Coasts Flashcards
Define Fetch
The distance the wind is blowing over water creating waves. Bigger fetch = bigger waves
What are the two different types of waves and how do they differ?
Destructive:
* Erosion - takes away coastline
* Large waves AKA plunging waves -> they plunge onto shore
* Backwash stronger than swash
Constructive:
* Deposition - builds features
* Small waves AKA spilling waves -> they spill onto shore
* Backwash is weaker than swash
How many constructive waves are there per minute?
6-8
How many destructive waves are there per minute?
10-14
What shape are constructive waves?
Flat
What shape are destructive waves?
Plunging
What season are constructive waves most prevalent?
Summer
What season are destructive waves most prevalent?
Winter/spring
Define swash
Water coming up onto beach/coast after the wave breaks
Define backwash
Water retreating back down the beach after a wave has broken
How many high and low tides are there daily?
Two high tides and two low tides
Name some erosional features of coastlines
- Bay and headland
- Cliff
- Wave cut platform
- Cave
- Sea Arch
- Sea Stack
- Sea stump
- Blowhole
- Geo
Name some depositional features of coastlines
- Beach
- Sandspit
- Sand bar
- Tombolo
- Lagoon
Define prevailing wind
The wind that occurs most frequently in an area
What is the fetch like on the west coast of Ireland and why?
It is large forming very powerful waves. This is because there is 5000km of open sea between the west coast and the USA
What is the prevailing wind in Ireland?
South west
What is the fetch on the east coast of Ireland like and why?
It is small so waves don’t have the same power because there is only 100km of open sea to Wales.
Define wave frequency
The number of waves passing a given point per second. High wave frequency means more energy delivered to coastline
Explain wave refraction
The bending of waves as they approach a coastline at an angle. This occurs because waves slow down in shallower water, causing them to align more parallel to the shore.
Define tide
The periodic rise and fall of sea levels due to the gravitational pull of the moon and sun
Define constructive waves
Low energy waves that deposit material onto the shore forming beaches. Strong swash and weak backwash
Define destructive waves
High energy waves that erode the coastline. They have a weak swash and strong backwash, removing material from the shore.
Define longshore drift
The movement of sediment along the coast due to waves hitting the shore at an angle
Define coastal erosion
The wearing away of land by natural forces such as waves, wind and rain
Draw a diagram to show constructive waves
See notes
Draw a diagram to show destructive waves
See notes
Name and explain some factors affecting coastal erosion
- Wave Energy: Destructive waves erode coasts because they are larger so have more energy
- Fetch: The longer a wave travels the more powerful it is
- Rock Type: Hard rock eg. Granite is more resistant to the erosive power of waves. Unconsolidated material such as silt/clay erodes much faster.
- Coastal Slope: Steep coastlines are more susceptible to erosion
- Tides and currents: Strong tidal currents erode coastlines by moving sediment along coasts
- Weather and climate: Storms erode coasts more. Global warming leads to rising sea levels which affects coastal erosio
- Vegetation: Vegetation eg. Maram grass stabilises the sand and makes erosion harder
Draw diagram to show the different processes of coastal erosion
See notes
Define hydraulic action in the context of coastal erosion
Power of the waves crashing against the coastline
Define abrasion in the context of coastal erosion
The sea using its load to erode the coastline
Define attrition in the context of coastal erosion
Eroded material collides against itself and waves causing friction
Define compression in the context of coastal erosion
Air is compressed in cracks and joints when waves hit. When they, retreat, the air expands causing an explosive effect
Define solution in the context of coastal erosion
Dissolving rock by salts in seawater
Example of Cliffs in Ireland
Cliffs of Moher, Co. Clare
What erosional processes form sea cliffs and wave cut platforms?
Hydraulic action, abrasion, attrition and compression
Define coastal transportation
Material eroded by waves and broken down further by attrition becomes light enough to be transported by sea currents
Draw a diagram to show longshore drift
See notes
Explain longshore drift
- Friction causes waves approaching shore to break
- This causes swash to carry pebbles and other material up the beach
- Water then flows back out to sea, carrying some materials with it
- Sometimes wind direction causes swash to push sediment along beach at an angle
- The backwash then flows back to sea at 90 degree angle
- This process causes deposited sediment to be moved along shoreline
Give an Irish example of a tombolo
Howth, Co. Dublin
Draw a diagram to show features of coastal deposition
See notes
What type of waves form a beach?
Constructive
Where is a beach found
Between the low tide and high tide marks
Give an Irish example of a beach
Salthill Beach, Galway
Name the different types of beaches
- Storm beach
- Pocket beach
- Sand beach
- Shingle beach
- Coral beach
What is a storm beach made up of?
Pebbles and stones
Where are pocket beaches found?
In sheltered bays
How do beaches form?
- Waves carry material up the beach (swash)
- The waves loses energy and deposits material on the shore
- Constructive waves have a weak backwash and do not carry material away
- The weak backwash with no energy to drag material back out to sea sorts material
- Larger materials are at backshore, finer materials are at foreshore
Define backshore
Steeper upper beach that contains coarse material such as angular rocks and shingle
Define foreshore
Gentle lower beach that contions fine material such as sand and mud
Name and explain some features found at beaches
- Cusps: Crescent shaped hollows
- Berms: Terraces on beach
- Ridges and runnels: Sandy mounds (ridges) parallel to the shore
Draw a diagram to show a beach and its features
See notes
Name and explain some hard engineering solutions to coastal defence with examples
- Sea Walls: Tall concrete walls designed to absorb and reflect wave energy. Eg. Promenade, Galway City costing €12 million
- Rock Armour (Riprap): Large boulders placed at the base of cliffs or dunes to break wave energy. Eg. Doolin, Co. Clare and Co. Wexford costing ~€1000 per metre of shoreline
- Gabions: Wire cages filled with rocks placed to support soft cliffs or protect roads. Eg. Villages in Donegal
- Groynes: Wooden or stone barriers built perpendicular to the shore to trap sand and slow longshore drift. Eg. Dublin Bay and Wicklow
Name and explain some soft engineering solutions to coastal defence with examples
- Beach nourishment: Sand is added to eroding beaches to build them up. Eg. Portraine, North Co. Dublin in 2020 to protect houses costing €500,000
- Managed retreat: Allowing certain areas to flood or erode naturally while protecting key assets elsewhere. Eg. Shannon Estuary
What is the difference between hard and soft engineering solutions to coastal defence?
Hard engineering: Building physical structures to protect coastline
Soft engineering: These aim to work with nature rather than against it
Name some places in Ireland worst affected by coastal erosion
- Portrane, Co. Dublin
- Lahinch, Co. Clare
- Clontarf and Dollymount, Co. Dublin
- Rosslare, Co. Wexford
Beaches (30m)
See notes
