Coasts Flashcards
(17 cards)
There are four main processes of erosion
- Hydraulic power (action): This is the force of the water against the cliffs. Air gets trapped in the gaps and
pressure builds up causing the gap to get bigger. - Attrition: particles collide with one another and are broken into sand sized pieces.
- Abrasion: This is when sand and pebbles are thrown at the base of the cliff causing particles to be eroded
away. - Corrosion: This is a chemical action on rocks where sea water contains a weak acid and wears away the
rocks.
Coastal Erosion Case Study Holderness
Causes: Geology of the coastline: Holderness is mostly comprised of boulder clay that was deposited during the last
ice age. This material is soft rock and so is easily eroded by the action of the sea.
Processes of erosion and weathering: The cliff foot erosional processes of hydraulic action and abrasion
undercut the cliffs at their base and erode the soft material. Rain water saturates the boulder clay at the top
of the cliff and lubricates a slip plane. The processes of undercutting and weathering cause material to
become unstable - eventually cliff material slips down into the sea under the force of gravity (cliff slumping).
The strong currents of the North Sea rapidly transport material along the shore (longshore drift operates from
north to south along this coastline). This leaves little opportunity for beach development and as a result cliffs
are exposed to the action of the sea. Today, Holderness is one of the fastest eroding coastlines in the world.
Variation in recession along the coastline: Most of Holderness is comprised of soft boulder clay, however, the
northern most part of the coastline is made up of chalk. Chalk is a more resistant rock and so less easily
eroded. Therefore, to the north of the coast we find a headland (Flamborough Head), this area protrudes out
to sea as it erodes much more slowly.
Effects of cliff recession Holderness
It is not cost effective to protect areas of low land value. This has resulted in 14 villages being lost from the
coastline since Roman Times. Many farmers have also lost their livelihoods, been forced to migrate or
diversify. For example, Ringborough Farm has lost 145 acres since 1939, meaning that half of the farm’s land
has been lost to the sea. The farmer has moved his farm buildings back from the coast (they are now
considered to be 300 years away from being lost as a result of recession). These changes have been at the
farmer’s expense, causing significant difficulties for the business. The farmer has also been forced to diversify
and now part of his business involves selling bottled gas, this was in substitution for pig farming as the piggery
was lost to the sea.
The rapid rate of cliff recession has meant that there has been a need to protect areas of high value with hard
engineering defences e.g., the settlement of Hornsea on the Holderness Coast. The problem with this is that it
can speed up the processes of erosion further along the coast (where there is an absence of protection). Not
only does this threaten other coastal communities (e.g. those further south in Lincolnshire) but it can also
have dire consequences for the environment. For example, groynes, such as those at Hornsea, trap sediment
and reduce the amount of material reaching the natural spit at the southern end of Holderness (Spurn Point).
Without replenishment, Spurn Point may erode; this area is an SSSI (site of special scientific interest) and it is
an important habitat for many bird species (e.g., oyster catchers).
Coastal Management at Holderness, East Riding, NE England the area that are effected the most
The 1949 Coast Protection Act allows local authorities in England to decide how best to manage their stretches of
coastline.
Coastal retreat is very rapid along much of Holderness – it is one of the fastest eroding coastlines in the world. The
decision as to what parts of Holderness to protect with coastal engineering is based on cost-benefit analysis. The areas
that receive protection are those that would be very costly to replace as a result of retreat. These areas include the
larger population settlements of Hornea, Withernsea and Bridlington. Mappleton is also defended, despite being a small
settlement of 249 people. This is because there is a coastal road that runs close to the cliffs that it would be very
expensive to re-route. Furthermore, residents at Mappleton have lobbied the government to demand protection for
their historic village. A further area that is defended is Easington, this is because Easington gas station is located here.
25% of the nation’s gas comes through Easington and so the loss of station to erosion could have dire consequences for
the English economy.
Defences at Holderness
use of groynes to trap moving beach material and provide a protective beach in front of
the cliff
the construction of sea walls and revetments as wave-resistant structures at the base of
the cliffs
artificial off-shore breakwaters like tyres and concrete blocks, forcing waves to break
off-shore.
sea wall used to protect Easington Gas Station (cost 4.5 million)
Case Study of a hurricane: Hurricane Katrina 2005 (Location: US Gulf Coast)
Impacts
*Katrina was a category 4 storm.
* Storm surges reached over 6 metres in height.
