Depositional Landforms - Beaches And Spits

Question 1

Why does deposition occur?

Answer 1

• occurs when sand and shingle accumulates faster than it’s removed
• associated with sheltered, low-energy sections of the coast, with a positive sediment budget
• rapid erosion nearby may provide an abundant source of material

Question 2

Formation of beaches?

Answer 2

• beaches are accumulations of sediment (sand and shingle) along the shoreline and are an important ‘shock absorber’ in front of cliffs
• shape and characteristics of a beach will vary depending on geology and will change over time in response to wave actions, tides and currents or human activity nearby

Question 3

What is a storm beach?

Answer 3

• found at the back of the beach
• the ridge composed of the largest sediment thrown by the waves above the usual high water mark
• most prominent on shingle beaches where larger material can build up into more obvious ridges.

Question 4

What is a berm?

Answer 4

• a series of ridges marking the successively high-tides as the cycle moves from springs to neaps
• they are built by constructive waves.
• most prominent on shingle beaches

Question 5

What is a cusp?

Answer 5

• semi-circular depressions which form at the junction between sand and shingle.
• the sides channel the swash towards the centre, which helps deepen the feature

Question 6

What are ripples?

Answer 6

• very small undulations in the sand, caused by movement of the waves and tides over the sand
• most commonly found on the foreshore between HWM and LWM

Question 7

What are ridges and runnels?

Answer 7

• these form parallel to the shore as drainage routes for the tide
• water flows via the runnel, creating a channel
• these ridges are raised sections next to the runnel

Question 8

Beach profiles

Answer 8

• sand tends to produce gentle beaches (gradient less than 5 degrees) because the sand becomes compacted and doesn’t allow much percolation - strengthening the backwash.
• larger the material, steeper the beach (10-20 degrees) because more percolation occurs and backwash is weaker.
• larger material can also “stack” more easily allowing the beach profile to increase in gradient

Question 9

Swash-aligned beaches?

Answer 9

• parallel to incoming waves
• minimal longshore drift - sediment moves up and down the beach with little lateral movement
• found in irregular coastlines (e.g. in a bay)

Question 10

Drift-aligned beaches?

Answer 10

• parallel to the direction of longshore drift - sediment transferred along the coast
• found on regular coastlines

Question 11

Formation of a spit?

Answer 11

• longshore drift moves material along the drift
• the coastline changes direction (e.g. at a headland or river mouth)
• sediment builds out to sea. This creates a spit - a “finger” of beach material extending out to sea
• Change(s) in the wind direction will cause the spit to curve at the end. (Recurved end)
• a saltmarsh develops behind the spit due to it being a sheltered area and the deposition of river sediment

Question 12

Difference between compound spits and simple spits?

Answer 12

Compound spits - several ‘hooks’
Simple spits - one curved end

Question 13

Formation of a bar (barrier beach)

Answer 13

• if a spit joins back to the land again, it creates a bar (barrier beach) with a lagoon behind
• this would only happen across a bay/cove rather than a river mouth
• e.g. Slapton Ley - Devon

Question 14

Formation of tombolos?

Answer 14

• if a spit joins up to an island, it creates a tombolo
• chesil beach

Question 15

Formation of offshore bars?

Answer 15

• ridges of sand or shingle running parallel to the coast in an offshore zone
• form from sediment eroded by destructive waves and carried seawards by strong backwash
• sediment deposited at the boundary of the offshore and nearshore zone, where the orbit of water particles ceased to reach the seabed, halting the transport offshore
• often fully submerged, but can sometimes be exposed by a spring tide

Question 16

Formation of barrier islands?

Answer 16

• similar to offshore bars except they are permanently above the level of the water
• can be formed either by the submergence (flooding) or a beach or by deposition on an offshore bar causing it to rise above the sea level
• often stabilised by dunes and can grow into very large features, many km long and several hundred metres wide