2.1 Coastal landforms Flashcards
What erosional processes affect coasts?
Abrasion - The wearing away of cliffs by the load carried by the sea. It increases when the load material (carried by the sea) is larger and more angular
Attrition - The wearing away of the load carried by the by the sea. Producing smaller and rounder pieces.
Hydraulic action - The force of the water wearing away rock. The force of water increases when wind increased
Solution/Corrosion - When rock such as limestone and chalk dissolves into the sea
What transportational processes affect coasts?
Traction - Larger rocks dragged along the sea bed
Saltation - Smaller rocks bounced along the sea bed
Suspension - Fine materials suspended in the water
Solution - Dissolved material in the water
What are the different types of weathering that affect coasts?
Biological:
- Organism that secrete acids which breaks down rocks. Additionally plant roots can cause cracks in rocks.
- Can also have animals such as rabbits and moles which dig away the ground
Chemical
Chemical:
- Hydration, especially in clays which take in water, expand and can cause stresses in the rock.
- Oxidation, which is common in iron rich rocks and can produce oxidized irons.
- Carbonation wich can occur when acidic waters combine with calcium carbonate to form calcium bicarbonate
- Solution - dissolving substances in the rock
Physical:
- Salt crystals expand (due to evaporation) which exerts pressure on the rocks causing cracks.
- Freeze thaw weathering is when liquid water seeps into the rocks inside rocks and then it freezes which causes water to expand causing cracks.
What mass movement affects coasts?
Mass movement - Rocks and loose material which has either been eroded or weathered from the cliff falls down to the base of the slope [usually the cliff] under the influence of gravity. This movement of loose debris is collectively called mass movement but it can happen in a number of ways. It can happen slowly or rapidly, dramatically or almost imperceptibly, in solid form or in liquid form.
Sliding - When large mass of rock moves downslope keeping a constant speed due to its mass.
Slumping - When a mass of rock tears away from a larger mass of rock and moves a short distance down a slope with a distinct rotational movement aon a concave slip-plane. It leaves a fresh scar on the landscape. It is especially common wherer hard, resistant rock overlie clay tha has become saturated with water, thereby reducing its strength.
Mudslide - Mudflows are viscous, fluid flow of water mixed with unconsolidated grainy rocks and soils. They require significant saturation of this material before a flow occurs.
Rockfall - blocks of rock topple off near vertical slope. They are common on cliffs that are undercut by the sea or on slopes where mechanical weathering, such as freeze-thaw, is taking place
What are the influences on coastal environements?
Geology - Hard rocks such as limestone give rugged landscapes, whereas soft rocks such as sand and gravels produce low, flat landscapes. On a local scale, hard rock generally form headlands where as soft rocks form bays
Geological structure - Accordant/concordant (Pacific-type) coastlines occur where the geolofical strat lie parallel t the coastline, for example, along the Califiornina coastline, USA. HWereas discordant (Atlantic-type) coastlines occur where the geological strata lie parallel to the coastline, for example, the sourthwest coastline of Ireland.
Vegetation - vegetation from coastal ecosytmes can affect coastlines through weathing and their indirect impact on human activites. Vegetation such as mangroves can aslo protect coastlines from storms.
Sea-level changes - Falling sea levels product relict cliffs and raised beaches whereas rising sea levels are associated with fjords (drowned glacial U-shaped valleys) and rias (drowned river valleys). Isostatic = local change; Eustatic = global change. Sea level cahnge is caused by melting and freeing of large ice sheets.
Human impacts - Coastal zones can be used for human purposes sucha s industry, recreation and towurism. For example Palm Jumeirah has reduced water ciruclation and had many detrimental ecological impacts.
How do headlands develop from erosional processes?
- Headlands and bays form most often in discordant geology where the bands of resistant and less resistant rock run at right angles or perpendicular to the coastline.
- The bands of rock are subject to differential erosion rates. The geology that experiences fastest erosion is the less resistant geology.
