Coasts - EQ3 - How do coastal erosion & sealevel change alter the physical characteristics of coastlines & increase risks? Flashcards
Define sea level
the level of the sea’s surface
what is sea level used to understand & measure
the height of geographical features in close proximity to it e.g hills
what is sea level determined by
- the height of the surrounding water above sea level
or - the atmospheric pressure at that level (below surface level)
In what 2 ways can sea level trends & activity be measured
technology & models
Explain a way in which sea level trends & activity be measured
Technology
- tide & water level monitoring stations are computerized & fitted with sensors
- that continually record both sea levels
Explain a way in which sea level trends & activity can be measured
Model
earth’s gravitational model - used to work out sea level in areas that are not obvious
Sea level change plays an important role in shaping (1)________ and (2)____________________both on global and local scale act to create (3)___________.
- coastlines
- fluctuations in sea levels
- a variety of coastal landforms
Why can changes in the mean sea level often be complex
- Sea level changes can be due to a change in the level of the sea or land,
- either upwards & downwards
- Sometimes, it can be both land and sea movements
cause or causes of a change in mean sea level are often ________
complex
What are the 4 causes of sea level changes
eustatic change
isostatic change
tectonic activity
climate change
how are coastlines influenced by sea levels
accretion - extended
post glacial adjustment - increased
submergence
emergence
on what timescales do sea levels rise
long term
contemporary (short term/modern)
Why is it difficult to measure sea level
sea level fluctuates greatly throughout time
how do sea levels fluctuate on the microscale
sea level changes according to the tide
how do sea levels fluctuate on the macroscale
caused by ice ages or other major global events & are harder to monitor
How does climate change impact the difficulty of measuring sea level rises
it can be unclear whether the sea level rise is down to being in an interglacial period or due to climate change
define eustatic
global scale sea level change caused by a change in the volume of water in the ocean store
define isostatic
- local scale sea level change
- caused by a change in the level of the land relative to the level of the sea
define emergence
the impact of a relative fall in sea level (marine segression)
define submergence
the impact of a relative rise in sea level
define accretion
- Occurs when sediment is added to a landform, enlarging it by deposition, such as a river delta
- It can build up to form new land, allowing a delta to grow out to sea
- It tends to be balanced by subsidence (sinking), caused by the weight of the newly deposited sediment
define post glacial adjustment
the uplift experienced by land following the removal of the weight of ice sheets
what are the 2 groups under which sea level rise can be classified
isostatic (local)
eustatic (global)
what are the 2 eustatic causes of sea level rise
melting ice
thermal expansion
Eustatic Change
refers to the change in…
sea level (up or down)
Explain how melting ice leads to fluctuations in sea level
- During an ice age, much of the world’s water is stored as ice sheets, ice caps, glaciers and frozen ground.
- Consequently, sea levels fall,
- which is why during the last ice age there was no North Sea and the UK was still joined to the rest of Europe.
- As the climate warms up the ice on the land melts and returns water to the sea.
It’s estimated that sea levels have risen about ………….m since the end of the last ice age 10,000 years ago.
12,000
What is critical to remember regarding eustatic melting ice changes to sea level
- melting sea ice does not count in this change as it already displaces its volume
- Artic - water already displaced
- Antarctica - underneath ice is land
What is one of the primary causes of sea levels rising
thermal expansion
Explain the process of thermal expansion
- The earth is getting warmer primarily due to the accumulation of heat trapping greenhouse gases
- 90% of which are absorbed by the oceans.
- As the water’s temperature rises, the volume of oceans expands
Thermal expansion has been occuring at a _____rate for decades & accounts for ___% of the sea level rise that occurred over the course of the 1900s
steady
75%
what are the 2 isostatic causes of sea level rise
- subsidence/ post glacial adjustment
- accretion
isostatic change occurs ……
locally
Describe the process isostatic subsidence
- During glacial periods & ice is km thick
- it’s very heavy & able to push the land downward because the upper mantle underneath the crust is soft.
- The sinking of the land is isostatic subsidence.
Describe how postglacial adjustment happens after isostatic subsidence
- During glacial periods, the weight of the ice depresses the crust in areas below the ice sheets.
- The rigid nature of the solid crust means that when sections of the crust are depressed by ice and forced down, adjacent areas are uplifted in a see-saw effect.
