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geography > Sea level change > Flashcards

Sea level change Flashcards

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1
Q

Name 3 factors effecting sea level change

A
  • high & low tides
  • atmospheric air pressure
  • winds
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2
Q

Definition of isostatic change

A

local rise/ fall in land level

-occurs when crust is forced down into mantle changing relative sea level

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3
Q

Definition of eustatic change

A

rise/ fall in water level

-caused by change in vol of water

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4
Q

Name 3 reasons for contemporary sea level change

A

global warming- melting of- mountain glaciers, polar ice sheets- increasing amount of water in ocean

  • thermal expansion- increases oceans temperature- causing water to expand
  • tectonic activity- geothermal heat- water to expand
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5
Q

When do emergent coastlines form

A
  • when water level has fallen- exposing land previously covered by sea
  • when land has risen
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6
Q

What are emergent coastlines

A

coastlines that have formed where water level has fallen/ land has risen

-happens due to isotatic change

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7
Q

What are submergent coastlines

A

coastlines that have been flooded due to rise in sea levels

-happens due to eustatic sea level change

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8
Q

Name 2 emergent coastline landform and how it forms

A

-raised beaches- as land rises due to isostatic recovery- beaches are raised above present sea level

-Fossil cliff
a steep slope found at the back of a raised beach

E.g. at Lendalfoot in Ayrshire, western Scotland, a flat raised beach surface is used as a route for the A77 main road. 40 m raised cliff at the back of the now now 200 m inland from the present-day beach.

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9
Q

Name 3 submergent coastline landform and how it forms

A

-rias- form when valleys in dissected area are flooded
(example- kingsbridge devon)

  • dalmatian coasts- rivers flow parallel to coasts (Dalmatian coast- Croatia)
  • fjords- form when deep glacial troughs are flooded by rise in sea level (Norway)
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10
Q

Definition of post-glacial isostatic adjustment

A

uplift experienced by land following removal of weight of ice sheets

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11
Q

What factors is coastal recession affecetd by

A

physical factors- geological (lithology & geoligcal structure)
-marine factors (wave fetch, longshore drift)

  • human factors- dredging
  • coastal management
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12
Q

How does geology affect coastal recession (in particular the Holderness coastline)

A
  • consists of boulder clay- structurally weak- has little resistance to erosion
  • erosion has occured along fault lines- cliffs, arches, stacks
  • chalk band surrounding boulder clay- created headland at Famborough Head
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13
Q

How does longshore drift and beach material affect coastal recession (in particular Holderness coastline)

A
  • boulder clay erodes to produce clay particles- fine, easy to transport out to sea
  • narrow beaches- don’t absorb wave energy
  • tides flow southwards- transporting sand south by longshore drift- cliffs at holderness- poorly protected against waves
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14
Q

Name 3 ways the Holderness coastline is affected

A
  • human actions
  • longshore drift, beach material
  • sub-aerial processes
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15
Q

Name the 4 key players on the Holderness coast

A
  • central government agencies- responsible for coastal management
  • local government- also responsible for coastal management
  • stakeholders in local economy- tourist industry, farmers, residents
  • environmental stakeholders
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16
Q

How do sub-aerial processes influence coastal erosion

-give 2 examples

A

free-thaw and wetting and drying weathering- weakens rocks above high tide mark -> wave cut notch -> mass movement -> erosion

-slumping- weakened cliff cant support the extra weight- clay slides downslope- collects at cliff base -> removed by sea -> cliff retreats

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17
Q

What is marine transgression

A

geologic event during which sea level rises -> flooding -> submergent coast

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18
Q

What is marine regression

A

geologic event during which sea levels fall -> emergent coast

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19
Q

When does a eustatic rise in sea level occur

A
  • end of glacial period -> melting ice sheets return water to sea -> sea levels rise
  • global temp increases -> vol of ocean water increases -> sea levels rise
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20
Q

When does a eustatic fall in sea level occur

A

-during glacial periods -> ice sheets form on land -> water evaporates from sea -> locked on land as ice -> fall in sea level

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21
Q

When does a isostatic rise in land level occur and what does this cause for sea level

