Chapter 3 How Do Coastal Erosion And Sea Level Change Alter The Physical Characteristics Of Coastlines And Increase Risks?

Question 1

Eustatic seas level change

Answer 1

Fall- glacial periods, ice sheets form on land in high latitudes

Water evaporated from sea is locked up on land as ice= global fall in sea level

Rise-end of glacial period, melting ice sheets return water to sea and rise

Global temp increases cause volume of ocean water to increase (thermal expansion) = sea level rise

Question 2

Isostatic sea level change

Answer 2

Fall- build up of land based ice sheets, colossal weight of ice causes earths crust to sag

Ice melts, land surface slowly rebounds
upward over thousands of years

Rise- land ‘sink’ at coast due to deposition of sediment

Especially in large river deltas where it leads to ‘crustal sag’ and delta subsidence

Question 3

Uk sea level change

Answer 3

End of last ice age (12,000 years ago)

Scotland still rebounding upward (up to 1.5mm per year) POST GLACIAL ADJUSTMENT

England and Wales subsiding (up to 1mm per year)

Uk is ‘pivoting’ south sinking and north rising

Sea level rise caused by global warming (eustatic) compounds the effect in the south and reduces it in the north

Question 4

Post glacial adjustment

Answer 4

Uplift experienced by land following removal of weight of ice sheets

Question 5

Emergent coastlines

Answer 5

Extent of isostatic/ eustatic changes during and after ice age were large:

Global sea levels fall 120m
Equal sea level rise happened when ice melted
N America and Europe post glacial isostatic adjustment was up 300m

Two linked changes happen a different rates:

Post glacial sea level rise very rapid, submerging coastlines
Isostatic adjustment v slow with land gradually rising out of sea

Raised beaches
Fossil stump/ cliff

Question 6

Submerging coastlines

Answer 6

Post glacial sea level rise

Southern England

Common landform= ria (drowned river valleys in unglaciated areas, caused by sea level rise flooding up the river valley making it much wider than would be expected based on the river flowing into it)

Fjords (Norway)
Drowned valley is U shaped glacial valley
Deeper than adjacent sea (up to 1000m deep)
Seaward end = submerged ‘lip’

USA east coast
Barrier islands ( offshore sediment bars, usually sand dune covered but not attached to coast 500m-30km offshore)

Question 7

Contemporary sea level change

Answer 7

Today 2mm per year

Stable between 1800-1870

Rose slowly 1870-1940 but accelerated after that

Between 1870 and today sea level measurements = more accurate

Tide gauges
Satellite measurements = more precise

Future IPCC some expect increase over 100cm 2100

Question 8

Sea level hard to predict

Answer 8

Thermal expansion (main driver of sea level rise, occurs because volume of ocean water increases as global temps rise)

Melting of mountain glaciers (Himalaya)

Melting of major ice sheets (Antarctica)

Locally change due to tectonic forces (earthquakes force land up/down as much as 2m)

Question 9

Rapidly eroding coastlines have physical features in common

Answer 9

Long wave fetch
Large destructive ocean waves
Soft geology
Cliffs with structural weaknesses (seaward Rock dip)
Cliffs vulnerable to mass movement and weathering
Strong LSD (sediment removed and cliff base exposed)

Question 10

Human actions interfere in sediment cell and influence coastal retreat

Answer 10

Aswan high dam on river Nile 1964
Reduced sediment volume from 130m tonnes to 15m tonnes
Erosion rates jumped from 20-25m per year to 200m+ as delta starved of sediment

Dredging (scooping or sucking sediment up from sea/river bed)
Removes sediment source
Knock on effects further along coast by increasing erosion

Question 11

Variations in erosion rate

Answer 11

Holderness coast East Yorkshire

Average erosion rate 1.25m year

Coastal defences (Hornsea/mappleton/withernsea) stopped erosion but starved further south as grounds interrupt LSD

