Coasts Flashcards
(37 cards)
what is a coast
the area where land and sea meet
what is the shoreline
the boundary of the land defined by the high water mark on a low-lying coast or the base of a steeply sloping coast
what is the shore
the area between the highest and lowest tide points
what are tides
- usually twice a day but vary from coast to coast and with the time of the year
- the difference between low and high tide is known as the tidal range
- the tide determines the waves’ height and depth
- the movement of waves and currents affects coastal features
what does the size of a wave depend on
The speed of the wind
The fetch (distance the wind travels)
The amount of time the wind blows (in the same direction)
what are destructive waves (5 features)
Destructive waves erode the beach and have:
- a steep wave gradient
- a short wavelength with high height
- a high frequency wave rate of 10-12 per minute
- high energy
- a strong, abrasive backwash that drags material out to sea and forms shingle beaches
what are constructive waves
Constructive waves are beach builders and have:
- a long wavelength with low height
- a low-frequency wave rate of 6-8 per minute
- a shallow wave gradient
- low energy
- a stronger swash that carries material up onto the beach and deposits a sandy beach
4 types of erosion
Hydraulic Action
Attrition
Corrosion
Abrasion
4 types of transportation
Traction
Saltation
Suspension
Solution
process of longshore drift
Longshore drift (LSD) is the main process of transportation along the coast
- waves approach the beach at an angle due to the prevailing wind
- as the waves break, the swash carries material up the beach at the same angle
- as the swash dies away, the backwash carries the material down the beach at right angles (90°)
- the process repeats, transporting material along the beach in a zig-zag movement
process of marine deposition
The waves carry sand or shingle as they travel
Backwash carries it away, while swash carries it onto a shore
- the largest material is deposited along the upper reach of the swash when a constructive wave carries sediment up the beach
- the backwash loses water and energy as it travels because of the sand’s porosity, resulting in smaller and smaller deposits.
- when a constructive wave carries sediment up the beach, the largest material is deposited along the upper reach of the swash
- during a storm, large shingle is thrown above the usual high tide level to form a ridge at the top of the beach called a berm
formation of cliffs and wavecut platforms
Cliffs are sloping or steep rocks with different profiles depending on the topography and geology
- geology and wave attack at the base of the cliff also affect the angle of the cliff face; low-energy waves cause less damage than high-energy ones
- Many cliffs have a ‘knick-point’ around the high-water mark called the ‘wave-cut notch’, which is where the wave has undercut the rock
- Abrasion, corrosion and hydraulic action further extend the notch back into the cliff
- As undercutting continues, the cliff above becomes unsupported and unstable and eventually collapses
- The backwash of the waves carries away the eroded material, leaving behind a wave-cut platform
- The process repeats and the cliff continues to retreat, leading to a coastal retreat
formation of headlands and bays
- Found in areas of alternating bands of resistant (hard) and less resistant (soft) rocks running perpendicular to oncoming waves (discordant coastline)
- Initially, less resistant rock (e.g. clay) is eroded back, forming a bay
- The more resistant rock (e.g. limestone) is left protruding out to sea as a headland
formation of cave, arch, stack and stump
- Hydraulic action, abrasion, and corrosion take advantage of any weaknesses in the headland
- As a crack begins to widen, erosion will act to form a cave
- The cave will become larger and eventually break through the headland to form an arch
- Due to weathering from above and erosion below, the arch’s foundation continues getting thinner and wider
- Eventually, the roof of the arch collapses, leaving behind an isolated column of rock called a stack
- The stack is undercut at the base by wave action and sub-aerial weathering above, until it collapses to form a stump
formation of a spit
- The process that moves sediment is longshore drift
- Where the coastline changes direction, a shallow, sheltered area allows sediment to be deposited
- More deposition happens as a result of higher friction
- Eventually, a spit slowly builds up to sea level and extends in length
- If the wind changes direction, then the wave pattern alters and results in a hooked end
- The area behind the spit becomes sheltered
what is a bar
A bar is when a spit grows across a bay and joins two headlands together
A bar of sand is formed (sandbar)
Sandbars can also form offshore due to the action of breaking waves from a beach
what is a lagoon
A lagoon is where a small body of water is cut off from the sea
A lagoon may form behind a bar or tombolo
Lagoons do not last forever and may fill with sediment and form new land
what is a tombolo
A tombolo is formed when a spit joins the mainland to an island
Chesil Beach in Dorset is a tombolo, as the mainland is joined to the Isle of Portland
formation of a sand dune
- Windblown sand is deposited against an obstruction, such as a pebble or driftwood
- As more sand particles are caught, the dunes grow in size, forming rows at right angles to the prevailing wind
- In a process known as succession, vegetation will eventually colonise and fix the ridges of the dunes
7 stages of a sand due
- embryo dune
- fore dune
- yellow dune
- grey dune
- dune slack
- mature dune
conditions required for coral reefs to grow
- temperature: cannot be below 18C but thrive best between 22 - 25C
- require photosynthesis due to the algae living in the tissue
- depth of less than 25m so that sunlight can penetrate
- require salty water
3 types of coral reefs
- fringing reef
- barrier reef
- atolls
4 characteristics of mangroves
- live on the coastline
- sit in water between 0.5-2.5m high
- range in size from small shrubs to trees 60m highs
- the roots have a filteration system with a filter to keep salt out
8 coastal opportunities
- Development
- Nature reserves
- Swimming and sports
- Industry
- Fishing and aquaculture
- Tourism
- Agriculture
- Ports and harbours
