2B.5 Flashcards
What is longshore drift?
1) When prevailing winds and waves approach coastlines at an angle
2) This means swash moves up beach at wind angle but backwash washes straight down due to gravity
3) this is repeated
What is a swash aligned beach?
When waves approach the coastline perpendicular to the beach. The sediment moves up and down the beach making stable and straight costs
What is a drift aligned beach?
When waves approach at an angle and sediment is moved along by LSD. This forms wide beaches but uneven in sediment.
Where does sediment come from?
Rivers
Cliffs
Constructive waves (seabed)
LSD
Why does deposition occur?
Gravity settling occurs in low energy coastal environments. Which drops coarse sediment first moving finer sediment away.
How is a spit formed?
1) Sediment is normally moved along the by coast by LSD (explain)
2) when there’s a change in coastline LSD continues
3) waves lose energy in slacker water larger sediments are deposited first in the same direction
4) deposition continues a spit if formed.
5) flocculation
6) spit grows may form a hook if wind changes
7) a salt marsh may grow behind the spit due to trapped sediment.
8) this causes halosere on a salt marsh
What is an example of a spit and bar?
Spit - spurn head
Bar - slapton sands Devon
What happens when a spit crosses the gap?
Creates a bar unless alternating currents are too powerful.
How is a Tombola formed?
An island is joined to the mainland which develops a low energy environment. This allows deposition which builds up sediment which makes a pathway to the island.
What is an example of a Tombola?
Chesil beach, Isle of Purbeck in Dorset where LSD happens NW to SE
How are double spits or cuspate forelands formed?
LSD happens from both directions leading to 2 spite forming and meeting.
Deposition occurs in slack water behind to create a triangle
What is an example of a cuspate foreland?
Dungeness
What is a barrier island?
When a plentiful supply of sand was deposited in sand dunes at the coast by waves and winds
Sea level rise and land behind floods create lagoons but prevailing dunes stand parallel as elongated islands
What is an example of a barrier island?
The USA Atlantic coast Fenwick island
What are offshore bars?
Long ridges of sand and pebbles found a short distance out to sea
How are offshore bars formed?
1) In shallow water destructive waves break before the beach
2) causes friction at base of wave causing it to slow and increase in height which scours sediment which is brought back building the bar
3) can be extremely altered during storms as lots of destructive waves
What is an example of an offshore bar?
Slapton Ley Devon
What is a sediment cell?
An area of coastline that acts like a closed system.
What are features of each cell?
Inputs sources transfers and sinks/stores
Self-contained
What are sediment cells broken down into on a meso scale?
Sub-cells which are managed by local SMPs.
What are sources (inputs) in a sediment cell?
Rivers Cliff erosion/weathering Constructive waves Human intervention Onshore winds
What are transfers in the sediment cell concept?
Long-shore drift
On-shore drift
Tidal movements and currents
What are sinks/stores in the sediment cell concept?
Beach
Sand dunes
Offshore bar
Submarine canyons
What is a sediment budget?
The amount of sediment gained from sources and lost to sinks.
Can be POSITIVE OR NEGATIVE
What is a negative sediment budget?
When the coastline degrades
Has positive feedback
What is positive feedback in a negative sediment budget?
When the budget falls and sediment is lost to sinks
Makes more deposition to balance the equilibrium
What is a positive sediment budget?
When the coastline aggrades
With negative feedback
What is negative feedback in a positive budget?
When the budget increases and there is more sediment gained from sources than lost
Causes more erosion to balance
What is word for when the sediment cell is constantly changing?
It is in a dynamic equilibrium
