Coasts Flashcards
2.4 - What influences the size of a wave?
- Wind speed
- Time the wind blows for
- Fetch (distance wave travels)
- Water depth
2.4 - What are wave characteristics
Friction - waves result from friction between wind and the sea surface
Fetch - length of fetch is important, the further a wave can travel uninterrupted the more powerful it will be when it reaches the shore
Strength + duration of wind - stronger the wind, the more powerful the waves
Prevailing + dominant waves - dominant produce largest + most damaging waves while prevailing are ones that blow more frequently
Wavelength - different winds create waves of different wavelengths
Frequency - time takes for successive waves to pass a point = water frequency
Water depth - movement of water particles within a wave in deep water is circular, movements getting smaller with depth
Potential wave energy - proportional to height
2.4 - What are the characteristics of destructive waves?
Short wavelength high frequency
Steep wave front
Waves have circular orbit
Weak swash, very strong backwash erodes sand
2.4a - What are the characteristics of constructive waves?
- Long wavelength so low frequency
- Low wave height
- Waves have a circular orbit
- Strong swash
- Weak backwash
2.4 - How do waves shape the beach(beach morphology)?
- Constructive - gently sloping beaches, tend to be flat - strong swash + water ‘spills’, sediment pushed up beach can cause a ridge
- Destructive - strong backwash, wave ‘plunges’, steep profile - cuts away at the beach, sediment eroded + deposited offshore, creates offshore ridges
2.4 - What might lead to variations of wave type?
○ Short term - Tides (neap/spring), Seasonally (storms), Change in wind direction, Change in currents, Sub-aerial processes
- Long term - Sea level rise, global climate change causing more storms, dams, coastal management
2.4 - How do waves influence the beach sediment profile?
- Largest material is thrown to the back of the beach during storms forming as storm beach or ridge.
- Bars are often made of coarse sand or gravel - thrown there by the force of the wave
- Finer material in between - more easily dragged back by the backwash.
- Finer sand is found further down the beach as this is the material most easily moved by the waves
2.4 - When is erosion the greatest?
○ Large wind speeds, direction and fetch creating high energy waves
○ Waves approach the coast at 90 degree angle to cliff face
○ High tide
- Heavy rainfall increasing sub-aerial erosion and weakening cliff face
2.4 - What are the 4 erosional processes and how do infleunce the lithology?
Hydraulic action - Water crashes into the cracks in the seabed/cliff face causing them to widen over time as water and air is forced into the cracks - heavily jointed sedimentary rocks are vulnerable
Abrasion - sediment or rocks bash against the side of the seabed/sediment picked up by breaking waves is thrown against the cliff face - softer sedimentary rocks more vulnerable
Attrition - Sediment knock against each other causing them to become smaller and rounder - softer rocks are rapidly reduced in size
Solution - Seawater and salt spray from waves may react with rock minerals to dissolve them - affects rocks with calcium carbonate
2.4 - How are wave cut notches and platforms created?
Wave cut platforms tend to be found in areas of harder rock which have many joints and bedding planes which can be exploited by marine erosion.
- erode at base at high tide
- hydraulic action exploit cracks widen creates wave cut notch abrasion enlarges
- sub aerial processes weaken cliff above
- gravity makes it collapse
- collapsed material broken by attrition further erodes cliff
- over time makes wcp
2.4 - How are cave, arches, stacks and stumps formed?
1) cracks at base exploited by hydraulic action
2) widened further by abrasion
3) cracks widen to develop wave cur notch - further hydro action and abrasion deepen notch to turn cave
4) wave refraction distort wave direction - destructive concentrate on sides of headland
5) waves deepen cave on both sides by abrasion - form an arch
6) over time becomes unstable collapses - forms a stack
7) stack further eroded at its base create new wave cut notches
8) eventually exposed stack collapses to form a stump
2.5a - How is material moved along a coastline?
Short answer: Waves, tides and currents
• Waves move sediment up and down the beach
• Currents move material offshore to onshore and vice-versa
• Tides influence the part of the coastal zone where processes are operating
- Rip currents move sediment from foreshore to nearshore
2.5a - What is the two ways in which deposition?
• Gravity settling - energy of water become too low to move sediment/heaviest load dropped first
- Flocculation - tends to happen when material is river sediments/bits of mud, wave energy lowers then particles become attracted to each other and stick together causing them to become heavier and be dropped/ happens mainly at mudflats
2.5a - How does longshore drift occur?
Longshore drift transports material along a coastline when the waves approach the beach at an angle
- Swash brings sediment forward at an right angle while backwash brings sediment back down the beach in a straight line
2.5 - What type of transportation and deposition will take place along these two beaches? Drift aligned and swash aligned?
• Drift-aligned coasts - Waves hit the beach at an angle - sediment is moved to the left by LSD
- Swash-aligned coasts - Waves hit the beach at 90 degrees and sediment moved seaward and landward
2.5 - How are beaches formed?
