coastal landforms Flashcards
(35 cards)
What is a tombolo?
Where a beach joins the mainland to an island a tombolo may be created
Give an example of a tombolo.
Chesil beach
How is a tombolo formed?
- Shingle bar in the English channel
- Waves ‘roll’ sand/shingle bar towards shore
- The shingle bar meets an island and the shore
- Salt marshes may develop in calm waters behind tombolo
What is a spit?
A landform of deposition resulting from long shore drift. It is a long, narrow accumulation of shingle with only one end attached to land. The other end projects into the sea.
Give an example of a spit.
Spurn Head
How is a spit formed?
- Direction of wind dictates wave direction and direction of long shore drift.
- Wave erosion destroys the coastline.
- Long shore drift transports material along the coastline.
- Where the coastline changes direction, material is carried beyond the coastline and deposition continues.
- Waves are unable to reach area behind the spit so quiet backwaters form. Mud and silt from their the river settle, creating mud flats and salt marshes.
- The ‘hooked’ or curved end is the result of short-term changes in wind direction (altering wave direction)
- The strong river current prevents the spit from progressing further.
What is a barrier beach?
Long, narrow stretch of sand which extends across a bay. A lagoon will often form on the landward side of the barrier beach.
Give an example of a barrier beach.
Slapton sands
How is a barrier beach formed?
- Shingle bar is ‘rolled’ onshore and deposited.
- A barrier or ‘bar’ of sand and shingle is created across the entrance to a shallow bay.
- A lagoon develops behind the barrier beach. In Slapton sands it is fresh water serviced by three rivers.
How do you answer a question about the formation of a coastal landform?
S - sequence
P - process
E - explanation
D - description
What is long shore drift?
Longshore drift is the process where waves transport eroded material along a beach and deposit it further down the coast.
Describe the process of longshore drift.
- Waves approach the coast at an angle.
- Swash carries sediment up the beach at an angle.
- Backwash carries sediment down the beach with gravity - at right angles to the beach.
- This creates a zig-zag movement of sediment along the beach.
What are some hard engineering methods?
Groynes
Concrete sea walls
Rip-rap
Gabions
How do groynes work?
Longshore drift causes sediment to pile up against the windward side of each groyne
What are the advantages of groynes?
Highly effective in a local context, such as in the maintenance of holiday beaches.
What are the disadvantages of groynes?
While relatively cost effective to construct, they do require on-going maintenance.
Aesthetically questionable, though they have acquire a visual acceptance through longevity rather than design.
How do concrete sea walls work?
Massive barriers both absorb and reflect wave energy. Recurved wall designs turn waves back on themselves.
What are the advantages of sea walls?
Provide effective property defence in high-risk locations
What are the disadvantages of sea wall?
Very expensive both to build and to maintain
By deflecting waves, rather than dissipating their energy, concrete sea walls, whether recurved or flat faced, are prone to relatively rapid erosion.
How does rip-rap work?
Blocks of hard resistant rock are laid at the foot of vulnerable cliffs and used to dissipate wave energy.
What are the advantages of rip-rap?
Cheaper than concrete constructions.
What are the disadvantages of rip-rap?
Rip-rap traps flotsam and jetsam, which can smell and cause rat infestation.
How do gabions work?
Metal cages filled with beach cobbles and pebbles both reflect and absorb wave energy.
What are the advantages of gabions?
Cheaper
