Sources of Energy at Coasts Flashcards
Sources of energy at the coast
The main energy source at the coast is from waves which are formed offshore, which are most commonly generated by wind or less frequently tectonic activity.
Wave Formation
Winds move across the surface of water, causing frictional drag which creates small ripples and waves. This leads to a circular orbital motion of water particles in the ocean.
As the seabed becomes shallower towards the coastline, the orbit of the water particles becomes more elliptical, leading to more horizontal movement of waves.
The wave height increases, but the wavelength and wave velocity decrease.
This causes water to back up from behind the wave until the wave breaks and surges up the beach.
Factors Affecting Wave Energy
Strength of the wind - Wind is essentially air that moves from an area of high pressure to low pressure. The differences in pressure are caused by variations in surface heating by the sun. The larger the difference in pressure the stronger the winds and stronger the waves.
Duration of the Wind - If the wind has been active for longer periods of time, then the energy of the waves will build up.
Size of the fetch - The distance over which the wind blows, the larger it is, the more powerful the waves will be.
Shape of the ocean floor.
Constructive Waves
Constructive Waves tend to deposit material, which creates depositional landforms and increase the size of the beach.
In the summer, constructive waves dominate.
Long wavelength
Frequency - 6-9 per minute
Low waves, which surge up the beach
Strong swash, weak backwash.
Occurs on gently sloped beaches
Destructive Waves
Destructive waves act to remove material, causing erosional landforms.
In the winter, destructive waves dominate with more storm event / stronger winds.
Short wavelength
Frequency - 11-16 per minute
High waves, which plunge onto the beach
Weak Swash, Strong backwash
Occurs on steeply sloped beaches
Tides
Tides are the periodic rise and fall in the level of the sea. They are caused by the gravitational pull of the moon and the sun on the oceans.
Spring Tide
When the sun and the moon are in alignment. Both of their gravitational forces combine to effectively pull the ocean towards them to cause the highest high tides.
On the other side of the planet, this creates the lowest possible low tides.
The spring tide creates the largest possible tidal range.
Currents
Rip currents are powerful underwater current occurring in areas close to the shoreline on some beaches when plunging waves cause water to build up at the top of the beach.
The backwash is forced under the surface due to the resistance from breaking waves, forming an underwater current. This flows away from the shore more quickly due to beach features, such as a gap in the sand bar, creating a rip current.
Rip current claim the lives at beaches every year, though it is possible to escape from them by swimming away from the direction parrel to the beach.
Neap tides
When the Earth, moon and the sun form a right angle. Their gravitational pull interfere with one another and this is when neap tides occur. Both their forces act against each other, so the overall pull is minimised.
The lowest high tide and the highest low tide
The neap tide creates the smallest possible tidal range.
Wave Refraction
Wave refraction is the process by which waves turn and lose their energy around a headland. The wave energy is focused on the headlands, creating erosive features in these areas.
The energy is dissipated in bays leading to the formation of features associated with low energy environments such as beaches.
