Geography - Coasts EQ1 Flashcards
What are the parts of a shoreline?
The submerged zone below the low tide shoreline is the offshore.
Between the low tide and high tide shorelines is the foreshore.
The backshore stretches landward from the high tide shoreline to the highest water line. The offshore, foreshore and backshore form the shore.
The berm is a raised part of the beach where vegetation often grows.
How are waves formed?
Ocean waves form when winds blow over the surface of the ocean. The friction from the wind causes
the water particles near the surface to move in an orbit i.e., in a circular motion, which creates the
waves.
What are the parts of a wave?
Crest: Highest part of the wave
Trough: Lowest part of the wave
Wave height: The vertical distance between the crest and the trough
Wavelength: The horizontal distance from crest to crest or from trough to trough
Wave steepness: The ratio of wave height to wavelength
Wave period: The time waves take to travel through one wavelength
Wave frequency: The number of wave crests or troughs that pass a fixed point in one second
What are the factors affecting wave energy?
Wind speed: How fast the wind is blowing
Wind duration: How long the wind blows
Length of fetch: The fetch is the distance the wind blows over the seas or oceans. The greater the fetch, the more energy the waves have.
What is the movement of waves?
Waves in the open ocean have a long wavelength and a low wave height. Water particles in the open ocean move in an orbit. This motion decreases with depth i.e, there is less orbital motion in deeper water.
What is the movement of waves when approaching the shoreline?
Although water particles in the ocean move in circular motion, this motion changes as waves approach coastlines. As waves move closer to the coastline, the water gets shallower. This causes friction between the water particles and the sea bed, and the base of the wave starts to slow down. As a result, the wave height will increase and the wavelength will decrease. (The waves become steeper and closer together.)
Eventually, the wave becomes so steep that the crest topples over. This causes the wave to break onto the coast, releasing the energy of the wave.
What is the swash and backwash?
Swash: The water rushes up the slope of the shore. Carries sediments onto the shore.
Backwash: Returns from shore into the sea. Carries sediments into the ocean.
Types of waves and their characteristics
Constructive waves: Gentle gradient, low wave height, long wavelength, low frequency, high wave period, swash more powerful than backwash, low energy waves, more deposition, spilling breakers
Destructive waves: steep gradient, high wave height, short wavelength, high frequency, low period, backwash more powerful than swash, high energy waves, more erosion, plunging breakers
What are the ways of coastal erosion?
● Hydraulic Action
Waves break against a rock surface by their sheer weight and power. They also trap air in the cracks in the rocks. This air is compressed by the oncoming waves, exerting pressure on the cracks. As the air is repeatedly compressed, the rock weakens and breaks apart.
● Abrasion or Corrasion
As waves break, sediments carried by waves, such as sand and rocks, are hurled against the coast. These sediments knock and scrape against the coastal cliffs. This weakens the surface and breaks down the coast. Over time, the impact is powerful enough to undercut a cliff.
● Attrition
When rock particles carried by waves rub or hit against one another, they break down into smaller pieces and become smoother and more rounded over time.
● Solution or Corrosion
Sea water reacts chemically with water-soluble minerals in coastal rocks and dissolves them. When solution of minerals occurs, rocks are weakened and eventually disintegrate.
What is the process of longshore drift?
The prevailing wind causes waves to approach the shore at an angle. The swash carries the sediments up onto the coast at an angle. The backwash then carries the sediments back to the sea at right angles to the coast due to the influence of gravity. This motion is repeated and causes a zig-zag movement of sediments along the coast. This zig-zag movement is one way in which
sediments are moved along the coast.
The overall movement of sediments parallel to the coast is known as the longshore drift.
What is deposition?
Deposition occurs when waves lay down sediments along the coast. When small or low- energy waves do not have the energy to carry the load, deposition occurs. Larger sediments are deposited first, followed by smaller sediments.
What is the formation of cliffs and wave-cut platforms?
When waves repeatedly pound against the rock surface, they weaken the rocks through erosional processes like hydraulic action and abrasion. A crack or joint on the rock surface will gradually enlarge
due to the erosional processes to form a notch. The notch may be further eroded to form a bigger hollow space called a cave.
The overhang of the cave becomes unstable with further erosion, and eventually collapses into the sea, forming a steep cliff. The collapsed material will be deposited at the foot of the cliff. Overtime, the cliff will retreat inland and a gentle sloping platform appears at the base where the cliff used to be. This platform is called a wave-cut platform.
What is the formation of headlands and bays?
Some coasts are made up of rocks with different levels of resistance. They may occur in alternate bands with less resistant rocks. (discordant coastline) The rocks form bands at right angles to the coast, which exposes them to continual wave erosion. The resistant rocks are less easily eroded by the waves and they remain as headlands, which jut out into the sea. The less resistant rocks are more easily eroded and are eroded away to form bays.
What is wave refraction (continuous of headlands & bays)?
Wave refraction is the process by which waves change direction as they approach a coast. On a coastline with alternating headlands and bays, waves tend to converge on headlands. This
gives rise to increased wave height and greater erosive energy. However, when waves approach
bays, they diverge, resulting in waves with less energy as energy dissipates on the coastline.
What is the formation of caves, arches, stacks and stumps?
Commonly found on headlands.
Wave erosion, especially by hydraulic action and abrasion, erodes the headline along a line of weakness. Continuous wave erosion results in the formation of a cave in the area. When two caves develop on the opposite sides of a headland, erosion may eventually join the two
caves together to form an arch. Overtime, the roof of the arch may collapse, leaving behind the pillar of the arch known as the stack.
Continued erosion reduces the stack to a lower level to form a stump.
