Coasts EQ1 - Coastal landscapes and processes Flashcards
What is the littoral zone?
Dynamic zone of rapid change - the wider coastal zone where land is subject to wave action
What are the 2 main types of coast?
Rocky - cliffs formed from rocks varying in height (resistant geology, high energy environment)
Coastal plains - land gradually slopes towards sea across area of deposited sediment (high sediment supply, low energy environment)
What are the 4 areas in the littoral zone?
Backshore, foreshore, nearshore, offshore
What are primary coasts?
Coastlines dominated by land-based processes such as deposition at the coast from rivers, or new coastal land formed from lava flows
What are secondary coasts?
Coastlines dominated by marine erosion or deposition processes
What is the difference between emergent and submergent coasts?
Emergent - coasts rising relative to sea level (e.g. due to tectonic uplift)
Submergent - coasts being flooded by the sea (due to rising sea levels or subsiding land)
What are the three types of tidal range?
- microtidal (0-2m)
- mesotidal (2-4m)
- macrotidal (>4m)
What is the difference between low energy and high energy coasts?
Low energy = sheltered, limited wave fetch, low wind speeds mean smaller waves
High energy = exposed, facing prevailing winds, long wave fetches result in powerful waves
What is a cliff profile?
The height and angle of a cliff face as well as its features such as wave-cut notches or changes in slope angle
What sub-aerial processes act on cliffs?
- weathering
- mass movement
- surface runoff
What is rock erosion resistance influenced by?
- how reactive minerals in the rock are when exposed to chemical weathering
- whether rocks are clastic or crystalline (crystalline = more erosion resistant)
- degree to which rocks have cracks, fractures and fissures
How are coastal plains maintained in a state of dynamic equilibrium?
2 balancing forces:
- deposition of sediment from rivers inland, and deposition of sediment from offshore/longshore sources
- erosion by marine action at the coast
What is coastal accretion?
The deposition of sediment at the coast and the seaward growth of the coastline, creating new land
What is dynamic equilibrium?
The balanced state of a system when inputs and outputs are balanced over time. By a process of feedback, the system can adjust to changes to regain equilibrium
What is geological structure?
The arrangement of rocks in three dimensions
What are the key elements to geological structure and what do they mean?
Jointing - division of rocks into blocks with regular shape
Dip - angle of rock strata in relation to horizontal
Faulting - weaknesses in rock layers (fractures)
Folding - crustal compression where horizontal strata are squeezed
What are concordant and discordant coastlines?
Concordant - rock strata run parallel to the coastline
Discordant - different rock strata intersect the coast at an angle
How are headlands and bays formed at discordant coastlines?
Softer rock eroded faster - creating bays (differential erosion)
Wave refraction means lateral erosion occurs at headlands (cave arch stack stump), while wave energy in bays is much lower and erosion is reduced
How do coves form on concordant coastlines?
More resistant rock broken through by marine erosion, and the softer rock behind is then rapidly eroded to form wide coves. At the back of the coves is more resistant rock which prevents erosion further inland
What is a Dalmatian coastline?
Coastline made up of anticlines and synclines that has been drowned by rising sea levels, creating concordant coastline of long narrow islands arranged in long lines offshore
What is a Haff coastline?
A concordant coastline where long sediment ridges topped by sand dunes run parallel to the coast offshore, creating lagoons between ridges and shore
What is strata?
The different layers of rock within an area and how they relate to each other
What 2 geological factors affect cliff profiles?
- the resistance to erosion of the rock
- the dip of rock strata in relation to the coastline
What is dip, and why is it important in determining cliff profiles?
Dip is the angle of rock strata in relation to the horizontal (tectonic feature)
It is important as determines the stability of the cliff
What are the different types of dip, which is the most/least stable?
- horizontal dip (vertical profile)
- seaward dip (very vulnerable to erosion)
- landward dip (steep profile but stable cliff with reduced rock falls)
What are joints?
