Physical - Coastal Landscapes Flashcards
Coasts as systems
What are the characteristics of destructive waves?
Swash/Backwash/Wave Frequency/Wave Height/Sediment processes/Beach Profile/Energy/Main Process
- Weak swash
- Strong backwash
- High frequency (8-10/min)
- High wave height
- Steep Beach Profile
- High energy
- Erosional processes
What are the characteristics of constructive waves?
Swash/Backwash/Wave Frequency/Wave Height/Sediment processes/Beach Profile/Energy/Main Process
- Strong swash
- Weak backwash
- Low frequency (5-7/min)
- Low height
- Low energy
- Shallow beach profile
- Depositional
What is fetch?
Fetch is the** maximum distance of open water** over which wind blows* uninterrupted by large obstacles*.
The fetch partly determines the energy and speed of waves. A longer fetch allows a wave to accumulate more energy.
Explain the negative feedback cycle of constructive and destructive waves
- Constructive waves break onto a beach and deposit sediment on the beach
- As sediment deposits, the gradient of the beach increases over time
- As the gradient increases, more destructive waves break on the beach due to the steeper beach profile
- Destructive waves remove (erode) sediment off the beach
- The gradient of the beach profile reduces and a switch is made back to constructive waves
- The pattern repeats, as a cycle, keeping the beach in dynamic equilibrium
What type of system is a coast?
Coasts are open systems, but at a smaller scale, we analyse *sediment cells *as closed systems.
What are the main inputs of a coastal system?
- Energy from the waves, winds, tides, and currents
- Matter from sediment
- The geology of the coastline
- Sea level change
What are the main outputs of coastal systems?
- Dissipation of wave energy
- Accumulation of sediment above high-tide mark
- Transportation/removal of sediment from local sediment cells
What are some examples of stores/sinks of coastal systems?
Any depositional or erosional landform (as they hold sediment and material in one place)
e.g.
* Arches, caves, blowholes, geos, stacks, stumps, wave cut platforms, wave cut notches, headlands and bays, cliffs
* Dunes, spits, tombolos, bars, salt marshes, tidal flats, beaches
What are some common flows/transfers in coastal systems?
- Sub-arial or marine processes
- Erosional processes
- Weathering
- Transportational processes
- Depositional processes
- Mass movement
- Wind-blown sand
Define erosion
The wearing away of the Earth’s surface by the mechanical action of winds, rivers, waves, and glaciers.
The wearing away and removal of material from parts of the Earth’s surface via mechanical action.
Define mass movement
The movement of material downhill under the force of gravity (it can also be assisted by rainfall).
Define Weathering
The breakdown/decay of rock in situ **at or near the Earth’s surface. **
Lateral erosional processes then move material.
Difference with erosion is weathering keeps rock in/near original area
Why is wind important as an input in coastal systems?
- Primary energy source for many processes (flows and transfers) e.g. important for erosion and transportation to occour
- The fetch determines speed and energy of waves (high wind speed = high wave energy
- Determine prevailing wind direction AND direction of material transport
- Wind is an agent of erosion - removes sediment and can use it to erode other features (abrasion)
Waves are created by winds blowing over the sea surface, which causes frictional drag
What are the 3 components of a wave?
Wave height - Height difference between peak and trough
Wavelength/apmplitude - The distance between two identical points of a wave
Wave frequency - time for a single oscillation
As a wave approaches shallow water…
- Friction between the wave and the sea bed increases
- The wave begins to slow down
- The height and steepness of the wave increases
- Eventually , the upper part of the wave plunges forward as the bottom slows down
- The wave breaks onto the shore
What happens as a constructive wave approaches the beach?
- The wave front steepens slowly
- The wave gives a gentle spill onto the beach
- The water of the wave percolated into the beach material, and the swash rapidly looses volume
- There is a weakened backwash due to the insufficient force of the low volume of water
- The backwash cannot pull sediment off the beach or impede the next swash of the next wave
- As a result, *sediment slowly advances up the beach leading to the formation of ridges known as berms
What happens as destructive waves approach the beach
- The wave front steepens rapidly
- When the wave breaks, it plunges down
- There is little forward movement, so a strong backwashs is created
-This inhibits the swash of the next wave also - Very little material moves up the beach, backwash pulls material back down the beach
What is a storm beach?
Sometimes, destructive waves can fling shingle to the rear of the beach, this forms a large ridge knows as a storm beach.
Explain the process of wave refraction
The topography of the coastline affects wave action. When the coastline is in an irregular shape, waves are refracted.
- As waves approach the coast, they drag and slow down in shallow water near a headland
- Waves will increase in height and steepness
- The section of the wave in deep water is still moving faster, causing the wave to bend
- Wave energy as a result becomes concentrated at the headland, causing greater rates of erosion
- The** low-energy waves** spill onto the bay, resulting in deposition from constructive waves
- As waves pile up against the headland, sea levels rise creating longshore currents (these transport eroded material to the bays)
Tides are affected by/ created by…
The gravitational pull of the moon, sun and earth. The moon is the most prominent in effect, 2.2x more powerful than the sun
What causes a high tide?
When the moon is above a section of the earth, the moon’s gracity exerts a force on the water, pulling it up, creating a high tide
The moon also pulls the whole Earth towards it. The oceans on the other side of the Earth are **less pulled **as the moon’s force is weaker, so a high tide is created on the opposite side of the earth too.
Tides cycles happen around twice a day (high–>low–>high–>low)
What causes a spring tide?
A spring tide is when there is a higher tide than normal. This is created when the sun and moon are in allignment, which amplifies the force of the moon’s gravity on the Earth
What causes a neap tide?
Neap tides are created when the sun and moon are at right angles to the Earth. The sun weakens the moon’s gravitational pull on Earth, resulting in lower than normal tides.
What other factors affect tides?
- Coriolis effect (direction)
- Proximity of land masses/coasts (strength)
- Morphology of the sea bed (topology for sea floor) (strength)
