Sources of energy at the coast Flashcards
sources of energy in a coastal environment High energy and low energy coasts
Describe a constructive wave.
Long wavelength, low in height, strong swash, weak backwash, have a frequency of 6-10 a minute, formed from far away storms.
Describe a destructive wave.
Short wavelength, high wave height, steep wave faces, weak swash, strong backwash, have a frequency of 11-15 a minute, formed by local storms.
What 4 factors determine the height of a wave?
. fetch
. strength of wind
. duration of wind
. sea depth
How are waves formed?
- The surface of the sea exerts a frictional drag on the lowest layer of wind.
- Then the higher layers of the wind move faster over the lower levels and fall forward pushing down on the sea surface.
- As the wind blows on the back of the small ripple the wave then grows.
Describe what happens when a wave approaches the shore.
Wave refraction occurs when the undersea typography causes the wave fronts to slow, bend and aim to break parallel with the shore.
What is wave refraction?
When waves approach the shore at an angle because of the wind. One end of the wave then feels the bottom of the sea floor and slows down while the rest of the wave continues.
What is the trough of a wave?
The lowest area of a wave
What is the crest of a wave?
The top of a wave
What is a wavelength?
The distance between two crests or two troughs
What is wave height?
The distance between the crest and the trough
What is wave frequency?
The number of waves per minute
What is the velocity of a wave?
The speed that a wave is travelling. It is influenced by the wind, fetch and the depth of the water.
What is swash?
The movement of water and load up the beach
What is backwash?
The movement of water and load back down the beach
Where are higher energy waves concentrated?
In the north and south of the earth.
Where are lower energy waves concentrated?
along the equator
What is a swash aligned beach?
When the waves break parallel to the shore
What is a drift aligned beach?
when the waves hit the coast at a 40-50 degree angle which leads to longshore drift.
What is the backshore?
The area between the high water mark and the landward limit of marine activity.
What is the foreshore?
The area between the high water mark and the low water mark
What is the inshore?
The area between the low water mark and the point where waves don’t have any influence on the land beneath them.
What is the offshore?
The area beyond the point where waves don’t have an influence on the land beneath them.
What is the surf zone?
The region of breaking waves.
What is the breaking zone?
The zone in which waves approaching the coastline begins breaking.
What is the swash zone?
The part of the beach alternatively covered and exposed by swash and backwash.
What is the nearshore zone?
The zone extending seaward from the lower water line beyond the surfzone.
Are high energy coasts usually rocky or sandy?
rocky
Are low energy coasts usually rocky or sandy?
sandy
What is a high energy coast?
when the rate of erosion extends the rate of deposition
What landforms are form at a high energy coast?
Headlands, cliffs and wave cut platforms
What is a low energy coast?
when the rate of deposition exceeds the rate of erosion
What landforms form at a low energy coast?
Beaches, spits, coastal plains and estuaries.
What causes tides?
The gravitational pull of the moon and the sun.
What is a spring tide?
High hightide, low lowtide
What is a neap tide?
Low hightide, high lowtide
What causes ocean currents?
. the tides
. the wind
. thermohaline circulation
. Wind density
What is the tidal range?
the vertical difference in height of sea level between high and low tide.
What is the spring tide?
tides that occur twice a month when the sun and moon align on the same side of the earth
What is the neap tide?
tides that occur twice a month when the sun and moon are at right angles to the earth
What is an ocean current?
a large scale movement of water in the oceans
What is a storm surge?
The pushing of water against a coastline to abnormally high levels, usually a combination of extreme low pressure and high tides.
