Sea level change Flashcards
How do erosion and sea level change alter the physical characteristics of coastlines and increase risk?
- Short and long term sea level changes influence the physical geography of coastlines and increase risks for people
- rapid coastal recession happens because of both physical and human influences
- coastal flooding is a significant risk on some coastlines, worsened by global warming, uncertain of extent
Isostatic change
A local rise or fall in land level
Eustatic change
Involves a rise or fall of water level caused by a change in volume of water. Global change, affects worlds connected seas and oceans.
Why is sea level change complex?
- both isostatic and eustatic change can happen at the same time
Why do sea levels change from day to day?
- high and low tides
- low atmospheric pressure causes slight increase in sea level
- winds push water towards coasts, wave height varies.
Emergent coast
Where a former seabed is exposed as sea level drops
How do isostatic and eustatic changes cause an emergent coast?
- Eustatic sea level fall caused by glacial periods and ice sheets on land lock water evaporated from the sea into ice at high altitudes.
- isostatic fall cause by a build up of land based ice sheets melting, causes land surface to rebound upwards over time
Submergent coast
Where the coastline is drowned.
How do isostatic and eustatic changes cause a submergent coast?
- Eustatic rise in sea level caused by melting ice sheets returning water to sea and causes a global sea level rise.
- As global temperature increases, causes the volume of ocean water to increase (thermal expansion), leads to sea level rise.
- Isostatic sea level rise caused when land sinks due to deposition of sediment. Weight of sediment deposition causes crustal sag.
Post glacial adjustment
refers to the uplift experienced by land when the weight of ice sheets is removed.
Emergent coastline example
West coast of North America
Submerging coast example
East coast USA
Features of an emergent coastline
Raised beaches reflecting previous sea levels
Submergent coasts landforms
- Ria
- Fjords
- Barrier island
Ria
Drowned rivier valleys in unglaciated areas, caused by sea level rise and flooding up the river valley, making it much wider than would be expected based on the river flowing into it.
Where can fjords be found?
Norway and Canada
How do fjords differ from rias?
- drowned valley is a u shaped glacial valley
- fjord is often deeper than adjacent sea
- at seaward end of the fjord, there is a submerged lip representing the former extent of the glacier that filled the valley.
Barrier Island
offshore sediment bars, usually sand dune covered, but not attached to the coast.
Where can barrier islands be found?
The east coast of the USA
How do barrier islands form?
- once coastal sand dunes attached to the shore
- sea level rise flooded land behind dunes, formed a lagoon, dunes not eroded so became islands.
Dalamtian coast and sea level rise
Consists of anticlines and synclines .
Post glacial sea level rise submerged the area, creating bays in areas that were once low-lying valleys.
Accretion
When sediment is added to a landform by deposition. Can build up to form new land, balanced by subsidence caused by the weight of the newly deposited sediment
How has sea level changed, or is changing?
- stable early 1800s
- started rising slowly, but accelerated after 1940, and is accelerating even faster now.
- expected to increase by 100cm by 2100
How has measuring sea level changed over time?
It has become more accurate as tide gauges and satellite measurements have became more accurate
Why is sea level difficult to predict?
- Thermal expansion depends on how high global temperatures rise
- melting of mountain glaciers will increase sea level rise
- melting ice sheets will increase sea level.
- can change locally due to tectonic forces, for example earthquakes can force land up or down
Thermal expansion
The main driver of sea level rise, occurs because the volume of ocean water increases as global temperatures rise
