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temp > Coastal Landscapes and Changes EQ3 > Flashcards

Coastal Landscapes and Changes EQ3 Flashcards

1
Q

Why is sea levels vary from day to day?

A
  • high and low tides alter lock sea level very few hours
  • atmospheric air pressure has an influence in sea level (low pressure causes a slight increase)
  • winds can push water towards the coast and cause variations in wave height.
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2
Q

What is eustatic sea level change?

A

Eustatic changes is the global rise or fall in water levels caused by a change in the volume of water.

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3
Q

What is isostatic sea levels change?

A

A local rise or fall in local land level.

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4
Q

What causes a eustatic fall in sea level?

A

During glacial periods
- ice sheets form on land due to the colder temperatures in high latitudes
- water evaporated from the sea falls as snow and compresses into ice sheets over time
- this means water is trapped in ice sheets and global volume of water in the sea is reduced

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5
Q

What causes an eustatic rise in sea level?

A

During interglacial periods the earths heats up causes a global use in sea water as
- ice caps/ sheets melt returning located up water to the sea
- thermal expansion were the warmer temperatures cause water molecules to expand by 9%

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6
Q

What causes a isostatic fall in sea levels?

A

Rises in local lands levels causes a fall in local sea level this happen due to
- post glacial adjustment
- accretion (sink region experiencing net deposition building land up and leading to a fall in sea level)
- tectonic activity

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7
Q

What causes a isostatic rise in sea level?

A
  • post glacial adjustment
  • subsidence
  • tectonics
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8
Q

How does subsidence cause a isostatic rise in sea level?

A

The deposition of sediment over time e.g. large river deltas (The Nile) causes crustal sag were the weight of the sediment becomes to much. Additionally hew bay infrastructure or building can have the same effect.

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9
Q

How has post glacial adjustment led to a isostatic rise or fall in sea level?

A

During glacial periods the weight of the ice sheets on the crusts causes the lithosphere to be compress downward. At the end of the glacial period the ice sheets melted and isostatic adjustment took place were the previously compressed crust would start rebound upwards causing a fall in local sea levels. This then creates a seesaw effect were adjacent areas subsides.

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10
Q

What is an example of post glacial adjustment in the UK?

A

At the end of the last ice age the UK was partially covered in ice in the northern regions. This meant when the ice caps melted northern England experienced a isostatic fall in sea levels with the crust rebounding back up and (1.5 mm annually) and Southern Britain is experiencing as isostatic rise in sea levels due o the the seesaw effect (1mm annually).

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11
Q

How has tectonic activity created eustatic changes in sea level?

A
  • rising magma at constructive plate boundary’s reduce capacity of the the ocean creating sea level rise
  • uplift of crustal plates reduce ocean capacity (Indian Ocean) creating eustatic rise
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12
Q

How does tectonic activity led to isostatic changes in sea level?

A
  • folding of sedimentary rock at a destructive plate margin produces an isostatic changes fall of anticlines and rise for synclines
  • lava or ash form volcanic active builds up the land height creating a isostatic fall.
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13
Q

What creates a emergent coastline?

A
  • eustatic fall in sea level (decreased volume of water)
  • isostatic fall in sea level (increase height if land)
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14
Q

What creates a submergent coastline?

A
  • eustatic rise in sea level (volume of water increased)
  • isostatic rise in sea level (land height decreased)
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15
Q

What is an emergent coastline?

A

Parts of the littoral zone where a fall in sea level exposed land once apart if the sea bed, produced by post glacial adjustment.

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16
Q

What are the landforms founds at emergent coastlines?

A
  • raised beaches
  • fossil cliffs
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17
Q

What’s a raised beach?

A

A raised beach is formed at emergent coastlines it is a relic beach now above high tide line. Normally a flat surface covered by sand or pebbles and is usually vegetated by lament succession.
E.g. Isle of Arran has a raised beach 5 metres above current sea level

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18
Q

What is a fossil cliff?

