Block 5 (Processes Of Coastal Weathering, Mass Movement, Erosion + The Characteristics + Formation Of Associated Landforms + Landscapes) Flashcards
What are sub-aerial processes?
Land-based processes that alter the shape of the coastline
- Weathering
- Mass movement
What is weathering?
The breakdown or changing of rocks at the Earth’s surface, in situ
- Biological/biotic
- Chemical
- Physical/mechanical
What is biological/biotic weathering?
The breakdown of rock caused by plants + animals
How can plants complete biological/biotic weathering?
- Roots can open up faults in the rock
- This increases the rock’s vulnerability to destructive processes (e.g hydraulic action)
How can animals complete biological/biotic weathering?
- Burrowing animals can weaken soft rocks
- Animals can hive off chemicals that contribute to chemical weathering (chelation) - e.g. seagull guano is very acidic, and can break down calcium carbonates, limestone, chalk etc.
How can humans complete biological/biotic weathering?
- Humans walking on rocks, etc, can break them down over time
What is chemical weathering?
The breakdown of rock caused by a change in its mineral composition
- Solution
- Hydration
- Hydrolysis
- Oxidation/reduction
- Chelation
How does solution complete chemical weathering?
Certain minerals are dissolved by acidic water (acids in seawater + acid rain)
- E.g. Limestone dissolved easily by carbonic acid via ‘carbonation’
How does hydration complete chemical weathering?
Absorption of water by rock weakens its crystal structure, making it more susceptible to other weathering
How does hydrolysis complete chemical weathering?
Water reacts with minerals in rock - causing changes related to hydrogen ion concentration
- E.g. Feldspar minerals in granite are very affected by these changes
How does oxidation/reduction complete chemical weathering?
Oxidation - rocks gain oxygen
Reduction - rocks lose oxygen
- E.g. Oxidation - (oxygen from water - mainly affects rocks with high ion concentration)
Reduction - common in waterlogged conditions (less oxygen)
How does chelation cause chemical weathering?
Organic acids bind to metal ions, causing breakdown of rock
- E.g. Acids from plant roots + decaying animals
What is physical weathering?
The breakdown of rock by water + the environment, without a change in chemical composition
- Salt water crystal growth
- Freeze-thaw
- Wetting + drying
How does salt water crystal growth complete physical weathering?
Salt left in cracks in rocks when seawater evaporates. Crystals grow, exerting pressure on rock + causing its breakdown.
How does freeze-thaw complete chemical weathering?
Repeated freezing + thawing causes ice crystal growth. Ice crystals exert pressure on rock, causing its breakdown.
- Common in high latitude areas (cold) + in rocks with lots of faults
How does wetting + drying complete physical weathering?
Minerals repeatedly expand (wet) + contract (dry), causing outer layers to break off.
(Also known as ‘onion-skin weathering’)
- Common in clays
What are mass movements?
Downslope movement of material under influence of gravity
What are 5 things that affect mass movement?
- Lithology - soft/hard rock, e.g clay is soft so slumps
- Structural geology - bedding planes, steeper is weaker
- Weathering - loose material from weathering makes cliff weaker
- Vegetation - less veg makes cliff weaker, not held together
- Water in cliff - more makes it heavier, weaker
What are the 4 rapid mass movements?
- Rock fall (FASTEST)
- Rock slides
- Rock toppling
- Rotational slides + slumps
What are the 2 slow mass movements?
- Creep (SLOWEST)
- Solifluction
How does mass movement happen through rock fall?
Blocks of rock, loosened by weathering, fall to cliff face
- Often when bedding planes are vertical
- E.g. Svalbard - rocks loosened by freeze-thaw
How does mass movement happen by rock slides?
Blocks of rock slide down cliff face
- Often when bedding planes are tilted backwards
- E.g. Gower Peninsula - limestone cliffs
How does mass movement happen through rock toppling?
Whole columns/blocks of rock fall seawards
- E.g. Giant’s Causeway - columnar basalt
How does mass movement happen through rotational slides/slumps?
Sections of cliff give way along a concave slip surface, leaving fallen material as visible mass until eroded
- Often when bedding planes are tilted backwards/concave
- Often when permeable overlays impermeable rock, so rock becomes saturated and lubricated slip plane forms
- E.g. Barton on Sea
How does creep cause mass movement?
Extremely low (1-3mm per year) downslope movement of regolith (loose material) - Almost imperceptible - seen by tilted fences + poles
How does mass movement happen through solifluction?
Slow downslope movement of regolith that is saturated by melting of active layer above permafrost
- E.g. In summer of periglacial regions (UK may have had this after Ice Age)
What are marine processes?
Processes associated with the action of waves
- Erosion
- Transportation
- Deposition
What is erosion?
The wearing away and/or removal of material (rock)
- Hydraulic action
- Abrasion/corrasion
- Solution/corrosion
- Attrition
How does erosion happen through hydraulic action?
Waves break against coast, entering rock faults + applying great pressure on air inside. Waves then retreat + pressure released with explosive force. Mini explosions break rock, which is removed by waves.
- Common in rock with many joints/faults - e.g. limestone
How does erosion happen through abrasion/corrasion?