- Processes such as hydraulic action and abrasion erode these rocks quickly pushing the coastline back to form a feature called a bay.
- This normally takes a semi-circular shape due to wave refraction. The land behind it is normally low and close to sea level because this less resistant rock would have been weathered over thousands of years.
- The resistant bands of rock are not eroded as quickly and so stick out into the sea forming headlands. These headlands often have wave cut notches and platforms as they are eroded at their base.
- The headlands encourage wave refraction, which concentrates the force of the waves onto the sides of the headland which can lead to caves, arches, stacks and stumps forming.
How do cliffs and wave-cut platforms develop from erosional processes?
- Vertical or steep cliffs will form on a coastline if the geology is resistant.
- The base of the cliff is eroded by the waves. Processes such as hydraulic action, where the power of the waves pound the cliff and air is forced into cracks and faults, and abrasion, where marine sediment is thrown against the cliff, take place forming a wave cut notch.
- This is normally found at the high tide mark where wave attack has undercut the rock. This erosion will continue over time (years) until the rock above is unsupported and collapses under the force of gravity.
- Over many tens-hundreds of years, these processes continue and the cliff retreats leaving an area of flat rock in front of it called a wave cut platform. This runs from the low tide mark to the high tide mark (at the cliff base).
- The surface of the platform slopes gently towards the sea and often contains many rock pools, which are like pot-holes. These features are very common if the geology is chalk or limestone because rocks containing calcium carbonate experience more corrosion.
How do Caves, arches, stacks and stumps develop from erosional processes?
- Caves, arches, stacks and stumps form in resistant rocks, often on headlands.
- Wave refraction concentrates the power of the waves onto the sides of the headland. Erosion exploits the lines of weakness in the side of the headland. Hydraulic action, abrasion and corrosion/solution attack the rocks.
- Eventually, a small feature called a cave forms. Over tens to hundreds of years, the cave is widened through erosion.
- Storm waves, in particular, contribute to the width, depth and height of the cave increasing it until the back of the cave has broken through to the side of the headland, this forms an arch.
- Eventually, the top of the arch which is left unsupported and, having been weakened by weathering it collapses under gravity.
- This leaves a stack of rock separated from the main headland. The stack is exposed to the open sea and the waves erode its base.
- Eventually, the base will become very narrow and unable to support the weight of rock above. The stack will collapse under gravity leaving a small stump.
How do beaches develop from erosional and depositional processes?
Beaches are formed when eroded material is brought up the beach in swash and is deposited. The greater the rate of deposition, the larger the beach and the more stable it is.
Destructive wave dominated beaches have a steeper beach gradient because the backwash has increased strength which carves out the beach. This leads to more concave sections on the beach. The heavy material can be chucked further up the beach as it goes upwards with more force than constructive but lighter material is dragged back to sea.
Constructive waves have stronger swash compared to backwash and therefore material is pushed up the beach. Due to percolation and friction this uses up the waves energy making backwash weaker. This means we usually get graded deposition, where the largest material is deposited at the top and the smallest (and lightest) is brought further down to the shoreline. Where the largest material is deposited at the top of the high tide mark, we find a berm.
How do spits, bars and tombolos develop from erosional and depositional processes?
- Longshore drift moves material along the coastline in the direction of the prevailing wind, this continues along the coastline until there is a change in direction of the headland.
- Longshore drift continues but now is depositing material off of the coastline. If this deposition is in a low energy environment, where the sea is generally calm, then, over time, there will be more deposition than removal of sediment.
- As this deposition continues, it increases the amount of friction experienced by waves, further reducing their energy leading to further deposition, eventually the deposited material grows above the low tide and eventually the high tide level.
- At this point, we may start to see salt tolerant vegetation grow on the spit and help stabilise it. If there is another, semi dominant wind, we may see a hooked spit, where the influence of the next most dominant wind causes the end of the spit to curve.
A tombolo is a spit that joins the headland to an island.
A bar is where a spit joins two headlands.
