Coastal Landscape Development Flashcards
What is the difference between a landform and a landscape?
Landforms are individual components of a landscape (e.g. cliffs, beaches, arches etc)
whereas,
landscapes are made up of a number of landforms which give them their key characteristics.
No two coasts are the same and the nature of the coastal landscape depends on the coastal geology,
climate, nature of the tides and waves and a range of other factors.
What are the inputs of coastal landscape development?
Coastal geology
Climate
Nature of waves
What are the processes of coastal landscape development?
Erosion
Weathering
Deposition
Wave refraction
Sea level change
What are the outputs of coastal landscape development?
Sediment
Landforms
What is a discordant coastline?
Alternating more and and less resistant rock at right angles to coastline.
Erosion occurs faster in less resistant rock.
Overtime this will form bays between protruding headlands
Due to wave refraction erosional energy is then concentrated on the headlands and the bays are subject to deposition due to lower energy waves.
This means that you find beaches forming in bays which then protect the coastline from further erosion.
What is a concordant coastline?
Alternating bands of hard/soft rock parallel to the coastline
Describe how a wave-cut platform is formed
Where destructive waves break at foot of cliff their energy is concentrated over a small area.
Erosion (hydraulic action and corrasion in particular) is close to high-tide line.
Cliff becomes undercut forming a wave-cut notch.
The cliff above is weathered and under stress - lack of support from below, results in the cliff collapsing.
Over a series of collapses a wave-cut platform develops between high and low water marks.
The wave-cut platform is smooth and flat and may be smoothed by further abrasion.
Explain why wave-cut platforms rarely grow further than 500m
Over time the waves break further out to sea - waves have to travel over more platform before the cliffs. means the wave energy is dissipated before it reaches the bottom of cliffs, so rate of cliff erosion decreases, and platform ceases to grow.
So wave cut platforms are unlikely to grow wider than 500 m - a good example of a negative feedback loop
Why do caves, arches and stacks tend to form on headlands?
Due to wave refraction, wave energy is focussed. Whether or not cliff profile features form again depends on the nature of the rocks and the waves.
What are the stages of the formation of cliff profile fractures (caves, arches and stacks)
Weakness in rock due to crack is exploited by hydraulic action and is enlarged - forming a Geo - cliff becomes undercut and cave forms.
Where cave faces oncoming waves full force is applied to rear of caves - enlarges cracks in cave roof. Overlying rocks may collapse forming a blow hole.
Often caves form in headlands as erosion is strongest here.
Where caves are eroded on either side of a headland, may erode right through and form an arch.
The roof of the arch is weathered through sub-aerial processes and chemical weathering from the sea-spray splashing, as it is unsupported the roof eventually collapses leaving a stack.
The stack’s base is in the intertidal zone, so subject to erosion.
The upper part of the stack also becomes weathered and over time the whole stack collapses - leaves behind a stump.
Example of cliff profile features: Old Harry’s Rocks in Dorset, the Twelve Apostles Victoria, Australia.
Which factors affect the height, shape and steepness of a cliff?
Depends on rock type and rate of
erosion and weathering.
Harder cliffs which have recently experienced cliff collapse are likely to be steeper, softer rocks with a wider wave cut platform and a slower rate of erosion, a gentler profile.
What is the difference between sand and shingle beaches?
Sand have a gentle in slope, shingle have a steeper slope.
Because sand have small sand grains easily compacted and shingle have large sediment size not as easily compacted.
Sand have lots of backwash, shingle, backwash doesn’t transport
What is a storm berm and how is it formed?
At the top of the beach a wide flatter area of sediment is deposited by a strong swash during spring high tides
Formed by constructive waves
What are cusps and how are they formed?
Where sand on lower parts of the beach meets the shingle on the upper part of the beach.
Formed where waves break directly onto beach
Where both swash and backwash are strong
What are ripples and how are they formed?
Further down the beach from the cusps.
In the sand
Due to the action of the tides moving back and forth across the sand.
What are ridges and how are they formed?
At the low water mark
Where backwash deposits sediments
What are runnels and how are they formed?
Runnels break ridges
Where water runs through to return to the sea
What are swash-aligned beaches?
Swash-aligned beaches tend to form in low-energy environments such as a bay, arriving waves are roughly parallel to the shore.
Wave refraction in the bay may cause a bay-head beach to form
What are drift-aligned beaches
Drift-aligned beaches form where waves approach the coast at an angle.
Longshore drift moves sediment along the beach, often culminating in the formation of a spit if the
coastline changes direction.
Finer particles are likely to be carried further by longshore drift and become increasingly rounded as they move.
What are spits?
Spits are long, narrow ridges of deposited sediment which are joined to the mainland at one end and
stick out into the sea or across an estuary or bay. They can be either simple or compound.
