Coasts Flashcards
How is a wave formed?
1) The wind blows over the sea
2) This creates ripples
3) These ripples become bigger swells
4) Swells approach land
5) The sea becomes shallower
6) The bottom of the wave slows due to friction
7) The top keeps going and forms a crest
8) The crest topples forming a breaking wave
Waves are created by:
The action of wind and its frictional drag on the surface of the sea.
Waves can be a product of:
Local winds (sea) or distant storms (swell).
Wave energy is determined by:
- Wind velocity (wind speed)
- Duration (period of time during which the wind blew)
- Fetch (distance over which the wind blew)
What are the two parts of a wave?
- Swash: the movement of the wave up the beach
- Backwash: the movement of the wave back down the beach
Wavelength:
the distance between two successive crests
Wave frequency:
number of waves per minute
Wave crest
highest point of a wave
Wave trough
lowest point of a wave
Wave steepness:
the ratio of the wave height to the wavelength
Wave period:
the time taken for a wave to travel between one wavelength
Wave energy:
a product of wind velocity, duration and fetch
Describe the features of a constructive wave:
- Created by short fetch
- Small, gentle waves with low energy
- Deposit sediment
- Swash is stronger than the backwash.
Describe the features of a destructive wave:
- Created by large fetch
- Big, strong waves with high energy
- Erode the coastline
- Backwash is stronger than the swash.
What is fetch?
Fetch is the distance the wind blows over the sea - the bigger fetch, the bigger wave.
Outline wave refraction
- As waves leave deep water they slowed by the frictional drag of contact with the bed
- Waves would ideally like to break parallel to the coast
- Irregular coastlines do not allow this – waves will slow in shallower water (approaching headlands) but remain unimpeded in deeper water (bays)
- Wave energy is therefore focused on the headlands
- Here the coastline is exposed to the full energy, velocity and power of the wave.
Outline the concept of sediment cells
A sediment cell (littoral cell) is section of coastline that is involved in the complete cycle of sediment transport and deposition.
Sediment budget describes the movement of sand sized particles and larger sediments into, within and out of a defined coastal segment (sediment cell).
There will be inputs of sediment (sediment sources) and outputs of sediment (sediment sinks).
What are tides?
Tides are the regular rising and falling of the surface of the sea
They are caused by the gravitational pull of the sun and moon on the ocean
What is the spring tide?
When the moon is between the Earth and sun their combined gravitational pull creates the biggest bulge of water and the highest tide.
At this time the high tides are at their highest and the low tides are at their lowest – so the tidal range is at its greatest.
What is the neap tide?
When the Earth, moon and sun form a right angle their gravitational pull interferes with one another giving the lowest high tides and highest low tides - small tidal range.
What is the tidal range?
The tidal range determines the vertical range of erosion and deposition and the length of time the littoral zone is exposed to subaerial weathering.
What are tidal bores?
When water from an open stretch of ocean is confined in narrow sections of estuaries the tide is amplified.
The Bristol channel narrows to become the Severn estuary.
When tides suddenly rise this sends on influx of water up the Severn River – known as the Severn Bore.
What is erosion?
EROSION IS THE WEARING DOWN OF ROCK BY MOVING FORCES.
This usually occurs at the base of our cliffs and by waves.
What is weathering?
WEATHERING IS THE WEARING DOWN OF ROCK ‘IN SITU’ BY ITS ENVIRONMENT.
Sub aerial forces (like rain, air and temperature) act on the cliffs to break them down.