Limber et al. (2014) - rocky coasts (headlands & beaches) Flashcards
What does this wave-forced negative feedback of coastline retreat rate increasing with wave energy and decreases with rock strength, headlands that are composed of more durable rock receive more wave energy (through refraction of waves and convergence of energy) to the detriment of bays backed by soft rock as the coastline amplitude increases eventually result in…?
equal landward erosion rates of the softer (bay) and harder (headland) rocks and controls rocky coastline amplitude: headlands persist in time because of rock strength differences, or headlands are transient because there exists no meaningful rock strength difference between bay and headland.
What can create persistent headlands and bays in the absence of rock heterogeneity?
Focusing on abrasion, recent modeling by Limber and Murray [2011] suggests that such internal sediment dynamics can.
Difference between sea cliff retreat and erosion?
Sea cliff retreat is the long-term landward movement of the entire cliff profile, while erosion refers to the shorter-term weathering and removal of cliff material from the cliff base that, over time, causes cliff retreat.
Wave Energy Focusing on Headlands
Refraction tends to focus wave energy and locally increase wave heights on protruding rocky headlands while dispersing wave energy (stretching wave crests and lowering wave heights) in neighbouring embayments.
The rate of sea cliff erosion increases with…
breaking wave height because wave impacts are a main driver of sea cliff erosion and retreat.
What causes headland retreat to accelerate relative to bay retreat?
As coastline amplitude increases, headlands will capture a greater amount of incoming wave energy at the expense of the adjacent, sheltered bays. This amplitude-dependent energy redistribution increases and decreases wave heights, respectively.
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.
Site-Specific Comparisons
Montara Beach in California, USA vs Holderness coast in Yorkshire, UK
At both sites, headland cliff lithology is more erosion resistant than bay cliff lithology.
But, at Montara, the wide beach dissipates wave energy so that the exposed headland cliffs are retreating slightly faster than the bay (amplitude is stable or decreasing), while at Holderness, there is no permanent beach and the bay is retreating faster than the headland (amplitude is increasing).
