UPPER SIXTH
COASTS
The coast is the narrow zone of direct interaction between land and sea. It is the most dynamic of all ecosystems.
Waves.
· Created by the transfer of energy from the wind to the surface of the oceans. Exceptions are tsunamis, which are created by submarine seismic shock waves.
· As the strength of the winds increase, so does the size of the waves.
· Waves which result from local winds and travel only short distances are known as sea, whereas those formed by storms and travel long distances are referred to as swell.
· The energy acquired by waves depends upon;· wind velocity·  duration of wind · fetch - the maximum distance of open water over which the wind can blow.
Wave terminology;

Crest

The highest point of a wave

Trough

The lowest point of a wave

Wave height (H)

The perpendicular distance between crest and trough

Wave period (T)

The time to complete one wavelength.

Wavelength (L)

Distance between two equal points on a wave.  L = CT

Wave velocity (C)

The speed of movement of a crest in a given time.

Wave steepness

The ratio of height to length, or gradient. If it exceeds 1:7 (0.14), the wave will break. Steepness determines whether a wave will be constructive or destructive. Most waves have a gradient of between 0.005 and 0.05.

Energy (E)

Energy is proportional to LH2. A slight increase in height means a very large increase in energy. Estimates suggest that the average power of a wave in winter is 11 tonnes per sq m.
Waves in deep water;
Deep water is when the depth is greater than half of the wavelength. Orbital motion. Size of orbit decreases rapidly with depth. Floating objects have a small net horizontal movement, but a larger net vertical movement.
Waves in Shallow water;
As waves approach shallow water, the net friction with the bed of the sea increases. As the wave base slows down, the orbits become increasingly elliptical. As the water depth decreases, so does the wave length. Height and steepness increase until the upper part spills (or plunges) over. The wave break point, or plunge line, is where the depth of the water and the height of the wave are virtually equal. The water which moves up the beach is known as swash, whilst the returning water is backwash.

Coastal Erosion;
Coastal erosion is accomplished in three main ways, with each of the three ways having subsidiary methods, as detailed below;

Erosion by Waves;
(1)  Wave quarrying affects previously unconsolidated rock. A wave exerts considerable impact, or shock pressure as many tonnes of water hit the rock face. Since energy is proportional to height, storm waves do large amounts of damage in a short space of time. Some storm waves have been recorded up to 50 kg/cm3. This high pressure exists for a brief instant, but can act along fault, joint and bedding planes. It is similar to hydraulic action in rivers. If air is trapped, then pneumatic pressure may assist in loosening blocks, which can extend the erosion above the water line.
(2)  Wave abrasion is the most effective type of wave erosion. The wave contains debris of varying sizes, which is hurled against the cliff. This wears away the rock. In hard rock areas, the action is slow, and produces smoothed areas. Differential erosion between hard and soft rock may accentuate the layering of the rock.
(3)  Wave attrition affects the debris within the wave. The particles reduce in size and angularity as they collide with each other within the wave. Most of this takes place within the breaker zone. The range of attrition varies with the tides.

Coastal Weathering;
(1)  Salt Crystallisation is effective where there is a high evaporation potential, and the growth of chloride slats derived from the salt in sea-water attacks a wide variety of rocks. It loosens fragments of rocks for erosion
(2)  Solution on the coast is notable on limestones. Sea-water is often saturated with calcium carbonate, and it is hard to see why it is so effective. This is particularly true if the tropics, where CaCO3­ levels decrease with temperature increase. It is possible that photosynthesis in plants oxygenates the water during daylight, but releases carbon dioxide in to the water at night, increasing the acidity and effectiveness of solution. The morphological effect is to produce sharp fretted pinnacles of limestone called lapies, low down in the inter-tidal zone. When wave attack is less prevalent, solution may cut notches at the edge of pools and leave overhanging lips. In tropical seas with microtidal or mesotidal ranges, these features become very large and are called visors.
(3)  Biological activity assists solution. Other rock types besides limestone are attacked by secretions, particularly from the blue-green algae which live between the tide lines. Seaweed firmly attaches itself to rocks, which effectively increases the exposed surface area.

Wave refraction.
When a wave approaches a headland, it must refract around the headland. This has several effects. The first of these is that the wavelength shortens. The wave depth decreases, and height increases. The energy is focused on to specific points either side of the headland, and it is in these points that caves often begin to form. The concentration of energy is accompanied by a rise in wave height. Since energy is proportional to wave height, then the power of the waves is greater on the headland. As waves approach the shoreline and enter progressively shallower water, the speed at which they move no longer depends on the size of the wave, but becomes entirely dependent on the depth of water. In the shallower water commonly found off headlands, a wave crest moves more slowly than it would in the deeper water of adjoining bays. The wave crest in the bay, therefore, moves ahead of the wave crests approaching the headlands on either side, and the wave appears to be bent into the bay. This phenomenon is known as refraction. Because of refraction, waves commonly approach the coast with their crests closely paralleling the line of the shore, although the actual plan shape of the wave will depend on the contours of the seabed close to the shore. Wave refraction also tends to concentrate wave energy on headlands, at the expense of adjoining bays; material eroded from the headlands washes into the bays.