*New Orleans was one of the worst affected areas because it lies below sea level and is
protected by levees. These protect it from the Mississippi River and Lake
Ponchartrain. The levee defences were unable to cope with the strength of Katrina,
and water flooded into the city.
*Despite an evacuation order, many of the poorest people remained in the city.
*People sought refuge in the Superdome stadium. Conditions were unhygienic, and there
was a shortage of food and water. Looting was commonplace throughout the city.
Tension was high and many felt vulnerable and unsafe.
*1 million people were made homeless and about 1,200 people drowned in the floods.
*Oil facilities were damaged and as a result petrol prices rose in the UK and USA.
Coastal Opportunities on the US Gulf Coast(Case study)
Opportunities:
Tourism: The gulf coast region contains some of the US’s best beaches e.g., beaches at Destin and Pensacola
in Florida. This creates a lot of opportunities for tourism which leads to jobs and economic growth for area of
the gulf coast.
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Commercial fishing is a multi-million-dollar industry in the Gulf of Mexico: Shrimp, snapper, grouper, and
stone crab are some of the Gulf’s most important commercial species.
Oil industry: The Gulf Coast region is the technical and financial centre of the US oil and gas industry, with
many company headquarters concentrated along coast. This region is home to 1/5 of total crude oil
production in the U.S., 45% of U.S. petroleum refining capacity and 51% of U.S. natural gas processing plant
capacity.
Ports: The Gulf Coast is a major centre of economic activity. The Port of Louisiana and the Port of Houston are
two of the ten busiest ports in the world by cargo volume.
What are coral reefs and what is their purpose?
- Coral reefs are large underwater structures composed of the skeletons of coral, which are marine invertebrate
animals. - The coral species that build coral reefs are known as hard corals because they extract calcium carbonate from
seawater to create a hard, durable exoskeleton that protects their soft, sac-like bodies. - Each individual coral is referred to as a polyp.
- New coral polyps live on the calcium carbonate exoskeletons of their ancestors, adding their own exoskeleton
to the existing coral structure. - As the centuries pass, the coral reef slowly grows, one tiny exoskeleton at a time, until they become massive
features of the submarine environment.
Where are coral reefs located?
- Coral reefs are located in tropical oceans near the equator.
- They are found 30 degrees north and south of the equator.
- The largest coral reef is the Great Barrier Reef in Australia.
- The second largest coral reef can be found off the coast of Belize, in Central America.
- Other reefs are found in Hawaii, the Red Sea, and other areas in tropical oceans.
Types of coral reef
There are 3 types you need to know about:
- Fringing Reef
- Barrier Reef
- Atolls
Fringing reefs
the most common type, extend outward from a body of land with no water separating the reef
from land.
Barrier reefs
Barrier reefs are platforms separated from the shoreline by a channel or a lagoon.
* Barrier reefs are created due to the sea level rising or the land sinking. The coral grows upwards so they can
continue to photosynthesize, and this leaves a gap between the land and the reef.
* The longest barrier reefs are found along the coasts of Belize and Australia.
Atoll reefs
coral islands that consist of a narrow, horseshoe shaped reef with a shallow, central lagoon.
* They often form around volcanic islands that have sunk due to the process of subduction.
* Over 300 atolls are found throughout the South Pacific.
What are mangroves
Mangroves are trees or shrubs which grow in tidal, tropical, coastal swamps.
* They have tangled roots that grow above ground and form dense thickets.
* It is thought that they originate from South-east Asia and then spread across the globe.
* Because they grow in the intertidal zone, they live in a constantly changing environment.
Where are mangroves located?
- In sheltered tropical and subtropical coastal areas.
- In general, this is an area between latitudes of 30 degrees north and 30 degrees south of the equator.
Conditions needed for development of mangroves
Mangrove trees thrive in hot, muddy, salty conditions that would quickly kill most plants.
* Temperatures – Most mangroves grow in warm waters within 30 degrees latitude of the equator.
* They only grow in areas where the temperature remains above 20 degrees Celsius
* They grow in calm, shallow, sheltered areas with no strong waves or currents.
* They develop in areas where there is a large area between the high and low water mark.
How are sand spits formed
- Sediment is carried by longshore drifts
- When there is a change in the shape of the coastline, depostioion occurs. A long thin ridge of material is deposited. This is the spit
- A hooked end can form if there is a change in wind reflection
- Waves cannot get past a spit, therfore the water behind a spit is very shelterd. Silts are deposited here to from salt mashes or mud flats .
