depositional landforms

Question 1

what is a beach?

Answer 1

the area of deposited material between the low water line to the limit of storm waves.

Question 2

how are sandy beaches formed?

Answer 2

• usually formed in a sheltered bay
• low wave energy (most energy focused on surrounding headlands), constructive waves transport material to the shore
• gentle profile (tend to be quite flat)

Question 3

how are pebbly beaches formed?

Answer 3

• more exposed beaches tend to be steeper and more pebbly.
• higher energy waves remove the sand, leaving the larger shingle behind, due to destructive waves having a large backwash.

Question 4

what are sand dunes?

Answer 4

small ridges or hills of sand found at the top of a beach (away from the reach of the waves).

Question 5

what conditions do sand dunes need to form?

Answer 5

• large supply of sand
• large, flat beach
• an onshore wind
• an obstacle for the dune to form against e.g. driftwood

Question 6

how do sand dunes form?

Answer 6

• wind transports sand across a beach through saltation.
• deposition occurs around obstacles such as rocks or seaweed.
• over time, the sand builds up, creating small embryo dunes.
• these dunes are stabilised by vegetation such as marram grass. the long roots bind the sand together.
• the dunes develop even more, and over time, the rotting vegetation adds organic matter to the sand, and so more vegetation is able to grow.

Question 7

what is a spit?

Answer 7

a long, narrow finger of sand or shingle jutting out into the sea from the land.

Question 8

how do spits form?

Answer 8

• prevailing wind blows at an angle to the coastline.
• longshore drift occurs, due to the swash and backwash of the waves, and material is transported.
• when the coastline changes direction (e.g. turns a corner), deposition continues out into the sea, forming a spit.
• the spit continues to grow overtime, until a cross wind creates a recurved end.
• the area behind the spit is now sheltered, so deposition occurs, and a salt marsh may form.

Question 9

why is the sediment at the end of the spit lighter and smaller than at the beginning of the spit?

Answer 9

• longshore drift can carry light material much further.
• the sediment has been transported further, so it may have been eroded more through attrition.

Question 10

what are bars?

Answer 10

when a spit has grown across a bay, trapping a lagoon behind it.

Question 11

how are bars formed?

Answer 11

• a spite grows across a bay
• it joins two headlands and becomes a bar

Question 12

what prevents bars from forming?

Answer 12

if there’s a river with a strong current that travels through the bay and into the water behind the spit, it can prevent a bar from forming.