The make-up of rocks - Rock hardness - Chemical composition (minerals + solubility) - Permeability

Block 4 (Factors Affecting Coastal Processes + Landforms) Flashcards by Freya Aylmore

What affects wave energy?

Fetch (longer=more energy)
Duration (longer=more energy)
Wind Velocity (longer=more energy)

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What is fetch?

Maximum length of open water over which wind can blow to produce wave

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What is the longest UK fetch?

SW across Atlantic from Gulf of Mexico

- 4000 km

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What is the shortest UK fetch?

NE across English Channel from France

- 34km

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What is duration?

Length of time wind blows over sea to produce wave

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What waves are formed by low energy?

Constructive, spilling

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What waves are formed by high energy?

Destructive, plunging

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What are the 3 factors that impact where wave energy is focused?

Wave orientation
Wave refraction
Wave reflection

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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

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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)

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What is wave reflection also known as?

Clapotis effect

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Where can wave reflection occur?

When wave hits a vertical surface

Rocky coastlines with deep offshore platform
Steep beaches
Cliff face
Sea wall

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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

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What is a standing wave?

The interaction between reflected + incoming waves

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What is lithology?

The make-up of rocks

Rock hardness
Chemical composition (minerals + solubility)
Permeability

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What is rock hardness?

How hard/soft the rock is

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What rock is usually harder/more resistant?

Igneous + metamorphic (heated + compressed in formation)

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What rock is usually softer/less resistant?

Sedimentary (layers that crumble)

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Where was the fastest recorded coastal erosion?

Sumatra

- 30m volcanic ash eroded /yr after 1883 Krakatoa eruption

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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

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What is chemical composition?

Minerals rocks are composed of + how chemically reactive/soluble they are

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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