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Coastal Processes
Page created by: Jason Passley and
David O’Neil
Class: 8PSY
Contents
Cracks, Caves, Arches, Stacks and Stumps
How can Coastal Erosion be managed?
Introduction
FOR THE
PURPOSE OF THIS WEB SITE WE WILL BE CONCENTRATING ON COASTAL PROCESSES
(GEOMORPHOLOGIC ACTION)
What is
erosion?
Erosion is the breaking down and removal of rocks by four
moving bodies. The fact that erosion removes its broken down material is what
sets it apart from weathering, which only breaks material down in situ. There
are four different erosive forces, which can be accessed from the menu choices
below.
What are
the different types of erosion?
SOLUTION
Chemicals in water, or the water itself in a river/sea, can
dissolve minerals in rocks such as chalk and limestone. These dissolved
chemicals then travel away down river.
HYDRAULIC
ACTION
The force of water pushing against a joint or crack in a rock can
compress the air in it, putting pressure on the surrounding rock face. After a
time, especially if the pressure is exerted in an on / off fashion, the rock
face will begin to break away and will be carried away with the river water
flow.
ATTRITION
Load (carried material) in the sea (such as pebbles and stones)
from erosion collide in the water, knocking pieces off each other. Large,
angular fragments eroded previously can be a lot smaller and rounder as a
result of attrition by the time they reach a resting place on the beach.
ABRASION
Large boulders can be picked up by the sea and carried and
dragged. They scrape the seabed, eroding it away, and are thrown against the
cliff forming a notch.
Headlands,
Bays and Beaches
What is a
headland? A headland is a large piece of hard, resistant rock that is left from
a cliff that has been eroded. The headland juts out to sea where softer rock
around it has been worn away by destructive waves. A headland may contain an arch, cracks & caves.
How is it
formed? A headland is formed when soft rock is rapidly eroded by the sea leaving the hard rock to stick out to sea. Lighthouses are often built on
headlands to warn ships from crashing into the land.
Give
examples of names and locations of headlands. 1= The Needles (Isle of
Wight) 2= Landsend (Cornwall) 3=The
Foreland (Dorset)
These are
all made of hard, resistant rock - for
example Portland and Purbeck Limestone (The Foreland) or sandstone.
What is a
bay? A Bay is formed in less resistant rock that has been eroded away by the
sea. It forms an inlet that is used as shelter for yachts and other boats. The
softer, less resistant rock is worn away quicker making a semi-circular shaped inlet. This natural landform has been
created over many years. Large bays are used as harbours or docks.Headland and
bay formations are common along all coastlines.
How is it
formed? It is formed when the sea erodes away the less resistant rock that is sandwiched between 2 more
resistant outcrops. While the hard,
resistant rock forms a headland, the softer rock is worn away much quicker and
forms a bay.
Give
examples of names and locations of bays? Studland Bay (Dorset), Lulworth Cove
(Dorset), Swanage Bay (Dorset), Alum Bay (IOW)
What is a beach? A beach is a
tourist attraction and it is often made of sand (fine rock material). It is a
natural landform, created by the seas action and constant erosive powers of the
waves.
How is it
formed? A beach is formed when a cliff is eroded into tiny pieces of rock that
collapses. Cliffs are undercut by waves forming a `notch’. This is an indent at the cliff base where
waves attack and erode the cliff. As this continually occurs the cliff retreats
(moves backwards) forming wave cut platform – a long flat, smooth area of rock.
The cliff becomes unstable and cracks form until the overhanging cliff eventually collapses making large
boulders fall. These large rocks are
constantly attacked and broken into smaller pieces which are eroded down into
beach materials e.g sand and pebbles. This material is constantly moving by the
force of the waves up and down the beach and can be moved by long shore drift.
Give
examples of names and locations of beaches. 1=Brighton 2=Margate 3=Portsmouth
Cracks, Caves, Arches, Stacks and
Stumps
Describe
the stages and processes of a stump forming from a crack to a stump.> If a
headland juts out to sea it is very exposed to constant wave attack and erosion
by the sea. If there is an area of weakness on the headland this will be
attacked by the sea until the headland here begins to crack. The constant
battering of the waves erodes this crack until hydraulic action, corrosion and
corrasion widens and deepens the crack into a sea cave. The sea will eventually
break through forming a natural arch. The arch is still further attacked until
the roof becomes unstable and collapses to leave a single pillar of rock.
This is left standing like an upright
column which is called a stack. A stack can be further undercut to leave a low
pillar of rock called a stump. Examples of stacks include Old Harry and Old
Harry’s wife (Dorset) and the Needles on the Isle of Wight.
Give
examples of Caves, Arches Stacks and Stumps in the UK. More examples include
the sea caves at Studland Bay and at Swanage (Tilly Whim Caves) and the natural
arches at Etretat in France.
Problems of Coastal Erosion
What
problems does coastal erosion cause? Coastal erosion wears away the land that
may have houses or other important buildings or farmland that will topple into
the sea. This means people will lose there homes and also money
What are
the dangers of erosion to coastal areas? People can lose money, their homes and
maybe their livelihood.
How far are
coastal areas being eroded every year? (Give specific examples). It ranges from
a few centimeters to up to 40 metres a year.
How can Coastal Erosion be managed?
What are
the different forms of coastal protection schemes?Sea walls, wooden revetments,
groynes, gabion baskets and large boulders. These are all placed at the base of
the cliff to protect it from the constant attack of the waves or stretch out to
sea to stop beach material being washed away by longshore drift.
What are
sea walls (advantages and disadvantages – give specific examples)? Strong
concrete barriers built at the base of the cliff to stop erosion. They are
strong but are very expensive – Rottingdean, Brighton.
What are
wooden revetments? (Advantages and disadvantages – give specific examples).
These are like a sea wall but made of wood and so are not as strong, they
protect the cliff but can crumble over time.
What are gabion
baskets? (Advantages and disadvantages – give specific examples). These are
like big wire baskets full of large pebbles (like shopping trolleys) that take
the force of the waves from battering the cliff. They are strong and cheaper
than sea walls but can eventually rust and breakdown
What is
boulder protection (advantages and disadvantages – give specific examples)?
This is when huge rocks are dropped at the base of the cliff to take the power
of the waves and so protecting the cliffs. They look natural but not in all
cases.
What are
other forms of coastal protection and management? Beaches stop cliffs being
worn away because the waves power crashes against the beach and not the cliff.
Beaches are often washed away by the seas movement (longshore drift). To hold
the beach in place groynes are built out to sea that stops material being moved
away from the bottom of the cliff..