Coastal Landscape Development (eustatic/isostatic) Flashcards
Compare and contrast the features of eustatic sea level change with those of isostatic
sea level change (outline similarities and differences).
Both eustatic and isostatic change in sea level change can lead to coastlines either emerging or submerging. Eustatic changes are global changes in the actual level of the water in the world’s oceans whereas isostatic changes are localised changes in the land relative to the sea.
Give the date of the last glacial maxim. How much lower was sea level at this time?
18 000 years ago. Sea level was 110m lower. UK joined to Europe. (Doggerland)
Describe the change in the pattern of sea level rise before and after the Industrial Revolution.
• 10 000 years ago, sea levels rose to but off UK from Europe. Rapid rise followed as the work entered an inter-glacial period.
• In the years prior to the Industrial Revolution, sea levels had been stable for 3000 years.
• Since then, sea level has risen as an increasingly fast rate.
What is the annual rise in sea levels today and what is the main cause?
3.2 mm per year due primarily to thermal expansion.
Future rates of sea level rise depend in part on the rate of melting of two major icesheets. Name these.
Greenland, Antarctic
Isostaticsealevelchangecanbecausedbytectonicactivity.Giveoneexampleto illustrate this.
At destructive margins fold mountains may form as the continental crust is pushed upwards. The land rises relative o the sea as a result.
Isostatic sea level change can be caused by glacial and post-glacial adjustments. Outline how the growth and retreat of ice sheets can impact on relative sea levels in affected areas.
During an ice age snow accumulates on land to form heavy ice sheets over time. The weight of the ice pushes the crust into the mantle causing the land to sink relative to the sea level. After a glacial period when the ice melts and the weight is lifted, the land can rise back up (isostatic rebound or adjustment) causing the land to rise relative to the sea.
Thermal expansion of water
Global warming is leading to higher ocean temperatures. As water is heated it expands, the volume of water in oceans increases so sea levels rise.
Melting ice sheet
Warmer global teperatures causes ice stored on land in ice sheets and glaciers to melt. This melt water eventually runs-off into rivers and into the ocean causing a rise in global sea levels.
Eustatic sea level change can result from tectonic activity, give an example to illustrate this
At constructive margins where new land is formed at mid-ocean ridges the water above is displaced resulting in a global rise in sea levels.
How is the total sea level change for a particular coastline calculated?
By working out the balance between eustatic and isostatic change in an area. For example, NW Scotland is experiencing eustatic sea level rise die to thermal expansion linked to global warming but is also experiencing post-glacial isostatic rebound where the land is rising relative to the sea. The overall effect is an overall gradual fall in sea levels producing an emergent coastline.
What causes an emergent coastline to develop? Name an example.
They are result of a fall in sea level relative to the land, because of either eustatic or isostatic change (or a combination of the two). An example is the west coast of the Isle of Arran in West Scotland.
Features + formation of raised beaches
Where the sea level drops, what was once a beach becomes stranded above the high- water mark. Overtime vegetation succession will occur making them appear like grassy terraces.
Features and formation of relict caves + cliffs
As the land rises out of the sea, cliff features such as caves are left above the high-water mark and above the reach of the waves that created them. They dry out and become relict features, as do the line of cliffs they formed in. They will still be changed by weathering and mass movement processes.
Place example of relict caves/ cliffs
Kings Cave, Arran, Scotland
Raised marine platform
These were original wave-cut platforms that are left exposed above the high-water line.
What causes a submergent coastline to develop? Name an example.
They have been subject to a rise in sea level whether this is because of eustatic or isostatic change or, as a combination of the two. Along the south coast of England, several distinct features of submergence can be seen as the isostatic tilt of the UK results in rising sea levels relative to the land as the land sinks.
Features of submergent coastline
-rias
-fjords
-Dalmatian coasts
Rias
Flooded river mouths/valleys where the sea level rises relative to the land river valleys flood. They look like wide coastal inlets with relatively steep slopes where the old valley sides are, and the floodplain has been flooded by the sea.
Place example rias
River Exe, Exmouth
Fjords
Flooded glacial valleys. The valleys were originally created by valley glaciers where flowing tongues of ice deeply eroded and widened what were previously river valleys. As sea levels rise the floor of the U-shaped valley is flooded creating a deep, long coastal feature with very steep, high valley sides.
Place example fjord
Sognefjord Norway
Dalmatian coast
These form where river systems which once ran parallel to the coast (generally due to concordant geology) are flooded resulting in a series of long islands which would once have been the hills along the valley sides parallel to the coastline. The key difference to rias and fjords is that where they run perpendicular to the coastline,
Dalmatian coast islands and peninsulas run parallel to it. They are named after the Dalmatian Coast in Croatia.
.Identify the main causes of the current rise in global sea levels.
Thermal expansion and melting icesheets linked to global warming.
Give reasons why future predictions of sea level rise vary so much.
There is uncertainty over how the Greenland and Antarctic icesheets will respond to rising global average temperatures in terms of the rate of melting. In addition, it is very hard to be certain about future emissions of greenhouse gases which depend on population growth, economic growth and government policies across the world.
Social impact of rising sea levels
• Major coastal cities close to sea level are at risk from flooding including London and Hull.
• Major transport routes such as the East Coast mainline (rail) and A1 are at risk.
Economic impact of rising sea levels
• Valuable agricultural land in Lincolnshire and East Anglia is at risk from flooding and saltwater intrusion.
• Power stations on the coast are at risk of flooding and coastal erosion, including major gas and nuclear station providing energy.
Environmental impact of rising sea levels
Loss of coastal habitats such as salt marshes and wetlands rich in biodiversity.
Sea level rise is likely to affect some particularly low-lying areas around the global more than other, particular in the tropics.
Inundation of low-lying coastal land, temporarily due to storm surges and permanently from sea level rise e.g., Bangladesh and the Sundarbans in India.
• Loss of coastal habitats such as mangroves (e.g., Sundarbans).
• Submergence of low-lying islands such as the Maldives and Kiribati – climate change
refugees.
Some processes affect the development of coastlines over a very long time. Give
examples of changes that have occurred over a long timescale.
• Fjords. Glacial valleys were formed during past glacial periods e.g., 18 000 years ago. Since then, the valleys have been submerged because of eustatic sea level rise.
• Barrier islands. The sediment forming barrier islands is believed to have been initially deposited when glaciers and icesheets melted at the end of the last Ice Age. Subsequent ocean currents deposited this glacial sediment on the coast which accumulated to become beaches. Further sea level rise due to the melting ice inundated these coastal areas, separating the beaches from the mainland and creating barrier islands. Since then, vegetation succession and helped stabilise the islands.
Some processes occur more quickly and can result in sudden changes to the coastline. Give examples to illustrate this.
• Mass movement processes such as rock falls and landslides can cause a sudden change in cliff profiles.
• Some landforms are temporary and reform each day, such as ripples on a beach formed from the daily action of the tides on beach sediments.
A coastal landscape is made up of a combination of short-duration, medium-term and long-term processes. Explain this statement using examples as evidence. You can also refer to Valentin’s classification shown below.
Some processes can alter coastlines in the short term. For example, tides reform beach features such as ripples daily, and cliff collapse due to mass movement can occur suddenly to alter a cliff profile and slow wave erosion of the base for a while. Other processes occur over the medium term, for example the build up of sediment across an estuary on a drift-aligned coastline to form a spit or the formation of a cave between the high and low water mark on a headland. Other landscapes are the result of several
