Geography Reference
In-Depth Information
On the other side of the spectrum, rocky coasts may be seen to
be solid, more stable landforms. However, they are actually charac-
terised by erosional features. This often makes for stunning scenery
with rugged cliffs and interesting
stack
features, arches and caves.
Nevertheless, the average rate of change along rocky coasts is slow,
although some changes such as landslips can be dramatic. Rocky
coast erosion occurs through mass movements, rock weathering
processes and rock transport processes. Mass movements are
common due to steep slopes. Rockfalls are characteristic of hard
rocks, landslides typically occur in thick deposits of clay, shale or
marl
, and flows occur when there is a high liquid content. Freeze-
thaw, wetting and drying, chemical weathering and the mechanical
abrasion and force of water undercutting the base of rocky slopes
by wave processes are principal drivers of mass movement. These
processes were discussed in more detail in Chapter 3. Typically,
once material has been removed from the cliff face onto the floor
below it can be removed by coastal transport processes, meaning
that the bases of cliffs do not receive protection for long by debris
deposited through mass movements.
Shore platforms
develop
when erosion of a rocky coast leaves behind a horizontal or gently
sloping rock surface.
Coral
reefs
are depositional environments yet are located in
high energy wave systems. They are the largest biologically con-
structed formations on Earth and consist of limestone that has been
created by animals forming their shells. When corals die, they leave
behind the limestone that formed their skeletons and so the sedi-
ment can build up over thousands of years. Coral reefs are in a very
delicate balance between erosion and biological construction.
Without the presence of living organisms the reefs would not exist
because weathering and wave erosion would destroy the landforms.
Corals can be found throughout the world but reef building corals
are only found in the sub-tropics between 30°N and 30°S.
Coral reefs occur in two main settings. The first is close to land
on the continental shelf where water depths are less than 200
metres such as in the Great Barrier Reef off the north-east coast of
Queensland, Australia. The second are those that rise several kilo-
metres from the ocean floor. These have formed around the edges
of volcanic islands above hot spots (see Chapter 3 for an explana-
tion of oceanic island formation). Often when the volcano becomes
