Geology and the coast Flashcards
Definition of strata
layers of rock
Definition of bedding planes (horizontal cracks)
natural breaks in strata caused by gaps in time during periods of rock formation
Definition of joints (vertical cracks)
fractures caused by contraction as sediments dry out/ earth movement during uplift
Definition of faults
major fractures in rock produced by tectonic forces
-faults then move along fault planes
Definition of dip
the angle at which rock strata is
Definition of lithology
physical characteristics of particular rocks
Definition of coastal morphology
shape and form of coastal landscape and their features
Definition of coastal recession
another term for coastal erosion
What produces concordant and discordant coasts
geological structure
What is a concordant coastline
where bands of more-resistant and less-resistant rock run parallel to the coastline
When do concordant coastlines form
- when rock strata runs parallel to the coast
- outer hard rocks acts as a protective barrier to erosion of the softer rocks further inland
- Sometimes outer hard rock is punctured- allowing sea to erode the softer rocks
- cove is produced (a circular area of water with a relatively narrow entrance from the sea)
- dalmatian
- haff
Definition of deformation
the degree of tilting or folding of rock.
The Isle of Purbeck’s southern coast is a concordant coastline. Explain how Lulworth Cove has been formed
- outer hard rocks acts as a protective barrier to erosion of the softer rocks further inland
- outer hard rock is punctured- allowing sea to erode the softer rocks
- cove is produced (a circular area of water with a relatively narrow entrance from the sea)
Name the 3 types of concordant coastlines
- dalmatian coasts
- haff coasts
- south dorset coast
How did the Dalmatian coast become a concordant coastline
- Geology is limestone
- folded by tectonic activity into series of anticlines and synclines- parallel to coastline
- drowned by rising sea levels creating
concordant coastline
How did Lulworth Cove become a concordant coastline
- The outer hard rock is limestone
- less resistant clay and limestone behind portland limestone
- sea has broken through barrier of portland in parts and eroded clays behind it
- This has allowed the formation of a cove
Name the concordant features found at haff coastlines
-long spits of sand and lagoons- parallel to coast
What is a discordant coastline
where bands of more-resistant rock and less-resistant rock run at right angles to the coast
When do discordant coastlines form
when different rock strata intersect the coast at an angle
Why are discordant coastlines dominated by headlands and bays
less resistant rock erodes rapidly to form bays
more resistant rock erodes slowly, leaving headlands
Why is there little erosion at discordant coastlines
- In deep water wave crests are parallel
As waves approach the shallow water offshore of a headland they slow down and wave height increases
In bays, wave crests curve to fill the bay and wave height decreases
The straight wave crests refract, becoming curved, spreading into out in bays and concentrating on headlands
The overall effect of wave refraction is to concentrate powerful waves at headlands (meaning greater erosion) and create lower, diverging wave crests at bays, reducing erosion
Give two examples of discordant coastlines
- Dorset Coastline
- West Cork coast of Ireland
How did West Cork coast of Ireland become a discordant coastline
- Rock strata that include: Limestone,
Mudstone and sandstone meet the
coastline 90 degrees in parallel bands
- Weak rocks have been eroded, creating
elongated, narrow bays, whereas more-
resistant rocks for headlands
- Especially resistant areas remain as
detached islands
How did Dorset Coastline become a discordant coastline
The limestone is resistant to erosion; then
to the north at Swanage bay the rock
type is softer greensand
- North of Swanage, the chalk outcrop
creates the headland which includes Old
Harry Rocks
What 2 characteristics influence cliff profiles
- resistance to erosion of the rock
- dip of rock strata in relation to the coastlin
What 3 geological features influence cliff profiles
- faults
- joints
- fissures
What is differential erosion
When different types of rocks are eroded at different rates
What type of cliff profile does horizontal dip produce
-vertical/ near vertical profile
with notches reflecting strata that are more easily eroded
What type of cliff profile does seaward dip, high angle produce
- sloping, low angle profile
- with one rock layer facing sea
- vulnerable to rock slides down dip slope
What type of cliff profile does seaward dip, low angle produce
- profile may exceed 90 degrees
- producing overhanging rock
- very vulnerable to rock falls
What type of cliff profile does seaward dip, landward dip produce
- steep profiles of 70-80 degrees
- producing very stable cliff with reduced rock falls
What controls the location of microfeatures
the location of faults and/ or strata which have a high density of joints and fissures
Explain how faulting influences the features of a Cliff profile
- Represents major weaknesses within rock
layers (cracks in crust) - Either side of a fault line, rocks are often
heavily fractured and broken and these
weaknesses are exploited by marine
erosion
Explain how jointing influences the features of a Cliff profile
- Occur in most rocks, often in regular
patterns, dividing rock strata up into
blocks with a regular shape
Explain how Folding influences the features of a Cliff profile
- Folding occurs due to crust compression
- Horizontal strata can be folded into a
series anticlines and synclines
When do headlands and bays form
when rocks of different strengths are exposed at the coast
What are folds and what are they produced by
bends in rocks
-produced by sedimentary rock layers being squeezed by tectonic forces
What are the 2 main types of folds
anticlines and synclines
Why are folds more easily eroded
Folded rock is often more heavily fissured and jointed
What is unconsolidated sediment
material such as sand, gravel, clay, silt
that are loose and easily eroded- haven’t been compacted
Name 2 geological factors affecting coastal erosion
