Sea Level Change Flashcards
What is eustatic change?
A change in SEA level (global). Tectonic movement changes the shape of the ocean basin. During ice ages, sea levels will fall due to more water being frozen.
What is isostatic change?
A change in LAND level (local). Caused by the vertical movement of the land. Ice melting allows the land to rebound causing the sea level to fall.
Explain how ice forming/melting is related to eustatic change.
In glacial periods, precipitation falls as snow, forming ice sheets that store water normally held in the oceans and so sea levels fall. Or the melting of glacials/climate change can lead to sea levels increasing. This is 40% of eustatic change.
Give an example of where ice is melting.
Greenland ice sheet, loses 250 billion metric tonnes of ice per year.
Explain how thermal expansion is related to eustatic change.
As global temperatures increase, temperatures of the oceans increase, causing the water to expand and therefore the sea levels to rise. This is 60% of eustatic change.
Give an example of where thermal expansion is happening.
Pacific ocean is said to have expanded by 30-55% in the last 50 years threatening SIDS like Tuvalu.
Explain how post-glacial adjustment is related to isostatic change.
Ice forms and weighs down the land causing it to sink for a long period of time, then the ice melts and land rebounds up slowly.
Give an example of where post-glacial adjustment is happening.
Scotland is rising by 1.5cm a year, for 8000 years.
Explain how subsidence is related to isostatic change.
When sediment from underground is extracted/removed and is accelerated by the extraction of groundwater. This causes the land to sink and can lead to flooding.
Give an example of where subsidence is happening.
In New Orleans they over pumped groundwater for civilian use, display rock layers.
Explain how accretion is related to isostatic change.
Accretion is the build up of material.
Deposition of sediment from river channels/sediment cells which build up over time. The land is built up = land increases in height = drop in sea level. After a few hundred years, too much sediment built up will start to have a similar impact as the ice from the ice age where the land is weighed down and starts to sink.
Give an example of where accretion is happening.
At the Nile Delta which is sinking by 5mm a year.
Explain how tectonics is related to isostatic change.
Local tilting of land can cause a change in sea level. Tectonic activity can cause an uplift of mountain ranges and coastal land and a resulting fall in sea level.
Give an example of where tectonics as led to isostatic change.
EQ that caused the Boxing Day Tsunami caused Indonesia to sink by 1 metre, areas were permanently flooded.
What is an emergent coastline?
Falling sea levels expose land that is normally covered by the sea.
How are raised beaches created (emergent coast)?
Formed when the fall in sea level leaves beaches above the high tide mark. Over time, beach sediment becomes vegetated and develops into soil. Sea level fall also exposes wave cut platforms, leaving them raised above their former level.
Give an example of a raised beach.
Fife, Scotland.
How are fossil cliffs/relict cliffs created (emergent coast)?
The cliffs above raised beaches are no longer eroded by the sea, and slowly get covered by vegetation.
Give an example of a fossil/relict beach.
Ayrshire, Scotland.
What is a submergent coastline?
Stretches along the coast that have been inundated by the sea by a relative rise in sea levels.
How are rias formed (submergent coast)?
By the submergence of the lower portion of the river valley. Drowning winding river valleys with long fingers of water stretching a long way inland. Wildest and deepest, nearest to the sea, progressively narrower and shallower inland. Tidal changes often reveal extensive areas of mudflats.
Give an example of a rias.
New York Harbor.
How are fjords created (submergent coast)?
Straight glaciated valleys that were drowned by rising sea levels at the end of the ice ages. A shallower area at the mouth where the ice thinned as it reached the sea and hence lost its erosional power. Typical steep-sided and deep cross profile associated with glacial troughs, can stretch kms inland.
Give an example of a fjord.
Sognefjorden, Norway.
