Sources of Energy and Sediment in Coastal Environments Flashcards
What is the primary source of energy in a coastal system?
Wind
What are the features of the wind?
Erosion
Wave formation
Fetch
Spatial variations
How can the wind erode?
It is able to pick up and remove sediment
Can cause erosion through abrasion
How are waves formed from the wind?
Transfers energy to the surface of the ocean (frictional drag) causing waves
How does the wind affect waves?
High winds - we have high energy waves
Prevailing winds which dominant winds in a certain area control the direction waves approach coasts
How is the wind affected by the fetch?
Being ‘the distance of open water a wind blows over uninterrupted by major land obstacles’
The longer a wind can travel uninterrupted, strengthens the wind determine the size and energy of waves
What are the crests of the wave?
The peaks of the wave - highest point
What is the trough of a wave?
The lowest point of the wave
How do you measure the height of a wave?
The distance between the trough of the wave and the crest
What is the wavelength of a wave?
The distance between the two crests
How can the frequency of waves be measured?
By measuring the time taken for first and second crest to pass a fixed point - longer the wavelength the lower the wave frequency/ shorter the wavelength the higher the wave frequency
What happens as a wave approaches land?
The BASE of the wave will slow down as the wave comes into contact with the sea bed (friction)
The wave on top will an increase in velocity, causing the crest to rise and wavelength decrease - the wave will continually steepen as it approaches the shore, until it eventually breaks
At what ratio will the wave break at?
When the wave length to height ratio is 1:7 (height is 7 times taller than the wavelength)
What are the two types of waves?
Destructive and constructive
What are the characteristics of constructive waves?
Low wave height
Long wavelength - therefore a low wave frequency
How long can the wavelength reach in constructive waves?
100m
What can be the frequency of a constructive wave?
6/8 waves per minute passing a certain point
What happens as a constructive wave approaches beach?
Wave front steepens very slowly - gentle spills onto beach surface
Has a weak backwash
What does the weak backwash during a constructive wave mean for the sediment?
Material/sediment is moved up the beach forming berms
Why are they called constructive waves?
They are almost constructing the beach by pushing sediment slowly up the beach
What are the characteristics of a constructive coastline?
Wide beach
Shallow gradient
- can potentially become steep after time as sediment os pushed up the beach
How are tides controlled?
Through the gravitational interaction between the earth and moon
What are tides?
A periodic rise and fall in sea level
What are spring tides?
Especially strong tides
When do spring tides occur?
When the earth, the sun and the moon and in line
Gravitational force is the greatest
What are neap tides?
Especially weak tides
When do neap tides occur?
When the gravitational forces of the moon and the sun are perpendicular to one another (90 degrees to one another)
What has the greatest influence on tides?
The moon
Why does the moon have the greatest influence on tides?
Because it is closest to the earth
How does the moon influence tides?
By pulling water towards it causing bulging in the sea (high tide) and low tide in between bulges
How often do bulges occur?
twice a day
How often is the moon in line with the sun in a lunar month?
Twice
What happens during neap tides?
Numerous smaller bulges occur as the sea is pulled towards both the sun and moon
