Enquiry Question 1 - Key Idea 2 Flashcards
Geological structure influences the development of coastal landscapes at a variety of scales.
What is Key point 2?
Geological structure influences the development of coastal landscapes at a variety of scales.
What does geological structure include?
It refers to the arrangement of rocks in 3D. It includes
- strata
- deformation
- faulting
Strata
The different layers of rock within an area and how they relate to each other
Deformation
The degree to which rock units have been deformed (tilted or folded) by tectonic activity
Faulting
the presence of major fractures that have moved rocks from their original positions
What two coastlines do geological structure form?
- concordant
- discordant
What is a concordant coastline?
Coastlines where one rock type runs parallel to a stretch of coastline
What are discordant coastlines?
Coastlines where alternating strata of differing rock types run perpendicular to the coastline
What is morphology?
The shape of the landscape features. It is influenced by geological structure (headlands and bays, Dalmatian and Haff).
What landforms are formed along a concordant coastline?
- Dalmatian coastline
- Coves
- Haff coastlines
Formation of Haff coastlines:
CC
- During the last glacial period (Devensian), the sea level was about 100m lower than today as water was retained in huge ice sheets.
- Meltwater rivers on land beyond the ice front deposited thick layers of sand and gravel, creating outwash plains. The deposition produced geological structure parallel to the coastline.
- In the Holocene, 12,000 yrs ago, Interglacial constructive waves pushed the ride of sands and gravel landwards as sea levels rose.
- Sand ridges formed bars across some bays and river mouths with trapped river water- forming a lagoon behind, called Haffs.
Formation of Dalmation Coast
CC
- Two tectonic plates push towards each other, compressing the crust to create folds.
- The folds have anticlines and synclines
- Post glacial sea level rise has submerged the synclines leaving the anticlines sticking up parallel to the coast.
Formation of Lulworth Cove
CC
- It is on a landscape of alternating bands of geology that lay parallel to the coastline, horizontally organised.
- Weaknesses in the layered rock (clay) are exposed to marine processes so are targeted and broke down by erosional processes.
- The cove is formed out of the landscape after it gets behind the clay.
It is unable to erode further due to the different type of rock behind it (chalk)
2 examples of a Discordant coastline
- Swanage Bay
- West Cork, Ireland
Formation of Swanage Bay
DC
- There are alternating bands of rock types (hard and soft) perpendicular to the coast.
- This is significant due to there being different levels of erosion
- The headland absorbs all the wave energy due to wave refraction
- As the wave gets more shallow, the wave experiences friction with the sea bed and breaks.
- Wave refraction occurs once headlands and bays exist because the headlands cause the wave to break due to the shallower water around them.
- Handlands absorb wave energy
- Rates of erosion are drawn towards the headlands; deposition occurs inside the bay - making a beach
Formation of West Cork, Ireland
DC
- Limestone eroded by waves but also verticle fluvial processes in the past creating a river valleyin the Bantley Bay coastline - (now inundated)
- As sea levels have risen, the river valley has been submerged - making the bay long and narrow
- Rivers eroded the softer rocks to form valleys
- Rising sea levels drowned the valleys
- Since then, marine erosion has continued to erode headlands and bays forming a Ria
West Cork, Ireland coastline description:
- South west of the UK
- Waves are more powerful
- It faces Bantry Bay, where it experiences high wave energy due to waves travelling through the Atlantic ocean with a large fetch
Holocene:
The geological epoch that began about 12,000 years ago at the end of the last Pleistocene ice age. Its early stages were marked by large sea level rises of about 35m and a warming interglacial climate.
How are coastlines ‘smoothed’ over time?
Because headlands are eroded more than the bays. This happens when:
- in deep water wave crests are parallel
- as waves approach the shallower water offshore of a headland, they slow down and wave height increases
- in bays - wave crests curve to fill the bay and wave height decreases
- the straight wave crests refract, becoming curved, spreading out in bays and concentrating on headlands
- the overall effect of wave refraction is to concentrate powerful waves at headlands (meaning greater erosion) and create lower, diverging wave crests in bays, reducing erosion
What are cliff profiles influenced by:
- the resistance of the rock to erosion
- the dip of rock strata in relation to the coastline
Dip:
the angle of rock strata in relation to the horizontal
Horizontal dip:
Vertical or near vertical profile with notches reflecting strata that are more easily eroded
Seaward dip, high angle:
Sloping, low angle profile with one rock layer facing the sea
- vulnerable to rock slides down the dip slope
Seaward dip, low angle:
Profile may exceed 90* producing areas of overhanging rock
- very vulnerable to rock falls