- The melting of ice causes previously ice-covered crust to slowly rebound upwards whilst adjacent areas subside.
Give an example of isostatic subsidence
- In the Uk, Scotland was pushed down by the weight of ice,
- while Southern England rose slightly.
What is isostatic recovery
- When ice sheets melt at the end of an ice age, the land that had been pushed down rebounds,
- while the land that has been tilted upwards slightly starts to sink,
- which is called isostatic recovery
Scotland is in isostatic …………..
recovery
It takes …………. of years to transition from isostatic recovery
thousands
Accretion
occurs when….
sediment is added to a landform, such as a river delta, by deposition
Accretion
sediment can build up to….
form new land, allowing a delta to grow out to sea
Accretion
it tends to be balanced by…
subsidence (sinking), caused by the weight of the newly deposited sediment
how can tectonics cause changes in sea level
can cause land to rise up out of the ocean, or sink (subside) into it
Tectonic plates on average move at about ….. per year
1-2 cm
Tectonic plates moving about 1-2 cm per year will alter…
landform relativity to the sea level
define destructive plate margins
- formed where an oceanic plate bounday meets a continental plate boundary
- and undergoes subduction due to the greater density of oceanic crust,
- causing sea levels to rise, possibly forming land forms
define constructive plate margins
plates being pulled apart, creating passive margins, causing sea levels to drop, creating landforms
Explain an example of how tectonics can cause changes in sea level
New Zealand
- Turakirae Head, Wellington, New Zealand
- successive major earthquakes in the area have repeatedly lifted the shoreline by several metres
- this has occurred 5 times during the last 7000 years
Explain an example of how tectonics can cause changes in sea level
Indonesia
- The earthquake that caused the 2004 Boxing Day Tsunami in the Indian Ocean that killed nearly 300,000 people
- the Indonesian island of Sumatra was worse hit
- the earthquake caused the Earth’s crust at Banda Aceh to sink permanently by 4m
Describe the location of Kiribati
Consists of 33 widely spaced islands, which stretch across an area of the Pacific Ocean nearly as wide as the USA
Kiribati is only ……. above sea level in most places
1 metre
What are sea levels expected to rise by in Kiribati
by around 40cm
How has the Kiribati government secured food security in the future
agriculture & fish farming projects on land purchased by the government in Fiji
In Kiribati their crops are being…
contaminated by sea water
What policy has the government launched in Kiribati
‘migration with dignity’
What is ‘migration with dignity’
- Policy aiding the application for jobs in neighbouring countries for citizens of Kiribati
- e.g New Zealand, as there is a reluctance to migrate from Indigenous tribes who take pride in their homeland, which is soon to be submerged
What are emergent coastlines the consequence of
isostatic rebound
Describe the isostatic uplift of a specific emergent coastline
In Scandinavia, isostatic uplift is at a rate of 2cm per year
What creates emergent coastlines
a fall in sea level exposes land previously covered by the sea
What are submergent coastlines the consequence of
sea level rise or eustatic changes
Describe the submergence of a specific submergent coastline
In the UK, Land’s end is sinking at a rate of 1.1mm a year
What creates drowned landforms
Eustatic rise since the end of the last ice age
Name 2 emergent coastal landforms
Raised Beaches
Fossil Cliffs
What is a raised beach
A landform that was once a beach, but now lies considerably above sea level
What factors affect the formation of raised beach
- tectonic activity
- climatic conditions - can affect changes in sea level
What is a fossil cliff
- a steep slope found at the back of a raised beach,
- exhibiting evidence of formation through marine erosion,
- but now lies above high tide level
What may fossil cliffs contain, providing evidence of formation by marine erosion
wave cut notches, caves & arches
Give a location example for both raised beaches & fossil cliffs
- Tay Valleys, in Eastern Scotland,
- sea levels are fallling by 1.8 - 2mm annually
Name 3 submergent coastal landforms
Rias
Fjords
Dalmatian Coasts
What is a ria
a drowned river valley
How do rias form
as sea levels rise, they flood river valleys, leaving only high land visible
________ are the most common coastal landform
Rias
Where are Rias commonly formed
- in periglacial areas that were adjacent to land covered by ice during the Devensian (last glacial period)
- e.g Southern England
Give a location example of a ria
South West England, Plymouth sound
What is a fjord
a drowned glacial valley
how do fjords form
as sea levels rise, U-shaped valleys left behind by glaciers are submerged
Characteristics of fjords
- steep valley sides
- that are straight & narrow
What is the difference between fjords & rias
Unlike Rias, fjords are much deeper in land than they are at the coast
Give a location example of a fjord
Milford Sound, in New Zealand
What is a dalmatian coast
- composed of long narrow islands running parallel to the coastline
- & separated from the coast by narrow sea channels called sounds
how are dalmatian coasts formed
sea level rise flooding the coastline with the geographical structure of folds aligned parallel to the coast
Give a location example of a Dalmatian Coast
The Dalmatian coast in Croatia
Define anthropogenic
(chiefly of pollution or environmental change) originating in human activity.
