Geological structure Flashcards
What is geological structure?
Geological structure is the arrangement of rocks in three dimensions. There are three elements to geological structure.
What are the three elements to geological structure?
Strata
Deformation
Faulting
What is strata?
The different layers of rock exposed in a cliff
What is deformation?
Tilting and folding by tectonic activity
What is faulting?
Major fractures that have moved rocks from their original positions
Geological structure produces which two main types of coast?
Concordant (or Pacific) coasts
Discordant (or Atlantic) coasts
What is a concordant coast?
When the rock strata run parallel to the coastline
What is a discordant coast?
When different rock strata intersect the coast at an angle, so rock type varies along the coastline.
What are discordant coastlines dominated by?
Headlands and bays
Less resistant rocks are eroded to form bays whereas more resistant geology remains as headlands protruding into the sea.
What happens at discordant coastlines?
Rock strata meet the coast at 90 degrees in parallel bands.
Weak rocks have been eroded, creating elongated, narrow bays.
More resistant rocks form headlands
Especially resistant areas remain as detached islands.
What effect do discordant coasts have on wave crests?
In deep water wave crests are parallel
As water shallows towards the coast waves 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 effect of wave refraction is to concentrate powerful waves at headlands (so greater erosion) and create lower, diverging wave crests in bays so reducing erosion.
What is wave refraction?
Wave refraction is the process causing wave crests to become curved as they approach a coastline.
What is the most well-known example of a concordant coast?
Lulworth Cove.
What happens at Lulworth Cove?
The hard Portland limestone and fairly resistant Purbeck Beds protect much softer rocks landward (the Wealden and Gault beds).
Marine erosion has broken through the resistant beds, and then rapidly eroded a wide cove behind.
There is resistant chalk at the back of these coves, which prevents erosion further behind.
What is the geology at the Dalmatian Coast in the Adriatic Sea?
The geology is limestone.
The limestone has been folded by tectonic activity into a series of anticlines and synclines, that rend parallel to the modern coastline.
