The document discusses the formation of beaches and cliffs through geological processes. It explains that: 1) Beach composition influences slope, with shingle beaches typically steeper than sandy beaches due to differences in percolation rates. Coarse shingle allows for rapid water drainage, while compact sand hinders drainage. 2) Cliffs form through both subaerial and marine erosion processes. Marine processes like wave pounding and hydraulic pressure undermine cliff bases, while subaerial processes like weathering from precipitation, freeze-thaw cycles, and evaporation cause mass failures and recession. 3) Cliffs are constantly changing features as coastal and atmospheric forces cause unpredictable rockfalls and large-scale collapses over various time

1. CAPE 2006 UNIT ONE #5 13-Feb-11
b) explain how the differences in the composition of the beach material influence the
slope of the beach [5marks]
c) discuss the role of subaerial and marine processess in the formation of cliffs
[20marks]
b) Reference Waugh (page 145-146)
Particle size complicates the influence of wave steepness on the morphology of the beach.
The fact that shingle beaches have a steeper gradient than sandy beaches is due mainly to
differences in percolation rates resulting from differences in particle size. This means that water
will pass through coarse grained shingle more rapidly than through fine grained sand. In shingle
beaches, shingle may make up the whole or just the upper part of the beach and like sand; it will
have been sorted out by wave action. The larger the size of the shingle, the steeper the gradient
of the beach.Shingle beaches are typically steep, because the waves easily flow through the
coarse, porous surface of the beach, decreasing the effect of backwash erosion and increasing the
formation of sediment into a steeply sloping beach. Regardless of whether the waves on shingle
beaches are constructive or destructive, most of the swash percolates rapidly downwards leaving
limited surface backwash. On the other hand, sand beaches produce beaches with a gentle
gradient. This is because the small particle size allows the sand to become compact when wet.
This severely impacts the rate of percolation. The percolation is also hindered by the storage of
water in pore spaces which enables most of the swash from constructive waves and destructive
waves to return as backwash.
c) Reference Waugh (page 149) , Cook (page 464)
A cliff is a vertical or near vertical rock face which typically comprises exposed situ rock
and capped with present day/ recent soils. The formation of cliffs is the result of sub aerial and
marine processes which include, wave pounding, hydraulic action and weathering.Coastal
processes act on timescales that range from the few seconds of a wave breaking to the many
millennia of sea-level change.
Cliffs are formed by a number of processes, in particular the explosive energy released
from waves crashing into their base, the result which leads to undercutting and eventual collapse
of the overlying rock. Such a process may be wave pounding. Wave pounding is an erosional
process by which steep waves which have considerable energy break the foot of cliffs and
generate shock waves. These shock waves may be as strong as 30 tonnes per m2.
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2. In addition to this, hydraulic pressure is another marine process which leads to the
formation of cliffs. Hydraulic action occurs when waves strike the shore. In storm conditions,
the force of the waves can have a heavy impact- equivalent to 100 kg per m2. Where there are
joints or weaknesses in the cliff face, air might become trapped and compressed by the incoming
waves. The resulting pressure expands and weakens joints. This can cause large blocks as well as
smaller fragments to be loosened and then removed by the waves. This is seen in the diagram
below where the waves break off pieces of the cliff causing it to recede causing an eventual
collapse and recession of the cliff.
STEEP WAVES BREAKING OFF CLIFF
CLIFF
SEA
Furthermore, sub aerial processes aid in the formation of cliffs. According to J. Pethick, “cliff
recession is primarily the result of mass failure.” Mass failure may be caused by such non marine
processes such as rain falling directly onto the cliff face, surface runoff of water from the land;
and the effects of weathering by the wind and frost. Precipitation (rain, snow and hail) penetrates
the natural cracks and fissures throughout the cliff, washing away and dissolving less resistant
rock and weakening the stability of the cliff. The rate of erosion is accelerated by freeze thaw
action during the winter months, during which time the expanding ice cracks the rock further.
This is most notable on the exposed outer surface. Erosion also occurs during the summer
months, at which the time the cliff is warmed and the evaporating water causes the sediment to
contract and crack (porous rock only).
From the aforementioned points, cliffs are constantly changing and on the retreat; inevitably rock
falls and large scale collapse occur unpredictably throughout the year.
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