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GEOGRAPHY - coasts > 3.A/B - emergent/submergent coastal landscapes > Flashcards

3.A/B - emergent/submergent coastal landscapes Flashcards

1
Q

when do emergent coastal landscapes form?

A

as sea level falls

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2
Q

what causes sea level change?

A
  1. global temp ↑ = thermal expansion and ice sheets/glaciers melting = greater volume
  2. climate change = extremes of weather
    - decrease in global temp = more precipitation falls as snow which turns into ice = ↓ vol of water in ocean = thermal contraction
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3
Q

what landforms occur as a result of sea level fall?

A

emergent landforms

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4
Q

what landforms occur as a result of sea level rise?

A

submergent landforms

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5
Q

what are the 2 types of sea level change?

A

eustatic and isostatic

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6
Q

what can eustatic change lead to?

A

coastlines being drowned/emerging from the sea

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7
Q

what are 3 key factors coastlines are influenced by?

A

geology, relief and human activity

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8
Q

when did the ice age happen and where was sea level in this time?

A
  • about 2 million years ago the world’s climate cooled and an ice age began that lasted until about 14,000yrs ago
  • during this Ice Age sea level was at least 120m lower than it is today
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9
Q

how can earthquakes cause sea level change?

A
  • earthquakes can cause vertical movements either side of faults; this can lead to an apparent rise or fall in sea level at the coast
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10
Q

how did the 2 different parts of Britain tilt?

A
  • during the ice age 2mill to 14,000 yrs ago, much of the British Isles was covered with ice to a line just north of London and Bristol, known as the Thames Severn line.
  • this additional weight on the crust pushed the northern part of the British Isles downwards (called compression), while the south, without the weight of the ice, rose slightly.
  • at the end of the ice age the loss of weight in the north led to the British Isles tilting the other way: Scotland and the North rose (isostatic rebound) while the south sank.
  • coastlines in scotland rose above sea level while coastlines in the south of england became submerged.
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11
Q

what are the potential positives of future coastal flooding?

A

new natural environment like salt marshes, which are important habitats for wildlife, being vital areas for migrating birds

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12
Q

what is eustatic change?

A

global changes in sea level due to changes in the atmosphere

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13
Q

what is isostatic change?

A

localised/regional changes in sea level due to movements of the Earth’s crust

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14
Q

what is a transgression?

A

advance in the sea/sea level rise

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15
Q

what is a regression?

A

retreat of the sea

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16
Q

what are the causes of transgressions/sea level rise?

A
  • EUSTATIC CHANGE
    > global
    > ice caps melting
    > happened between 10-6000 yrs ago
    > will submerge existing landforms e.g. river/glacial valleys
    > ↑ input of sediment
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17
Q

what are the causes of regressions/sea level fall?

A
  • actually a rise in land level which seems like a fall in sea level
  • ISOSTATIC CHANGE/rebound of land
  • creates emergent landforms (e.g. relic cliffs)
  • ice sheets sit on land = weight
  • increased temperatures = ice sheets melt = weight removed = land rebounds faster than sea levels rise
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18
Q

what is happening in Southern Iceland?

A
  • in Southern iceland we have an isostatic change in sea level because the ice sheets are reduced in weight and volume, and the land rebounds and rises up
  • this relative drop in sea level happens in spite of a eustatic rise in sea level
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19
Q

what is the recent trend of global eustatic changes in sea level?

A
  • over last 6000 yrs = quite a lot of stability which leads to civilisation progressing and development
  • over the past 18,000 yrs change has been big - roughly 120m rise in sea level
  • sea level has risen at a linear rate as the Devensian Ice melts
20
Q

what is the recent trend of isostatic changes in sea level around the UK?

A

isostatic = changes in the level of land due to ice melting.
- localised e.g Scotland.
- from tectonic activity (eqs)
- from removal/addition of weight from land

emergent Scotland/north.
- becomes risen above sea level = DECOMPRESSION/ISOSTATIC REBOUND

South/kent starting to become submergent.
- 3.5mm/yr change difference

21
Q

what is a long term natural reason for the changes in global temperature?