A
  • post glacial adjustment- where earths crust was formerly depressed under ice sheets, crust rises as ice sheets recede -> fall in sea level
  • accretion-sink regions in sediment cell are experiencing deposition -> land built up -> fall in sea level
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22
Q

When does a isostatic fall in sea level occur

A
  • during build up of land-based ice sheets -> weight of ice sheets -> Earth’s crust to sag
  • when ice sheets melt -> land surface rebounds upwards -> rise in land level
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23
Q

What is a ria

A

drowned river valley caused by sea level rise

24
Q

What are barrier islands

A

offshore sediment bars

25
Q

Name 2 reasons for longer-term sea level change

A
  • eustatic change

- isostatic change

26
Q

How does global warming affect sea level change

A
  • > eustatic sea level rise
  • > melting of mountain glaciers, polar ice sheets -> water in the ocean store increases
  • > thermal expansion of existing ocean water as its temp rises
27
Q

How does tectonic activity affect sea level change

A
  • eustatic change -> emission of geothermal heat -> thermal expansion of ocean water -> rise in sea level
  • isostatic change -> faulting uplifts sections of crust -> rise in land
28
Q

Name the 3 main factors which influence rapid coastal recession

A

-PHYSICAL- (geological: soft lithology, jointed, faulted, geological structure)

(marine factors: long wave fetch, strong longshore drift)

-HUMAN- (dredging)

(coastal management)

-TEMPORAL VARIATIONS- (fetch, tides, seasons)

29
Q

How do physical factors influence rapid coastal erosion

A

GEOLOGICAL:
-> lithology: soft rock type, weak cohesive bonds, porous rocks

-> geological structure: well jointed rocks, rocks with seaward dipping beds, heavily faulted rocks

MARINE:
->long wave fetch -> large, destructive waves -> erosion

->strong longshore drift -> removes sediment -> erosion restarts

30
Q

How do human factors influence rapid coastal erosion

A

DREDGING

  • > removing sediment for construction purposes -> starves beach -> no buffer zone -> coasts eroded
  • > e.g. hallsands -> devon

COASTAL MANAGEMENT

  • > interupts operation of sediment cell
  • e.g. dams trap sediment behind wall -> starves coast -> no buffer zone -> erosion
31
Q

Name 2 reasons why erosion isn’t constant but varies

A
  • varies in time -> peaks of erosion occurring in some seasons
  • varies spatially -> some areas have lots, some don’t
32
Q

Why does erosion vary on the Holderness Coastline

A
  • coastal defences: Hornsea, Mappleton, Withernsea -> stopped erosion
  • terminal groyne syndrome -> sediment starvation further south (Holmpton)
  • variations in cliff height
33
Q

What is dissipation

A

how energy of wave is decreased by friction with beach material during swash

34
Q

Rates of erosion are not constant, what 5 temporal variations influence it to occur

A
  • wind direction and fetch -> rates of erosion ^ -> wind is blowing onshore
  • -atlantics fetch is 5000km- so its currents add energy to waves -> destructive waves
  • low pressure weather systems produce strong winds- ^ sea levels -> higher tides -> ^ erosion
  • tides -> high tide -> deeper water in foreshore -> waves maintain higher energy -> ^ erosion
  • seasons -> erosion ^ -> winter
  • weather systems
35
Q

Name 3 low-lying areas that are at risk of flooding

A
  • coastal plains
  • estuaries
  • river deltas
36
Q

Name 3 economic reasons why people choose to live in areas at risk from coastal flooding

A
  • low-lying coastlines -> popular with tourists -> beaches
  • deltas -> extremely fertile -> ideal for agriculture -> attract farmers
  • estuaries, deltas -> ideal for trade -> good navigable access inland up rivers
37
Q

Name 3 local factors that increase the flood risk of some coastlines

A

-Height- Low lying coastlines -> 1-2 m high above sea level -> risk of flooding

-Subsidence -> the sinking of an area of land ->
Deltas experience periodic -isostatic subsidence -> weight of delta sediment reaches sufficiency -> crust depresses -> marine transgression, flooding
-Human activity -> subsidence ->
drainage of saturated sediment/soil for agriculture

