Dorset Coast Flashcards
(27 cards)
What is the difference between sand and shingle beaches? Explain
sand:
- flat + wide -weak backswash can move the small sand particles back down the beach, creating a long, gentle slope
shingle:
- steep + narrow - weak backswash cannot move the heavier and larger shingle particles down the beach. so they build up and create a sreep slope
Where is the Foreland, Old Harry and His Wife and which type of rock? What iit is?
Near Swanage Bay, Western region of Dorset
chalk
the foreland; the headland
stack called old harry and a stump called old harrys wife
Where is Durdle Door? Which rock?
an arch Southern part of Dorset
hard limestone headland
Where is Swanage Bay? Rock? What is it?
-clay (Swanage BAY is made of CLAY)
beach/bay
Where is CHesil BEach? WHat rock? What is it? What is BEHIND it?
a tombolo(a type of spit that extends out o an island) that joins the Isle of Portland to the mainland
South-Eastern part
a lagoon called The Fleet Lagoon
composed mainly of flint and chert pebbles that are gradually graded (pebbles get smaller from east to west due to longshore drift and wave energy)
Dorset has warm, dry summers of around ____ in ____.
21 degrees
July
… and mild and wet winters of ___ in ___
3 degrees
January
What is the dominant form of mechanical weathering?
- salt weatheting
-when warm temp causes sea water to evaporate from rocks quickly, leaving a build up of salt crystals in tiny cracks in the rock.
Is there freeze-thaw weatehring here?
No its too warm/not cold enough
What do the strong prevailing winds from the south-west mean?
- they bring storms from the Atlantic OCean
- these storms bring high energy, destructive waves which increase erosion of the cliffs
- so, hydraulic action and abrasion both increase during a storm and erode the base of cliffs
-this makes cliffs unstable, making mass movement likely to happen
What do Dorset’s VERY WET winters mean?
- soil and rocks become heavier when they r saturated, making them prone to mass movement
- In Jan 2016, intense rainfall combined with high energy waves during Storm Frank to cause the collapse of cliffs between Burton Bradstock and West Bay (sandstone)
What are the soft and hard rocks in Dorset?
soft:
-clay and sandstone
hard:
- chalk and limestone
What type of erosioin are harder rocks more vulnerable to?
solution:
-the sea water chemically reacts with the rock causing it to dissolve ( du to dissolved co2 that gradually dissolve the calcium carbonate in limestone rocks)
Give two example of how climate, geology and weather interact
lots of rain makes chalk and limsteone vulnerablle to carbonation weathering because the rain water is slightly acidic.
prolonged heavy rain causes clay to become heavier, softer and more slippery, making mass movemtn more likely. During the winter, there are often slides and slumps on the clap cliffs, such as the mudslides and rock falls near Kimmeridge
What are the 3 types of management strategies?
groynes, sea walls and beach replenishment
what are groynes?
wooden/stone fences that are built at right angles to the coast, trapping material transpoorted by long-shore drift, creating wider beaches effectively slowing beaches and giving greater protections from erosion
When were new groyned put? WHere? What material?
timber groynes
swanage beach
2005-6
One positive and one negative of groynes
- stop the loss of beach material, wideing beach and protecting from erosion
- by stopping beaches material from mocing along the coast, theyve starved areas further down the coast of sediement, making them narrower. These beaches stand less resistance against erosion, so there would be more erosion there
Where were sea walls enforced?
Swanage beach
WHat doo sea walls do?
reflect waves back out to see, absorbing some of their energy to make them eeaker and then preventing the erosion of the coast
when were the concrete sea walls initially contstructed? How long?
1890s!!!
then extended and reinforcved in the 1920s and 30s
stretches around 1.8km along the seafront
negatives of sea walls? w/ example in 2019
- VERY expensive
- they can create a strong backswah which removes sediment from the beach and can erode under the wall
in 2019, voids beneath the historic stone sea wall in Swanage were identifies, so geopolymer injection was used to stabilise the structure. - they can also prevent the cliffs from being eroded, so there r no new material to replenish the beach. This gradually lowers the level of the beach
When were sand an shingle dredged from the sea bed at Poole Harbour added to the upper parts of Swanage beach?
Winter 2005-6
One positive of beach replenishemtn
- this has created wider beaches, slowing waves and helping protect cliffs and coastal properties from erosion
- however, it costs £5 million to replenish the beach and it needs to be repeated roughly every 20 years.
