Enquiry Question 1 - Key Idea 3 Flashcards
Rates of coastal recession and stability depend on lithology and other factors
What is Key Idea 3?
Rates of coastal recession and stability depend on lithology and other factors
Meaning of rates of recession:
How fast a coastline is moving inland.
What are the three rock types:
- metamorphic
- igneous
- sedimentary
Examples of igneous rock
- Granite
- Basalt
- Dolerite
Examples of metamorphic rock
- Slate
- Schist
- Marble
Examples of sedimentary rock
- Sandstone
- Limestone
- Shale
What is the lithology of igneous rock?
They are crystalline with interlocking crystals
What is the structure of igneous rock?
Rocks such as granite have a few joints so there are limited weaknesses
What is the erosion rate of igneous rock?
Very slow. The interlocking crystals make for strong, hard erosion-resistance rock.
Rocks such as granite have few joints, so there are limited weaknesses.
What is the lithology of metamorphic rock?
Crystalline. Many exhibit a feature called foliation, where crystals are all orientated in one direction (producing weaknesses)
What is the structure of metamorphic rock?
They are often folded and heavily fractured
What is the erosion rate of metamorphic rock?
Slow. They are resistant to erosion. Many exhibit a feature called foliation, where crystals are all orientated in one direction (producing weaknesses). They are also often folded and heavily fractured, which are weaknesses that erosion can exploit.
What is the lithology of sedimentary rock?
Clastic and are younger than igneous and metamorphic rock.
What is the structure of sedimentary rock?
Tend to have many bedding planes and fractures e.g shale. The weakness materials is known to be unconsolidated sediment. However, some limestones and sandstones are actually crystalline sedimentary. They have been compressed and compacted over hundreds of millions years.
What is the erosion rate of sedimentary rock?
Moderate - fast. Geologically younger rocks are weaker and therefore erode faster.
Permeable rocks:
Allows water to flow through the rock.
- Includes many sandstones and limestones
Impermeable rocks:
Do not allow groundwater flow
- Include clays, mudstones, and most igneous and metamorphic rocks
Permeability is important because…
groundwater flow through rock layers can weaken rocks by removing the cement that binds sediment in the rock together.
+ can create high pore water pressure within cliffs - affects stability
+ water emerging from below ground onto cliff face at a spring can run down a cliff face and cause surface runoff erosion, weakening the cliff
+ groundwater flow and pore water pressure can cause slumping in unconsolidated sediments on the cliff top
Pore water pressure:
The pressure water experiences at a particular point below the water table due to the weight of water above it