Coasts Gateway 1 (Factors affecting coastal environment) Flashcards
WAVES: Constructive waves
○break far away from the shore with little wave energy → carry finer materials such as sand onto the shore, → forms gentle slopes.
○low wave frequency of 6-8 waves per minute.
○strong swash → carry more material ashore, →weak → removes little material from the shore back into the sea.
○Overtime, the coasts is built up and sandy beaches are formed.
○The overall process of deposition is more prominent for constructive waves.
○They also have a low wave height.
WAVES: Destructive waves
○ break violently onto the shore with high energy → finer materials such as sand are transported away by turbulent water → leaving coarser materials such as pebbles on the shore →leading to steeper slope.
○They have a high frequency of 10-14 waves per minute.
○They also have a weak swash →carry little material ashore, →strong backwash →carry more material from the coast back to the sea.
○The overall process of erosion is more prominent due to the strong backwash,
○high wave height.
WAVES: Wave refraction
As waves approach an uneven coastline with shallower depths of water, parts of the wave start to slow down due to friction, relative to other parts of the wave.
Headlands: Waves approach the headland and bend towards it, increasing wave height and concentrating wave energy. More erosion occurs as the wave has higher erosive energy, as they slow down due to friction, causing them to slow down and break onto it.
Bays: Waves approach the bays and diverge away from one another, decreasing wave height and spreading out wave energy. More deposition occus as the wave has lower erosive energy, parts of the wave that reach shallow water first slow down while other parts of the wave continue at the same speed.
WAVES: Process when waves break
The water is shallow and the waves interact with the sea bed.→ The waves start to change at a depth that is equivalent to half of their wavelength. →As the waves enter shallow water, the base of the wave starts to slow down due to friction → causing the wave length to decrease and the wave height to increase.→ Eventually, the base of wave stops but the rest of the wave continues to move, causing the wave crest to steepen over and topple over.→ This causes waves to break onto the coast, causing the wave energy to be released.
CURRENTS: Longshore Drift/Currents
When waves approach the coast at an angle due to the direction of the wind blowing → they generate longshore currents which flow parallel to the coast →It will carry materials up onto the shore in the same direction as the swash, and the backwash, owing to friction and gravity, returns to the sea at right angles to the coast, dragging some materials from the shore back into the sea. → This process repeats when the next wave breaks. → Materials are transported parallel to the coastline in a zig-zag manner, known as a beach drift.
TIDES: Low and High tides
Caused by the effects of the gravitational pull of the moon and the sun on the earth,→ a cycle of alternating rise and fall in the sea level occurs, changing every 6 hours.
During high tides,→ waves reach parts of the coasts that may not be subjected to wave action at low tides → waves erode and transport more sediments away from larger parts of the coasts than at other times.
At low tides, as waves are unable to reach certain parts of the coasts, erosion of materials is less prominent.
GEOLOGY: Well jointed rocks
Joints are breaks and fractures on rock surfaces, which can be both hoizontal and vertical. These cracks trap air, making them more vulnerable to erosion when attacked by waves, speeding up the rate of erosion of sediments.
GEOLOGY: Rocks arranged in layers
Clay and Chalk are arranged in an alternate manner. Clay is a soft rock compared to chalk, making it easier to be eroded to from sheltered bays. The harder chalk that is more resistant to erosion by waves protrude outwards into the sea to from headlands.
HUMAN ACTIVITIES
More in Gateway 2
As people trade, live, and engage in recreational activities in coastal environments, they can alter coastlines when building marine and port facilities, causing pollution in these environments by dumping waste. (More in Gateway 2)
ECOSYSTEM: Mangroves
The aerial roots hold the sendiments firmly onto the ground, preventing them from being washed away. Therefore, mangroves act as a barrier that protects sediments from erosion from waves. The trapped sediments can then form small islands and extend further seawards.
ECOSYSTEM: Coral Reefs
They are structures comprising colonies of billions of tiny polyps. They provide natual barriers that help slow down the speed and impact of waves on the coastline. They dissipate wave energy and reduce the wave height, decreasing the erosive energy of the wave. Therefore, there would be less erosion.
EROSION PROCESS: Hydraulic Action
When the waves strike against a rock surface, the waves trap air in the rock joints. The air is compressed by the oncoming waves, exerting pressure on the joints. As the air is repeatedly compressed, the joints weaken and the rocks shatter.
EROSION PROCESS: Abrasion
As waves break, sediments carried by waves such as sand and rocks are hurled against the coast. The loosened sediments knock and scrape against the coastal cliffs. This weakens the surface and breaks down the coast. Over time, the impact from abrasion is powerful enough to undercut a cliff.
EROSION PROCESS: 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.
EROSION PROCESS: Solution
Sea water reacts chemically with water-soluble minerals in coastal rocks, causing them to dissolve in sea water. This causes rocks to eventually weaken and disintegrate.