Material carried by waves is thrown against cliff face, breaking down and removing the rock
- Common in high energy conditions, e.g storms
How does erosion happen by solution/corrosion?
Salt water (+ acids within it, e.g from waste) can slowly dissolve + remove rock on coastline
- Common in carbonates that are soluble in slightly acidic water, e.g limestone + chalk
How does erosion happen by attrition?
Weathered material carried by waves hit into each other, becoming increasingly smaller + smoother
- Breaks down material carried by waves, NOT coastline
What is a cliff? Give an example
A steep rock face, common next to the Sea
- E.g resistant - Cliffs of Moher, Ireland
- E.g less resistant - Holderness Coast, England
How does a cliff form?
- Destructive waves attack base (mainly ha+abrasion), forming wave cut notch
- Cliff becomes undercut + unsupported
- Concordant coastline
- Weathering from above + notch enlarged, until gravity causes rock collapse
- Steep cliff face left, with old cliff base as smooth wave cut platform
- Cliffs continuously retreat + are shaped through erosion, weathering, mass movement
How are cliffs affected by geology?
More resistant geology forms tall, steep cliffs
- Harder rock
- Insoluble
- Permeable
- Few joints, bedding planes, faults, folds (weaknesses)
(E.g. Cliffs of Moher - Ireland)
Less resistant geology forms small, gentle cliffs
- Softer rock
- Soluble
- Impermeable
- Many joints, bedding planes, faults, folds (weaknesses)
(E.g. Holderness Coast - receding fastest in EU, by 2m/yr)
What is a headland? Give an example
Point of land (often high) that extends out into body of water
- E.g Ballard Point, Dorset Coast
What is a bay? Give an example
An inlet of the sea where land curves inwards, usually with a beach
- E.g Swanage Bay, Dorset Coast
How do headlands and bays form?
- Discordant coastline
- More resistant rock erodes slower (forming headlands)
- Less resistant rock erodes faster (forming bays)
- After formation, wave refraction reverses erosion rates (converging orthogonals increase erosion of headlands, diverging orthogonals decrease erosion of bays)
How are headlands + bays affected by geology?
- Always form on discordant coastline - with rocks of contrasting resistance running perpendicular to coast
What is a cave? Give an example
Natural opening in the rock
- E.g caves at Durlston Head, Dorset Coast
What is an arch? Give an example
A cave that extends through the headland
- E.g Durdle Door, Dorset Coast
What is a stack? Give an example
Detached pillar of rock located off a headland
-E.g Old Harry, located off Ballard Point (Dorset Coast) - headland folded by tectonics 65 mill yrs ago made line of weakness to start sequence
What is a stump? Give an example
Collapsed stack that is less than half the height of the original cliff
- E.g Old Harry’s Wife, Dorset Coast
How does a CASS system form?
- Line of weakness (e.g. fault) enlargened by erosion (e.g. ha)
- Crack grows to cave, as destructive waves converge on headland
- Cave grows from wave refraction + may form back to back
- Waves break through headland to form arch
- Weathering attacks top of arch, waves attack base, weakening it
- Top of arch collapses to leave detached stack
- Waves attack base of stack
- Stack eventually becomes too unstable + falls to leave stump
How are CASS systems affected by geology?
- Rock must be resistant (as headland needed)
- Rock must have some lines of weakness (e.g faults) that can be exploited by destructive waves during wave refraction to start sequence
Does the CASS system always form in a linear order?
No
Give an example of the rocks involved in a headland/bay system
- Bagshot beds (less resistant)
- Chalk (more resistant)
- Wealdon clays + greensands (less resistant)
- Purbeck + portland limestone (more resistant)
What is a wave cut platform? Give an example
Wide, horizontal/gentle sloping section of rock (that was once the cliff base) backed by cliffs
-E.g Nash Point, South Wales
How are wave cut platforms formed?
- Waves attack base of cliff
- Wave cut notch (indent) formed at high tide mark
- Over time, notch enlargenedl, undercutting cliff
- Cliff becomes unstable + collapses
- Wave cut platform left, smoothened over time by abrasion
- Process continues, causing cliff retreat + growing platform
How are wave cut platforms affected by geology?
- Rock is resistant - must be able to be undercut without crumbling
What is a geo? Give an example
Deep inlet in a cliff face
-E.g Sclaits Geo, Scotland
How do geos form (2 ways)?
- Line of weakness is exposed to significant erosion + widened
- Roof of a sea cave collapses
How are geos affected by geology?
- If formed from erosion, must have a line of weakness (e.g fault)
What is a blowhole? Give an example
Opening in ground connected to underground cave system, out of which water is forced
- E.g Kiama Blowhole, New South Wales, Australia - can spray 50L of water 25m into air, accompanies by Little Blowhole
How are blowholes formed?
- Sea cave exposed to erosion
- Vertical line of weakness in cave exploited + widened to form small blowhole
- Water forced up through blowhole, due to pressure difference between large cave + small blowhole
How are blowholes affected by geology?
- Must have vertical line of weakness within cave
What are the 6 landforms of erosion?
- Cliffs
- Headlands + bays
- CASS sequences
- Wavecut platforms
- Geos
- Blowholes