How can climate change cause sea level rise
- Anthropogenic activity
- causes increased global ocean temperatures
- oceans experience thermal expansion
Give evidence of the correlation between sea level rise & global temperatures
- 0.85 degrees celsius increase in global temps from 1880 to 2012
- coincided with a sea level rise of 21cm from 1870-2010
What are the 2 reasons for sea levels rising from climate change
main reason - thermal expansion
secondary reason - melting of land ice in Polar regions & glaciers
Scientists estimate that by 2100, average sea levels will have risen by ….
30cm-1m
What are the four factors which result in coastal retreat
- geology/lithology
- marine processes
- subaerial processes
- human factors
Characteristics of locations with slower rates of recession
lithology
resistant consolidated rocks
Characteristics of locations with slower rates of recession
wave type
small constructive waves
Characteristics of locations with slower rates of recession
mass movement
small scale
Characteristics of locations with slower rates of recession
coastline
emergent
Characteristics of locations with slower rates of recession
patterns of weathering
occasional or slow
Characteristics of locations with rapid rates of recession
lithology
weakly consolidated rock
Characteristics of locations with slower rates of recession
wave type
large destructive waves
Characteristics of locations with slower rates of recession
coastline
submergent
Characteristics of locations with slower rates of recession
mass movement
large
Characteristics of locations with slower rates of recession
pattern of weathering
constant
Name 4 ways in which humans causes coastal retreat/ recession
- coastal defences
- offshore dredging
- anthropogenic climate change
- people building on unstable cliffs
How do coastal defences cause coastal retreat/recession
- Coastal defences in one location might slow erosion,
- but they also stop or reduce the amount of sediment available, in another part of the cell,
- which could limit the amount of sediment for beach building
As a result of coastal defences limiting the amount of sediment for beach building, when the beach gets….
narrower, it is less able to absorb wave energy & waves hit the backshore with more force
what is offshore dredging
removing sand & gravel for construction, beach nourishment & deepening of port entrances
How does offshore dredging, specifically the removal of sediment, cause coastal retreat/recession
- sediment would originally have reduced wave energy before they hit the coast,
- now the waves are not slowed,
- & the full force hits the cliff
How does offshore dredging, specifically the deepening of ports, cause coastal retreat/recession
- deeper water caused by dredging may also allow waves to maintain their circular motion
- & energy closer inshore
- & become more destructive
what is a delta
wetlands that form as rivers empty their water & sediment into another body of water, such as an ocean, lake or another river
How does a delta form
- a river moves more slowly as it nears its mouth or end
- this causes sediment, solid material carried downstream by currents to fall to the river bottom
- as silt builds up, new land is formed - this is the delta
A delta extends a river’s ….
mouth into the body of water into which it is emptying
What are the factors which contribute to retreat along the 240km coast of the Nile Delta
- holiday beach resorts
- fisheries
- land reclamation
- agriculture
- settlements
- transport & port infrastructure
- general tourism
- marine recreation
- coastal defences
Because the Nile Delta is retreating, it is estimated that …..% of Delta land area will be lost, with significant erosion to ……. of it
3.3&
half
Name 4 impacts of sea level rise along the Nile Delta
- salt intrusion into the delta’s fresh water
- more frequent coastal flooding
- 2 million hectares of fertile land will be lost
- 6 million people displaced
How is coastal recession being combatted along the Nile Delta
The UNDP have created an integrated coastal zone management plan, to ensure “environmental stability” - by creating a manmade delta
How does anthropogenic climate change cause coastal retreat/recession
increasing storm energy & frequency, so waves have more energy to erode coasts
How does people building on unstable cliffs cause coastal retreat/recession
the weight of buildings can increase the risk of mass movement & slumping
Name the 6 factors which cause coastal flooding
- removing vegetation/deforestation
- subsidence e.g post glacial adjustment
- sea level rise
- increased frequency & magnitude of tropical storms
- low altitude e.g Dutch
- storm surges
reasons why Bangladesh is vulnerable to coastal flooding
- densely populated with 46% of the population lives less than 10m above sea level
- large coastline - 580km
- 3 rivers converge in Bangladesh
- tropical monsoon climate
What features of Bangladesh’s climate make it vulnerable to coastal flooding
- Tropical monsoon climate
- leads to floods & cyclones - storm surges
- himalayan snow melt + monsoon rains + high tides
Bangladesh is located within the ……. so has a high risk of ……..
