3.3- Sea Level Change Flashcards
There are two ideas relating to sea level change:
- eustatic change
- isostatic change
What is eustatic change?
A global change in sea level resulting from an actual fall or rise in the level of the sea itself- one clear example of this is is that as temperatures increase, water expands meaning that sea levels rise when sea temperatures are warmer
What is isostatic change?
Local changes in sea level resulting from the land rising or falling relative to the sea- one of the most obvious examples of this is that continents collide and fold mountains form as the land is forced to rise up out of the sea
Sea level does not remain
Constant- it has changed throughout Earth’s history and continues to do so
Changes in sea level create
Distinct landforms of emergence (falling sea level relative to land) and submergence (rising sea level relative to land)
Describe the history behind sea level change
- at last glacial maximum 18,000 years ago, sea levels were on average 110m below their current level which meant that the UK was joined to mainland Europe and Scandinavia by a large land bridge where the North Sea is now called Doggerland
- by 10,000 years ago the northern North Sea was flooded and the coastline of Europe was beginning to look like it does today but Doggerland still linked with what is now the UK to what is now the Netherlands and Denmark
- this was followed by a rapid increase in which sea levels rose by 10m in just 500 years. Prior to the industrial revolution,sea levels had been fairly stable for about 3000 years but from the mid-19th century they started increasing exponentially
Current sea levels are rising
At 3.2 mm per year, largely due to thermal expansion
It is thought that a 4-6m rise in sea level is likely by
2100= which could have huge effects, although this could be greater depending on how the Greenland and Antarctic ice sheets respond to warming temperatures
What are the 3 causes of isostatic change?
1- tectonic activity
2- glaciation
3- post-glacial readjustment
Explain how tectonic activity can lead to isostatic change
- land can move up or down as a result of tectonic activity
- this could be a few metres as a result of one event
- alternatively, this could be on a much larger scales fossils in the Andes, Alps and Himalayas all show that the rocks found in these fold mountains were once on the ocean floor, but have been forced up thousands of metres as part of the formation of mountains
Explain how glaciation leads to isostatic change
- during an ice age, glaciers and eventually ice sheets form over the land in areas cold enough
- this causes the land surface to become pressed into the upper layer of the mantle (asthenosphere) and therefore relative sea level rises
Explain how post-glacial readjustment causes isostatic change
following the melting of ice sheets and glaciers on the land, the land is able to rise back up as the asthenosphere rebounds = called isostatic recovery and is responsible for falling sea levels in Scotland today as during the last ice age Scotland was the part of the UK covered with the thickest ice and it melted last
What are the causes of eustatic change?
- thermal expansion of water
- changes in ice sheet extent
- tectonic activity
Explain how thermal expansion of water causes eustatic change
As water is heated it expands, so even if the mass of the ocean (total amount of water) stays the same, the warmer water has a larger volume so takes up more space and sea level therefore rises
Explain how changes in ice sheet extent cause isostatic change
- where ice forms on a land during a glacial period it removes water from other stores including the ocean so sea levels fall
- when ice on the land melts there is less water locked up in ice on land so more available to other stores including the ocean = sea levels rise