Landforms Of Coastal Wri Flashcards
How are wave cut platforms formed?
When waves break against the foot of a cliff, hydraulic action and corrosion tends to be concentrated closet
O the high-tide line. This creates a wave-cut notch. As the notch gets bigger the cliff is undercut and the rock above it becomes unstable, eventually collapsing.
As these erosional processes are repeated,the notch migrates inland and the cliff retreats leaving behind a gently sloping wave cut platform which is usually only completely exposed at low tide. Wave cut platforms rarely extend for more than a few hundred metres, because a wave will break earlier and its energy will be dissipated before it reaches the cliff, thus reducing the rate of erosion, limiting the further growth of the platform.
This is an example of negative feedback
When do steep cliffs tend to occur?
Where the rock is strong and resistant to erosion, such as most igneous and metamorphic rocks. Sedimentary rocks that are dipping steeply or even vertically tend to produce steep and dramatic cliffs, as will the absence of a beach and an exposed orientation with a long fetch and high-energy waves that encourage erosion and undercutting by the sea
When do gentle cliffs occur
Gentle cliffs usually reflect weak or unconsolidated rocks that are prone to slumping. Rocks that are dipping towards the sea also tend to have low- angle cliffs. A sheltered location with low energ6 waves and a short fetch will result in subaerial debris building up at the foot of the cliff, reducing its overall angle. A wide beach will absorb wave energy, preventing significant undercutting and steepening
What does the rate of retreat depend on ?
Depends on the balance between marine factors - such as wave energy, fetch, presence of a beach- and terrestrial factors such as subaerial processes,rock geology and lithology
Caves, arches, stacks and stumps
The erosion of rocks like limestone and chalk tends to exploit any lines of weakness- joints, faults and cracks
When joints and faults are eroded by hydraulic action and abrasion, this can then create caves. If the overlying rock then collapses, a blowhole will develop. During stor high tides, seawater can be blown out of these blowhole with considerable and spectacular force
If two caves join up, or a single cave is eroded through a headland, an arch is formed. The base is widened and the gap is further enlarged by erosion and weathering
Eventually, the top of the arch collapses leaving an isolated pillar of rock called a stack. As it continues to be eroded by the sea, the stack collapses to leave a stump, which may only appear above the surface at low tide
