8.2. Erosional Landforms

Question 1

Factors determining the nature of erosional landforms

Answer 1

1) Direction, strength, frequency of waves

2) Geology of the coastline

Question 2

Direction, strength, frequency of waves as a factor determining the nature of erosional landforms

Answer 2

• waves that break the foot of a cliff tend to be very powerful and often have great erosive power
• wave refraction can concentrate the waves on headlands so that they can be attacked from the side as well as head-on

Question 3

Geology of the coastline as a factor determining the nature of erosional landforms

Answer 3

• rock type and rock structure are important in determining the nature of the landforms that are produced
• the waves are able to exploit any weaknesses in the geology and it is where the rocks are weak that the greatest erosion tends to occur

Question 4

Cliffs

Answer 4

• common erosional landform

- over time cliffs retreat due to a combination of sub-aerial (weathering) and coastal erosion processes

Question 5

Cliff and Wave-cut platform Formation

Answer 5

• waves erode the base through processes of corrasion, hydraulic action and solution, until over time a wave-cut notch forms
• as the notch enlarges, the cliff face becomes undermined until at some point it collapses under its own weight
• attrition and transportation then remove the cliff debris leaving behind a small, flat bedrock shelf, which marks the old cliff line
• this process is repeated over time as the cliff retreats forming a larger wave-cut platform
• wave-cut platforms are characterised by their gentle sloping angle, hard bedrock and rock pools

Question 6

Concordant Coastline

Answer 6

coastlines where the same rock runs along the length of coast

Question 7

Disconcordant Coastline

Answer 7

coastlines where the rock type alternates between soft and hard rocks

Question 8

Landforms at Disconcordant Coastlines

Answer 8

• tends to lead to headland and bay formations
• cliff is subject to differential rates of erosion, due to bands of varying resistant rock types
• bays are sheltered, low energy zones that form in bands of weak geology (e.g. clays)
• here the cliff erodes at a faster rate
• bays are flanked by headlands which are exposed rocky outcrops positioned 90 degrees perpendicular to the bay
• headlands consist of more resistant rock (limestone)
• due to the way waves refract around headlands, destructive waves concentrate their energy on their sides and overtime develop unique coastal features such as caves, arches and stacks

Question 9

Formation of caves, arches and stacks

Answer 9

• any points of weakness in the headland’s rocks, such as faults and joints are eroded, particularly by hydraulic action and corrasion
• this is likely to lead to opening of a cave
• if a cave is enlraged and extends back through to the other side of the headland, possibly meeting another cave, an arch is formed
• continued erosion by the sea widens the arch
• as the sea undercuts the pillars of the arch, the roof is weakened and eventually collapses
• this leaves a stack separated from the headland
• further erosion at the base of the stack may eventually cause it to collapse
• this will leave a small, flat portion on the original stack as a slump
• it may only be visible at low tide

Question 10

Landforms at Concordant Coastlines

Answer 10

• the rock type lies parallel to the shore
• at first this presents a minimal variety of rocks for the sea to erode
• differential erosion usually results, from the wearing away of a joint or a fault line which acts as a weakness for sea to develop into a cove
• a cove is a small type of bay that has a narrow entrance and is often circular or oval
• over time neighbouring coves can coalesce (join) by erosion to form a wide bay
• residual (leftover) parts of the original harder rock form stacks

Question 11

Real Life example of a cliffed coastline

Answer 11

• found facing the Andaman Sea, in Krabi
• termed as a “karst coastline”
• formed from limestone rock