Coasts EQ3 - Coastal erosion and sea level change

Question 1

What is eustatic change?

Answer 1

A rise or fall in water level caused by a change in the volume of water - GLOBAL change

Question 2

What is isostatic change?

Answer 2

A local rise or fall in land level

Question 3

How can eustatic change cause rises and falls in sea level?

Answer 3

During glacial periods, ice sheets form and ‘lock up’ water from the sea, causing a fall in sea level (MARINE REGRESSION)
At the end of glacial periods, melting ice sheets return water to the sea. Global temperature rise also cause thermal expansion, causing sea level rise (MARINE TRANSGRESSION)

Question 4

How can isostatic changes cause rises and falls in land level?

Answer 4

Post glacial-adjustment causes isostatic rebound due to the weight of ice sheets melting off of crust - lifting the land surface out of the sea (MARINE REGRESSION)
Land can sink at coasts due to accretion of sediment and a seesaw effect causes subsidence (MARINE TRANSGRESSION)

Question 5

What is an emergent coastline?

Answer 5

Parts of the littoral zone where a fall in sea level has exposed land once part of the sea bed

Question 6

What features are found on an emergent coastline?

Answer 6

Raised beach
Fossil cliff

Question 7

What is a raised beach?

Answer 7

A relict beach now above high tide level, usually vegetated by plant succession

Question 8

What is a fossil cliff?

Answer 8

A steep slope found at the back of the beach exhibiting evidence of formation through marine erosion, now above high tide level

Question 9

What is a submergent coastline?

Answer 9

Sections of the littoral zone where sea level rise has inundated areas that were previously part of terrestial land

Question 10

What features are found on a submergent coastline?

Answer 10

Rias, fjords and Dalmatian coastlines

Question 11

What is a ria?

Answer 11

A drowned river valley, flooded by the sea and wider than expected (estuarine coastline)

Question 12

What is a fjord?

Answer 12

Drowned glacial valley flooded by the sea

Question 13

What is a Dalmatian coastline?

Answer 13

Long narrow islands running parallel to the coastline, separated from the coast by narrow sea channels called sounds

Question 14

What are some of the key facts on past and future sea level rise?

Answer 14

Past - in the last 18,000 years sea levels have risen by 140m
Future - IPPC predicts sea level rise of 50cm by 2100, every degree rise in temperature causes a 0.8mm sea level rise

Question 15

Why is sea level rise difficult to predict?

Answer 15

• uncertainties in science of relationship between climate change and melting ice
• thermal expansion depends on global temperature rise and is hard to predict
• uncertainty on when and how much ice sheets will melt
• uncertainty on GHG emissions and climatic warming

Question 16

What is rapid coastal recession caused by?

Answer 16

Caused by physical factors but can be influenced by human actions

Question 17

What are the physical factors contributing to rapid coastal recession?

Answer 17

Geological - lithology, geological structure
Marine - strong longshore drift, long fetch promoting destructive waves

Question 18

What are the human actions influencing coastal recession?

Answer 18

Anything that disrupts the operation of the sediment cell - dams and dredging
Dams - starve coast of a sediment source
Dredging - scoops up sediment from beaches, rivers or sea

Question 19

How has the Aswan High Dam impacted the Nile Delta’s sediment cell?

Answer 19

Reduced sediment volume from 130mil tonnes to just 15 mil tonnes per year
Erosion rates have jumped from 20/25m per year to over 200m per year

Question 20

How do weathering and mass movement work together to influence the rate of coastal recession?

Answer 20

Weathering weakens rocks above the high tide mark, making mass movement easier by reducing the internal cohesion of the rock
Repeated mass movement causes coastal recession

Question 21

What different temporal factors affect coastal recession?

Answer 21

• wind direction and fetch
• tides
• storms
• seasons
• weather systems

Question 22

What local factors increase flood risk in low lying and estuarine coasts?

Answer 22

• height
• degree of subsidence
• vegetation removal

Question 23

What else increases the risk of flooding in low lying countries apart from local factors?

Answer 23

Global sea level rise

Question 24

How will sea level rise impact the Maldives?

Answer 24

Only 2.3m above sea level
A 50cm sea level rise by 2100 would mean the Maldives would lose 77% of it’s land area

Question 25

What is a storm surge?

Answer 25

A temporary rise in local sea level produced when a depression, tropical cyclone or storm reaches the coast

Question 26

What factors worsen the impacts of a storm surge?

Answer 26

• high tide
• shape of coastline funneling into a narrow shape
• sea bed shallowing towards the coast

Question 27

What are the short term impacts of a storm surge?

Answer 27

• deaths and injury
• destruction of infrastructure
• homes destroyed
• business destroyed
• loss of agricultural land

Question 28

What were the impacts of Cyclone Sidr’s storm surge in 2007?

Answer 28

• Drinking water was contaminated by debris and many sources were inundated with saline water from tidal surges, and sanitation infrastructure was destroyed.
• Death toll over 3,000
• Cost estimated at US $1.7 billion
• Infrastructure damage

Question 29

What was in the 2014 IPCC report’s ‘high confidence’ area?

Answer 29

• sea level will rise between 18-59cm by 2100
  However the pace and extent is uncertain due to population growth, economic development and political commitment to GHG reduction
• The area of the world’s major deltas at risk from coastal flooding is likely to increase by 50%

Question 30

What was in the 2014 IPCC report’s ‘medium confidence’ area?

Answer 30

• some evidence of increased wind speeds and larger waves
• erosion will generally increase

Question 31

What was in the 2014 IPCC report’s ‘low confidence’ area?

Answer 31

• tropical cyclone frequency remains unchanged but severity worsens
• more storm surges and depression

Question 32

What is coastal recession?

Answer 32

The loss or displacement of land, or the long-term removal of sediment and rocks along the coastline