lithology- soft rock type, weak cohesive bonds, porous rocks
geological structure- well jointed rocks, seaward dipping beds, heavily faulted rocks
Name 3 characteristics of igneous rocks
-give one example of this type of rock
- erode very slowly
- crystalline -> interlocking crystals -> resistant rocks
- impermeable
- > granite
Name 4 characteristics of metamorphic rocks
-give one example of this type of rock
- erode slowly
- crytalline -> hard and resistant
- many exhibit feauture called foliation -> crystals orientated in one direction - produces weaknesses
- Often heavily folded and faulted
- > slate
Name 4 characteristics of sedimentary rocks
-give one example of this type of rock
- erode moderately to fast
- clastic
- weak bedding planes
- heavily jointed -> formed by the compaction and cementation of deposited material
- younger rocks
Name 3 ways lithology affects the resistance of rocks
- mineral composition -> some rocks contain reactive minearls- chemically wetahered -> some are inert -> slowly chemically wetahered
- rock class -> igneous, sedimentary, metamorphic
- structure -> fissures, joints, faults, air spaces (porous) erode quicker
Why are older rocks more resistant than younger rocks
Older rock- buried deeper -> more intense compaction -> stronger sedimentation -> more resistant than younger rocks
What is differential erosion
Explain how complex cliff profiles are formed
- formed where cliffs are made of strata of differing lithology
- composite cliffs with diff rock layers
What is pore water pressure
pressure water experiences at a particular point below water table due to weight of water above it
What can complex cliff profiles be influenced by
- permeablity of strata
- permeable rocks allow water to flow through them
- impermeable rocks don’t allow water to flow through them
Name the 4 stages that occur in the erosion of complex cliff profiles
1) spring creating erosion
2) Groundwater flow removing cement
3) Pore water pressure -> slumping and sliding
4) Saturation -> slumping and sliding
Explain the stages that occur in terms of erosion that [produces complex cliff profiles
- permeable rock overlays impermeable rock -> groundwater unable go down into impermeable roc
- water flows along impermeable rock weakening it (removes cement binding rock) -> slumping
- also produces pore water pressure -> pushes rock particles apart -> affects stability
-surface run off erosion -> groundwtaer emerges onto cliff face
- Saturation promotes mass movement -> adds weight.
- > slumping and sliding producing a complex cliff profile.
Name the 2 main types of cliff profile
-steep, unvegetated cliffs ->
where marine erosion dominates -> steep profile -> active undercutting ->
little/ no debris at base -> broken up by attrition, transported offshore/ along coast
Shallow-angled, vegetated cliffs -> sub-aerial process dominated -> curved slope profile -> lower angle face
-> debris at the base- sub-aerial processes (weathering, mass movement, surface run-off erosion) slowly move sediment downslope, but marine erosion is unable to remove it from base
produced
What are the three types of coastal vegetation that can protect a coastline from erosion
- Coastal sand dunes
- Coastal salt marshes, found in many river estuaries
- Coastal mangrove swamps
How does vegetation stabilise sediment, slowing erosion
roots of plants bind sediment particles -> stronger
- submerged plants growing in sediment -> protective layer -> surface not exposed to moving water
- plants protect sediment -> reducing wind speed at surface -> friction w vegetation -> reducing wind erosion
What are Halophytes
Plants -> tolerate salt water,
around their roots/ being submerged at high tide/ salt spray from the sea
What are Xerophytes
Plants -> tolerate very dry conditions
e.g found on coastal sand dunes where sandy soil retains very little water due to drainage
What is Plant succession
changing structure of plant community over time as an area of initially bare sediment is colonised.
What are pioneer plants
first plants to colonise freshly deposited sediment
What 3 steps do embryo dune pioneer plants initally do to begin first stage of plant succession
what does this allow?
modify the environment:
- Stabilising sediment
- reduce wind speed at sand surface -> more sand deposited
- Add dead organic matter -> that retains moisture, contributes nutrients and provides shade
- alters harsh, salty sand -> environment other plants can tolerate
What occurs after the pioneer species have successfully modified the environment
new plant species colonise the embryo dune -> creating fore dune
-as environment changes overtime -> diff species colonise until its stable
What is (climatic) climax community
The end result of plant succession when final community are adjusted to climatic conditions of area
Explain the timeline of plant succession
- embryo dunes -> dry sand
- fore dunes -> sea rocket
- yellow dunes -> marram grass
- grey dunes -> low shrubs
- dune slack -> aquatic plants
- woodland -> pines
What is plant succession on sand known as
psammosere
Explain the 7 steps that occur during Psammosere
1) embryo dunes form _> barrier/ shelter forms -> trap sand
2) embryo grows -> colonised- xerophytic pioneer plants -> alter conditions
3) Pioneer plants stabilise sand-> marram grass colonises
4) dune grows rapidly -> yellow dune
5) marram grass dies -> adds hummus to sand -> grey dune
6) dune -> above sea level -> soil has nutrients -> non-xerophytic plants colonise
7) climax plant community -reached
What are salt marshes
areas of flat silty sediments that accumulate around estuaries or lagoons
Explain the 7 steps that occur during Halosere
?do i need to know seral stages
1) fresh water, sea water mix -> clay particles stick together and sink -> flocculation
2) Blue-green algae, gut weed grow and bind mud,
3) roots stablise mud -> mud accretion
4) continous carpet of vegetation established -> salt marsh height increases
5) area of salt marsh -> rarely submerged
6) Rainwater washes salt out of the high marsh’s soil, allowing land plants to colonise.
7) continues until climax community is reached.
Where do salt marshes develop
- sheltered areas
- where salt, fresh water meet
- no strong tides
