Rocky coasts to barriers Flashcards
What happens if you have a wide beach in front of cliff face?
The beach dissipates wave energy so that the exposed headland cliffs are retreating fasters than the bay (amplitude is stable or decreasing).
What happens if you have no permanent beach in front of cliff face?
The bay is retreating faster than the headland (amplitude is increasing).
When does a coastline reach a stable steady state amplitude?
When the bay and headline cliff retreat rates converge.
What happens if there are no negative feedbacks operating on sea cliff retreat rate?
The differential retreat rate between the bay and headland exists in perpetuity and amplitude grows to infinity.
What happens with wave energy redistribution to make sea cliff retreat rates of bay and headland converge to a steady state?
If wave energy is able to redistribute some of the sediment then what you have is a way to slow down retreat rate in the bay and speed up the retreat of the headland.
When does a steady state exist in homogenous lithology?
When beach width drives bay retreat at the same rate as sediment free headlands retreat.
The combination of these feedbacks- whether sediment dynamics or wave energy is dominant, what is all you need to know to determine the type of coastline your’e looking at- sediment starved, sediment rich, bedrock erosion rates, material is soft etc etc
The relative strength of the rock
What is the Bruun rule?
The Bruun Rule states that shoreline erosion caused by sea-level rise is a function of the average slope of the shore-face, which is typically the steepest part of the nearshore profile.
How does a barrier form?
If your landscape slope is shallower than your shore-face slope you get a barrier because sediment piles up above the water.
Top of the shore face sits above background landscape.
Wave action builds that “missing” land
Result is a barrier (shore face + black + crest + back barrier)
What does a barrier system do in dynamic equilibrium?
The island takes sand from this tow out in front of it and throw it behind it and build backwards onto that.
Maintains height and width and moves along with sea level rise over time, travelling up the background landscape slope.
What does a barrier system do where the height is drowning?
if there is not enough over-wash and the shore-face slope shallows out and can’t move its tow to throw sediment behind it.
It can drown = wide barrier and a sand flat.
Not enough material to build height with.
What does a barrier system do where the width is drowning?
If the shore-face is too slow move it can lose the barrier from shoreline erosion by narrowing it out.
What does a barrier system do in periodic retreat?
If the shore-face slope that’s moving along has these chatters in it you can have periods where its too wide or too skinny or not tall enough (it’ll jump around).
Barrier width and height depend entirely on…
Strength of storms
What does the fact that the island is connected to the seabed mean?
It can’t move independently of the shore-face.