A

MILANKOVITCH CYCLES - most significant

  • variations in the earth’s orbit and tilt
  • long term climatic shifts (e.g. glacial cycles) are caused by astronomical events such as changes in the Earth’s axis and orbit
  • affect the amount of solar radiation reaching the planet’s surface and its spatial/temporal distribution
  • they operate on time scales that vary from 10,000-100,000 yrs with long glacial periods followed by shorter interglacials
22
Q

what is the first short term natural reason for the changes in global temperature?

A
  1. CHANGES IN SOLAR OUTPUT= only in past 30 yrs have satellites been able to measure solar irradience accurately
  • sun’s output varies over time
  • there is a positive correlation between the number of sunspots and solar energy outputs
  • solar output follows an 11 year cycle. the difference in energy output between max and min sunspot activity is only 0.1% - not enough to impact global climate significantly
  • longer timescales = solar output is more variable
  • difficult to isolate the impacts of this from other influences
23
Q

what is the second short term natural reason for the changes in global temperature?

A

2: VOLCANIC ACTIVITY

  • eruptions = huge amounts of volcanic ash and sulphur dioxide into stratosphere = potential to change the climate
  • sulphur dioxide has a cooling effect and is more persistent. in atmosphere it is converted to sulphuric acid = sulphate aerosols
  • these reflect solar radiaton back into space and lower temps in the troposphere
24
Q

what are emergent features affected by?

A
  • after their emergence, these landforms were no longer affected by wave processes
  • however, they continue to be affected by weathering and mass movement
25
Q

what is a raised beach?

A
  • areas of former shore platforms that are left at a higher level than the present sea level
  • they are often found a distance inland from the present coastline.
  • behind the beach along emergent coastlines it is not uncommon to find abandoned cliffs w/ wave cut notches, caves and even arches and stacks.
  • deposits are likely still sand and pebbles
26
Q

what is a marine terrace?

A
  • much larger scale landscape features than raised beaches which are quite small scale and localised at the base of relic cliffs
  • terraces don’t necessarily have cliffs above them
  • their formation is essentially the same as raised beaches - marine erosion during a previous period of higher sea level
  • found as far as 50m higher up than raised beaches
27
Q

what is a relict cliff?

A
  • there is a sharp rise in the level of the land that marks the position of former coastal cliffs; now known as relic cliffs
  • found behind the raised beach/marine terrace
28
Q

what current processes could be modifying emergent landforms today?

A
  • landforms aren’t affected by marine/wave processes yet are affected by weathering and mass movements
  • cliffs arent undermined = slope will decrease in gradient and are far more stable
  • people pressure and footpath erosion will alter landforms
  • relic cliffs may become vegetated
29
Q

what do emergent coastlines represent?

A
  • coastlines that are now raised above present day sea-level.
  • this means the coastline has experienced a relative fall in sea-level (marine regression)
30
Q

where do emergent coastlines originate?

A
  • such coastlines may have 2 origins:
  1. they may have formed at times when eustatic sea-level was higher, for example, during warmer interglacial periods
  2. they may have formed and become lifted by isostatic rebound. this is when there is a relative rise of the land above present day sea levels (e.g Scotland)
31
Q

when do submergent coastlines occur?

A
  • when sea level rises, submerging existing landforms
  • due to climate change, thermal expansion of water, glaciers melt = ↑ volume of sea water
  • eustatic change = global rise in sea level
32
Q

what do submergent coastlines represent?

A
  • coastlines that are now below present day sea level
  • this means the coastline has experienced a relative rise in sea-level (marine transgression)
  • they will have formed at times when eustatic sea-level was lower for example during colder glacial periods
33
Q

what are the 3 examples of submergent features?

A
  1. glacial valley floods = fjords
  2. river valley floods = rias
  3. sediment “rolled” onshore by rising sea level = shingle beach
34
Q

what is a ria?

A
  • rias are drowned river valleys
  • in hilly areas, e.g. cornwall and devon, river valleys that were previously at sea level become submerged
  • the result is often a very large estuary at the mouth of a relatively insignificant river (or else sediment would quickly fill the ria)
35
Q

what do rias look like?