A

This is a steep slope found at the back of a raised beach, which exhibits evidence if formation through marine erosion (wave cut notches) by now above high tide level.

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19
Q

What is a submergent coastline?

A

Sections of the littoral zone where sea level rise is inundated areas that were previously part of terrestrial land. Formed by areas subsiding due to post glacial adjustment creating a marine transgression.
E.g. Southern England

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20
Q

What are the landforms found at a submergent?

A
  • rias
  • fjords
  • Dalmatian coastline
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21
Q

What is a ria?

A

A ria is a drowned river valley. It’s a sections of river valley flooded by the sea making in wider than it would be expected based on the size of river flow.

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22
Q

How are rias formed?

A

Sea level rise, causes the encroachment of sea water inland onto low lying coastlines ‘drowning’ river valleys.

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23
Q

What is an example of a ria?

A

Kingsbury Estuary, South Devin Coast. This is a 6 metre long ria.

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24
Q

What is a fjord?

A

Fjords are drowned U-shaped glacial valleys. They form when a glacially eroded valley is flooded by the sea.
E.g. Sognedjord, Norway is 205 km long and 1.3 metres deep.

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25
Q

What is a Dalmatian coastline?

A

A Dalmatian coastline is long narrow islands running parallel to the coastline, separated from the coast by narrow sea channels called sounds.
E.g. Croatia, with a limestone coastline stretching 520 km with 1,240 smaller islands (synclines p) running parallel to the coast.

26
Q

How do Dalmatian coastlines form?

A

Tectonic activity causes sedimentary rock to be compressed into rises called anticlines and dips called synclines at a concordant coastline. As sea levels rise the synclines are flooded to form sounds and the anticlines are left sticking out from the coastline.

27
Q

What are barrier islands?

A

Offshore sediment bars, usually sand dune covered. They are unlike spits in the sense that they are not connected to the coast.

28
Q

What is the trends in sea level rise?

A

The current rate six sea levels rise is around 2 mm annually with the noticeable patterns being
- sea levels relatively stable between 1800 - 1870 (c > accurate measurement not possible)
- sea levels rose slowly between 1870- 1940 before beginning to rise rapidly
- since 1980 sea level rise has accelerated further

29
Q

How is climate warming accelerated sea level rise?

A

Climate change has led to rapid eustatic sea level rise with the warming earths temperature
- melting mountain glaciers (Alps and Himalayas)
- melting polar ice sheets (Greenland and Antarctica) contributing to 50% of all sea levels rise
- thermal expansion accounting for 40 % of sea level rise

30
Q

How is tectonic activity accelerating sea level change?

A

Accounts for 10% of all sea level rise
- emissions of underwater geothermal heat (volcanic activity) causing thermal expansion
- rising magma at constructive boundary reducing ocean basin volume
- earthquakes can cause uplifts of lithosphere (2004 Boxing Day Tsunami lifted sections of Indian Ocean raising sea levels by 0.1 mm.

31
Q

What re the future predictions of sea level rise?

A
  • IPCC predicts sea level rise of 18-59 cm by 2100
  • US National Research council predicts 56-200 cm
32
Q

Why doe predictions vary about future sea level rise?

A
  • uncertainty in relationship between greenhouse gas emission and sea level rise as it has complex feedback effects
  • uncertainty in future political commitment to introducing new measures to reduce GHG emissions.
33
Q

What are the main coastlines at risk from sea level rise?

A
  • low lying coastlines (coastal flooding due to marine transgression)
  • low lying coaling islands (Kiribati Islands in Pacific)
34
Q

What’s are the main physical factors that’s contribute to coastal erosion?

A

Geological factors
- lithology (type of rock, porosity)
- geological structure (jointed, faulted rocks)
Marine factors
- long wave fetch prompting large destructive waves
- strong long shoe drift that quickly removes collapsed sediment allowing erosion to restart

35
Q

Why does human activity increase erosional rates?