tropics
cyclones
Bangladesh lies on the…
floodplain of 3 major rivers (Brahmaputra, Meghna & Ganges) which converge there
Describe Bangladesh’s population density
densely populated with 46% of the population lives less than 10m above sea level
name 3 human actions which can increase the risk of coastal flooding
- local subsidence
- local vegetation removal
- global sea level rise due to climate change (eustatic change)
How is human induced subsidence increasing flood risk in Bangladesh
-embankments
- embankments, which were poorly constructed in the 1960s
- by deposited sediments, that can be easily infiltrated by water,
- which result in poor drainage and low land elevation
How is human induced subsidence increasing flood risk in Bangladesh
-vegetation
- the clearance & drainage of more than 50 large island’s worth of vegetation increases flood risk,
- & is then worsened by improper land use
The Sundarbans Mangrove forest is one of the ……… forests in the world, ………. hecatres
largest
140,000
describe the ongoing ecological processes in the Sundarbans Mangrove forest
this site is intersected by a complex network of tidal waterways, mudflats & small islands of salt tolerant mangrove forests
What do mangroves provide, which decrease the risk of coastal flooding
- absorb coastal water
- reduces wave height by 13-66%
- roots bind sediment together stabilising the coast
- large carbon store (indirect)
- ecosystems & shelter (to wide range of fauna eg Bengal tiger)
- natural sea defence/barrier
The suburban forest helped to take the sting out of ……… Isla in 2009
cyclone
Recent studies show that ….% of Bangladesh’s mangrove coastline is retreating by as much as ……m per year
71%
200m
How has the conversion of land led to the destruction mangroves, and subsequently sea levels rising
forests have been converted into lucrative shrimp farms, which accounts for 25% of this loss
Sea levels are expected to rise ………. due to climate change
eustatically
Bangladesh in expected to sink …………because of the loading of sediment on the delta
isostatically
What are the social impacts of global sea level rise in Bangladesh
-mental health trauma
-houses destroyed
-unemployment (farming jobs lost)
-migration
-food insecurity
-diseases
-17 million people affected by 22,000m of land lost
What are the environmental impacts of global sea level rise in Bangladesh
- ecosystems damaged
- salt water contaminating freshwater, killing the fauna as there are few halophytes
- coastal cities such as Chittagong face inundation & ever greater threat from cyclones
What are the economic impacts of global sea level rise in Bangladesh
- 75% of agricultural land lost
- cannot export food
- major fishing villages will be affected agricultural land
- and rice paddies will suffer the effects of salinization
What were the social impacts of Cyclone Sidr in 2007
- ports were blocked
- wounds & injuries
- 3363 dead
- inaccessibility to resources
What were the economic impacts of Cyclone Sidr in 2007
- infrastructure e.g roads lost
- $1.7 billion in monetary damages
- farmland & businesses lost
What were the environmental impacts of Cyclone Sidr in 2007
- trees uprooted –> soil erosion
- 1.87 million livestock dead
- habitats destroyed
- water pollution
What were the social impacts of the North Sea Surge 2013
-40,000 homes lost power
-45 commercial properties were flooded
-7 homes fell into the sea
What were the environmental impacts of Cyclone Sidr in 2007
- 140,000 acres flooded
- erosion of coastal dunes
- the reactivation of a barrier island
- notching of soft rock cliffs & coastline retreat of barrier island washed over deposits
What were the economic impacts of Cyclone Sidr in 2007
£1billion in damage
rail services in Scotland cancelled