A
  • drowned river valley = formed as sea levels ↑
  • lower part of river course may be drowned but higher land forming the tops of the valley side at middle/upper course remains exposed
  • relatively shallow water becomes deep as you go towards centre because of an original river channel there
  • valley sides are gently sloped
  • can be found on the south coasts of Devon and Cornwall e.g. Helford Passage = formed during post glacial sea level rise (Flandrian Transgression)
  • dendritic pattern (see pic)
  • surrounding land used for farmland predominantly
36
Q

how has sea level change (eustatic) changed rias?

A
  • ↑ sea level = floods = flood plains created = makes centre deeper as original river channel was there
37
Q

how are current geomorphic processes altering rias?

A
  • rivers flooded = deposition at mouth - gradually filling up. causes sedimentation
  • weathering = causes mass movement
  • eustatic change
  • coastal erosion
38
Q

how can you tell a ria from a fjord?

A

ria:
- no hanging valleys/waterfalls
- dentritic pattern
- much smaller than fjords
- wave cut platforms, cliffs and mudflats

39
Q

what marine/subaerial processes will be dominant in rias such as the Helford Passage?

A
  • in upper course, lots of potential energy focused downwards (erosion concentrated on valley floor)
  • abrasion, hydraulic action
  • sea level ↑ is very sig.
  • wave cut platforms and cliffs = marine processes are v influential
40
Q

what is a fjord?

A
  • drowned, U-shaped GLACIAL valleys
  • originally formed by glacier eroding the valley sides and deepening the valley floor to create a glacial trough (u shaped valley)
  • they are long inlets with very steep, straight valley sides
41
Q

what do fjords look like?

A
  • fjords are submerged glacial valleys.
  • they have steep cliff like parabolic valley sides and the water is uniformly deep, often reaching over 1000m
  • the Sogne Fjord is nearly 200km long (those in Scotland are less developed as the ice was not as thick during the glacial period)
  • the U Shaped valley cross section reflects on the original shape of the valley itself
  • they consist of a glacial rock basin w/ a shallower section at the end known as the threshold. this results from a lower rate of erosion at the seaward end of the valley where the ice thinned in warmer conditions
42
Q

how has sea level change altered fjords?

A

due to the depth of the water that occupied fjords during the Flandrian Transgression, marine erosion rates remained high and the fjords were further deepened

43
Q

how are current geomorphic processes altering fjords?

A
  • weathering and sediment deposition
  • weathering = mass movement = sides less steep
  • rivers deposit sediment at end of fjord which will fill them in
  • ongoing eustatic rise will continue to deepen them
  • current coastal processes will cause a notch/beaches to form
44
Q

what are shingle beaches?

A
  • chesil beach is an example of shingle barrier beaches that have formed at time of lower sea levels and then rolled onshore as sea levels has risen
  • the shingle refers to the size and shape of the material found on the beach (typically between 2 and 200mm and often rounded).
  • it is likely the shingle is glacial in origin - glaciers bulldoze morraine and that is the sediment
45
Q

what do shingle beaches look like?

A
  • when sea level falls as the volume of land based ice grown, large areas of “new” land emerge from the sea
  • sediment accumulates on this surface, deposited by rivers, meltwater streams and low energy waves
  • as sea levels rose at the end of the last glacial period, wave action pushed these sediments onshore
  • in some places, they beached at the base of former cliff lines, elsewhere they may form tombolos and bars
  • occurs everywhere in the world
46
Q

how has sea level change altered shingle beaches?

A
  • eustatic change
  • sea level rose at end of last glacial period which pushed deposited sediment onshore all over the world
47
Q

how are current geomorphic processes altering shingle beaches?

A
  • currents and LSD/prevailing wind action
  • as they are composed of unconsolidated material they are especially vulnerable to modification
  • with further sea level rises predicted, shingle may well be moved even further to NE at Chesil Beach
  • destructive and constructive waves = causes erosion

GEOGRAPHY - coasts (9 decks)

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