Erosion rate generally increase from N to S

Boulder clay areas = more vulnerable

Some cliffs susceptible to mass movement

Question 12

Erosion of holderness varies over time

Answer 12

winter: 2-6m of erosion common (storms combined with spring tides increase erosion)

Summer erosion (constructive waves) much lower erosion

Northeasterly storms cause most erosion( long wave fetch 1500km from north Norwegian coast)

Question 13

Shape of holderness beach can change and promote erosion

Answer 13

Ords- deep beach hollows parallel to cliff
Concentrate erosion in particular location by allowing waves to directly attack cliff with little energy dissipation
slowly migrate downdrift (500m per yr) location of most erosion changes

Ord locations erode four times faster

Question 14

Dissipation

Answer 14

Energy of waves is decreased by friction with beach material during wave swash up the beach

Wide beach slows waves down and saps their energy so when break most energy has gone

Question 15

Coastal flooding risk

Answer 15

Low lying coasts densely populated for several reason:

Popular with tourists (Access to beach)

Deltas and estuaries ideal locations for trade between up river and places along coast

Deltas and coastal plains fertile and ideal for farming

Question 16

Worlds major deltas (some few m above sea level)

Answer 16

Some have largest cities

Ganges/brahmaputra- Dhaka (14.3million)

Question 17

Causes of coastal flood risk in river deltas

Answer 17

River straightening for navigation means faster riverflow and sediment propelled to far offshore

Ground water extraction causes subsidence and accelerated sinking

Destruction of mangrove forests for wood and charcoal exposed the coast to erosion

Delta subsidence caused by weight of sediment deposition which is balanced by new deposition on delta surface

Question 18

Maldives

Answer 18

Indian Ocean

Population of 340,000 across 1200 islands

Highest pint is 2.3m above sea level

Sea level rise of 50cm by 2100 would see 77% of Maldives disappear into sea

Question 19

Storm surge

Answer 19

Localised, short term rise in sea level caused by air pressure change (1millibar fall in air pressure = 1cm rise in sea level

Question 20

Causes of storm surge

Answer 20

Depression- (low pressure weather system) in mid-latitudes (uk)

Tropical cyclone- (hurricane) in areas just north and south of equator

Strong winds from weather systems push waves onshore (increase height of sea)

High tide and storm surge at same time

Question 21

North Sea storm surge

Answer 21

Coastal topography had an effect

Coastline narrows into funnel shape for storm from north

Storm funnelled into increasingly narrow space between coasts

As sea shallow towards coast the effect is severe coastal flooding

Question 22

Impacts of North Sea storm surge

Answer 22

2013

80+mph winds

Storm surge 6m

Coastal flooding hull and Skegness

Scotland’s Rail network shut and 100,000 homes lose power

2500 coastal homes and businesses in uk flooded

Across country= 15 deaths

Question 23

Bangladesh vulnerable to impacts of tropical cyclone storm surges

Answer 23

Low lying river delta (1-3m)

Incoming storm surge meets out flowing discharge from Ganges and Brahmaputra (river and coastal flooding combine)

Intense rainfall from tropical cyclones contributes

Much of coastline is unconsolidated delta sediment

Deforestation of coastal mangroves removes veg that stabilised coastal swamps and dissipated wave energy

Question 24

Bangladesh cyclones

Answer 24

1970 bhola cyclone

Storm surge height 10m

Lowest air pressure 966mb

Deaths and economic loss 300,000-500,000
US$90 million

Question 25

Coastal risks from global warming (ipcc 2014)

Answer 25

Delta flooding- area of worlds major deltas at risk from coastal flooding (likely to increase by 50%) HIGH CERTAINTY

coastal erosion- generally increase because of combined effects of changes to weather systems and sea level MEDIUM CERTAINTY

storm surges- storm surges linked to depressions are likely to become more common

Question 26

Coasts of coastal recession

Answer 26

Economic- loss of property (relatively easy to quantify)

Social- costs of relocation and loss of livelihood (can be quantified) and health (harder to quantify)

Environmental- loss of coastal ecosystems (impossible to quantify financially)