Systems and processes in coastal environments Flashcards
(50 cards)
What is the definition of erosion?
Erosion is the weathering away of the earths surface by the mechanical action of processes of wind, rivers ,waves etc.
What is Fetch?
Fetch refers to the distance of open water over which wind blows uninterrupted by major land obstacles.
What is Mass movement?
Mass movement is the movement of material downhill under the influence of gravity, but may also be helped by rainfall
What is weathering?
Weathering is the breakdown and/or decay of rock at or near the earths surface. Weathering can be biological mechanic or organic
How does the coastal system receive its energy?
The energy to drive the coastal system is provided by waves, winds, tides and currents
Why is wind important for coastal systems?
-Most coastlines will have a prevailing wind direction where the wind generally reaches the coast from one direction.
-The length of the fetch helps determine the magnitude and size of waves reaching the coast
-Waves are created by the transfer of energy from the wind blowing over the sea surface
-Wind can help in erosion, most commonly in the form of abrasion.
How does abrasion occur through wind?
The wind picks up sediment from the coast and carries it to wear away landscape features.
What are constructive waves?
These waves tend to have low wave height but with a long wavelength often up to 100m.
-The have a low frequency of around 6-8 per minute
As the approach te beach they rise slowly which gives a gentle spill onto the beach surface
-Tend to have a very weak backwash which cant pull sediment off the beach so as a consequence material is slowly moved up the beach through deposition causing ridges
What are destructive waves?
-These have a high wave height with a steep form and a frequency of 10-14 per minute.
-They rapidly steepen as they approach the beach and plunge down when breaking
-Due to their powerful backwash the waves pull material down the beach.
-Destructive waves are commonly associated with steeper beach profiles
How does negative feedback occur with waves?
Constructive waves build up the beach resulting in a steeper beach profile which encourages waves to become more destructive. With time destructive waves move more material back to the sea which reduces the beach angle and encourages constructive waves.
-However this is often not possible due to other factors like wind not being constant
What are longshore currents?
Longshore currents occur as most waves do not hit the coastline ‘head on’ but approach at an angle to the shoreline. This generates a flow of water running parallel to the shoreline which also transports sediment parallel to the shoreline.
What are rip currents?
Rip currents are strong currents moving away from the shoreline. They develop when seawater is piled up along the coastline by incoming waves.
-Initially the current may run parallel to the coast before flowing out through a breaker zone.
-Can be dangerous for swimmers and small boats
What is Upwelling?
Upwelling is the movement of cold water from deep in the ocean towards the surface. The more dense cold water replaces the warmer surface water and creates cold ocean currents.
What is longshore drift?
Also known as littoral drift it is where waves approach the shore at an angle and transport material along the coast in the direction of prevailing winds
What is wave refraction?
When waves approach a coastline that is not a regular shape they are refracted and become increasingly parallel to the coastline
-Overall effect is the wave energy becomes concentrated in the headland causing greater erosion and the ow energy waves spill off into the bay resulting in deposition
How are tides caused?
They are caused due to the gravitational pull of the sun and the moon. The moon pulls water towards it creating a high tide and There is also the same bulge on the opposite side of the earth.
As the moon orbits the earth, the high tides follow it.
What are tidal/Storm surges?
These occur when meteorological conditions give rise to strong winds which can produce much higher water levels then those at high tide
What is the definition of coastal sediment budget?
This is the balance between sediment being added to and removed from the coastal system, that system being defined within each individual sediment cell.
What is the difference between high and low energy coasts?
High energy coasts have strong prevailing winds leading to a higher rate of erosion then deposition whilst low energy coasts have a higher rate of deposition then erosion
What is a sediment cell?
A sediment cell is a distinct area of coastline separated from other areas by well defined boundaries such as headlands and stretches of deep water.
-In theory sediment cells can be regarded as closed systems from which nothing is gained or lost however in reality is it easy for fine sediments to make their way into neighboring cells
Where does coastal sediment come from?
-Streams and rivers
-Estuaries
-Cliff erosion
-Offshore sand banks
-Material from a biological origin including shells skeletons and marine organisms
When does a positive coastal sediment budget occur?
When more material is added to the cell then is removed- A net accretion of material.
-This gives a positive budget and the shoreline builds towards the sea
When does a negative coastal sediment budget occur?
When more material is removed from the cell then is added a negative budget occurs and the shoreline retreats inwards
What are marine processes?
Marine processes operate upon a coastline and are connected with the sea, such as waves,tides and longshore drift
