question 3

Cliff erosion as sediment sources

Answer 3

• important in areas with unconsolidated cliffs that are eroded easily
• most erosion occurs during winter months due to frequent storms

Question 4

Wind as a sediment source

Answer 4

• wind is a coastal energy source + can cause sand to be blown along or up a beach
• sediment transported by winds may occur where there are sand dunes or in glacial and desert environments which provide sediment inputs

Question 5

Glaciers as sediment source

Answer 5

• coastal systems such as in Antarctica, glaciers flow directly into the ocean depositing sediment that was stored in the ice

Question 6

Offshore as a sediment source

Answer 6

• sediment is transferred to the coastal zone when waves, rides and currents erode offshore sediment sinks such as offshore bars
• the sediment is transported onto the beach, helping to build up the beach

Question 7

Longshore drift as a sediment source

Answer 7

• waves hit the beach at an angle determined by the direction of the the prevailing wind
• the waves transport the sediment in this direct + up the beach in the Swash
• due to gravity, the wave then carrries the sediment back down the beach in backwash
• this moves sediment along the beach over time

Question 8

The main processes of transportation:

Answer 8

• traction = large, heavy sediment rolls along the sea bed pushed by currents
• saltation = small sediment bounce along seabed pushed by currents
• suspension = small sediment carried by the slow of water - greater velocity = heavier load carried by
• solution = dissolved material is carried within the water

Question 9

What are the two types of sediment transport?

Answer 9

• bedload
• suspended load

Question 10

what is bed load?

Answer 10

• grains transported by bed load are moved through continuous contact (traction) or discontinuous contact (saltation) with the sea floor
• weak currents may transport sand, or strong currents may transport pebbles + boulders in traction
• in saltation grains hop along the bed = moderate currents transport sand or strong currents transport pebbles

Question 11

What is suspended load?

Answer 11

• grains are transported by turbulent flow + are generally held up by water
• suspension occurs when moderate currents are transporting silts or strong currents transport sand
• grains transported as wash loads are permanently in suspension + typically consist of clays + dissolved material

Question 12

What are sediment cells?

Answer 12

• part of a coastline which is self contained, and are in a dynamic equilibrium
• therefore a change in one area (in terms of erosion or deposition) will lead to a change in other sections
• this makes them vulnerable to human interference

Question 13

Process of a sediment cell

Answer 13

1. Cliff erosion on left - high energy area - destructive waves - creates sediment through erosion
2. Sediment transported + washed onto beach - constructive waves
3. Long shore drift moves sediment along beach
4. River both provides sediment but a,so acts to wash sediment offshore (bigger river can stop sediment cell)
5. LSD towards next cliff
6. Right cliff - high energy area- destructive waves - drags sediment offshore + prevents movement past headland
7. Offshore sediment, picked up by shallow waves + bought in by high energy waves (1)