What is a compound spit?
Compound spits have a series of minor spits or recurved ridges along their landward side which may show their former position.
What are simple spits?
Simple spits are either straight or recurved but do not have minor spits or recurved ridges along their
landward edge.
How are spits formed?
where material is moved along the coast through longshore drift but where the coastline
changes direction (often due to an estuary or river mouth) sediment starts to build up in the sheltered
lee of the headland which begins to form a spit.
During storms larger material is deposited above high-water mark which makes the spit more permanent. Finer material continues to be moved along the spit through longshore drift and into the deeper water of the estuary/bay where energy is lost, and the sediment is deposited which extends the spit further.
If the spit is growing across a river mouth turbulence where the river current and the coastal currents meet may cause further deposition.
The end of the spit may become recurved as wave refraction and secondary winds and waves
carry and deposit sediment round the end of the spit.
A river flowing out to sea is likely to prevent the spit from growing right across an estuary but very fine sediment may be deposited in the low energy zone behind the spit.
This forms a salt marsh which is an important coastal habitat which may then be further stabilised by the growth of salt-tolerant plants.
What is a tombolo?
An island connected to the mainland by a mound or ridge of sediment.
How are tombolo’s formed?
Longshore drift - where a spit grows and connects an island to the mainland.
Wave refraction - waves move towards a coastline and are slowed down as they reach shallow water.
When waves meet on other side of headland, energy falls and sediment is deposited. Sediment builds up until it connects the island to the beach.
How do barrier beaches form?
Where a spit extends across a bay or joins two headlands together.
Thought to have been formed when gravel deposited in the English Channel when glaciers melted after last ice age was despised on the coast by constructive waves.
Longshore drift has since added more material
Can only form where there is no current flowing off land. Behind a lagoon forms
Give an example of a barrier beaches
Slapton Ley
What are barrier islands?
Where barrier beaches become separated from the mainland.
Made of sand or shingle
Long (up to 100miles), narrow and become vegetated as they get older and vegetation succession occurs.
Usually found in areas with low tidal ranges and gently sloping offshore coastlines.
very long barrier islands can become split into shorter islands as inlets develop between them to allow tides to rise and fall around the island.
How are barrier islands formed?
Formation not entirely understood
Thought they are formed from sediment that was originally deposited when glaciers melted 18,000 years ago at the end of the last ice age.
Currents may have deposited this material in barrier beaches and that melting ice also meant sea levels rose leaving these beaches separated from the mainland.
What are offshore bars?
submerged ridges of sand or coarse sediment created by waves
and currents offshore from the coast.
Destructive waves erode sand from the beach with strong backwash and deposit it offshore.
Act as sediment sinks and, sometimes sediment input stores.
Absorb wave energy so reduce the impacts of wave energy.
can be a source of sediment for sand dunes.
What are embryo dunes features?
1st stage of sand dune formation:
Sand trapped by obstacles. Often on storm berm
As sand is trapped obstacle grows slowing wind and contributing to further deposition.
May be colonised by pioneer species eg) marram grass or sea crouch.
Plant roots stabilise the dune.
1m high
80% exposed sand
What are yellow dune features?
2nd stage of sand dune formation:
Dunes grow and become out of reach of high tide
5m high
20% exposed sand
What are grey dunes features?
3rd stage of sand dune formation:
More sand accumulates and plants continue to flow and add organic matter to dunes - they become fixed and ‘grey’ as humus (organic content) increases.
8-10m high tide 5m
Less than 10% exposed sand
Able to support larger plants which require more water and organic matter eg) gorse bushes
What are dune slacks?
May form between dunes where water table is at the surface.
In these ponds aquatic ecosystems form
What are mature dunes features?
Last stage of sand dune formation:
Trees eg) Birch, shrubs and heather grow
- Further increases humus levels and moisture retention
Decreases the pH.
Final stage in succession called climax vegetation
What is psammosere?
The process of succession started on sand
Give a named example of a simple spit
Spurn Head, Humberside.
Where do mudflats and salt marshes form?
Low energy coastlines
Areas of lower energy such as river estuaries where tidal currents are slowed or behind spits where slack (low energy) water is found.
Identify features of estuaries that encourage the deposition of sediment
In estuaries or behind spits slow flowing water from the river carrying lots of suspended sediment meets saline sea water which causes flocculations as clay particles aggregate (join together)
Sheltered estuary environment
Reduction in water velocity as river flows to sea
Larger, heavier clay particles sink to bed of estuary. At low tide in inter-tidal area mud is exposed with water left flowing in channels between mudflats - overtime mudflats become salt marshes
Outline the formation sequence of mudflats
Step-by-step sequence of succession called halosere (to do with salt)
Vegetation eg) eelgrass grows in mudflats
Slows currents - leads to more deposition but uneven according to where eelgrass is
Pioneer species begin to colonise area (halophytes, salt-tolerant)
Pioneer species eg) cordgrass dominant on UK mudflats as it has a fine mat of roots which binds mud together and traps more sediment
Outline the formation sequence of salt marshes following the formation of mudflats
Deposition continues and plants continue to grow/die which raises surface of the marsh.
