EQ3 Coasts Flashcards
(19 cards)
what is the cause of Eustatic sea level change?
Caused by a change in the volume of water in the sea, or by a change in the shape of the ocean basins. The causes and effects are global and happen relatively quickly
What is thermal expansion- Eustatic sea level change
An increase in temperature causes the melting of ice sheets. This increases the volume of water in the sea, so increases sea level. Higher temperatures also cause water to expand, because the particles have more energy and hence take up more space. This raises sea level further.
Tectonic movement - Eustatsic sea level change
The spreading of the sea floor in the Atlantic slowly increases the volume of the basin, lowering sea level.
What us Isostatic sea level change?
It is caused buy the vertical movements one the land in relativity to the sea. A depression of land causes the sea level to rise and an uplift of land causes the sea level to fall. This effect occurs at a local scale and can take a long time to happen. During the last ice age, the North of the Uk had more ice than the south, the muscle memory of this weight is imprinted into the earth, hence causing vertical uplift in the North of the Uk, in relativity to the sea and the opposite in the south, e.g Somerset.
Post-glacial adjustment - causes of isostatic sea level change
The large volume of ice that built up in the last ice age caused some crust to sink. This is known as isostatic subsidence. The melting of these ice sheets can slowly uplift the land as the lost weight of the ice releases the downward pressure.
This is known as Isostatic rebound. It can continue for thousands of years after the retreating glacier has gone, causing sea levels to slowly fall. Some areas of Scotland are still moving upwards at up to 1.5mm a year!
Subsidence- causes of isostatic sea level change
The subsidence of land due to shrinkage after extraction of ground water can cause the land to compact. This means the surface can become flooded with seawater.
Accretion- causes of Isostatic sea level change
The accretion of sediment, mostly in the mouths of major rivers and at the coast, or the accumulation of ice can also add weight to the earth’s crust. This can make it sink down and cause sea levels to rise.
Tectonic processes- causes of isostatic sea level change
e.g as one plate is forced beneath another at a plate margin (e.g subduction, convergent). This can cause uplift of the crust which can either increase or decrease sea level.
Features of emergent coastlines- Raised beaches
- example in the UK
Form when the fall in sea level leaves beaches above the high tide mark. Overtime, this beach sediment becomes vegetated and develops into soil. A fall in sea level also exposes wave-cut platforms, leaving them raised above their former level.
In the Uk, raised beaches frequently occur along the west coast of Scotland and particularly on the Isle of Arran Isle of Iona (Scotland)
Features of emergent coastlines- fossil/relif cliffs
The sea no longer erodes the cliff above raised beaches, meaning vegetation slowly establishes and covers them. These are known as fossil/relic cliffs. It is common to see wave-cut notches caves, arches and stacks within fossil cliffs. Overtime, weathering changes the shape and size of these raised features.
What are emergent coastlines caused by
When sea levels fall relative to the coast, new coastlines emerge from the sea, which create different landforms (raised beaches and relic cliffs). They have formed by FALLING sea level.
What are submerging coastlines caused by?
When sea levels rise relative to the coast, the sea submerges the existing coastline and creates new landforms. They have formed by RISING sea level.
Features of submergenct coastlines- rias
- example in the UK
Rias (sheltered winding inlets with irregular shorelines) are one of the most distinctive features associated with rising sea level. They form when valleys in a dissected upland area are flooded. Deepest at mouth.
Rias are common in south-west England, where sea levels rose after the last ice age- drowning the lower parts of any rivers and their tributaries to form rias.
e.g - the Kingsbridge estuary in Devon. It provides a natural harbour with the deepest water at its mouth.
Features of submergence coastlines- Dalmation coastlines
- example in Europe
A Dalmatian coastline is characterised with numerous islands lying parallel to the coast. These islands are the tops of a series of anticlines and synclines, that become isolated when there is an increase in sea level and the valleys between them flood.
e.g - the Dalmatian coastline, Croatia
Features of submergence coastlines- Fjords
Fjords are formed when deep glacial troughs are flooded by a rise in sea level. They are long and steep-sided, with a U-shaped cross-section and hanging valleys.
Unlike rias, fjords are much deeper inland than they are the the coast. They are submerged GLACIAL valleys, rather than submerged river valleys (rias).
The shallow entrance marks where the glacier left the valley, caused by a raised bit of ground (the threshold).
e.g - Sognejjorden in Norway is over 1000m deep in some places.
Reasons for sea level change:
post-glacial adjustment, subsidence, accretion, tectonic processes, thermal expansion, GREENHOUSE GAS EMISSIONS!
what can effect our ability to predict sea level rise?
Although instruments used to record and model sea level changes have improved in accuracy, the multiple variables that can affect sea level rise can affect our ability to predict the future.
Sea level change due to tectonic activity- Boxing Day tsunami, 2004
the 2004 Boxing Day earthquake was caused by an estimated 1600km of fault line slipping about 15 metres along the subduction zone, where the Indian plate slides under the Burma plate. The seabed rose several metres- displacing an estimated 30km 3 of water and triggering the tsunami.
The raising of the seabed reduced the capacity of the entire Indian Ocean- producing a permanent rise in sea level of an estimated 0.1mm
