Limber et al (2014) Rocky Coasts Flashcards
Why do headlands persist in time?
Rock strength differences between bay and headland.
Why are some headlands transient?
There exists no meaningful rock difference between bay and headland.
How do beaches exert a fundamental control on the rate of sea cliff erosion
By acting either as a protective cover that buffers the cliff from wave attack or as an abrasive tool that enhances wave action.
New sediment is brought to the coast by…
Sea cliff erosion
Coastal rivers
Wave climate
What else can create persistent headlands and bays in the absence of rock heterogeneity?
Internal sediment dynamics
What happens along rocky coasts experiencing a low angle wave climate?
A gradient in alongshore sediment flux is set up whereby sediment is transported and deposited into embayments, forming pocket beaches while leaving the emerging headland largely sediment free
The transmission of wave energy from the deep ocean, across the continental shelf, and ultimately to the
coastline is modulated by…
the deep-water wave angle and height, bathymetry, as well as coastline shape
The greater the cross-shore amplitude is relative to the initially flat coastline…
the more wave energy is captured by the headland and lost to the embayment
Three overarching factors control large-scale (>1 km) and long-term (centuries to millennia) plan view rocky
coastline evolution:
Waves deliver the energy necessary to do geomorphic work on the coastline including eroding sea cliffs and distributing beach sediment alongshore.
Sea cliffs provide resistance to incoming wave energy depending on their spatially variable strength and composition.
The fronting beach regulates the efficacy of wave and cliff interactions by protecting sea cliffs from erosion when the beach is sufficiently wide or encouraging sea cliff erosion through abrasion when the beach is narrow
As amplitude increases and coastline curvature develops, two simultaneous negative feedbacks are initiated that slow and eventually stop further amplitude growth by equalising the cliff retreat rates alongshore.
First, the embayed coastline shape induces wave refraction so that wave energy converges on headlands and diverges in bays. This slows the further development of coastline relief by reducing the rate of sea cliff retreat in softer-rock bays and increasing cliff retreat on more erosion-resistant headlands.
Second, the processes of beach sediment production by sea cliff retreat, distribution of sediment by alongshore sediment transport, and pocket beach growth controls future embayment sea cliff retreat by buffering wave impacts. This feedback is tied to amplitude because, as amplitude increases, the coastline becomes longer (more sinuous). More sea cliff is available to erode, and the net
sediment production rate increases. Pocket beaches respond by becoming wider and more efficient at
dissipating wave energy as amplitude grows, thereby reducing the retreat rate of the weaker embayment
cliffs (along with wave energy divergence).
