Coasts GW 1 - done Flashcards
How are waves generated and what factors affect wave energy?
Waves are generated when energy from wind blowing across oceans is transferred to the water surface.
Factors affecting wind energy will also affect wave energy (all proportional):
- distance travelled by winds
- wind speed
- wind duration
Explain how a wave releases its energy onto the beach.
- The wave approaches the coastline and begins to interact with the seabed due to the shallow coast.
- As the seabed gets shallower, the base of the wave slows down due to friction.
- The base of the wave stops, but the crest continues moving. The wave becomes taller and steeper.
- The wave eventually breaks onto the coast, releasing wave energy.
Define ‘swash’ and ‘backwash’.
Swash: water that rushes up a beach after the wave breaks, carrying sediments up the shore.
Backwash: water that returns to the sea after the swash loses energy due to gravity and friction, carrying sediments back into the sea.
Describe and explain wave refraction.
Waves change direction as they approach an uneven coastline. The shallower depths of water causes parts of the wave to slow down due to friction.
Waves tend to converge on headlands, leading to more concentrated wave energy, and more destructive waves. Erosion happens more often.
Waves tend to diverge at bays, spreading out the wave energy and leading to more constructive waves. Deposition happens more often.
State the differences between constructive and destructive waves.
6 main differences
- Constructive waves have less energy than destructive waves.
- Constructive waves are smaller in height and longer in wave length than destructive waves.
- Constructive waves have a smaller (6-8/min) wave frequency than destructive waves (10-14/min).
- Constructive waves have a more powerful swash than backwash, compared to a destructive wave.
- Constructive waves occur on gentle coastal slopes while destructive waves occur on steeper coastal slopes.
- Constructive waves deposit finer materials (closer to the sea) while destructive waves deposit coarser materials (closer to the sea).
Describe currents and explain how they affect coastal environments.
Currents are large-scale continuous movements of water in seas and oceans.
- driven by prevailing winds that generally blow in 1 direction.
- important in distributing sediments and shaping coasts through erosion and deposition of sediments
Longshore currents flow parallel to the coast and move sediments parallel to the coast in longshore drift.
Describe tides and explain how they affect coastal environments.
The daily alternate rise and fall in sea levels, caused by effects of the gravitational pull of the sun and moon on the earth.
Each coastal area receives 2 high tides and 2 low tides daily.
- waves during high tide erode sediments away from the coast
- waves during low tide deposit more sediments
Describe geology and explain how it affects coastal environments.
Geology of a location is the arrangement and composition of rocks found in the area.
- Harder rocks are harder to erode and vice versa
- Areas with different compositions (layers of different rocks) have uneven erosion
- soft rocks: limestone
- hard rocks: granite
Describe human activities and explain how they affect coastal environments.
People alter coastlines when they alter coastlines to live, fish and engage in recreational activities.
- coastlines are altered to build ports and marine facilities
- waste dumping leads to pollution
- activities disrupt ecosystems of existing plants and animals
Explain the different coastal erosional processes.
CASH
- Corrasion/Abrasion
- sediments carried by waves are hurled against the coast
- the sediments knocks and scrapes the rock faces on the coast, weakening the surface and breaking it down
- Attrition
- rock particles carried by the waves hit against each other
- the particles break down into smaller pieces and get smoother and rounder over time
- Solution
- seawater reacts chemically with water-soluble minerals in rocks, causing them to dissolve
- weakens the rocks, which will eventually disintegrate
- Hydraulic action
- waves strike against the rock surface, trapping air inside rock joints
- as air gets compressed, extreme pressure is exerted on the joints
- the air repeatedly gets compressed, leading to weakening joints and the rocks shattering
Explain why deposition takes place.
- Sediments from the coasts are eroded and transported elsewhere via waves.
- When the waves’ wave energy decreases, they cannot continue carrying the sediments and drops the sand, rock particles and pebbles it has been carrying.
- Larger sediments are deposited first, followed by smaller sediments.
- coasts sheltered from strong winds will have waves with lower wave energy, leading to more deposition
Explain how sediments are transported.
with the help of longshore drift
Beach drift
1. Waves approach the beach at an angle, carrying sediments up the beach as an angled swash, depositing them.
2. The backwash moves perpendicularly down the beach, eroding the beach and carrying sediments away.
3. The repeated zig-zag pattern is known as beach drift. This allows sediments to move parallel to the beach along the coast.
Longshore currents
1. Ocean currents that flow parallel to a coast.
2. Waves approach the beach at an angle, generating longshore currents in the nearshore zone, moving sediments along the beach.
The combined effect of sediment mvovement by beach drift and longshore currents is called longshore drift.
What are cliffs and shore platforms?
A cliff is a steep and nearly vertical rock face along the coast.
A shore platform is a gently sloping expanse of rock debris at the base of a cliff resulting from erosion.
How are shore platforms formed?
- Waves repeatedly pound against a rocky coast and weakens the rocks, causing lines of weakness to form in the rock face.
- Over time, hydraulic action and abrasion may erode a crack on the rock surface, enlarging it to form a notch.
- The notch is deepened to form a bigger, hollow space called a cave.
- The roof of the cave collapses due to continuous erosion of the bottom section, forming a cliff.
- As the cliff continues to be eroded by waves, it retreats inland. A gently sloping flat surface called a shore platform forms at the base of the cliff.
What are headlands and bays?
Headlands are protruding areas on a coast made up of more resistant rocks.
Bays are areas on the coast curving inwards made up of less resistant rocks.
