Coasts Flashcards
What is the littoral zone?
The boundary between the land and the sea
Why is the littoral zone dynamic?
Because the boundary moves depending on the tide, and sea level change
Define the back shore?
The area above the waves’ influence
Define the nearshore
The area where waves break
Define the offshore
The area out at sea beyond the waves’ influence
What short-term criteria classify coastlines?
River discharge, high/low tide, weather
What long-term criteria classify coastlines?
Geology, sea-level change, high/low energy, rate of erosion
What kind of landforms do high-energy coasts form?
Rocky landforms
Where do high-energy coasts occur?
Where there is a long fetch
Where erosion > deposition
What kind of rocks are resistant, and erode slower?
Igneous
What three factors erode the coast?
Sea, rain, wind
What are coastal plain landscapes formed from?
Weaker, younger, sedimentary rock
What feeds coastal plains?
Sediment from river discharge; ocean deposition
Describe concordant coasts
“Bands” of rock types parallel to the coast. This forms “smooth” coastlines or Dalmatian coasts
Describe discordant coasts
“Bands” of rock types perpendicular to the coast. Soft rock erodes quicker, forming headlands and bays
How do coves form?
A band of hard rock is eroded through, and the soft rock behind it starts to erode much quicker
How does a Dalmatian coast form?
Sea-level rise fills in the concordant valleys between ridges
Define strata
Layers of rock
Define bedding planes
Horizontal cracks/gaps, caused by time differences in when rocks formed
Define joints/fractures
Vertical cracks caused by movements in the earth
Define folds
Rocks buckle and crumple due to tectonic activity
Define faults
A rock fractures, then slips along the fault plane
Define dip
The angle of the strata
What is the order of coastal plant succession?
Embryo, fore-, yellow, grey, dune slack, woodland
What are colonising coastal plants called?
Pioneer species
How do pioneer species help plant succession?
They bind sand/soil, and add nutrients when they decay, allowing larger plants to grow
What kind of plants are found at yellow dunes?
Marram grass
What kind of plants are found at grey dunes?
Low shrubs
What kind of plants succeed pioneer species?
Invader species
What is the peak of a coastal ecosystem called?
Climatic climax community
What are the characteristics of a constructive wave?
Low waves, long wavelength
Strong swash, weak backwash
Beach gain
Wave energy absorbed by beach
What are the characteristics of a destructive wave?
High waves, short wavelength
Weak swash, strong backwash
Beach loss
Wave energy NOT absorbed; attacks the cliff face
Why does beach morphology change with wave type?
They are made of loose material; sand
When is sediment removed from beaches?
Winter
What are the characteristics of winter at a coast?
Storms and destructive waves
What wave type characterises summer at a coast?
Constructive waves
When is sediment returned to beaches?
Summer
Explain what season the beach profile is steepest
Summer, as sediment is deposited into a berm
Define abrasion
Sediment/rocks are thrown at the cliff base, eroding it
Define hydraulic action
Water trapped in cracks increases pressure, air expands when it subsides. This repeated process causes erosion
Define corrosion
Rock made of alkaline rock dissolves in slightly-acidic seawater
Define attrition
Rock particles erode each-other in water
What are the four types of erosion at coasts?
Abrasion, hydraulic action, corrosion, attirition
What is the progression of erosional landforms at coasts?
Wave-cut notch → shoreline platform
Wave-cut notch → cave → arch → stack → stump
How are joints and faults eroded?
Hydraulic action and abrasion
How does longshore drift happen?
Waves act on the beach at angle, moving sediment in the direction of the prevailing wind
How does a spit form?
Sand and shingle build up past a ‘bend’ in the coast
How does a spit become recurved?
Wave refraction carries sediment around the bend
How is a beach formed?
Waves swash and longshore drift
How are offshore bars formed?
Backwashed sediment is deposited offshore
What is a barrier beach?
A spit that connects two headlands
How is a tombolo formed?
