Coasts-Lesson 5-6 Coastal Processes Flashcards
What are the 6 marine erosion processes?
Wave pounding Wave quarrying Hydronic action Abrasion/corrasion Attrition Solution/corrosion
What is wave pounding?
- Mass of water in a wave is very powerful
- steep waves have a lot of energy and when they break against the cliff foot or sea wall they release shock waves
What is wave quarrying?
- the action of waves breaking against unconsolidated material such as sand and gravels
- waves scoop out the loose material
What is hydronic action?
- the weight of water being forced into a joint traps air
- force of water compresses the air causing pressure to build on the surrounding rock
- process continues leading to eventual weakening and breaking off of rock pieces
- storms may remove large chunks of the cliff which leads to extensive damage to sea defence
- the changing pressure leads to cavitation
What is cavitation?
- the violent effervescence of air bubbles coming out of solution as the pressure drops
- the resultant shockwaves can enlarge rock fractures and fragment the cliff
What is abrasion/corrasion?
- pebbles stones and smaller sized particulate are moved by waves and then hurled against the cliffs by waves
- the greater the wave the larger the load meaning the wave causes more damage
What is attrition?
-the breaking down of already eroded rocks as well as smoothing and rounding them
What is solution/ corrosion?
-chemical reaction of seawater or spray which can corrode several rock types
What are the 5 processes of transportation?
- traction
- saltation
- solution
- suspension
- longshore drift
What is traction?
-traction is when rocks and pebbles are rolled along the seabed by the seawater
What is saltation?
-saltation transports small stones and material in a leapfrogging motion across the seabed
What is solution? Transportation
-solution is when dissolved material is moved with a mass of water
What is suspension?
-suspension is when material is suspended and carried by a body of water
What is longshore drift?
- waves approach the shore in a diagonal direction depending on the dominant wind
- LSD occurs when waves approx the shore at an angle
- material is pushed up the beach by swash at the same direction as the prevailing wind
- waves run back down the beach, backwash drags the material down the steepest gradient perpendicular back down the beach towards gravity
- sediment moves in a zig zag fashion overtime
What are the 6 sub-aerial weather in processes?
Frost shattering Salt crystallisation Wetting and drying Solution Biological action Chemical weathering
What is frost shattering?
- it is promoted by the presence of large amounts of water and the tendency for coastal rocks to be severely cracked by the process.
- repeated freezing and melting creates expansion and exerts pressure in the rock widening the crack
What salt crystallisation?
-in Tidal or wave splash zone, salt water is readily available and evaporation leads to the formation of salt crystals. As these crystals grow they exert pressures within the rock causing it to gradually break apart
What is wetting and drying?
- active in tidal or splash zone
- Clays and shales are present they are prone to expansion and contraction associated with wetting and drying (wet=expand, dry=contacts)= cracks form in the rock
What is solution? Weathering
-involving the dissolving of soluble minerals is an active process at the coast. Enlarge joints in the rocks creating pitted and jagged rock surfaces
What is biological action?
- shellfish have paddocks, adapted shell to enable them to drill into rock
- they protect the rock surface from wave action but could be removed by storm waves
- seaweed attaches to rock and swaying seaweed may prise loose rocks from sea floor
- blue-green algae secrete chemicals promoting solution
What is chemical weathering?
-occurs where there is alternate wetting and drying towards the bottom of slopes where material and moisture often accumulate
What are human sub-aerial processes which increase erosion?
- walkers along cliffs cause vegetation and soil to be worn away which contributes to rockfall
- footpaths are heavily used and eroded
- trampling exposes vegetation more readily weathered and eroded
- pressure of cliff tops due to building and removal of protective beach material increases coastal erosion
What is mass movement?
Non marine erosion process where the mass downhill movement of material under several influences
What are the 7 types of mass movement?
- landslides
- rockfalls
- mudflows
- slides and slumps
- soil creep
- run off
- solifluction
What is a landslide?
-mass movement of material (rocks, earth and debris) down hill following lubrication of the foundations
What are rockfalls?
-fragment of rock detached by sliding or falling along a vertical cliff
What are mudflows?
-heavy rain can cause large quantities of fine material to flow downhill due to soil becoming saturated and excess water cannot infiltrate soil so, surface layers become fluid and flow downhill
What are slides and slumps?
A slump is a type of mass wasting that results in the sliding of coherent rock material along a curved surface. A slump is sometimes referred to as a rotational slide because a portion or block of the slope ‘slides’ down as it ‘rotates’ around an axis parallel to the slope.
What is soil creep?
Slow downward progression of individual soil particles down a low grade slope
What is runoff?
Flowing into a storm water drain
What is solifluction?
Movement of wet soil down a slope especially in cold weather conditions
What are the 5 types of chemical weathering?
- oxidation
- hydration
- hydrolysis
- carbonation
- solution
What is oxidation?
The process of addition and combination of oxygen to minerals. The absorption is usually from O2 dissolved in soil water and that present in atmosphere. The oxidation is more active in the presence of moisture and results in hydrated oxides. Minerals containing Fe and Mg.
What is hydration?
Chemical combination of water molecules with a particular substance or mineral leading to a change in structure.
Why is hydrolysis?
Mildly acidic water reacts or combines with minerals to make clays and dissolved salts. Degrades rock making it susceptible to further erosion
What is carbonation?
Carbon dioxide when dissolved in water it forms carbonic acid.
2H2O + CO2 -> H2CO3
This carbonic acid attacks many rocks and minerals and brings them into solution. The carbonated water has an etching effect up on some rocks, especially lime stone. The removal of cement that holds sand particles together leads to their disintegration.
What is solution?
Some substances present in the rocks are directly soluble in water. The soluble substances are removed by the continuous action of water and the rock no longer remains solid and form holes, rills or rough surface and ultimately falls into pieces or decomposes. The action is considerably increased when the water is acidified by the dissolution of organic and inorganic acids.
