CASE STUDIES Flashcards
Where are high energy coastlines found in the UK?
Stretches of the Atlantic-facing coast such as Cornwall or north-western Scotland.
Rate of erosion exceeds the rate of deposition.
What’s the UK’s most south-westerly peninsula?
Cornwall - it bears the brunt of the worse weather from the Atlantic therefore its rocky coastline can withstand frequent winter storms without suffering from rapid erosion.
Describe Cornwall’s geology
Like the rest of Western Britain, Cornwall consists of older resistant rocks like:
* igneous rocks e.g basalt and granite
* old compacted sedimentary rocks e.g old red sandstone
* metamorphic rocks e.g slates and schists
These rocks are all resistant to the erosive power of the sea, wind and rain
Where are low energy coastlines found in the UK?
Lincolnshire and Northumberland
Example of a coastal plain
The Wash in Norfolk
Describe the features that make The Wash a coastal plain
- 20km wide and 30km long - it is the largest estuary systemic the UK (formed by four rivers)
*Range of habitats from tidal creeks to mud flats and lagoons.
Where are low-lying sandy beaches found in the UK?
Much of the coast of eastern England e.g Bamburgh beach in Northumberland, Lincolnshire and Norfolk coasts.
Coasts that are predominantly low energy
Holderness in the East Riding of Yorkshire
Chalky cliffs
Flamborough Head (Yorkshire coast)
Example of estuary in western Britain
Camel estuary in Cornwall
Examples of sea stacks
Bedruthan Steps - Cornwall
Beach in Scotland containing depositional landforms
Luskentyre peninsula on South Harris in the Outer Hebrides, Scotland - lots of sand dunes
Rockfall in December 2015
Charmouth beach, Dorset
Attracted many fossil hunters as over 100 metres of cliff fell onto the beach and fossil were exposed.
In The Wash, how does the sediment originate?
- The main source is from cliffs eroding between West Runton and Weybourne, east of The Wash along the north Norfolk coast. These cliffs have eroded at about 1m per year for thousands of years. Because they are sandstone, 60% of sediment consists of sand.
- Some sediment comes from tidal currents, which pick up glacial deposits from the shallow sea floor.
- The erosion of the Holderness cliffs further north also provides some sediment, carried southwards in suspension.
- Sand is carried southwards in suspension.
- Four rivers also discharge into The Wash - bringing very fine sediment.
What do the Wash and the Norfolk coast form part of?
One of the eleven sediment cells around the English and Welsh coasts.
Describe cliffs eroding between West Runton and Weybourne, east of The Wash
These cliffs have retreated at about 1m per year for thousands of years.
Case study to show that no classification system in definitive
- Cornwall’s high-energy coast is mainly rocky, but also has long stretches of sand and some estuaries.
- Similarly, the low-lying coasts of eastern and southern England still have high cliffs e.g at Beachy Head in East Sussex
In 2001, UNESCO awarded “World Heritage” status to a stretch of what?
The coast of South Devon and East Dorset - known as “The Jurassic Coast”. World Heritage status comes form its unique “geological walk through time” - it demonstrates the whole Jurassic period with abundant fossils.
Stair Hole
Stair Hole - less than half a mile west of Lulworth Cove. The sea has eroded through limestone and clays to create a small cove. It’s the best place to see the Lulworth Crumple.
Example of limestone folding
Lulworth Crumple at Stair Hole - thin beds of Purbeck limestone and shale are clearly visible in the side of the cliff. These layers of rock were folded (crumpled) in response to tectonic movements about thirty million years ago, collision of African and Eurasian plates
Example of folds (limestone folding) - formed by pressure during tectonic activity which makes rocks buckle and crumple
Lulworth Crumple at Stair Hole, Dorset
Example of loose, unconsolidated material at the coast
Boulder clay of the Holderness coast
What is Cornwall’s coast mainly made up of?
Granite (1mm annual rate of recession so resistant)
Glacial till
Holderness coast, Yorkshire
1-10m annual rate of recession
Isle of Purbeck
Located in East Dorset, near Poole. Combination of different rock types on the Isle of Purbesck has led to coastal landscapes ranging from Lulworth Cove to Kimmeridge Bay (Kimmeridge Bay consiststs of less resistant clays where fossils can easily be found).
Example of concordant coast
- The eastern coast of the Adriatic Sea (near Croatia)
- Southern coast of Isle of Purbeck e.g Lulworth Cove
How did Lulworth Cove form?
Over time, the sea gradually eroded the resistant Purbeck limestone at the entrance to Lulworth Cove. Then, rapid erosion of the less-resistant clays behind the limestone led to the formation of a cove or a bay.
How did Lulworth Cove form (sheet)
- Formation began after the last ice age. A river swollen by melt water flowed overland to the sea.
- The river cut a valley and breached the Portland Stone. The rising sea flooded into the valley and started to exploit joints and weaknesses in the Purbeck Beds.
- Erosion then occurred of the soft Wealden clay, which had already been scoped out by the river.
- The cove formed as a pan-shaped inlet.
- The cove continued to enlarge, eroding through the greensand rock.
