Sea level change Flashcards
Name 3 factors effecting sea level change
- high & low tides
- atmospheric air pressure
- winds
Definition of isostatic change
local rise/ fall in land level
-occurs when crust is forced down into mantle changing relative sea level
Definition of eustatic change
rise/ fall in water level
-caused by change in vol of water
Name 3 reasons for contemporary sea level change
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
When do emergent coastlines form
- when water level has fallen- exposing land previously covered by sea
- when land has risen
What are emergent coastlines
coastlines that have formed where water level has fallen/ land has risen
-happens due to isotatic change
What are submergent coastlines
coastlines that have been flooded due to rise in sea levels
-happens due to eustatic sea level change
Name 2 emergent coastline landform and how it forms
-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.
Name 3 submergent coastline landform and how it forms
-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)
Definition of post-glacial isostatic adjustment
uplift experienced by land following removal of weight of ice sheets
What factors is coastal recession affecetd by
physical factors- geological (lithology & geoligcal structure)
-marine factors (wave fetch, longshore drift)
- human factors- dredging
- coastal management
How does geology affect coastal recession (in particular the Holderness coastline)
- 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
How does longshore drift and beach material affect coastal recession (in particular Holderness coastline)
- 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
Name 3 ways the Holderness coastline is affected
- human actions
- longshore drift, beach material
- sub-aerial processes
Name the 4 key players on the Holderness coast
- central government agencies- responsible for coastal management
- local government- also responsible for coastal management
- stakeholders in local economy- tourist industry, farmers, residents
- environmental stakeholders
How do sub-aerial processes influence coastal erosion
-give 2 examples
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
What is marine transgression
geologic event during which sea level rises -> flooding -> submergent coast
What is marine regression
geologic event during which sea levels fall -> emergent coast
When does a eustatic rise in sea level occur
- 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
When does a eustatic fall in sea level occur
-during glacial periods -> ice sheets form on land -> water evaporates from sea -> locked on land as ice -> fall in sea level
When does a isostatic rise in land level occur and what does this cause for sea level
- 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
When does a isostatic fall in sea level occur
- 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
What is a ria
drowned river valley caused by sea level rise
What are barrier islands
offshore sediment bars
Name 2 reasons for longer-term sea level change
- eustatic change
- isostatic change
How does global warming affect sea level change
- > 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
How does tectonic activity affect sea level change
- 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
Name the 3 main factors which influence rapid coastal recession
-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)
How do physical factors influence rapid coastal erosion
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
How do human factors influence rapid coastal erosion
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
Name 2 reasons why erosion isn’t constant but varies
- varies in time -> peaks of erosion occurring in some seasons
- varies spatially -> some areas have lots, some don’t
Why does erosion vary on the Holderness Coastline
- coastal defences: Hornsea, Mappleton, Withernsea -> stopped erosion
- terminal groyne syndrome -> sediment starvation further south (Holmpton)
- variations in cliff height
What is dissipation
how energy of wave is decreased by friction with beach material during swash
Rates of erosion are not constant, what 5 temporal variations influence it to occur
- 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
Name 3 low-lying areas that are at risk of flooding
- coastal plains
- estuaries
- river deltas
Name 3 economic reasons why people choose to live in areas at risk from coastal flooding
- 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
Name 3 local factors that increase the flood risk of some coastlines
-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
Name a country at risk of coastal flooding and 2 reasons why
Bangladesh
- 46% population -> lives less than 10m above sea level
- lies on floodplain of 3 major rivers
Name the 4 main causes of coastal flooding
- storm surges
- height
- subsidence
- vegetation removal
What is a storm surge
short-term change in sea level caused by low air pressure
-produced when a depression, storm or tropical cyclone, reaches the coast.
Name the 2 types of storm surges
- depression -> low-pressure weather system in mid-latitudes
- tropical cyclone -> hurricane, typhoon -> areas north/ south of equator
What occurs to the sea level when air pressure is high
sea level lowers
What occurs to the sea level when air pressure is low
sea level rises
Give 3 short term impacts of storm surges
- death/ injuries -> drowning, collapsing buildings
- infrastructure destroyed/ flooded -> roads, railways, ports
- homes destriyed -> houses on low-lying land -> cheaper -> most vulnerable to flooding
Give an example of storm surge
- > type of storm surge
- > when it occurred
Bangladesh
Tropical Cyclone Sidr
2007
Name 4 reasons why Bangladesh is vulnerable to impacts of tropical cyclones
- 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
How many people were killed, injured and how many homes were destroyed in the Bangladesh storm surge
- 15,000 deaths
- 55,000 injured
- 1.6 million homes destroyed.
What was the total estimated damage of the Bangladesh storm surge
Total damage estimated at $1.7 billion
Give an example of a storm surge that has happened in the UK
Storm Xavier
December 2013
What caused Storm Xavier in the UK
- 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
Name 5 impacts the UK storm surge had
UK
-coastal flooding -> 1,400 homes flooded -> evacs
- 2 ppl died
- overall damage -£100 mill
Name 3 ways the impact of the UK storm surge reduced
- improved flood defences -> Thames Barrier -> protected 800,000 homes
- Improved forecasting
- Efficient evacuation
How may climate change increase coastal flood risk
- sea level rise ->causes storm surges to be higher
- frequency & magnitude of storms
Give a summary of the IPCC report on global warming affects on coasts
(give 6 points)
- 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
-
Name the 2 approaches to dealing with the risk of rising sea levels
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
What is post glacial adjustment
- 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
What is accretion
sink regions in sediment cell are experiencing deposition -> land is built up -> decrease in seas level
