2.2 Geological Structure

Question 1

What is geological structure?

Answer 1

• it refers to how the rock is arranged on a macro scale (sometimes meso)
• it looks at the arrangement of different rock types in relation to each other

Question 2

What is a concordant coastline?

Answer 2

In a concordant coastline layers of rock strata lie parallel to the coast
They form coves, Dalmatian coast, Haff coasts

Question 3

How does a cove form?

Answer 3

• in a concordant coastline destructive waves hit the coastline, particularly in winter, and result in hydraulic action and abraision, attaching joints and faults in the resistant rock (e.g. limestone)
• eventually the waves erode through to the less resistant clays behind the limestone
• erosion is now rapid in all directions
• eventually, erosion slows down as the more resistant chalk layers are reached and a cove has been produced
• e.g. lulworth cove

Question 4

How do Dalmatian coasts form?

Answer 4

• tectonic activity folded limestone layers so that anticlines (ridges) and syclines (valleys) formed parallel to the coast
• following the end of the ice age the sea levels rose and drowned the valleys creating a submerging coastline
• e.g. the Dalmatian coastline of Croatia

Question 5

How do Haff coastlines form?

Answer 5

• they are long sediment ridges (sand and mud) topped by sand dunes that run parallel to the coast
  The build up of these have created lagoons (haffs) between them and the shore
• they are concordant e.g. the south coast of the Baltic Sea

Question 6

What is a discordant coastline?

Answer 6

Where layers of rock strata run perpendicular to the coast forming headlands and bays

Question 7

How do headlands and bays form on discordant coastlines?

Answer 7

• wave action eroded the less resistant rock quicker due to hydraulic action and abrasion to produce bays
• the more resistant rock is left sticking out as a headland. This causes incoming waves to refract (bend) as water becomes shallower (wave refraction)
• wave energy is now concentrated in the headland and waves become higher and steeper increasing their erosive power
• the bays become sheltered as wave energy is dissipated
• this results in the formation of beaches as sediment is deposited in the low energy environments
• e.g. swanage bay

Question 8

What is meso scale?

Answer 8

• medium

- smaller stretches of cliffs and their layers / lithology

Question 9

What is micro scale?

Answer 9

• one cliff and it’s profile + features

Question 10

How does vertical joints and faults have an effect on coastal recession?

Answer 10

• verities last cracks are produced by contraction or tectonic earth movements
• joints are opened by weathering (biological and chemical e.g. tree roots or guano) and pressure release
• a slight seaward dipping bedding plane can increase the recession rate as gravity speeds up weathering and mass movement

Question 11

How does having rock strata effect the rate of coastal recession?

Answer 11

• rock is made up from layers of sedimentary rock
• horizontal cracks can easily form between strata
• these produce steep cliffs which are relatively stable but can lead to differential erosion at the base and further up the cliff if layers are weak enough
• recession rate is quicker if softer layers are at the base as wave cut notches can form

Question 12

How do landward dipping bedding planes affect the rate of coastal erosion?

Answer 12

• the produce a stable, steep cliff profile which decreases recession rate
• this is exacerbated if there are well developed joints at right angles to the bedding planes as the joints act as slide planes

Question 13

How do seaward dipping bedding planes affect the rate of coastal recession?

Answer 13

• they can be unstable because rock slabs can easily slide along the bedding planes
• this increases the rate of coastal recession