- Erosion was contained and slowed down by the semi hard chalk beds to produce the semi landlocked cove of today.
How does the rock type on Dorset’s coast vary?
Varies between resistant Purbeck limestone, which forms steep cliffs, to less-resistant clays and sands. These rock types alternate along the coast so that where a resistant rock is eventually eroded (e.g at entrance to Lulworth Cove) - allowing the sea to break through to the less-resistant rocks behind - erosion follows more quickly.
What was the erosion at Lulworth Cove helped by?
A local stream, the valley of which makes erosion inland easier.
Geology of the Isle of Purbeck
- Bagshot and tertiary beds - sand and clay - relatively unconsolidated
- Chalk - mechanically strong
- Wealden beds - mainly clay - relatively unconsolidated
- Portland and Purbeck beds - mainly limestone - strong and hard, but with regular joints
- Kimmeridge clay - relatively unconsolidated
Example of a Dalmatian coastline
The Dalmatian coast in Croatia
What are Dalmatian coasts also known as?
Pacific coasts e.g in southern Chile
Haff coasts
Southern fringes of the Baltic Sea i.e the Baltic Sea coastline of Poland e.g 𝘁𝗵𝗲 𝗩𝗶𝘀𝘁𝘂𝗹𝗮 𝗛𝗮𝗳𝗳 which is a large lagoon that has formed behind the Vistula spit
Example of discordant coast
- South-west Ireland
- Isle of Purbeck’s EASTERN coast, which runs south from Studland Bay to Durlston Head.
Example of bay in discordant coastline
- Studland Bay on the Isle of Purbeck, where the bagshot and tertiary beds consist of unconsolidated sands and clays and are less resistant to erosion.
- Swanage Bay on the Isle of Purbeck - the Wealden beds consist of unconsolidated clay which are less resistant to erosion.
More resistant Jurassic Portland Limestone forms the Peveril Point headland to the south, projecting out by 1 km. Resistant Cretaceous Chalk forms the Foreland headland, projecting 2.5 km to the north. ALSO Swanage bay faces east, and is sheltered from the prevailing south westerly wind and highest energy waves. - Bantry Bay - located in Cork in the south west of the Republic of Ireland. Formed from less resistant Carboniferous Limestone. Beara Peninsula to the north formed from more resistant Devonian Old Red Sandstone. he high degree of indentation of Bantry Bay is not solely influenced by the relative resistance of rock types, but also the orientation of strata SW-NE means that they directly face high energy Atlantic waves driven by the prevailing SW wind.
Example of a headland on a discordant coastline
- The Foreland on the Isle of Purbeck - the chalk is strong there and resistant to erosion.
- Peveril Point and Durlston Head - here the Purbeck and Portland beds are made of limestone which is resistant.
Examples of headlands
The Foreland
Peveril Point
both in Isle of Purbeck, Dorset.
What’s Dorset famous for?
Its Jurassic Coastline - a world heritage site protected because of its extensive rows and fossil, some bating back 185 million years. Its an example of both a discordant and concordant coast.
Chesil Beach Dorset
- Barrier beach that has created a fleet lagoon which is saline.
- Made of pebbles and is 18 miles long
HIGH ENERGY SHINGLE COASTLINE
Dorset coast spit
Weymouth Spit, a recent change in prevailing wind has caused spit to curve and a salt marsh has formed behind.
Old Harry
Example of stack, made of cretaceous chalk which is strong enough to support itself as a vertical stack.
Coastal plain, estuary and lagoon coastline. Sedimentary rocks.
East coast (Norfolk)
Northumberland
Rocky outcrops, igneous
Cornwall
Where is there resistant granites?
Land’s End - only eroded by 10cm in a century. In comparison to Holderness where the weak bolder clays have eroded inland by 120m in the same time period.
Berms
Brighton Beach
Example of tombolo
St Ninian’s in the Shetland Islands
Offshore bar
Southern coastline, east of Hopetoun
Bar
Start Bay, Devon - 9km long and formed from rounded shingle deposits mostly of flint and quartz gravel
Large scale barrier islands examples
Along the coast of the Netherlands, and in North America along the South Texas coast.
Sand dunes example
- Studland, Dorset
- Bolonia, Andalusia, Southern Spain
Examples of salt marshes
Common around the British coast
What percentage of the world’s population live in lowland coastal zones? (less than 10m above sea level)
12% of the world’s population, so it is not surprising that the coast plays an important role in the lives of many people.
Where are more hard and resistant rocks found in the UK?
Western side - so even though the prevailing westerly wind creates powerful waves, erosion rates are low.
Where are softer rocks found in the UK?
Eastern side of England. Luckily, when waves do approach from the east across the North Sea, they are smaller than in the Atlantic, so erosion rates are less than they could be.
When did a section of the sea wall collapse and leave the railway to Cornwall suspended in mid-air?
Dawlish in Devon, February 2014
According to United Nations Environmental Programme (UNEP), what percentage of coastal regions are at risk of degradation?
33% - mainly from infrastructure development and pollution. Then there is climate change, which is increasing storm activity and energy in waves, as well as the risk of coastal flooding.
