Erosional landforms - P Flashcards
What are erosional landforms
Landforms created by erosional processes
Define bay
a recessed, coastal body of water which is partially surrounded by land
Define headland
an area of usually more - resistant rock which extends into the sea, surrounded by water on 3 sides
define cliff
a steep, often m vertical or overhanging, face of rock
define shore platform
a flat or gently sloping rock surface found at the base of cliffs
Define geo
a narrow steep-sided inlet
Define blowhole
a vertical shaft between a cliff top and a cave, where spray from waves may burst out of during storm conditions
define cave
a natural opening in a cliff face, large enough for humans to explore
define arch
a wave - eroded passage through a small headland
define stack
a steep and often vertical column of rock in the sea
Define stump
a short, eroded remnant of a sea stack that juts above the sea surface
How to bays and headlines usually form
Adjacent to each other - usually due to the bands of rocks
What is a disconcordant coastline
when the rocks are perpendicular to the coastline so the weaker rocks are eroded to form bays while more resistant rocks remain as headlands
What is a concordant coastline
when rocks lie parallel to the coastline, more resistant rocks could protect softer rocks inland - usually a straight coastline.
What is the width and depth of bays determined by
- width of band of weaker rocks
- differential rates of erosion
What is wave refraction
is more significant where bays and headlands form
What is an orthogonals
imaginary lines, perpendicular to wave fronts, representing the transfer of energy as a wave moves towards the coast
Explain wave refraction
- waves refract around the headland causing orthogonal to converge and wave energy too be focused on the headland
- in bays the orthogonal diverge and the energy is dissipated leading to deposition
Can bays and headlands be formed on concordant coasts
Yes but usually they are small - e.g. Lulworth Cove, Dorset - the limestone has been eroded through the softer clays to form a cove
Why do cliff profiles vary
They depend on the geology
Which two types of cliffs have a near vertical profile
- horizontally bedded strata
- landward dipping strata
Which type of cliffs has the profile following the angle of the strata
- seaward dipping strata
What causes the horizontally bedded strata to be near vertical
Undercutting leads to rockfall and rocks retreating inland parallel to the coast
What causes the landward dipping strata to be near vertical
rocks are loosened by weathering and are difficult to dislodge so the profile is gradually lowered by weathering and mass movement
What causes the seaward dipping strata to follow the angle of the dipping strata
Undercutting removes the basal support - rock layers loosened by weathering slide into the sea along the bedding plane
Explain how a shore platform is formed
- destructive waves cause undercutting between low and high tides, forming a wave cut notch
- continued undercutting weakens support off rock above so it collapses
- regular removal of debris means cliff retreats and is steep
- as the process continues the cliff becomes higher
- at the base a gently sloping shore platform is formed
When is a shore platform exposed
during Low tide
What process eroded shore platforms the most
abrasion as there is a lot of rock debris thats dragged across the surface by wave action
What stops the undercutting of a cliff (shore platform)
- as they become wider, friction slows approaching waves causing them to break before reaching the cliff
- this slows down and eventually stops undercutting
How wide does the shore platform have to be to stop undercutting of the shore platform
usually 500m away from the cliff
What types of weathering are key process in the formation of a shore platform
- solution, freeze thaw and salt crystallisation take place depending on rock type and climate
- algae can accelerate weathering when exposed at low tide
- algae makes water more acidic by releasing CO2 (chemical weathering)
How do shore platforms usually slope
slope seawards between 0 and 3 degrees
When is erosion concentrated in one location
during low and high tide
What is formed due to concentrated erosion at the low water mark (LWM) and high water mark (HWM)
- a ramp at the HWM
- A small cliff at the low water mark
When do cliffs and ramps form better
when the tidal range is less than 4m
Why is a higher tidal range that 4m worse at forming ramps and cliffs
the erosion is spread over a larger area of the platform
What are goes
narrow, steep sided inlets - occur even on coasts with resistant geology as there can be lines of weakness
Explain how geos form
- weak points are eroded more rapidly by wave action that the more resistant rock around them
- this continues until a steep sided inlet is formed
What is a key process in the formation of a geo
hydraulic action - as forcing air and water into the joins will weaken the rock strata
What is an example of a geo
Huntsman’s Leap - Wales is 35m deep in Limestone
How is a blowhole formed
when part of a tunnel-like cave collapses along a master joint, it may form a vertical shaft that reaches the cliff top
what happens to a blowhole ion storm conditions
water may spray out of it in plumes of white aerated water
What is unique about the size of blowholes
they are usually quite small but large in diameter
What is an example of a blowhole
Trevone, Cornwall - 25m deep and 25m wide
Where do a caves, arches, stacks and stumps tend to form
- develop around headlands - and represent the erosional stages
Explain how a cave is formed
- due to wave refraction, energy is concentrated on the sides of headlands
- points of weakness, such as faults or joints are then exploited by erosional processes
- a small cave may develop one one side or even both
Where do caves usually form
between high and low tide levels as wave attack is more concentrated here
Explain how an arch is formed
if a cave enlarges to an extent that it extends through to the other side of the headland (possibly meeting another cave) an arch is formed
Explain how a stack is formed
continued erosion widens the arch and weakens its support, weathering processes may cause the arch to collapse, leaving a stack isolated form the headland
Explain how a stump is formed
further erosion at the base of the stack may eventually cause further collapse, leaving a small, flat portion of the original stack as a stump (may be only visible at low tide)
What is an example of caves, arches, stacks and stumps
Old Harry Rocks, Isle of Purbeck
