3.3.2 Sea Levels Changes Flashcards
Define eustatic change
Eustatic change occurs when there is a greater volume of water in the ocean basins
Define isostatic change
Isostatic change occurs when the height of the land changes relative to the water level
Isostatic change happens more slowly than eustatic change
Processes that allow eustatic sea level change to happen
Eustatic change happens due to changes in the amount of ice, as a result of thermal expansion and tectonics
This change will be global
Thermal expansion
Thermal expansion occurs as water warms, warmer fluids expand to take up a greater volume
Tectonics
Magma rising to the surface lifts the crust and reduces the capacity of the oceans causing sea levels to rise
Outline 4 processes that allow isostatic sea level change
Post-glacial adjustment
During a period of glaciation extremely heavy icy sheets weigh land down
When the glacial period ends and the ice melts the land will rebound to a higher level, lowering sea level in a process known as isostatic recovery or readjustment
Accretion
Within the sediment cell there are areas of net deposition causing land to build up
Subsidence
Caused by the lowering of the water table or increased deposition weighing down the sediment
Tectonics
The folding of the sedimentary rock
Lava and ash from volcanoes increase the height of the land relative to the sea level
Define emergent coastline features
Landforms that exist because of a reduction in sea level are called emergent landforms
This happens during isostatic recovery
Outline 2 examples of emergent coastline features
When land rebounds through isostatic recovery landforms which are the result of previous sea levels are revealed including:
Raised beaches
These are:
Beaches which are above high tide level
They are flat and covered by sand/pebbles
Experience succession
Raised beaches can be seen on the Scottish islands of Islay, Jura, Colonsay and Mull
Fossil cliff
This is a:
Steep slope at the back of a raised beach
Wave-cut notches, caves and arches may be evident
Define submerging coastline features
Landforms that exist because of a rise in sea level are called submergent landforms
This happens when coastlines are flooded
Outline 3 submerging coastline features and their characteristics
When coastal areas are flooded the lower course of river valleys can be flooded, creating the submergent landform called a ria or drowned river valley which:
Have a V-shaped cross-section
Are an estuarine coastline
Are the most common coastal landforms
Glacial valleys are also flooded as a result of eustatic change creating a fjord
Fjords are deeper than rias, particularly inland, as they were originally the flat-bottomed U-shaped valley carved out by a powerful glacier
They have a relatively straight profile
Maybe deeper than the adjacent sea
A Dalmatian coast is a submergent landform
Where a landscape of valleys and ridges are parallel to the coastline the low parts of the valleys will be flooded when sea level rises
The exposed tops of the ridges become small offshore islands parallel to the coast
The best known example of this is the Dalmatian Coast in Croatia that the landform is named after
Outline current trends is sea level change associated with climate change
The current levels of sea level stabilised around 3000 years ago
Since the industrial revolution took flight in the nineteenth century global sea level has risen by about 235mm
This is enough to overcome some coastal defences and create coastal flooding through storm surges in some areas
As the world warms there will be increase eustatic sea level change and thermal expansion in ocean basins
By how much sea levels are predicted to rise by 2100? What are the impacts?
The IPCC predicts that sea levels by 2100 will be between 0.3 - 1.0m higher than they are now
This could inundate many coastal cities and settlements
It could also salinise aquifers in low lying regions and increase coastal erosion
In many parts of the world, particularly low lying cities and coastal settlements that are particularly vulnerable climate change sea level planning has already started to take place
These places are likely to see land values drop as formerly valuable land is increasingly eroded, salinised or flooded by sea level rise
More than 1 billion people live on high risk coasts
75% of the world’s cities are coastal