As this happens mudflats are submerged shorter and mudflat becomes a salt marsh.
More complex flowering species become established eg) sea lavenders as they are less tolerant of salt than pioneers.
More deposition and vegetation becomes dense - further raises surface level and soil conditions improve
Where marsh rises above level of spring hide trees scrub start to grow - climax vegetation
Give an example of a mudflat / salt marsh
Morecambe Bay
What is Eustatic Sea level change?
A rise or fall in sea level as a result of change in actual level of water in oceans.
These are global changes
Eg) as temperature increases, water expands meaning sea levels rise when sea temps are warmer.
What is isostatic sea level change?
A change in the level of land relative to sea as a result of changing level of land.
These are local/regional changes
Eg) as continents collide and fold mountains form, land is forced up to rise out of sea.
When was the last glacial maximum?
18,000 years ago - UK was joined to mainland Europe and Scandinavia as sea levels were on average 110m below current level
What are the causes of isostatic change?
Tectonic activity - land can move up or down as a result eg) following Tohoku earthquake, Japan some sections of coastline dropped 0.84 metres
Glaciation - during ice age glaciers and ice sheets form over land in areas cold enough. Causes land surface to become pressed (loading) into upper layer of asthenosphere relative sea level rises.
Post-glacial readjustment - following melting of ice sheets and glaciers on land, land is able to rise back up (unloading) as asthenosphere rebounds. Called isostatic recovery.
Responsible for falling sea levels in Scotland today as during last ice age Scotland was the part of the UK covered with thickest ice and it melted last.
What are the causes of eustatic change?
Thermal expansion of water - as water is heated it expands so even if mass of ocean stays the same, warmer water has a larger volume so takes up more space and sea level rises.
Changes in ice sheets and glaciers extent - ice forms on land during glacial period, removes water from other stores eg) ocean so sea levels fall.
When ice on land melts, less water locked up in ice on land so more available to other stores eg) ocean, sea level rises.
Tectonic activity - new land formed under ocean usually at mid-ocean ridges. New rock takes up space in ocean basin which would’ve been occupied by water so water is displaced and sea levels rise.
Define total sea level change
The balance between isostatic and eustatic change
Why have coastlines of emergence formed?
Fall in sea level as a result of isostatic or eustatic change or more likely a combination of the two
West coast of Scotland - isostatic recovery has resulted in formation of landforms of emergence
Give examples of coastlines of emergence features and how they are formed?
Raised beaches - where sea level drops relative to land so beach becomes stranded above high water mark. Subject to vegetation succession. Common on west coast of Scotland eg) Isle of Arran.
Rasped marine platforms - left exposed above level of current wave cut platform. Often less visible as may be covered in beach sediment from current beach
Other marine features - relict features eg) cliffs and caves left above tide level
Why have coastlines of submergence formed?
Rise in sea level - as a result of eustatic or isostatic change or, more likely a combination of the two.
Run perpendicular to coast.
Describe features of Rias, coastlines of submergence?
Rias - flooded river mouths/ valleys
Sea level rises relative to land ricer valleys, they flood and appear as coastal inlets.
Steep coastlines where old valley sides are and floodplain has been flooded by the sea. Eg) mouth of River Exe at Exmouth
Run perpendicular to coast
Describe Fjords, coastlines of submergence?
Fjords - like rias, flooded valleys but they are flooded glacial rather than river valleys. When glaciers erode - create steep sided U-shaped valleys . Eg) Songefjord Norway.
Run perpendicular to coast
Describe Dalmatian coasts, coastlines of submergence?
Occur where river systems which once ran parallel to coast are flooded - so a series of long islands form, once the hills along the valley sides parallel to coast.
Run parallel to coast
Eg) in Croatia
What are the impacts of recent and predicted climate change on coasts?
Globally sea level is increasing eustatically as climate change causes thermal expansion and melting of ice sheets.
Summarise some of the impacts of sea level change on coasts?
Major centres of UK population including London, Hull and Middlesbrough are at risk from inundation / flooding.
Lots of UK agricultural land could be lost through flooding and increased coastal erosion.
Along east coast is valuable arable land.
Major road and rail links such as the east coast mainline are at risk.
Power stations and gas and oil terminals often built along the coast risk flooding.
increased frequency of river flooding as rising sea level reduces gradient of the long profile of the river.
Loss of coastal habitats eg) mangroves.
Submergence of low-lying islands eg) Maldives.
