2.9. Sea Level Change

Question 1

Long term changes in sea level

Answer 1

• sea levels fluctuate over the Earth’s history
• around 20,000 years ago, sea levels were 120m lower than the present day
• about 10,000 years ago, sea levels began to rise at an average of 1.5cm a year

Question 2

Eustatic changes

Answer 2

• global change in sea level resulting from a rise or fall of the sea
• decrease in global temps = more precipitation as snow
• this snow turns to ice so water is stored in the cryosphere rather than being returned to the ocean store
• there’s a global fall in sea level
• if global temps rise, glaciers retreat and ice melts causing rise in global sea level

Question 3

Causes of eustatic changes

Answer 3

• thermal expansion as water gets warmer due to global warming
• melting of ice caps
• tectonic activity -> rising of sea bed which reduces capacity of ocean -> e.g. 2004 earthquake caused by estimated 1600km of fault line slipping around 15m along the subduction zone where Indian Plate slides under Burma Plate; sea bed rose several metres, displacing 30km cubed of water and triggering tsunami; raising of sea bed reduced capacity of entire Indian Ocean producing permanent rise in sea level of estimated 0.1mm

Question 4

Isostatic changes

Answer 4

Local change in sea level resulting from the land rising and falling relative to the sea (tectonic)

Question 5

Isostatic changes and readjustment

Answer 5

• Glacial periods -> weight of ice in ice sheets and glaciers adds weight to earth’s crust which causes crust to sink lower into mantle rock beneath. This results in apparent sea level rise.
• End of glacial periods -> ice melts. weight is lost from crust, causing it to rise slowly and sea levels appears to fall e.g. east coast of Scotland rising 7mm per year
• Much slower than eustatic
• When large ice sheets cover land, it weighs down land making it sink and when ice melts, land begins to rise as weight is removed -> isostatic readjustments
• Past tectonic has led to uplift of mountain ranges and coastal land at destructive and collision plate margins, resulting in relative fall of sea level
• local tilting of land at destructive margins so some ports submerged and others stranded above sea level

Question 6

Landforms of submergence

Answer 6

the impacts of a rise in relative sea level

when the eustatic rise in sea levels take place faster than the isostatic rebound after an ice age

Question 7

What are rias?

Answer 7

• a river valley that’s been flooded by the eustatic rise in sea level
• the tributaries of the river are flooded
• only leaves the high land visible

Question 8

What are fjords?

Answer 8

• a drowned valley -> as sea levels rise, U shaped valleys left by glaciers are submerged
• combination of localised isostatic readjustment and global eustatic sea level change has led to flooding of these valleys
• long and steep sided with a U shaped cross section

Question 9

What are Dalmatian coasts?

Answer 9

• submergent coastlines that form in a landscape of ridges and valleys running parallel to coast
• when sea level rises, the valleys flood, although the tops of the ridges remain exposed, forming a series offshore islands running parallel to the coast

Question 10

Landforms of emergence

Answer 10

• the impact of a relative fall in sea level
• occurs when isostatic rebound takes place faster than eustatic rise in sea level
• features of coastal erosion that appear to have developed well above current sea level -> really the develop when the sea was at that level and then sea level fell and now they’re above sea level
• these emergent features no longer experience coastal erosion but are still weathered, often being weathered biologically, chemically and through freeze-thaw weathering

Question 11

Raised beaches, relic cliffs and wave cut platforms

Answer 11

• Land rose as result of isostatic recovery, former wave cut platforms and their beaches were raised above present sea level
• Common on west coast of Scotland where remains of eroded cliff lines (relic cliffs) can often be found behind the raised beach, with wave cut notches and caves showing past erosion

Question 12

Environmental impacts of climate change

Answer 12

• coastal habitats threatened
• ecosystems can adjust but depends how fast the sea level rise is

Question 13

Socio-economic impacts of climate change

Answer 13

• more developments are occurring on at risk areas
• insurance is expensive which may prevent people from moving into these areas