2.a - coastal landforms

Question 1

why does deposition at coastlines occur?

Answer 1

material is deposited where there is a loss of energy caused by a decrease in velocity or increase/decrease in volume of water.
where rate of sediment accumulation exceeds rate of removal (large supply of sediment)
when waves slow down immediately after breaking
at the top of the swash where for a brief moment the water is no longer moving
during the backwash, where water percolates into the beach material
in low energy environments, such as those sheltered from wind and waves (e.g. estuaries)

Question 1

what 3 sources of sediment are there for beaches?

Answer 1

cliff erosion
offshore
rivers

Question 2

what sediment type are beaches?

Answer 2

consists of sand, pebbles and cobbles

Question 3

how significant is cliff erosion as a source of sediment for beaches?

Answer 3

typically only around 5%

Question 4

how significant is offshore as a source of sediment for beaches?

Answer 4

combed from the sea bed, often during periods of rising sea levels
about 5% but even less sig than cliff erosion as its not all the time

Question 5

how significant are rivers as a source of sediment for beaches?

Answer 5

the remaining 90% of sediment is carried into coastal system as suspended and bed load through river mouths
most significant

Question 6

when does a drift aligned beach form?

Answer 6

form when longshore drift moves material down the coast producing a range of partly detached features.
spits are created in this way

Question 7

when does a swash aligned beach form?

Answer 7

form when waves break parallel to the coast
bay beaches, bay bars and barrier beaches

Question 8

how does size of sediment affect beach morphology - SAND?

Answer 8

sand produces beaches with a gentle gradient because its small particle size means that it becomes compact when wet, allowing little percolation during backwash
as little energy is lost to friction and little volume is lost to percolation, material is carried back down the beach rather than being left at the top, resulting in a gentle gradient and the development of ridges and runnels parallel to the shore.

Question 9

how does size of sediment affect beach morphology - SHINGLE?

Answer 9

-shingle produces steeper beaches because swash is stronger thsn backwash so there is a net movement of shingle on shore.
- shingle may back up the upper part of the beach where rapid percolation due to larger air spaces means that little backwash occurs and so material is left at the top of the beach.

Question 10

what is a runnel (and a ridge)?

Answer 10

ridges are areas of the beach that are raised
and the dips are water filled troughs called runnels

Question 11

what is a berm?

Answer 11

smaller ridges that develop at the position of the mean high tide mark, again resulting from deposition at the top of the swash

Question 12

what is a cusp?

Answer 12

small, semi-circular depressions
they are temporary features formed by a collection of waves reaching the same point when swash and backwash have similar strength.
the sides of the cusp channel incoming swash into the centre of the depression.
further down the beach, ripples may develop in the sand due to the orbital movement of water in the waves.

Question 13

what does the size of a spit depend on?

Answer 13

the size of the spit depends on the period of time that the LSD has consistently been acting
but they will typically take 5-10,000 yrs to form

Question 14

how are spits recurved?

Answer 14

secondary wave action and currents from the deeper water will cause the spit to be recurved at the distal end.
this can happen multiple times along a spit and reflect relict wind and wave pattern

Question 15

why are spits often heavily protected for environmental reasons?

Answer 15

over time, halophytic (salt tolerant) such as sea samphire will colonise the mudflats and in turn trap more sediment to form a salt marsh.
these are populated with wading bird speaciece, meaning spits are often heavily protected for environmental reasons

Question 16

how do salt marshes form behind spits?

Answer 16

over time, halophytic (salt tolerant) such as sea samphire will colonise the mudflats and in turn trap more sediment to form a salt marsh.

Question 17

why is fluvial sediment deposited behind spits?

Answer 17

e.g hurst spit, hampshire
clay and silt carried by the river Test and Itchen are deposited behind the spit
this is because flocculation occurs when the river water meets salt water in the estuary

Question 18

what wave type will dominate around spits?

Answer 18

constructive waves will dominate in this depositional region.
a steady supply of sediment from up stream is needed.

Question 19

where do spits usually form?

Answer 19

spits usually form over river estuaries where river sediment gets deposited as it is a low energy environment
the combination of fresh water and salt water creates brackish environments, where salt marshes form.

Question 20

why will spits continue to grow?

Answer 20

spits will continue to grow as long as there is LSD acting
often because they develop across an estuary, their size is limited by the river water forcing its way throughout the ocean

Question 21

what is a spit?

Answer 21

spits are long narrow beaches of sand/shingle that are attached to the land at one end and extend across a bay, estuary or indentation in a coastline

Question 21

how are spits formed?

Answer 21

generally formed by longshore drift occuring in 1 dominant direction which carries beach material to the end of the beach and then beyond into the open water
as storms build up more + larger material they make the feature more substantial and permanent

Question 22

what happens to spits over time?

Answer 22

the end of the spit often becomes recurved as a result of wave refraction around the end of the spit and, possibly, the presence of a secondary wave/wind direction
over time spits may continue to grow and a number of recurves/hooked ends may develop.
if a spit forms across an estuary its length may be limited by the actions of the river current
in the sheltered area behind the spit, deposition will occur as wave energy is decreased.
the silt and mud deposited build up and eventually salt tolerant vegetation may colonise, leading to the formation of a salt marsh

Question 23

what happens in the sheltered area behind a spit?

Answer 23

in the sheltered area behind the spit, deposition will occur as wave energy is decreased.
the silt and mud deposited build up and eventually salt tolerant vegetation may colonise, leading to the formation of a salt marsh

Question 24

what is a tombolo?

Answer 24

beaches that connect the mainland to an offshore island
e.g. chesil beach, dorset

Question 25

how do tombolos form?

Answer 25

1. from spits that have continued to grow seaward until they join an island
   - LSD- sand build up between beach and island = bar
   - influenced by wind direction
2. wave diffraction and refraction
   - waves slowed as enter coastline => picks up more sediment, sediment deposited around the island

Question 26

what is an onshore bar?

Answer 26

linear ridges of sand/shingle extending across a bay that connects land on both sides
e.g. slapton sands

Question 27

how does an offshore bar differ to a spit?

Answer 27

spit - proximal end connected, distal end is not
onshore bar - both ends connected

Question 28

give 3 ways an onshore bar could form

Answer 28

• spit grows across an indentation (cove/bay) until it joins onto land on the other side
• increased sea-level means sediment is pushed up beach (flandrian transgression)
• increased sea-level causes constructive waves to drive a ridge of sediment onshore

Question 29

what is flandrian transgression?

Answer 29

a period of fairly rapid sea level rise