3.7 sea level change

Question 1

What is isostatic change?

Answer 1

It’s a local rise or fall in land level

Question 2

What is eustatic change?

Answer 2

it’s a rise or fall in water level caused by a change in the volume of water. This is a global change affecting the world’s connected seas and oceans

Question 3

What is marine regression?

Answer 3

The former sea bed is exposed as sea level drops

Question 4

What is marine transgression?

Answer 4

Areas of land flood, so that the coastline is drowned

Question 5

What is a eustatic fall in sea level

Answer 5

Ice sheets form on land in high latitudes, so evaporated water from the sea is locked on land as ice, leading to a fall in sea level

Question 6

What is a eustatic rise in sea level?

Answer 6

At the end of a glacial period, melting ice sheets return water to the sea, causing the sea level to rise globally. Also, a global increase in temperatures causes the volume of water to increase via thermal expansion, leading to sea level rise

Question 7

What is an isostatic fall in sea level?

Answer 7

The weight from the ice sheets causes the earth’s crust to sag. When the ice melts, the surface slowly rebounds over 1000s of years. This lifts the land out of the sea. This is called isostatic recovery

Question 8

What is an isostatic rise in sea level?

Answer 8

Land can ‘sink’ at the coast due to deposition of sediment, e.g. large deltas, where the weight of sediment leads to slow crustal sag, due to compression. This is known as isostatic subsidence

Question 9

What are some facts about sea level changes over the last 10,000 years?

Answer 9

-The world’s sea level was lowest in 16,000BC, when sea level was 110m less than now. This was the maximum extent of the last ice age
-The formation of estuaries occurred in 9,000 BC when the sea level was 40m less from now
-Britain was separated from France in 4,000BC due to eustatic sea level rise
-In future, green house effects could raise world temperatures enough to cause a 60m sea level rise if all the ice melted (although 5-20m is likely)

Question 10

What is a submergent feature?

Answer 10

a rise in sea level floods the coast and creates a submergent coastline

Question 11

What is an emergent feature?

Answer 11

isostatic readjustment causes a fall in sea level and exposes land previously covered by sea. Therefore, landforms of marine deposition or erosion are lifted

Question 12

What is an example of an emergent coast feature?

Answer 12

A raised beach and relict cliffs

Question 13

What are submergent coast features?

Answer 13

Rias and Fjords

Question 14

What are raised beaches/ relic cliffs and how are they formed?

Answer 14

As the land rose, as a result of isostatic recovery, former shoreline platforms and their beaches were raised above the present sea level. Often, the remains of eroded cliff lines (relic cliffs) can be found behind the beach with wave-cut notches and caves as evidence of past marine erosion.

Question 15

What is an example of a raised beach?

Answer 15

On the Isle of Arran, three distinct raised beaches separate changes in sea level

Question 16

What is a ria?

Answer 16

It’s a sheltered winding inlet with irregular shorelines.

Question 17

How are rias formed?

Answer 17

They form when valleys in a dissected upland area are flooded.

Question 18

Where are rias common and what is an example?

Answer 18

They are common in south west England, where sea levels rose after the last ice age, drowning the lower parts of many rivers and their tributaries
The Knightsbridge estuary in Devon is an example. It provides a natural harbour within the deepest water at its mouth

Question 19

What are fjords and how are they formed?

Answer 19

forms if the valley was glaciated. A fjord is formed when a glacier retreats, after carving its typical U-shaped valley, and the sea fills the resulting valley floor.
This forms a narrow, steep sided inlet (sometimes deeper than 1300 metres) connected to the sea.
The terminal moraine pushed down the valley by the glacier is left underwater at the fjord’s entrance, causing the water at the neck of the fjord to be shallower than the main body of the fjord behind it.

Question 20

What are examples of fjords?

Answer 20

Norway, New Zealand (Milford Sound in New Zealand’s south island) and Chile

Question 21

How is the UK changing due to isostatic readjustment?

Answer 21

Scotland is rising (by 4-20mm per year), which causes the south to sink. Local tilting is called epeirogeny.

Question 22

What is thermal expansion?

Answer 22

As water particle temperature increases, volume increases
When 1.4 billion km cubed of water is heated, thermal expansion happens as the particles move more and begin to take up more space, causing the ocean volume to increase and rise

Question 23

What is an example of sea level change due to tectonic activity?

Answer 23

On Boxing Day 2004, the Indian Ocean tsunami killed nearly 300,000. The devastation was made worse, because the earthquake caused the Earth’s crust at Banda Aceh to sink, permanently flooding some parts of the city.
The earthquake was caused by an estimated 1600km Faultline, slipping about 15m along the subduction zone where the Indian Plate slides under the Burma Plate.
The seabed rose several metres, displacing and estimated 30km cubed of water and triggering a tsunami. Not only that, but the raising of the seabed reduced the capacity of the entire Indian Ocean- producing a permeant sea level rise of 0.1mm

Question 24

Why has past tectonic activity had a direct impact on some of the coasts around the world?

Answer 24

-the uplift of mountain ranges and coastal land at destructive and collision plate margins
-local tilting of land. For example, some ancient Mediterranean ports have been submerged and others have been stranded above the current sea level.

Question 25

Why are sea levels rising?

Answer 25

Global warming
Average global temperatures rose by 0.85 degrees Celsius from 1880 to 2012. During a similar period, average sea levels rose by 21cm. Sea levels are rising because of polar ice sheets melting and because of thermal expansion

Question 26

How far are sea levels estimated to rise in future?

Answer 26

Climate scientists estimate that, by 2100, average sea levels will have risen between 30cm and 1m with perhaps a ‘best guess’ at 40cm

Question 27

What is some context on the island of Kiribati?

Answer 27

consists of 33 widely spread islands, which stretch across the Pacific ocean nearly as wide as the USA
100,000 residents, half of which is under 25, so they could lose the islands within their lifetimes
Kiribati’s islands are very low-lying sand and mangrove atolls - only one metre or less above sea level in most places

Question 28

What’s the sea level rise situation looking like for Kiribati in the next 50 years?

Answer 28

It’s predicted that many of its islands could disappear in the next 50 years
In places, the sea is rising by 1.2cm a year (four times faster than the global average).

Question 29

What’s next for Kiribati?

Answer 29

Their purchase of land in Fiji will be used in the immediate future for agriculture and fish farming projects - to guarantee the nation’s food security. In future, if necessary, people could move from Kiribati to Fiji. The government has launched a ‘migration with dignity’ policy to allow people to apply for jobs in neighboring countries , such as New Zealand. If the islands are submerged, the population will become environmental refugees

Question 30

What problems have already been caused in Kiribati due to rising sea levels?

Answer 30

Rising sea levels are contaminating the ground water and its ability to grow crops.
Lots of people have moved to the capital island, causing high population density- just as much as Tokyo. This has led to poor sanitation and pollution