Waves travelling between two lands lose energy, depositing sediment that forms a joining beach
How does a cuspate foreland form?
Longshore drift in different directions causes a triangle of deposition. Marshland may grow behind it
How many sediment cells are in England and Wales?
11
What is terminal groyne syndrome?
Groynes prevent longshore drift from bringing sediment further downdrift
What are examples of soft engineering?
Beach nourishment, cliff regrading, dune stabilisation
What are the subaerial processes?
Mass movement, weathering
What are the mechanical weathering processes?
Freeze-thaw, salt crystallisation, wetting and drying
Describe freeze-thaw weathering
Water in cracked rock freezes. It expands 10%.
The repeated action puts pressure on the rocks until the rock breaks.
The fragments accumulate at the base of the cliff as scree
Describe salt crystallisation
Salt crystals deposited in cracks accumulate and apply pressure to the rock
Describe wetting and drying
Clay-rich rocks expand when wet and contract when dry. This results in cracks for other weathering
Describe chemical weathering
Rainwater + CO2 in atmosphere forms Carbonic acid.
This reacts with calcium carbonate in limestone to form calcium bicarbonate, which is soluble in water
What is the ‘role’ of weathering?
To weaken cliffs, speeding up the rates of erosion.
What is the rate of soil creep?
1cm / year
Describe soil creep
The sum of many small, discrete movements of slope material caused by gravity
Where are landslides most common?
On a weakened, saturated slope
Describe slumping
Unconsolidated material slides down on itself at slip planes
What is rockfall?
Loose rock falls down the cliff
Where is the Dalmatian Coast?
Croatia
Describe a horizontal cliff profile
Strata/bedding planes lay horizontal.
The causes a steep cliff
Describe a seaward-dipping cliff profile
Strata/bedding planes point down towards the sea
Loose material can fall, making cliff unstable
Describe a landward-dipping cliff profile
Strata/bedding planes point up towards the sky
Can be quite steep but stable
What is the erosion rate of igneous rock?
0.1 cm / year
What is the erosion rate of metamorphic rock?
0.3 cm / year
What is the erosion rate of sedimentary rock?
0.5 - 10 cm / year
Describe the structure of igneous rock
Few joints, less weaknesses
Describe the structure of sedimentary rock
Many bedding planes and fractures
What is eustatic sea level change?
The sea level changing
What is isostatic sea level change?
The land level changing
What might cause isostatic sea level change?
Glacial rebound
Define glacial rebound
The rise of land masses that were depressed by the weight of glaciers
What are the characteristics of an emergent coast?
Raised beaches, relic/fossil cliffs, fossil stump
What is a fossil cliff?
A raised cliff that no longer touches the sea, exposing fossils
What is a ria?
A submerged, unglaciated river valley filled with seawater
What is a fjord?
A submerged, glaciated river valley filled with seawater
What is a barrier island?
An island formed by submergent concordant coasts
e.g Dalmatian Coast
What causes contemporary sea level change?
Global warming - melting polar ice cap
Thermal expansion - water takes up greater volume
How much of contemporary sea level change is due to thermal expansion?
1.1 mm / year
What proportion of contemporary sea level change is due to melting ice?
About two-thirds
What is the rate of contemporary sea level change?
3.2 mm / year
What is the name of holistic coastal management?
ICZM
Intercoastal Zone Management
What is cliff regrading?
Reducing the angle of a cliff to increase stability
When do rocky coasts form?
From resistant geology, in a high-energy environment
When do coastal plains form?
Near low-relief areas, from the supply of sediment from terrestrial and offshore sources
In low-energy environments
What landform does rotational slumping form?
Rotational scar
What is scree?
Collection of rock fragments at the base of cliffs
What landform does rockfall form?
Talus scree slopes
What can cause terraced cliff profile?
Mass movement or isostatic sea level change
What is a terraced cliff profile?
A cliff with a step-like shape
What uncertainties are there about the increasing coastal flood risk?
Pace and magnitude of this change
