Y13 MB - Sea Level Change

Question 1

What are the two kinds of landform sea level change can create?

Answer 1

Landforms of emergence (falling sea level relative to the land) and submergence (rising sea level relative to the land)

Question 2

What is ecstatic sea level change?

Answer 2

Rise or fall in the sea level as a result of change in the actual level of water in the oceans

These are global changes

Question 3

What is isostatic sea level change?

Answer 3

Change in the level of the land relative to the sea as a result of the changing level of the land

Local / regional changes

Question 4

When was the last glacial maximum and during this time how much lower were sea levels on average?

Answer 4

Last glacial maximum - 18,000 years ago (end of the last Ice Age)
Sea levels were on average 110m below their current level (Uk was joined to mainland Europe and Scandinavia by a large land bridge where the North Sea is, now called Doggerland)

Question 5

When did the rapid increase in sea level begin?

Answer 5

Following the Industrial Revolution in the mid-19th century
Now levels are rising by 3.2 mm per year on average

Question 6

What are the three causes of isostatic change?

Answer 6

Tectonic activity
Glaciation
Post-glacial readjustment

Question 7

How does tectonic activity cause isostatic change?

Answer 7

Lands can move up or down due to tectonic activity
This could be a few meters as a result of one event such as the Tohoku earthquake in Japan where some sections dropped by almost 1m
This could also be gradual and on a much larger scale such as the Andes and Alps which are fold mountains which have been forced up from the ocean floor

Question 8

How does glaciation cause isostatic change?

Answer 8

During an ice age, glaciers and ice sheets form over land in cold enough areas
This causes the land surface to be pressed into the asthenosphere and therefore cause relative sea level rise

Question 9

How does post-glacial readjustment cause isostatic change?

Answer 9

Following the melting of glaciers and ice sheets over the land, it is able to rise back up as the asthenosphere rebounds
This is isostatic recovery
E.g falling sea levels in Scotland as during the last ice age over 18,000 years ago this was the area of the Uk covered with the thickest ice

Question 10

What are the three causes of eustatic change?

Answer 10

Thermal expansion of water
Changes in ice sheet extent
Tectonic activity

Question 11

How does thermal expansion cause eustatic change?

Answer 11

As water is heated, it expands so even if the total mass of the oceans stay the same, the warmer water has a larger volume and takes up more space

Question 12

How does change in ice sheet extent cause eustatic change?

Answer 12

Where ice forms on land during glacial periods it removes water from stores such as in the ocean so sea levels fall
When ice on the land melts there is less water stored as ice in the cryosphere so more available for other stores such as the ocean. this leads to sea level rise

Question 13

How does tectonic activity cause eustatic change?

Answer 13

Where new land is being formed under the ocean (usually at mid-ocean rises) the new rock / crust takes up space in the ocean basins so water is displaced and sea levels rise

Question 14

What is total sea level change?

Answer 14

The balance between isostatic and eustatic change
E.g in Scotland today isostatic recovery is causing the level of the land to rise faster than thermal expansion and ice melt, causing the overall effect of sea level rise fall in Scotland and the formation of emergence landforms

Question 15

What are coastlines of emergence?

Answer 15

Coastlines that have been subject to a fall in sea level as a result of eustatic and isostatic change

Question 16

Give some examples of landforms of emergence

Answer 16

Raised beaches
Marine platforms
Relic cliffs / caves

Question 17

How is a raised beach formed?

Answer 17

Where the sea level drops relative to the land so a beach becomes stranded above the high-water mark
Subject to vegetation succession once above high tide level so may appear as flat, grassy terraces
E.g the Isle of Arran in Scotland

Question 18

How are relic cliffs / caves formed?

Answer 18

Where there is sea level fall so cliffs and cliff profile features such as caves are left above the high tide level
E.g King’s Cave in the Isle of Arran, Scotland

Question 19

How are marine platforms formed?

Answer 19

Where there is a fall in sea level so wave-cut platforms become exposed above high tide level
Often not very visible as they may become covered in sediment

Question 20

What is a coastline of submergence?

Answer 20

Coastlines that have been subject to a rise in sea level as a result of eustatic and isostatic change

Question 21

Give some examples of landforms of submergence

Answer 21

Rias
Fjords
Dalmatian coasts

Question 22

How does a ria form?

Answer 22

Due to sea level rise relative to the land
Therefore river mouths / valleys become flooded by the sea
They appear as coastal inlets with relatively steep sides due to the old valley sides being exposed and floodplain being flooded by the sea

E.g River Exe mouth in Exmouth

Question 23

How does a fjord form?

Answer 23

Fjords are like rias but are flooded glacial valleys instead of river valleys
When glaciers erode the land they create steep sided U-shaped valleys
As the glaciers reached further towards the coastline, they lost energy and power so it is usually shallower as you move further towards the mouth of the fjord
When these glaciers melted at the end of the last ice age 18,000 years ago they then flooded these glacial valleys

E.g Sognefjord in Norway (over 200km long)

Question 24

How did the Dalmatian coast form?

Answer 24

Occur due to sea level rise as a result of eustatic and isostatic change
occur where river systems once ran parallel to the coast (usually concordant geology)
Flooding from sea level rise meant the former river valleys became drowned and submerged so only the hills along the river valley sides remain, leaving islands running parallel to the coastline

E.g the Dalmatian coast in Croatia

Question 25

What do sea level rise predictions say?

Answer 25

Increase of between 18 and 59cm rise between 1990 and 2090
Large variability due to how much global warming will occur and how Antarctic and Greenland ice sheets respond

Question 26

What are the impacts of future sea level change?

Answer 26

Major UK population centres e.g London, Hull, Middlesborough at risk of inundation
Agricultural and valuable arable farmland at risk of flooding and erosion
Major transport links e.g the east cost mainline at risk
Groundwater could become contaminated with seawater so it can no longer be used
Submergence of low-lying areas such as in Bangladesh 11% of land area is likely to be permanently flooded
Loss of coastal habitats e.g mangroves