-Vegetation Removal
Vegetation (salt marshes, mangrove forest) reduces flood risk
->stabilises existing sediment -> raising height of land above sea level
-> absorbs wave energy, reducing wave impact and erosion

38
Q

Name a country at risk of coastal flooding and 2 reasons why

A

Bangladesh

  • 46% population -> lives less than 10m above sea level
  • lies on floodplain of 3 major rivers
39
Q

Name the 4 main causes of coastal flooding

A
  • storm surges
  • height
  • subsidence
  • vegetation removal
40
Q

What is a storm surge

A

short-term change in sea level caused by low air pressure

-produced when a depression, storm or tropical cyclone, reaches the coast.

41
Q

Name the 2 types of storm surges

A
  • depression -> low-pressure weather system in mid-latitudes

- tropical cyclone -> hurricane, typhoon -> areas north/ south of equator

42
Q

What occurs to the sea level when air pressure is high

A

sea level lowers

43
Q

What occurs to the sea level when air pressure is low

A

sea level rises

44
Q

Give 3 short term impacts of storm surges

A
  • death/ injuries -> drowning, collapsing buildings
  • infrastructure destroyed/ flooded -> roads, railways, ports
  • homes destriyed -> houses on low-lying land -> cheaper -> most vulnerable to flooding
45
Q

Give an example of storm surge

  • > type of storm surge
  • > when it occurred
A

Bangladesh
Tropical Cyclone Sidr
2007

46
Q

Name 4 reasons why Bangladesh is vulnerable to impacts of tropical cyclones

A
  • 60% of Bangladesh low lying
  • Intense rainfall from cyclone increases flooding
  • almost all of coastline -> unconsolidated delta sediment -> susceptible to erosion
  • deforestation of mangrove swamps -> removed vegetation that slowed wave energy -> erosion
47
Q

How many people were killed, injured and how many homes were destroyed in the Bangladesh storm surge

A
  • 15,000 deaths
  • 55,000 injured
  • 1.6 million homes destroyed.
48
Q

What was the total estimated damage of the Bangladesh storm surge

A

Total damage estimated at $1.7 billion

49
Q

Give an example of a storm surge that has happened in the UK

A

Storm Xavier

December 2013

50
Q

What caused Storm Xavier in the UK

A
  • intense low pressure
  • sea shape, depth and coastline -> funnel shaped coastline -> sea shallows towards coast -> severe flooding
  • high seasonal tides
  • strong northerly winds -> push storm further south -> increasing height of surge
51
Q

Name 5 impacts the UK storm surge had

A

UK
-coastal flooding -> 1,400 homes flooded -> evacs

  • 2 ppl died
  • overall damage -£100 mill
52
Q

Name 3 ways the impact of the UK storm surge reduced

A
  • improved flood defences -> Thames Barrier -> protected 800,000 homes
  • Improved forecasting
  • Efficient evacuation
53
Q

How may climate change increase coastal flood risk

A
  • sea level rise ->causes storm surges to be higher

- frequency & magnitude of storms

54
Q

Give a summary of the IPCC report on global warming affects on coasts

(give 6 points)

A
  • sea level -> rise between 28cm - 98cm by 2100
  • worlds major deltas -> risk coastal flooding -> ^ by 50%
  • increased wind speeds
  • larger waves
  • erosion ^ -> changes of weather systems, sea level
  • storm surges- more common

-

55
Q

Name the 2 approaches to dealing with the risk of rising sea levels

A

mitigation- making efforts to reduce emission of greenhouse gases -> reducing impacts of climate change

-adaptation- making changes to reduce impact of flooding -> building sea walls -> mangrove forests

56
Q

What is post glacial adjustment

A
  • process where earths crust was formerly depressed under ice sheers -> rises as ice sheets recede
  • causes rise in local land level
  • leading to fall in sea level
57
Q

What is accretion

A

sink regions in sediment cell are experiencing deposition -> land is built up -> decrease in seas level

geography (55 decks)

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