KQ3 Coasts Flashcards
What are eustatic changes?
Changes in the global volume of water
What are isostatic changes?
Changes in land level, localised effect
What are 2 major contributors impacting eustatic changes?
Thermal expansion and ice melt
What are 4 factors affecting global temperatures and volume of water in the oceans?
- Changes in the earths orbit around the sun, altering about every 400000 years
- Changes in the tilt of the earths axis, changing about every 41,000 years
- variations in solar output, where solar radiation peaks every 11 years or so
- changes in atmospheric composition, due to major volcanic eruptions
Describe how a decrease in global temperatures is directly linked to a decrease in sea level
When temperatures decrease, more precipitation falls in the form of snow, which upon reaching the ground, turn into ice and water is stored in solid form rather than being returned into the ocean store, result is a reduction in global sea levels.
1 degree Celsius fall in temperatures causes global sea levels to…
drop by approximately 2m
Give an example of an inter glacial period and a glacial period, and the contrasts in global temperatures and sea level
- Tyrrehenian inter-glacial period- 130,000 years ago, temperatures estimated at 3 degrees Celsius higher than today, with 20m higher sea level
- Riss glacial period- about 103,000 years ago, temperatures averaged at 7 degrees celsius lower than today, with sea levels also 83m lower .
What are emergent landforms?
Formed by wave processes, and left exposed as sea levels fell, and as a result may be found further inland from the present day coast
Describe how raised beaches are formed along side abandoned cliffs and marine terraces?
-Raised beaches are area of former shore platforms, formed during times of higher sea level, they are found a distance inland from the coast. Behind the feature, its not uncommon to find abandoned cliffs with wave cut notches, caves and even arches.
-Marine terraces although, are at a much larger scale than raised beaches which are often localised at the base of relic cliffs
What is the similarity between raised beaches, marine terraces and relic cliffs?
They all form similarly by marine erosion, but marine terraces are often at a much larger scale
Give an example of emergent landform with relic cliffs and raised beach. Explain when it was formed and the erosion rates
On the isle of Portland, Dorset, there is an example of an emergent landform thought to have formed about 125K years ago during the Tyrrehenian period, at a height of about 15 m above present day sea level. Portland limestone though to have been eroded partly by hydraulic action, with estimated erosion rates of 1m/year
How are emergent landforms impacted by geomorphic processes in the modern day?
By mass movement and weathering although not substantially by wave processes any more
What evidence from Portland shows us that there were periglacial conditions?
On the top of the abandoned cliff, there is a 1-1.5 meter layer of frost shattered limestone debris deposited in the last periglacial conditions, cliff was gradually eroded by weathering and there is also evidence of other periglacial conditions such as cryoturbation
How have warmer conditions modified emergent landforms at isle of portland?
Warmer and wetter conditions have led to the growth of vegetation, more difficult to recognise
How is climate change expected to impact emergent landforms?
Degradation perhaps more likely, with enhanced chemical weathering, such as carbonation of limestone cliffs and platforms
what is the link between sea level rise and temperatures rising?
An increase in global temperatures leads to a rise in ice melt from ice caps and valley glaciers, and a consequent rise in global sea levels as more water is added to the global ocean store
an 1 degree Celsius rise in temperature leads to
rise in mean global sea level by 2 m approximatley
an 1 degree Celsius rise in temperature leads to
rise in mean global sea level by 2 m approximately
What is the flandarian transgression?
At the end of the Wurm glacial period, about 25,000 years ago, temperatures were about 9 degrees Celsius lower than today with sea levels about 90m lower, since then as sea levels have risen as global temperatures have raised, this period of significant sea level rise is also known as the flandarian transgression
What are rias?
Rias are submerged river valleys, mainly in the lower part, forming as sea levels rise, the floodplains may be completely drowned but the upper part of the valley is usually exposed
Describe the profile of rias
They contain relatively shallow water, and become increasingly deeper towards the center, exposed valley sides are often gently sloping
Give an example of a ria, and explain when it was formed
There are a few, e.g. the Kingsbridge exhibits this, formed during the Flandarian transgression.
Describe the process of deposition in a ria
- rias are usually underlain by alluvial deposits buried channel eroded by rivers that flowed to the lower sea levels of Pleistocene glacial periods
-during interglacial periods when sea levels rose, further deposition would of occurred as the rivers had less surplus energy for erosion
Why does water at the Salcombe ria have shallow water?
Due to a sand bar deposited at the low energy environment of the entrance at the mouth of the Kingsbridge estuary
What are fjords?
Submerged glacial valleys of U-shaped
What is the depth of fjords?
They are quite uniform in terms of depth and ca reach up to 1000m
How does sogne fjord in Norway compare to that in Scotland?
Over 200km long, however those in scotland are often less developed as the ice was not as thick during the glacial period
How does the planform of fjords compare to that of rias?
They are often straighter, than rias as the glacier would have truncated any interlocking spurs present
Give an example of how sediment supply has increased due to fjords.
Example: west coast of south island, NZ, glaciers meltwater has increased sediment supply in the area as glaciers have receded
Describe how shingle beaches form
As sea levels decreased and volume of land-based ice grew, ‘new’ lands emerged, sediment accumulated on the surface from rivers, and low energy waves and as sea levels rose at the end of the last glacial period, these sediments were pushed onshore and in some places they beached at the base of former cliff lines
Explain how the tombolo at Chesil beach formed
Believed to have formed during the Flandarian Transgression, sediment carried into the English Channel by meltwater during the Wurm glacial accumulated in places such as Lyme bay, travelled about 50km by southwestern prevailing winds before attaching with the Isle of Portland and mainland
How much sediment is found at Chesil beach?
Roughly 100 million tonnes ranging from 1-2 cm to 5-7cm
How may the steep valley sides of Fjords be modified in the future?
Reduction in the steepness by the operation of sub-aerial processes or present day and future climatic conditions
How much sea levels expected to rise by in the next 100 years?
0.6 m, with perhaps greater marine erosion due to climate change causing stormier conditions
What is the rate at which shingle will move across the beach and how will the tombolo at Chesil beach be effected by future climate change?
Shingle may move at a rate of 17cm/ year towards northeast, with a breach likely during storm surges
1n 2009, 1-meter sized shelly clay were eroded and moved up to the beach at
West Bexington in a winter storm
