Coastal Geography, Rocky Coasts Flashcards
What is the difference between depositional and erosional coasts?
Depositional coasts (beaches and estuarine systems) are developed through sediment accretion.
Contrarily, rocky coasts develop via erosion (erosional coasts)
What are the three main characteristics of a rocky/erosional coast?
- Very low sediment supply
- Less responsive to short term change in wave and tidal energy
- They are a product of long term wave and tide action, ranging from 10 to 10,000+ years)
What are the three main characteristics of a rocky/erosional coast?
Cliff, stack, and shore platfrom
Cliff
The archetypical erosional front of the coast
Stack
Remnants of cliffs, representing the former outline of the coast
Shore platform
The rock surface at mean tide level, including the foot of the cliff
What are the two steps of cliff erosion and how do they operate?
- Undercutting of cliff base which forms debris (often occurs in the form of mass failure)
- Debris is subsequently removed by a variety of marine processes, forming a sheer cliff face
How do shore platforms form?
An eroded rocky coast leaves behind a shore platform marking the mean tidal range
What are the two main mechanisms acting on rocky coasts?
The mechanical action of waves, and weathering
What are the four physical forces of wave quarrying?
Wave shock, hammer, compression, and abrasion
Wave shock
Results from steep, high energy waves breaking against the coast
Wave hammer
The repititive action of waves breaking and eroding the coast
Wave compression
Air enters the cracks of rocks, becoming increasingly compressed until the rock breaks off
Wave abrasion
Eroded material/sediment rubs against the coast, further eroding it
What are the three types of weathering?
Physical, chemcial, and biological
Water-layer weathering
A type of physical weathering whereby alternating periods of dampness and dryness cause the rocks to experience a constant rate of expansion and contraction, slowly eroding it over time
Solution of calcareous rocks
A type of chemical weathering whereby sea water erodes the calcium carboate found in many sedimentary rocks
Bio-erosion
A type of biological weathering that produces minor changes to a marine environment’s morphology. Bio-erosion is caused by marine organisms in the form of dissolving substances or burrowing within sediment
What two characteristics of rock are important to the effect of the mechanical action of waves and weathering?
Bedding planes and permeability
Bedding planes
Planes separating strata of sediment, thus indicating times of sediment change and/or a change in the depositing medium
Permeability
Strata have different levels of permeability which influences how easily waves/water can erode the substance
What are the two main types of coastlines
Concordant and discordant coastlines
Concordant coastline
A unfiorm coastline with strata composed of similar material
Discordant coastline
A non-uniform, splintered coastline with strata compsoed of disimilar material
How does tide infleunce shore platform growth
The smaller the tidal range the greater the duration of wave quarrying.
Smaller tidal range = Faster cliff retreat
What are the two factors of variable tidal influence?
Tidal elevation and tidal duration
Tidal elevation
The position of wave quarrying on a shore platform
Tidal duration
The distribution of wave energy on a shore platform
What is the changing rate of cliff retreat?
Initally cliff retreat is modest, eventually speeding up only to slow down again
What causes the changing rate of cliff retreat, otherwise known as the neagtive feedback relationship?
Acceleration is due to increased abrasion from more sediment.
Deceleration is due to the removal of sediment from the foreshore. This sediment is deposited offshore, causing waves to break earlier and approach the shore with less energy.
What is the difference in wave energy between broken and breaking waves?
Broken waves spread their energy out over a greater area while breaking waves exert more force over a smaller area
Why doesn’t a cliff in deep water experience much erosion?
Since waves don’t encounter the seafloor in deep water, they don’t shaol. This causes the wave energy to be reflected with little erosion occuring on the cliff face
