Block 4 (Factors Affecting Coastal Processes + Landforms) Flashcards
What affects wave energy?
- Fetch (longer=more energy)
- Duration (longer=more energy)
- Wind Velocity (longer=more energy)
What is fetch?
Maximum length of open water over which wind can blow to produce wave
What is the longest UK fetch?
SW across Atlantic from Gulf of Mexico
- 4000 km
What is the shortest UK fetch?
NE across English Channel from France
- 34km
What is duration?
Length of time wind blows over sea to produce wave
What waves are formed by low energy?
Constructive, spilling
What waves are formed by high energy?
Destructive, plunging
What are the 3 factors that impact where wave energy is focused?
- Wave orientation
- Wave refraction
- Wave reflection
What is wave orientation?
Direction waves come in to coastline
- Most often from prevailing wind
- Can be changed by different weather systems, e.g. storms
Outline the process of wave refraction
- Sea shallower near headlands, deeper in bays
- Waves approaching headland have increased friction with bed, slow down
- Waves approaching bay not influenced by friction, continue moving at high velocity
- So, direction of wave energy - ‘orthogonals’ - appear to bend
- Orthogonals converge on headlands (most erosion)
- Orthogonals diverge on bays (most deposition)
What is wave reflection also known as?
Clapotis effect
Where can wave reflection occur?
When wave hits a vertical surface
- Rocky coastlines with deep offshore platform
- Steep beaches
- Cliff face
- Sea wall
Outline the process of wave reflection
- Platform causes waves to reflect back out to sea
- Waves don’t break at shoreline
- Cliffs protected from erosion + rate of recession decreases
What is a standing wave?
The interaction between reflected + incoming waves
What is lithology?
The make-up of rocks
- Rock hardness
- Chemical composition (minerals + solubility)
- Permeability
What is rock hardness?
How hard/soft the rock is
What rock is usually harder/more resistant?
Igneous + metamorphic (heated + compressed in formation)
What rock is usually softer/less resistant?
Sedimentary (layers that crumble)
Where was the fastest recorded coastal erosion?
Sumatra
- 30m volcanic ash eroded /yr after 1883 Krakatoa eruption
Which areas erode fast/slow due to rock hardness in GB?
NW erodes slow - granite (igneous) - resistant headlands
SE erodes fast - glacial boulder clay + sandstone (sedimentary) - bays
What is chemical composition?
Minerals rocks are composed of + how chemically reactive/soluble they are
Do chemically inert rocks erode fast or slow? Give example
Slow - low chemical weathering
- E.g quartzite
Do soluble rocks erode fast or slow? Give an example
Fast
- Dissolve in water
- E.g chalk + limestone (calcium carbonates)
What is permeability?
Ability of water to enter and pass through rock
What is a concordant coastline + its landforms?
Different rock types run parallel to coastline
- Coves, cliffs, wave cut platforms
Give an example of a concordant coastline
Jurassic Coast - Lulworth Cove
- Resistant layers of purbeck limestone at front + back
- Less resistant layers of clay + chalk in middle
What is a discordant coastline + its landforms?
Different rock types run perpendicular to coastline
- Bays, headlands
Give an example of a discordant coastline
Holderness Coast
- Resistant chalk cliffs at Flamborough
- Less resistant boulder clay at Holderness Bay
What is structural geology?
The way that rocks are geologically arranged
- Joints
- Bedding planes
- Folds
- Faults
What are joints?
Blocks of rock in coastal cliffs
How do the number of joints affect rock’s resistance?
More joints = More susceptible to weathering + erosion, as more lines of weakness
Give an example of where joints can be seen
Daepo, South Korea
What are bedding planes?
Surface that separates two successive layers of stratified rock (strata)
How do the number of bedding planes affect a rock’s resistance?
More bedding planes = More vulnerable to weathering + erosion, as more lines of weakness
How does the configuration of bedding planes affect rock’s resistance?
- Tilting landwards: least resistant - slides + slumps common
- Vertical: medium resistance - rock falls
- Horizontal: medium resistance - wave cut notch/platform
- Tilting seawards - very resistant
What are faults?
Cracks/lines that have opened up in the rock, along which there is movement
What causes faults to form?
- Tectonic shift
- Earthquakes
- Mass movement
What are the 3 types of fault?
- Dip-slip fault
- Strike-slip fault
- Oblique fault
What is a dip-slip fault?
Vertical movement
- Normal: hanging wall moves down
- Reverse: hanging wall moves up
What is a strike-slip fault?
Horizontal movement
- Right lateral: when standing on one side, other side appears to move to right
- Left lateral: when standing on one side, other side appears to move to left
What is an oblique fault?
Vertical + horizontal movement
What is a strike?
Point where horizontal + tilted planes meet (on a dip-slip fault)
What is a dip?
Angle of incline (on a dip-slip fault)
How does the number of faults impact rock’s resistance?
More faults = more susceptible to weathering + erosion, as act as lines of weakness
What is a fold?
Rock stretched + compressed by earthy movements, causing undulation of rock layers
What are the two types of folds?
- Anticlines
- Synclines
What are anticlines? Give an example
Rock folds up in the middle
- E.g. Saundersfoot, Gower Peninsula
What are synclines? Give an example
Rocks fold down in the middle
- E.g. Malta Coast
How does number of folds affect rock’s resistance?
More folds = Weaker, less resistant rock - can form weak area known as a SHATTER ZONE
What is porosity?
Whether water can be stored in holes in rock
What is perviousness?
Ability for water to move through cracks in a rock, but not actually enter the rock itself
How does permeability affect rock resistance?
- Permeable: water can enter rock + (if porous) can remain inside, increasing density + resistance (e.g. White Cliffs of Dover)
- Impermeable: water cannot enter rock, rain weighs rock down (e.g. clay) so it’s more susceptible to mass movements (e.g. slumps)
- Permeable over impermeable: water enters first rock, but not second, so a ‘zone of lubrication’ can form, more susceptible to mass movements (e.g. slides)
What is the term for erosion not all happening at same rate?
Differential erosion