Places that have low energy coasts
- Mediterranean Sea coasts
- East Anglian coast
Places that have high energy coasts
- Atlantic coasts of Norway and Scotland
- Pacific coasts of Alaska and Canada
Example of igneous rock and recession rate
Granite - typical annual recession rate is 1mm
Example of sedimentary rock and recession rate
Thinly bedded limestone - typical annual recession rate is 2.5cm
Example of metamorphic rocks
Gneiss, marble, slate, schist.
Where is recession fastest?
On new islands formed as a result go tectonic activity, with recession rates of around 40m a year.
When can there be slipping and slumping?
If there is a porous rock above an impermeable rock, such as a weakly consolidated sandstone above a layer of clay, water percolating through will collect in the upper layer, creating an instability that often leaders to slipping and slumping.
Example of places with the feldspar mineral in granite cliffs? (hydrolysis weathering)
Cornwall and Devon
How much of the UK’s coastline do rocky coasts occupy?
Rocky coasts occupy about 1,000 km of the UK’s coastline, mainly in the north and west.
Example of area with high relief
Conachair Cliff on the Isle of Hirta in the Outer Hebrides - 427m cliffs
Example of area with low relief
Chapel Porth in Cornwall
Coastal plain - when the falling sea level exposes a flat continental shelf
The Atlantic coastline of the USA
Formation of Dalmatian coasts
- On the Adriatic Sea.
- A concordant coastline produced by the geological structure of folds parallel to the coast.
- Tectonic forces produced by the collision of African and Eurasian plates compressed Carboniferous Limestone during the Alpine Orogeny 50 million years ago.
- Created up folded ridges (anticlines) and down folded valleys (synclines) aligned parallel to the coast.
- Sea level rise at the end of the Devensian Glacial overtopped the low points of the anticlines and the sea flooded synclines.
- This produces lines of narrow islands parallel to the coast formed by projecting sections of anticlines.
Lines of islands separated by narrow sea channels parallel to the coast (sounds)
Haff coast near Szczecin
At the mouth of the River Oder near Szczecin, Stettiner Haff formed where sand ridge connected islands, leaving river to emerge through three narrow outlets.
Concordant coasts: Barrier islands, sand banks and mud flats parallel to the coast
Frisian Islands off the North Sea coast of the Netherlands, Germany and western Denmark.
Named places on discordant coastlines
- Studland Bay - Isle of Purbeck
- Swanage Bay - Isle of Purbeck
- Bantry Bay - Cork in south-west Republic of Ireland
Example of a bay which is a product of sea-level rise
Bantry Bay - sea flooded inland, creating a ria at the start of the Holocene.
Example of a place that has lots of joints
Bantry Bay - carboniferous Limestone is heavily jointed, leading to more rapid fluvial and marine erosion than in adjacent sandstones, contributing to the formation of headland and bay coastal morphology.
Example of a place that has a fault
Bantry Bay, Cork, Republic of Ireland - a major fault runs SW-NE down the centre of the bay. The Carboniferous Limestone is significantly weakened by faulting, allowing rapid fluvial erosion, and the resulting river valley was inundated to form a ria when sea levels rose.
Explain how granite, limestone, sandstone and boulder clay varies in terms of resistance
Granite erodes at a rate of 0.1 cm per year
Carboniferous limestone at 1 cm per year
Sandstone at 10 cm per year
Boulder clay at 1 m per year
Examples of igneous rock
Granite, Dolerite, Basalt and Pumice
Igneous rock coastlines recession rate
Igneous coasts recede at less than 0.1 cm p.a
What are the exceptions to igneous coastlines being resistant?
* Newly formed lava and solidified ash layers (tuff) erode easily.
* Newly formed volcanic islands can exhibit very rapid erosion rates of 40m p.a.
Why are metamorphic rocks less resistant than igneous?
* Their crystals are often orientated in the same direction (foliation) making them weaker than the interlocking crystals of igneous rocks.
* Often heavily folded and faulted.
Metamorphic rock coastlines recession rate
About 0.1-0.3 cm p.a
Examples of sedimentary rocks
Sandstone, limestone, shale
Why are sedimentary rocks less resistant than igneous and metamorphic?
- Weak bedding planes
* They’re clastic - Often heavily jointed as a result of compaction and pressure release
- Rocks like shale may have many bedding planes and fractures.
Sedimentary rock coastlines recession rate
Varies because older sedimentary rock is buried deeper and is subject to more intense compaction with stronger sedimentation - so tend to be more resistant than younger sedimentary rocks.
- Carboniferous limestone 1 cm p.a
- Young sandstones 10 cm p.a
Examples of unconsolidated material
- Fluvial alluvium
- Glacial boulder clay
- Aeolian loess
Unconsolidated material coastlines recession rate
They are very easily eroded, resulting in very fast rates of recession. The boulder clay of Holderness coast in Yorkshire retreats at 2-10 m p.a.
Examples of spits
- Weymouth spit
- Blackney Point (has cut off Clay-next-the-sea from the sea, causing the loss of their harbour and migration of fishermen families away)