A

Human activity can increase rates of coastal recession by interrupting the operations of a sediment cell.

36
Q

What human activities increase the rate of erosion?

A
  • damn building (sediment starvation)
  • mismanagement (groynes causing sediment starvation)
  • dredging
  • Removal of natural defences (mangrove and coral reefs)
  • Removal of vegetation
37
Q

How does Damns cause the rate of coastal erosion to increase?

A

The construction of major damns on rivers can trap river sediment behind the damn wall. This then staves the coast of a sediment source leading to serious consequences.

38
Q

What is dredging and how does it increase the rate of coastal recession?

A

Dredging involves the removing of sediment from the seabed, beach or river. This is to make room for construction of maintain navigable channels for ship transport. This means that there will be no beach to dissipate the wave energy.

39
Q

What an example of human activity leading to increased rates of coastal erosion?

A

Aswan High Dam in the River Nile:
Built in 1964 the damn reduced sediment volume form 130 million tonnes to 15 million tonnes causing rates of erosion to increase by almost 175 cm annually as delta starved of sediment.

40
Q

How does subaerial processes work together to increase rates of coastal recession?

A

Weathering weakness rocks above the high tide mark, this increases the likely hoof of mass movement by reducing the internal cohesion of the rock. Repeated mass movements leads to relaid coastal recession.

41
Q

What influences rates of coastal erosion (short and long term)?

A

Short term variation
- wind direction/ fetch
- tides
- seasons
- weather systems
- occurrence of storms
Long term variation
- physical factors (geological and marine)
- human activity (coastal management and dredging)

42
Q

How does wind direction increase rates of coastal recession?

A

Wind changes direction daily in the uk. Rates of recession will be higher when
- when winds in blowing onshore
- prevailing wind is the primary wind direction
This all leads to large destructive waves and rapid recession.

43
Q

How does rates of recession very due to tides?

A

Rates if recession are more rapid during high tide when deeper water allows the waves to maintain more energy resulting in created impacts on the coast.

44
Q

How does rates of recession very due to storms?

A

Storm event take lake in low pressure (depressions), they produce high energy destructive waves and fast rates of erosion. (Expected to increase in intensity due to global warming)

45
Q

How does rates of erosion vary due to seasonality?

A

Storm event are more likely to happen in the winter when contrast in temperature and pressure between tropical and Polar air are the greatest.
E.g. In Holderness, erosions in the winter is 2-6 metres whereas in the summer sound 1.25 metres.

46
Q

How does erosional rates vary due to weather systems?

A

The UK is lacked at the polar front between the boundary of warm tropical air (Ferrell) and cold polar air (polar). Interaction between the two can cause
- high air pressure anticyclone with gentle winds and small waves resulting in low rates of recession
- low air pressure depressions with strong wind and high energy destructive waves resulting in high rates of erosion.

47
Q

What are low lying coastlines that experience a high risk of coastal flooding?

A
  • coastal plains
  • estuaries
  • river deltas
48
Q

Why do people choose to live in areas at risk from coastal flooding?

A
  • coastlines are popular with tourists (beach and sea)
  • Deltas and estuaries are ideal locations for trade
  • deltas are extremely fertile and ideal for farming
    E.g. Shanghai, Yangtze Delta China supporting 24 million people (megacity)
49
Q

What are the local factors that increase flood risk?

A
  • height of the land
  • degree of subsidence
  • vegetation removal
    Global sea levels rise is increasing the risk.
50
Q

How does land height increased flood risk?

A

-low lying coastlines are only 1 - 2 metres shive high tide so any sea level rise with have significant consequences
- at risk to temporary flood risk from storm surges
E.g. the Maldives, with the capital island Male only 2.3 m above sea level. The high flood risk has meant a 3 metre high sea wall was built around the island.

51
Q

How does subsidence increase flood risk?

