Notes on Coastal Landscapes and Earth's Life Support Systems which are in the Physical Systems exam of OCR A level Geography. Also includes case study examples.
A system is a set of interrelated objects comprising stores and links that are
connected together to form a working unit. Coastal landscape systems are
recognised as open systems1. So this means energy and matter can be transferred
from another system as an input or matter can be transferred into another system as
an output.
When a systems inputs and outputs are equal, a state of equilibrium is reached.
When this equilibrium is disrupted, the system undergoes self-regulation and
changes in order to restore equilibrium. This is known as dynamic equilibrium as the
system produces its own response to the disturbance (negative feedback).
A sediment cell is a stretch of coastline and it’s associated near shore area within
which the movement of sediment is largely self-contained. A sediment cell is
generally regarded as a closed system but it is inevitable that sediment is transferred
between cells.
Factors influencing the coast
Winds – the source of energy for coastal erosion and sediment transport is
wave action. Wave energy is generated by the frictional drag of the wind
moving over the surface of the water. The higher the wind speed and the
larger the fetch, the larger the waves and the more energy they possess.
Wind can also carry out transport, erosion and deposition itself.
Waves – possess energy as a result of its position above the wave trough
and kinetic energy caused by the motion of water within the wave. Moving
waves don’t move water forward, but rather the water molecules impart a
circular motion.
Amount of energy in a wave is calculated by P=H 2T where P is power in
kilowatts per metre of wave, H is wave height in metres and T is the time
between wave crests in seconds (wave period). Relationship between wave
height and energy is non-linear.
1
A type of system whose boundaries are open to both inputs and outputs of energy and matter
, In shallower water, the deepest circling water molecules come into contact
with the seafloor which changes the speed, direction and shape of the waves.
Firstly, waves slow down as they drag across the bottom, the wavelength
decreases and waves start to bunch up. The deepest part of the wave slows
down more than the top of the wave. The wave begins to steepen as crest
advances ahead of the base before the wave topples over and breaks on the
shore.
Spilling – steep waves breaking onto gently sloping beach, water spills
forward gently as the wave breaks
Plunging – moderately steep waves breaking onto steep beaches,
water plunges downwards as the crest curls over
Surging – low angle waves breaking onto steep beaches, the wave
slides forward and may not actually break
It is only when the wave breaks that there is a forward movement of water and
energy (swash) and hen there’s no more energy available to move forward,
the water is drawn back down the beach as backwash.
Constructive waves – low height, long wavelength, low frequency,
usually break as spilling waves and swash travels far up the beach.
Backwash returns to the sea before the next wave breaks so swash
movement isn’t interrupted and retains its energy (swash exceeds
backwash).
Destructive waves – large height, shorter wavelength, higher
frequency, and usually break as plunging waves so waves carry little
swash energy/forward movement. Friction from the steep beach profile
slows down the swash so it doesn’t travel far before returning as
backwash. With a short wavelength, the wave doesn’t return before the
next wave breaks so this is slowed by the friction of meeting another
wave.
Tides – tides are the periodic rise and fall of the sea surface and are
produced by the gravitational pull of the moon and to a lesser extent, the sun.
The moon pulls water towards it creating a high tide and there is a
compensatory bulge on the opposite side of the earth. Areas in between the
high tides experience low tides. Spring tide = moon, sun and earth are all
aligned so there’s a high tidal range. When the sun and moon are at right
angles to one another, gravitational pull is at its weakest, producing neap
tides with a low range. Tidal range can be a significant factor in the
development of coastal landscapes as it influences where wave actions
occurs.
Geology – lithology describes the physical and chemical compositions of
rocks which determines how resistant they are to erosion, weathering and
mass movements. Structure concerns the properties of individual rock types
such as jointing, bedding and faulting. It also includes the permeability angle
, of dip of the rocks which has a strong influence on the cliff profile. Structure is
an important influence on the planform of coasts at a regional scale – whether
the coastline is concordant2 or discordant3.
Currents – rip currents play an important role in transporting coastal
sediment. They are caused by either tidal motion or by waves breaking at
right angles to the shore. A cellular circulation is caused by differing wave
heights at right angles to the shore. Rip currents modify the shore profile by
forming cusps which help perpetuate the rip current. Ocean currents are a
much larger scale, generated by the earth’s rotation and convection.
Warms ocean currents transfer heat energy from low latitudes towards the
poles whereas cold ocean currents transfer heat to the equator. The transfer
of heat can be significant as it directly affects the air temperatures and
therefore, sub-aerial processes.
Geomorphic processes
Weathering - uses energy to produce physically or chemically altered materials from
surface or near surface rock.
Freeze-thaw Water enters cracks/ joints and expands as it freezes.
This exerts pressure on the rock causing it to split or
Physical weathering
pieces to break off.
Pressure release When overlying rocks and removed by weathering and
erosion, the underlying rock expands and fractures.
Thermal expansion Rocks expand when heated and contract when cooled. If
subjected to frequent cycles of heating and cooling the
outer layers may crack and flake.
Salt crystallisation Solutions of salts can seep into pore spaces in porous
rocks. Here the salt precipitates and crystals form. The
growth of these crystals puts stress on the rock causing it
to disintegrate.
Oxidation Some minerals in rocks react with oxygen in the air or
water. Particularly common with iron.
Carbonation Rainwater combines with dissolved carbon dioxide from
Chemical weathering
the atmosphere to produce a weak carbonic acid. This
reacts with calcium carbonate in rocks such as limestone
to produce calcium bicarbonate which is soluble.
Solution Some salts are soluble in water. Any process by which a
mineral dissolves in water is known as solution.
Hydrolysis This is a chemical reaction between rock minerals and
water. Silicates combine with water to form secondary
minerals such as clay.
Hydration Water molecules added to rock minerals. Causes surface
flaking due to expansion when absorbing water.
2
Where rock types run parallel to the coast producing straight coastlines.
3
Where rock types lie at right angles to the coast producing headlands and bays within the coastline.
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