coastal landscapes Flashcards
Discordant coast example
West Cork, Ireland (headland and bay) Clear Island (detached island)
Concordant coast example
Lulworth cove, Dorest (Bay)
Croatia - Dalmatian Coastline
Baltic Sea, Germany - Haff coastline
Rock coastline example
Conochair Outer Hebrides, highest cliff in UK
sandy coastline example
Belgium 65km strech
estuarine coastline example
Severn Estuary Wales
Sand Dunes example
Braunton Burrows, UK
one of the largest systems in the UK, 400 plant species, 60 lichen species.
Conflict between nature conservation and local estate on issue of grazing
Bar example
Chesil Beach Dorset
Tombolo example
Portland Bill Dorest
Cupsate Foreland example
Dugeness Kent
Spit example
Hurst Castle, Hampshire
Define Littoral Zone
The wider coastal zone ranging from adjacent land areas to shallow offshore areas,
Closed system in dynamic equilibrium
Eleven littoral zones in England and Wales, separated by topography and landforms such as peninsulas.
Sections of a littoral zone
Backshore - above high tide, only effected by waves during storms
Foreshore- between high and low tide, main wave activity.
Nearshore- intense human activity e.g fishing, shallow water, transfer of sediment by currents (physical system)
Offshore - deep water, limited activity
Rocky coastline characteristics
Formed from cliffs of variable hardness, dominated by erosion and transportation, destructive waves (high energy coast) long fetch abrupt transition from land to sea storm conditions are common caves, arches, stacks, wavecut platform
Sandy Coastline features
Can be sandy or estuarine Gentle transition from land to sea Dominated by deposition constructive waves (low energy) short fetch beaches, bars, sand dunes, mudflats
Formation process classification
primary coasts - dominated by land processes
secondary coasts - dominated by marine based processes
Relative sea level change classification
Emergent coasts - coasts rising relative to sea level
Submergent coasts - coasts flooded by sea.
Change can be isostatic (land moving relative to sealevel) or eustatic (sea moving relative to land)
Tidal range classification
Microtidal - 0-2m
mesotidal 2-4m
macrotidal above 4m
wave energy classification
low energy - sheltered coast, low wind and limited fetch= small waves
high energy- exposed coast, prevailing winds, long fetch = powerful waves.
cliff profile definition
The height, angle and features on a cliff face.
cliff profile types
marine erosion dominated - steep face, active undercuting, limited cliff debirs, constant erosion and transportation of material away from the cliff base.
sub-aerial process dominated - gently sloping profile, accumulated debris, limited erosion at base.
Erosion resistance of rock type influences
- how reactive minerals are in rocks when exposed to chemical weathering
- clastic or cystalline
coastal accretion definition
The deposition of sediment, being stabilised by vegetation, causing the seaward growth of the coastline.
geological structure
The arrangement of rocks in three dimensions.
strata- the different layers of rock and how they relate to each other.
deformation- the degree to which rock units have been tilted/folded by tectonic activity.
faulting- the presence of major fractures that have moved rock from their original position.
freeze-thaw weathering
mechanical, water expands by 9% in volume when freezing exerting a force to widen cracks, repeated cycles.
any rocks with cracks/fissures away from salt spray, relatively uncommon in UK
salt crystallisation weathering
growth of salt crystals in cracks when sea water evaporates exerts a breaking forces.
more common in hotter drier climates
carbonation chemical weathering
the slow dissolution of limestone due to rainfall which reacts with calcium carbonate.
hydrolysis chemical weathering
the effect of water and dissolved CO2 breaks down minerals into new clay minerals and material in solution
oxidation chemical weathering
the addition of oxygen to minerals produces oxides which expand in volume contributing to mechanical breakdown. Common on iron compounds
Biological weathering
action of plants, bacteria or animals.
plant roots or rock boring (animals bores and secrete chemicals on rocks)
concordant coasts
pacific coasts
rock strata runs parallel to the coast line
Dalmatian coast line
location: Croatia
limestone was deformed by tectonic activity into s series of anticlines and synclines that run parallel to the modern coastline.
Synclines drowned by eustatic change during Holocene when sea levels rose by over 30m.
Left anticlines as a series of long narrow island running parallel to the coast.
Synclines were previously eroded by abrasion from rivers.
Haff coastline
location: Baltic sea
Result of previous glaciers, meltwater rivers deposited material that was then transported as sea levels rose during Holocene.
Forms a parallel bar of unconsolidated sediment along the coast.