A

Low lying coastlines (estuaries and deltas) are subject to natural, subsidence through the settling and compaction of deposited sediment weighting the land down. Subsidence is normally outpaced by further depositions, however human actions have increased local subsidence (drainage of saturated sediment, weight of infrastructure) as well as isostatic readjustment.

52
Q

How does vegetation removal increase flood risk?

A
  • Vegetation stabilises sediment as well as encouraging the deposition of further sediment raising the height of land above sea level.
  • vegetation absorbs wave energy reducing the distance waves can travel onshore (a 1km belt of mangroves reduce wave height by 40%)
    E.g. estimated 50% of the worlds mangroves forest removed by 1950
53
Q

Where and why is global sea level rise exacerbating flood risk (predicated rise)?

A
  • increases flood risk on low lying coastlines
  • destruction of natural defences
    IPCC predicts a further 18-59 cm rise in sea level by 2100. A 40 cm rise will permanently submerge 11% of Bangladesh creating 7-10 million environmental refugees.
54
Q

What is an example of rising sea levels increasing flood risk?

A

The Maldives:
- population 340,000 people spread out across 1200 islands.
- 50 cm sea levels rise would permanently flood 77% of the Maldives islands
- highest point in the islands only 2.3 metres above sea level
- Malé the capital city island is now ringed with a 3m sea wall
- Hulhumalé is a new artificial island built ($32 million) which is a full metre higher then Malé built in order to maintain tourist industry
- conflict created as the smaller islands feel ignored as governments main focus in maintaining tourism rather than the traditional industry (fishing and farming)
- environmental refugees to Australia
C > educational programme have started on the importance of maintaining the mangroves and mangroves farms.

55
Q

What are storm surges?

A

A storm surge is s temporary rise in local sea level produced when a depression, storm or tropical cyclone reached the coast. A fall in air pressure of 1milibar leads to a 1 cm rise in local sea level as air pressure drops the weight of air pressing down on the sea surface drops causing it to rise.

56
Q

What accentuated a storm surge?

A
  • high tides (spring tide)
  • shape of the coastline (funnel shaped)
  • shallow seabed towards to the coast
57
Q

What are the short terms effects of a storm surge?

A
  • deaths and injuries from drawling, collapsed buildings, hypothermia and the spread of water borne disease (cholera)
  • destruction of infrastructure (roads, railways and ports)
  • damaged water pipes, electricity transmission and sewage systems
  • home destroyed leaving people homeless
  • business destroyed or inter upped
58
Q

What is an example of a storm surge?

A

Bangladesh, Tropical Sidr 2007:
Tropical Sidr was a category 4 cyclone with an air pressure of 944 mb, 240 kmph and 6m storm surge.
Impacts
- 15,000 people died
- 600,000 ha of agricultural land destroyed
- $1.7 billion of damage
The impacts were exacerbated by
- funnel shape coastline of Bay of Bengal
- intense rainfall
- Deforestation of mangroves (a 100 m belt of mangrove reduce height of a storm surge by 0.5m.

59
Q

How may climate change increase coastal flood risk?

A
  • frequency and magnitude of storms
  • sea level rise
60
Q

What are the IPCC confident predictions on climate change?

A
  • sea levels will rise by 18-59 cm by 2100 (pace and extent fairly uncertain)
  • Delta flooding is likely to increase by 50%
61
Q

What at the IPCC medium confidence predictions in impact of climate change?

A
  • increased winds speeds creating larger more destructive waves
  • coastal erosion will also increase due to the combined effects on the weather system and sea level rise.
62
Q

What are the weaker predictions of the IPCC on the impacts of climate change?

A
  • frequency of tropical storms is likely to remain unchanged but intensity might increase. (Predicted to increase in strength by 2-11% in 2100)
  • storm surges linked to depression likely to become more common (polar front jet streams will accelerate?

temp (29 decks)

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