2B.4C + 2B. 6 a Coastal Erosional Landforms and Weathering Flashcards
coastal morphology
shape of coastline
cliff profile
characteristics and appearance of a cliff face
describe how wave-cut platforms are created
- as waves break at the foot of the cliff, a wave cut notch is created, which undercuts the cliff
- this is due to erosional processes such as hydraulic action and abrasion
- this becomes unstable and collapses as abrasion erodes the cliff
- the notch moves inland creating a shoreline platform
- the cliff will collapse, causing the cliff to receed and retreat backwards due to instability as the weight was too much. temporary rock armour forms at the base of the cliff.
briefly describe shoreline platforms
has a gentle slope, normally exposed at low tide
-absorb energy- act as a beach as they cause the waves to break earlier.
give an example of a shoreline platform
Southerndown Glamorgan in South Wales
give an example of a wave-cut platform
Flamborough Head in Yorkshire
describe how caves, arches, stacks and stumps are created
- joints, faults or vertically dipping bedding planes create weaknesses in the rock
- hydraulic action deepens and widens the weak points, forming a sea cave
- marine erosion deepens the sea cave, until a tunnel forms in the headland, forming an arch
- the undercutting leads to material collapsing- mass movement. additionally, weathering and sub-aerial processes attack the arch roof.
- it collapses and leaves a tall vertical column called a stack
- marine erosion at the base will cause a blockfall, a stump which is only exposed at low tide
give an example of a stack and stump
Old Harry’s Rocks, Handfast Point, isle of Purbeck in Dorset
(three chalk formations)
cliffs
-steep vertical rock faces at the edge of the sea
-chalk cliffs can lead to the formation of caves, arches, stacks and stumps
give an example of a cliff (reteating)
The White Cliffs of Dover
(chalk cliffs)
example of coastal retreat
describe how headlands and bays are formed
- they only form on discordant coastlines where there are alternate geology bands of hard and soft rock
- soft rock is more susceptible to erosion, so it erodes at a faster rate
- bays form where the waves erode soft rocks , but headlands are left as land that juts out into the water.
give an example of a headland and bay
Swanage Bay, Dorset
- the clay here erodes at a faster rate than the limestone and chalk
-between the two headlands Ballard Point an Durlston Head
what type of coastline do headland and bays form on? and why?
discordant coastline- differential erosion takes place
give 4 types of erosion
hydraulic action
abrasion (corrasion)
solution (corrosion)
attrition
describe hydraulic action
as water crashes into small cracks in the cliff, air gets trapped, it is compressed and expands, weakening the rock, leading to it breaking
describe abrasion/ corrasion
as the sea crashes into the cliff the rocks are hurled up against the cliff, becoming more rounded and smooth
describe solution (corrosion)
small pieces of sediment dissolve in the sea water, the acidic water dissolve minerals in the rock face (can cause a holey face)
describe attrition
as material in the sea bash into each other breaking into smaller fragments of rock as the collide in the water. this is how beach material is made.
explain the influence of lithology and geology with hydraulic action
-weaker rocks are eroded at a faster rate
-sedimentary rocks have many faults and weaknesses
explain the influence of lithology and geology with abrasion
rocks with bedding planes are very vulnerable
-high energy coastlines experience this with igneous rocks
-areas with an abundant supply of material suffer from this a lot
explain the influence of lithology and geology with solution
limestone experiencing solution as the calcium carbonate minerals dissolve in the acidic, salty sea water
-warm water increases the pace of this chemical reaction (corrosion)
explain the influence of lithology and geology with attrition
sedimentary rock such as sandstone is more susceptible to this as it breaks down into sand for beach material.
differential erosion
erosion that occurs at irregular or varying rates
-caused by the differences in the hardness and resistance of surface materials
complex cliff profiles
-produced where cliffs are composed of strata differing in lithology
-less resistant strata erodes and weathers faster, being cut back rapidly, for example wave cut notches may be formed.
strata
a layer of rock
what are joints
a fracture dividing rock into two sections, no movement
-they cut across bedding planes
what are faults
a crack across bedding planes, they come out of alignment as movement occurs
give reasons has to why cliff profiles vary
-lithology and integrity of rock in which the cliff is formed of
-direction in which the strata is dipping
-level of wave energy
-the role of subaerial erosion on the upper parts of the cliff face
what main factor does geology have on waves
wave refraction occurs as waves slow down in shallow water
-as waves hit headlands, the waves change angle
-energy is concentrated on headlands and dissipated onto the bays
weathering
the breaking or decomposition of rocks in situ, the breakdown is gradual and the process creates sediment which the sea can then use in erosional processes
Sub-aerial processes
Sub-aerial processes are land-based processes and occur above the waterline. They include weathering and mass movement, which happen on the cliff rocks.
what are the three types of weathering
mechanical/ physical
chemical
biological
what are the 3 main physical types of weathering
freeze-thaw
salt crystallisation
wetting and drying
describe the process of freeze-thaw weathering
water fills cracks in the cliff face, when the colder months come, the nights freeze, freezing the water. this causes it to expand, loosening the rock around it causing loose material (scree)- frost shattering.
describe the process of salt crysallisation
as salt water enters cracks in the rock, over warmer months, the water evaporates, leaving salt crystals to form and expand, weakening the sediment around it.
describe the process of wetting and drying
frequent cycles of wetting and drying on the coast crack and break up rocks such as clay and shells. -creates a holey rock surface appearance.
what are the 3 main types of chemical weathering
carbonation
hydrolysis
oxidation
describe the process of carbonation weathering
the slow dissolution of limestone due to rainfall, this dissolves the calcium carbonate, producing calcium biocarbonate in solution
-affects all carbonate rocks
describe the process of hydrolysis weathering
a new solution (a mixture of two or more substances) is formed as chemicals in rock interact with water
the breakdown of minerals to form new clay minerals, due to the effect of water and dissolved CO2- affects igneous and metamorphic rocks
describe the process of oxidation weathering
this is the addition of oxygen to minerals, particularly in iron compounds
-produces iron oxides and increases the volume contributing to mechanical breakdown e.g. sandstones, siltstones and shales
what are the 3 main types of biological weathering
plant roots
rock boring
animals
describe the process of plant root weathering
as tree and plant roots grow into small cracks in the rock faces, causing the rocks to break apart
-as the roots grow more, this occurs more
describe the process of rock boring
species of clams and molluscs bore into the rock face, secreting chemicals that dissolve rock
-this affects sedimentary rocks such as limestone in the inter-tidal zone (foreshore)
describe the process of animal weathering
different birds (e.g. puffins) and animals (e.g. rabbits) dig burrows into cliffs, causing rocks to break.