The long sediment ridges are gradually consolidated by a process of succession, being more vegetated and growing sand dunes. Lagoons form behind.
discordant coastlines
Atlantic coasts
Different rock strata intersects the coast at 90 degree angles, causes the coastline to vary.
headlands and bays
discordant coast, marine processes, differential rates of erosion,
crescent shaped bays=deposition forms beaches, may be long and narrow
headlands are resistant remaining jutting out, especially resistant remains as detached islands when the headland erodes,
concordant coasts=rock strata has a pre existing weakness.
wave refraction at headlands
In deep water wave crests are parallel.
Shallow offshore water near a headland slows a wave and increases its wave height. Erosion
In bays the wave crests curve to fill the bay and wave height decreases.
Lulworth cove
Hard Portland limestone and resistant Purbeck protect landwards less resistant rock.
Pre existing weakness (e.g tectonic fault line) has been exploited by marine erosion.
Less resistant rock eroded into coves, back of coves protected by limestone preventing further erosion inland
factors affecting cliff profiles
resistance of rock to erosion
dip of rock strata in relation to the coastline
dip
angle of the rock strata in relation to the horizontal, caused by tectonic movement.
horizontal dip
vertical or near vertical profile with notches showing differential rates of erosion within strata.
seaward dip high angle
low angle profile, vulnerable to rock slides, sloping with one rock layer facing the sea
seaward dip low angle
profile may exceed 90 degrees, areas of overhang, vulnerable to rockfalls,
landward dip
steep profiles, stable cliff with reduced mass movement, higher rates of erosion.
geological features comparison
Faults - major weaknesses, either side is heavily fractured and broken
Joints - occur in most rock, regular patterns dividing strata into blocks.
Fissures- smaller cracks in rocks, often centimetres or millimetres wide.
igneous rock
formation- crystallised magma
Very slow erosion rates
Crystalline, few joints
e.g Granite
Metamorphic rock
formation- changes in sed/ig rock structure due to high pressure/temperature
slow erosion
crystalline but show foliation, often folded and heavily fractured
e.g marble
sedimentary rock
formation- sediment that has been deposited then compressed and cemented.
fast erosion
clastic, geographically young erode faster, many bedding places and fractures.
e.g shale
unconsolidated sediment
newly deposited sediment, the easiest to erode.
permeability effect on erosion
Less resistant to erosion.
Permeable rocks allow water to flow through them.
Groundwater flow removes cement that binds sediment.
High pore water pressure, increases chance of slumping.
Springs cause surface runoff erosion.
lithology erosion exceptions
limestone- sedimentary but is crystalline so resistant
sandstone- ancient is compressed over millions of years so is resistant
igneous- recently erupted volcanic lava flows and tephra are easy to erode.
How does vegetation stabilise sediment?
Roots bind sediment together.
Provide protective layer against moving water + marine erosion.
Provide friction with wind reducing wind speed and erosion.
Succession definition
The changing structure of a plant community from initially bare sediment to diversity rich colony.
Each step is called a seral stage, results in a climatic climax community such as a psammosere (sand dune ecosystem)
Role of pioneer plant in embryo dune
Stabilise mobile sand with their roots
Reduce wind speed at sand surface allowing more material to be deposited
Add dead organic matter to the sand contributing to soil formation.
Explain the formation of waves
Friction between the wind and water causes energy to be transferred.
Generates ripples which when sustained grow into waves.
Circular particle movement in open water but no net forward movement.
Size depends on strength/duration of wind, water depth and wave fetch.
UKs largest waves
Cornwall, 4000km fetch from Florida, sustained southwesterly wind.
swell waves
Gentle spilling waves, appear on the beach when wind has dropped but remaining waves gradually may their way onshore.
Waves breaking
At water depth of half the wave length the bottom of the orbital motion touches the seabed.
This generates friction slowing the wave trough.
The waves length decreases and the height increases causing waves to bunch together.
The wave crest eventually outruns the trough and the wave topples forward.
Constructive waves
spilling waves
low wave height <1m
long wave length up to 100m
gentle and flat
stronger swash than backwash deposits sediment up the beach forming a ridge or berm.
This beach morphology means most of the backwash percolates the beach
destructive waves
plunging waves wave height over 1m wave length of 20m strong backwash erodes beach material and deposits it as an offshore ridge or bar. may result in storm beaches
beach morphology
The shape of the beach including the width, slope and type of sediment found at various locations.
long term changes to beach morphology
sediment supply from rivers is reduced due to the construction of dams.
climate change influences e.g more destructive waves
interference of sediment supply along the coast due to coastal management.
when does most erosion occur?
Largest waves
Waves at 90 degrees to the cliff face
High tide
Heavy rainfall, percolation and surface runoff weakens he cliff.
Debris from previous erosion has been removed from the cliff base.
Spit
A sand or shingle ridge extending along a turn in the coastline.
Longshore drift.
Length determined by wind and secondary currents.
Winds in an opposite direction to the prevailing wind caused a recurved end landward into shallower water.