Joints divide rock strata up into blocks with a regular shape
What are fissures?
Much smaller cracks in rocks, often only a few centimetres or millimteres long
How does folding occur and how does it create anticlines and synclines?
Folding occurs due to crustal compression - when horizontal strata are ‘squeezed’ they can be folded into a series of anticlines and synclines.
Anticlines - A shaped (convex up)
Synclines - U shaped (concave down)
What are faults?
Major fractures in rocks produced by tectonic forces and involving the displacement of rocks on either side of the fault line
What is unconsolidated sediment?
Material such as sand, gravel, clay and silt that has not been compacted and cemented to become sedimentary rock, so is loose and easily eroded
What is igneous rock (give examples) and what is it’s erosion rate?
Igneous rock is formed from the cooling and solidification of magma - e.g. granite or basalt
VERY SLOW rate of erosion (< 1mm a year) - as they are crystalline and have few joints
What is metamorphic rock (give examples) and what is it’s erosion rate?
Metamorphic rocks are rocks that have become changed by intense heat or pressure while forming. e.g. slate, marble
SLOW erosion rate (1mm to 10 cm per year) - some are crystalline, others are folded and heavily fractured
What is sedimentary rock (give examples) and what is it’s erosion rate?
Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. e.g. sandstone, limestone
MODERATE TO FAST erosion rate (10cm to several metres) - often clastic, and have many bedding planes and fractures
What is the difference between impermeable and permeable rocks?
Permeable - allow water to flow through them
Impermeable - do not allow groundwater flow
What is pore water pressure?
The pressure water experiences at a particular point below the water table due to the weight of water above
How does vegetation stabilise sediment?
- Roots of plants bind sediment particles together making them harder to erode
- When submerged, plants growing in sediment providing a protective layer (surface of sediment not exposed to moving water)
- Plants reduce wind speed to reduce wind erosion because of friction with vegetation
What is the difference between halophytes and xerophytes?
Halophytes - tolerate salty conditions
Xerophytes - can tolerate very dry conditions
What is a psammosere and a halosere?
Psammosere - sand dune ecosystem
Halosere - salt marsh ecosystem
What are the stages in sand dune succession?
- embryo dunes
- fore dunes
- yellow dunes
- fixed dunes (grey)
- heath/woodland
What are the roles of embryo dune pioneer plants?
- stabilise mobile sand with their root systems
- reduce wind speeds at the sand surface, allowing more sand to be deposited
- add dead organic matter to the sand, beginning the process of soil formation
Why are sand dunes a dynamic environment?
- periods of wind erosion can create low areas within dune systems called dune slacks
- embryo and fore dunes are prone to wind and wave erosion, particularly during major storms, but the dune front will stabilise as long as the supply of sediment to the coast resumes
Why are estuaries ideal for the development of salt marshes?
- sheltered from strong waves so sediment can be deposited
- rivers transport a supply of sediment to river mouth, which may be added to by sediment flowing into an estuary at high tide
What are the stages in salt marsh succession?
Algal stage - algae grows on and within bare mud, binding it together
Pioneer stage - roots begin to stabilise mud
Establishment stage - continuous carpet of vegetation established
Stabilisation - area of salt marsh rarely submerged
Climax vegetation - developed soil profile, only submerged once or twice each year, land plants can colonise (rainwater washes salt out of soil)
What is the difference between permeable and impermeable rock?
Permeable = allow water to flow through them
Impermeable = do not allow water to flow through them
Permeable rocks tend to be less resistant to weathering because water percolating comes into contact with a large surface area that can be chemically weathered.
What is the effect of pore water pressure?
Produces slumping and sliding
Pushes rock particles apart, reduces friction between grains in unconsolidated sediment, lubricates lines of weakness
Where are complex cliff profiles produced?
In cliffs with strata of differing lithology
Differential erosion rates leads to formation of features like wave cut notches/overhangs
