Coasts Flashcards
(21 cards)
What are Ridges and Runnels?
Ridges & Runnels
Parallel “hills and valleys” of sand found at the low water mark. These are formed due to the interaction of tides, currents and shallow beach topography and so are often formed as breakpoint bars.
What are Storm Beaches?
A ridge of boulders and shingle found at the back of the beach which have been thrown up to the back of the beach by the largest waves at high tides.
Cusps
Semicircular depressions formed by waves breaking directly on the beach with a strong swash and backwash.
Ripples
Develop on sandy beaches as a result of wave and tidal movements.
Headlands and Bays
Headlands & Bays (e.g. Swanage Bay)
Headlands and Bays, such as Swanage Bay, form on discordant coastlines, where hard and soft rock run in layers at 90˚ to the water. Alternating layers of hard and soft rock allow the sea to erode the soft rock faster, forming a bay but leaving hard rock sticking out, known as a headland. The altering rate of erosion of hard and soft rock is known as differential erosion. As the bay develops, wave refraction around the headlands begins to occur, increasing erosion of the headlands but reducing the erosion and development of the bay due to a loss of wave energy. Headlands and bays can form on concordant coastlines too, as has happened with Lulworth Cove, but this requires the rock to have already been weakened, possibly during an ice age.
The Formation of Wave-Cut Notches and Shoreline Platforms
A wave cut notch is simply a small indent at the base of a cliff formed when a cliff is undercut by the sea. When a wave breaks on a cliff, all of the wave’s energy is concentrated on one specific point and this section of the cliff experiences more rapid erosion via corrasion. This eventually leads to the formation of a wave cut notch, when the cliff has been undercut. As the cliff has been undercut, the section of the cliff above the notch (the overhanging rock) no longer has any support and will, eventually, collapse. The repeated process of the collapse of the cliff and then the undercutting of the cliff is often referred to as the “retreat” of the cliff. As the cliff retreats, a gentle platform (with a gradient less than 5˚), referred to as a wave cut platform, is left behind. This platform is heavily scarred by erosion from the transportation of rock across it. As the platform grows, the waves have to travel further to reach the cliff and they’ll lose more and more of their energy. Once the platform reaches a certain size, the waves will have too little energy by the time they reach the cliff to undercut it and so there is a physical limit on the size a wave cut platform can be.
Formation of Caves, Stacks, Stumps, Arches, Blowholes
Stacks, caves and arches are all iconic features of coastlines. They are also all linked together, along with stumps and arches as they are part of a series of landforms that form as a coast is eroded. Areas on a stretch of coast that have small cracks and joints on them are particularly susceptible to attack from waves, along with bedding planes that lie inline with the direction of the waves. These areas will be eroded very quickly and can be eroded in one of two ways. The first way is simply eroding the crack and causing it to collapse, forming a geo, a steep sided inlet into the side of the coast. Alternatively, the area below the crack or joint is undercut and a small cave will form. If the cave forms on a headland, then on the opposite side of the headland, a second cave can also begin to develop simultaneously. The water erodes the cave via corrosion and hydraulic action, flooding the cave and swilling around it, widening the cave and creating a unique pattern on the surface of the cave. As the two caves are eroded and cut into the headland, they will eventually meet. The resulting, iconic, landform is then referred to as an arch. The roof of the arch has no support however and is highly susceptible to weathering via exfoliation, salt crystallisation and biological weathering. As the weathering continues, the roof of the arch will collapse leaving a stack, a tall, lone piece of land sticking out in the sea. This stack is exposed to the full force of the water and is weathered and eroded heavily. The base of the stack receives a lot of erosion from hydraulic action and corrosion and, eventually, the stack will collapse into the sea leaving behind a small piece of land called a stump.
Formation of Sand dunes:
Formation
There are several conditions that need to be met for sand dunes to develop. First, a large supply of sediment is needed. The best place to get this is from a large tidal flat. An area with a large tidal range (a big difference between the high and low tide) will result in a lot of sand being exposed to the wind, ready to be transported. This brings us to our next condition. A (relatively) strong and continuous wind is needed to move sand grains and transport them inland via saltation. The best place to find strong winds that don’t change direction is in areas that face the prevailing wind direction.
With these conditions met, it’s now only a matter of time until a sand dune starts to form. Obstacles such as rocks or human rubbish are deposited at the strandline—essentially the high water mark. These objects block the wind causing sand grains that are being transported to be deposited. Over time, the sand grains will build up and encompass the object forming a very small embryo dune.
Eventually pioneer species of plants will start to grow on the embryo dune. As they do so, they bind the sand together, increasing the stability of the dune. The vegetation itself also traps sand causing the embryo dune to grow even more. As the dune grows it becomes a foredune and a new embryo dune begins to develop in front of it. This is the beginning of a sand dune succession.
Define Neap Tides
Neap tides, are formed when the earth, sun and moon form a right angle. This causes the sun and moon to pull the water in two different directions. Neap tides happen during a quarter or three-quarter moon. The width of the shoreline strip that is affected by waves depends on the tidal range.
Define Spring tides
During full or new moons—which occur when the Earth, sun, and moon are nearly in alignment—average tidal ranges are slightly larger. This occurs twice each month. The moon appears new (dark) when it is directly between the Earth and the sun. The moon appears full when the Earth is between the moon and the sun. In both cases, the gravitational pull of the sun is “added” to the gravitational pull of the moon on Earth, causing the oceans to bulge a bit more than usual. This means that high tides are a little higher and low tides are a little lower than average.
The Coastal Zone
ORDER
Offshore
Foreshore
Nearshore
Coast
Backshore
The Coastal Zone
Coast- Land by the sea
Backshore Zone- Above high tide level and affected by waves during exceptionally high tides and major storms.
Foreshore-Where wave processes occur between the high and low tide marks.
Nearshore- Shallow areas of the sea
Offshore- The Open Sea
Hydraulic Action
(Wave Quarrying)
Air trapped in cracks and fissures is compressed by the force of wavess crashing against the cliff face.
Pressure forces cracks open, meaning more air is trapped and greater force is experienced in the next cycle of compression.
This Process dislodges blocks of rock from the cliff face.
Abrasion
(Corrasion)
Sediment picked up by breaking waves is thrownagainst the cliff face.
The sediment acts on the cliff lika a tool, chiselling away at the surface and gradually wearing it down.
Attrition
As sediment is moved around by waves, the numerous collisions between particles slowly clip fragments off the sediment, making it smaller and more rounded over time.
Corrosion
(Solution)
Carbonate rocks (limestones) are vunerable to Corrosion by rainwater, spray from sea and seawater.
Beach Morphology:
The Shape of a beach, icluding its width and slope the beach profile and features such as berms, ridges and runnels.
Deposition: Traction
Boulders are rolled along, pushed by waves and currents.
Deposition: Saltation
Sand-sized sediment is bounced along, either because ofthe force of water or wind.
Deposition: Suspension
Silt and Clay particles are carried in a column of water.
Deposition: Solution
Chemical compounds of material are dissolved in water as a solution.