Beaches are a depositional coastal landform that sit between the high and low-tide levels. They are formed by constructive waves which push material up a beach. As the swash moves up the beach it loses energy and deposits material on the beach.
- can be sandy or shingle
- sandy is flatter
- shingle tend to be steeper
2.5 - How is a spit formed?
1) LSD occurs
2) where coastline ends - material is deposited
3) in time material builds up to form a ridge of sand + shingle
4) wind and sea currents may curve the end
5) river estuary - meeting of waves and river causes a change in speed - both waves and river drop sediment
6) on land side, silt and alluvium are deposited - salt marshes form
2.5 - How is a bar/barrier beach formed?
A bar is a long, narrow stretch of pebbles and sand which grows across a bay attached to the land at both ends.
1) It forms when longshore drift occurs on a coastline.
2) When the coastline changes direction longshore drift continues to transport material and deposits it in the sea so eventually a sandy or shingle ridge forms.
3) If a spit develops in a bay, it may build across it, linking two headlands to form a bar.
2.5 - How is a tombolo formed?
Tombolo is a narrow ridge of sand and pebbles that joins the mainland to an island
1) When waves hit the mainland at an angle the coast becomes drift aligned and longshore drift takes place.
2) Longshore drift moves sediment along a coast for a long period of time.
3) When the sediment reaches the end of the coastline, it is carried for a short time in the same direction until it is deposited on the sea bed.
4) Over time so much material is deposited that it breaks the surface on the water forming a narrow stretch of land called a spit.
5) An island can also act as a barrier to the waves. Waves are refracted around the island and therefore there is little energy behind the island and material is deposited.
6) This can join up with the material being deposited from the mainland.
7) Where there is an island at the end of a coastline this strip of land may eventually link them together and is no longer called a spit but a tombolo
2.5 - How is a cuspate foreland formed?
A cuspate foreland is a triangular extension of the shoreline eg Dungeness in Kent
There is ongoing debate as to their formation. One accepted process of formation is:
1) They are formed due to longshore drift operating on a coastline from two different directions.
2) This forms two spits, one from each direction, each protecting the material behind it, creating the triangular feature.
3) Because the area behind is sheltered there is little wave motion so lots of deposition occurs. Therefore mudflats and salt marshes build up here
4) Overtime enough deposition may be enough to form a new area of land
2.5 - How is an offshore bar formed?
Offshore bars are elongated ridges and mounds of sand or gravel deposited beyond a shoreline by currents and waves.
1) Some form as a result of longshore currents that develop a trough and bar feature in the nearshore zone.
2) In other cases, storms, with destructive waves with high breakers and strong backwash drag berm sediment offshore to help form longshore bars. These bars then migrate shoreward under calmer more constructive wave patterns.
2.5 - Why do spits developed hooked ends?
Two explanations are offered:
• A change from the prevailing winds direction, condiding with the direction of second most dominant fetch and wave direction
- Wave refraction occurs at the end of the spit which carries some material into more sheltered areas.
2.5 - Why is vegetation particularly important in stationary depositional landforms?
• Made of unconsolidated material so susceptible to change
• They are dynamic landscapes
• Help prevent the removal of sediment
- They bind loose sediment together + encourage further deposition
2.5 - What are sediment cells?
Coastlines operate in dynamic equilibrium. In theory, erosion in one place is balanced by deposition in another. Every sediment cell is made up of sources - transfers and sinks. Where there is erosion this will be a source of sediment. When the sediment is transported this is known as a transfer. And where it is deposited this is a sink.
Coastlines operate in dynamic equilibrium. In theory, erosion in one place is balanced by deposition in another. Erosion - transportation - deposition. Sediment budget - balance between gains and loses.
There are 11 sediment cells in England and Wales. Each cell is a closed system with little transfer of sediment between one cell and another.
To be effective, Shoreline Management Plans (SMPs) take into account the whole sediment cell, not just one small stretch.
2.5 - What are some sources, transfers and sinks?
Source - transfer - sink:
Erosion of cliffs - Longshore drift -Backshore depositional landforms (eg sand dunes)
Land sediments eroded by rivers - Wave transport through swash and backwash- Foreshore depositional landforms (eg beaches)
Wind-blown sediments from land - Tides - Nearshore depositional landforms (eg bars)
Subaerial processes - Currents (local or large scale) - Offshore sediment deposition to deep offshore waters
2.6 - What are the types of weathering?
- Mechanical
- Chemical
- Biological
2.6a - What happens during freeze-thaw (mechanical)?
Water enters cracks in rock. Temps fall at night = water freezes, turns to ice expands 10% - pressure on rock - prises it apart - ice melts - water seeps deeper and process repeated
Vulnerable - any rocks with cracks or fissures
Effects - Angular rock fragments and a jagged cliff face are created, with scree slopes at the base
