Coasts: Why are coastal landscapes different and what processes cause these differences Flashcards
What is the littoral zone?
The area from the shoreline from the sea to the land, which is where waves, currents and tides move sediment around.
What are the four subzones of the littoral zone?
- Backshore
- Foreshore
- Nearshore
- Offshore
What is the Offshore?
The area of deeper water beyond the point at which waves begin to break.
What is the Nearshore?
The area of shallow water beyond the low tide mark. Friction between seabed & waves distort the waves making them break.
What is the Foreshore?
The area between the hide tide and the low tide mark.
What is the Backshore?
The part of the beach lying between the beach face and the coastline.
What is the Breaker/Surf zone?
Where waves break as a consequence of depth limitations and surf (foamy bubbly surface) onshore as waves bore (change in depth)
What are berms?
Terrace of a beach that has formed in the backshore, above the water level at high tide.
What is meant by dynamic equilibrium?
refers to the maintenance of a balance in a natural system, despite it being in a constant state of change.
Inputs: natural processes examples
- Sediments from the sea
- Weathering & mass movement occuring on the backshore
- Constructive and deconstructive waves casing deposition and erosion
- Longshore Drift
Inputs: Human activity examples
- Dredging of rivers to make them deeper for shipping
- dredging of offshore areas to get sand and gravel for construction
- The building of coastal defences against erosion and flooding
What are some characteristics of a high-energy coastline?
- More powerful (destructive) waves
- Long fetches (generate larger waves)
- Erosion and transport processes
- Cliffs, wave-cut platforms, arches, sea caves, stacks
- Exposed to largest waves
- Rocky landscape
- Highland and lowland coasts
What are some characteristics of a low-energy coastline?
- Less powerful (constructive) waves
- Short fetches (generate smaller waves)
- Rate of deposition exceeds erosion
- Beaches, spits, salt marshes, sand dunes, bars, mudflats
- Sheltered from large waves
- Lowland coasts
Is the coast an open or closed system? And what does it mean?
Open system, meaning it receives inputs from outside the system and transfers outputs away from the coast and into other systems.
Examples of outputs:
- Evapouration
- Sediment transfer
Examples of transfers:
- Wind-blown sand
- Mass movement processes (landslide)
- Longshore drift
- Weathering
- Erosion
Examples of stores:
- Beaches
-Sand dunes
What is a concordant coastline?
When the arrangement of rock types on a large scale are parallel to the coast, meaning the alternating hard and soft rocks lie in the same direction as the coastline.
- More resistant rocks form elongated Islands
- Less resistant rocks form long coves
Example: South-facing coast of Dorset
What is a discordant coastline?
When the arrangement of rock types on a large scale is at a right angle to the coast with alternating hard and soft rock bands.
- More resistant rocks form headlands
- Less resistant rocks form bays
Example: East-facing coast of Dorset
What is a haff coastline?
- A concordant coastline which consists of long spits of sands and lagoons
- Form in low-energy coastlines
- There is deposition of muds and sands
What is coastal morphology?
The shape and form of coastal landscapes and their features
What is lithology?
The physical characteristics of particular rocks
ithology characteristics:
- Strata
- Bedding planes
- Joints
- Folds
- Faults
- Dip
What is strata?
Layers of rock
What are bedding planes?
- Horizontal cracks
- Natural breaks in the strata, caused by gaps in time during periods of rock formation
What are Joints?
- Vertical cracks
- Fractures caused either by contraction as sediments dry out, or by earth movements during uplift
What are Folds?
- Formed by pressure during tectonic activity, which makes rocks buckle and crumble
- Example: Lulworth crumple
What are Faults?
- Formed when the stress or pressure to which a rock is subjected, exceeds its internal strength (causing a fracture)
- The faults then slip or move along fault planes
Whats is a Dip?
- The angle at which rock strata lie
- Horizontally, vertically, dipping towards to sea or dipping inland
What is coastal recession?
Another term for coastal erosion
What does permeable mean? Give an example of a permeable rock
Rocks with spaces, or pores that water can pass through the rock
Example: limestone
What does impermeable mean? Give an example of a permeable rock
Rocks that do not have spaces or many joints so do not let water in
Example: Granite
What are subaerial processes? Examples
Land-based processes that occur above the waterline
Examples: weathering, mass movement
Where are salt marshes and sand dunes found?
Lowland UK areas
What is vegetation and why is it important?
It stabilises soft sediment, low energy coastlines based on sand and mud
What is plant succession?
The changing structure of a plant community over time as an area of initially bare sediment is colonised
How does plant succession happen?
- Pioneer plants change the conditions of the soil by adding humus (decayed vegetation)
- retain moisture
- stabilise loose sand or mud
- Eventually new plants take over
- This continues until there is a balance between all natural factors and the vegetation
What are sand dunes known as?
Psammosere - where xerophytic plants (e.g. marram grass) can survive with little fresh water
What are salt marshes known as?
Haloseres - with halophytic plants (e.g. samphire) can survive in salty conditions
Where are salt marshes found?
Low-energy environments of estuaries and sheltered bays
*as well as behind a spit which sometimes forms across the mouth of an estuary
How are salt marshes formed?
- Tidal conditions bring seawater & sediments in and out
- Fine muds & silts are deposited at the sides of the estuary by rivers
- Tiny clay particles stick to each other (flocculation) then are colonised by algae
- pioneer plants have to survive being covered with slightly salty water 2x a day
- Overtime the plant changes the conditions by trapping more sediment, which builds the salt marsh up, so other plants can then colonise
Where are sand dunes formed?
where there is a plentiful supply of sand
How are sand dunes formed?
- Large areas of sand must dry out
- onshore winds blow sand towards the land
- vegetation or shingle ridges trap the sand
- Embryo dunes form first, they collect more sand & get larger
- pioneer plants (e.g. sea rocket) are able to colonise the stable dunes and help to hold sand together & trap more sand
- Between 50-100 years is when a significant dune sequence develops (oldest dunes closest to land & youngest closest to the sea)
- Yellow dunes= highest, may form a ridge of marram grass near dune front
- not fully vegetated
-subject to alteration by wind & waves
8 Grey dunes= mature dunes
- the climax vegetation is either pine forest (where acidity is high) or oak forest (where shell deposits neutralise the soil a little)
