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Summary - Unit 1 - Dynamic Landscapes (9GEO-01) - TECTONIC HAZARDS
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Topic 2 – Coastal Landscapes and changeEnquiry Question 1: Why are coastal landscapes different and what processes causes these differences?
2.1 Key Idea: The coast, and wider littoral zone, has distinctive features and landscapes
2.1a) Parts of the littoral zone
Littoral Zone:
- The area of shoreline where land is subject to wave action
- Subdivided into offshore, nearshore, foreshore and backshore:
o Offshore: the area of deeper water beyond the point at which waves begin to break
o Nearshore: the area of shallow water beyond the low tide mark
o Foreshore: the area between high tide and low tide mark
o Backshore: the area above the high tide mark, affected by wave action only during major storm
events
Types of coastlines:
- Cliffed:
o Areas of high relief varying from a few metres to hundreds of metres in height
o Formed in areas:
Resistant geology
High energy environments
Erosion > deposition
Destructive waves
- Sandy:
o Areas of low relief with sand dunes and beaches, that are much flatter
o Formed in areas:
Less resistant geology
Low energy environments
Deposition > erosion
Contrastive waves
- Esturarine:
o Areas of low relief with salt marshes and mudflats
o Formed in areas:
Less resistant rock
Low energy environments
Deposition > erosion
In river mouths
2.1b) Classifying coasts
Short term criteria:
- Energy inputs:
o High energy:
where the water hits
, exposed to strong steady, zonal winds wit
o Low energy:
Where water flows after being absorbed
Sheltered areas from storms and swells, where beaches form
- Sediment inputs:
o Sediment is added to the coastline via deposition and is removed via erosion
o The coast receives sediment input form: waves, wind, tides, current, mass movement and
tectonic processes
o Eroding coastline = erosion > deposition, a net loss of sediment and coastline retreats
o Outbuilding coastline = deposition > erosion, a net gain of sediment and coastline advances
- Advancing/retreating:
o Coasts are classified as advancing or retreating due to long term processes
(emergent/submergent) and short term (outbuilding /eroding)
Long term criteria:
- Geology:
o Based on rock type, structure of rocks
o Used to classify coasts as cliffed, sandy or estuarine / concordant or discordant
- Sea level change:
o Can be used to classify coasts as emergent or submergent
o Caused by:
Tectonic processes: can lift sections of land up, causing local sea fall / allows land to
subside, causing local sea rise
Climate change: causes seal level to rise and fall in a 100,00-year cycle due to change in
earth’s orbit
2.1c) Rocky coasts and coastal plains
Characteristics of rocky coasts:
- Occupy about 1,000km of UK’s coastline
- Cliffs vary in heigh form high relief to low relief areas
- Found in north and west of UK
- Usually form in areas:
o Geology that is resistant to erosive forces of the sea, rain, and wind
o Lithology and structure making them erode and weather slowly.
- Form in high energy environments, where erosion > deposition
Characteristics of coastal plains (sandy and estuarine):
- Relatively flat, low relief areas adjacent to the sea
- Found in south and east of UK
- Often contain freshwater wetlands and marshes due to the poor drainage of the flat landscape
- Their littoral zones are composed of sand dunes, beaches, mud flats and salt marshes.
- Form in low energy environments, where deposition > erosion
= Weathering: The breakdown of rock in situ, and may be mechanical, biological or chemical process
,= Erosion: The breakdown of rock and its immediate transport by the eroding agent
= Mass Movement: The downslope movement of material due to the force of gravity
2.2 Key Idea: Geological structure influences the development of coastal landscapes at a variety of scales
2.2a) Concordant and discordant
Concordant (aka. Dalmatian coasts):
- Forms where rock strata or fold run parallel to the coast
- Have long narrow islands running parallel to coastline
- E.g Dalmatian Islands, Croatia
Discordant:
- Forms where strata or structure are aligned at an angle to the coastline
- Have a crenelated pattern of projecting headlands and indented bays
- E.g. Atlantic coasts, cork islands, Ireland
2.2b) Morphology
Morphology:
- The shape of landscape feature
- Influenced by geological structure
o Headlands and bays = discordant
o Dalmatian and haff = concordant
Coastal systems:
2.2c) Geological structure and cliff profiles
Definition: Example:
Joints: - Fractures in rocks created without Bantry bay:
displacement - Carboniferous Limestone is heavily jointed,
- Occur in regular patterns dividing leading to more rapid fluvial and marine
rock strata up into blocks with a erosion than in adjacent sandstones,
regular shape contributing to the formation of headland
- Jointing increases erosion rates by and bay coastal morphology.
creating fissures which marine
, erosion processes
Faults: - Major factures in rock created by Bantry bay:
tectonic forces, with displacement - A major fault runs SW-NE down the centre of
of rocks either side of the fault line the bay.
- Increase rate of erosion since zones - The Carboniferous Limestone is significantly
are faulted rock are much more weakened by faulting, allowing rapid fluvial
easily erodes erosion, and the resulting river valley was
inundated to form a ria when sea levels rose.
- Faulting also allowed more rapid marine
erosion than in unfaulted Old Red Sandstone,
contributing to headland and bay coastal
morphology.
Folds: - Bends in rocks
- Produced by sedimentary rock layers being squeezed by tectonic forces
- Folded rock is more heavily fissured and jointed, therefore eroded more easily
- Increases erosion rates by increasing angle of dip and by causing joint formation as rock is
stretched along anticline crests and compressed in syncline troughs
Dip: - The angle of inclination of the rock strata from the horizontal
- Sedimentary rocks are deposited horizontally but can be tilted by folding and faulting by
tectonic forces.
- It can have dramatic effects on cliff profiles.
Cliff profile:
- The heigh and angle of a cliff face + its features (e.g., wave-cut notches pr changes in slope angle)
Micro-features:
- Small-scale coastal features (e.g., caves and wave cut notches) which from part of a cliff profile
- They form in areas weakened by heavy jointing, which have faster rates of erosion, enlargement he
joints to form a sea cave
- The location of micro-features within cliffs and is controlled by the location of faults and strata which
have particularly high density of joints and fissures
2.3 Key Idea: Rates of coastal recession and stability depend on lithology and other factors
2.3a) Lithology
Igneous: - Formed from solidified lava or magma Granite
- Erode and weather very slowly, producing very slow rates of coastal Basalt
recession (composed of interlocking crystals, forming hard, resistant Pumice
rock, have fewer joints)
Metamorphic: - Formed by the recrystallisation of sedimentary and igneous rocks Slate
through heat and pressure Schist
- Hard and resistant (crystalline structure) Marble
- Less resistant than sedimentary as they are often faulted and folded Gneiss
Sedimentary: - Formed by the compaction and cementation of deposited material, Sandstone
or sediment Limestone
- Least resistant type of rock due to weak bedding planes, and heavily Shale
jointed
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