Geography - Folding and faulting Flashcards
Folding
Bending of rocks into folds due to strong compressional forces.
When tectonic plates converge, the sedimentary rock along the plate boundaries becomes compressed and folding occurs.
The buckling of a rock layer that was once horizontal.
What are the main types of folds?
- Anticlines
- Synclines
Faulting
It is the result of the movement of the Earth’s plates. Faults occurs where there is stress along a weak point in the Earth’s crust.
In unstable parts of the earth the crust is subjected to tension, compression and lateral forces.
Fold Mountain
The resultant landforms associated with converging plates.
What are some examples of plate mountains?
Himalayas
Alps
Rockies
Andes
Cape Fold Mountains
How are fold mountains formed?
- A thick layer of sedimentary rock strata builds up on the ocean floor.
- Plate movements (convergent) slowly compress the rock strata causing the strata to form folds.
- Further plate movement closes the ocean basin and pushes the strata onto the land to form a range of mountains (fold mountains)
What landforms are associated with folding?
When rocks are first folded, the anticlines stand out as hills and the synclines form valleys.
What are the different kinds of folds?
- Symmetrical folds
- Asymmetrical folds
- Overtured folds
- Overthrust folds
Describe a symmetrical fold
They have equal limbs and usually indicate an equal amount of pressure from either side.
Describe an asymmetrical fold
They appear to lean to one side. Pressure may have been greater from one side.
Describe an overturned fold
The pressure is even greater on one side.
One limb is very steep.
Describe an overthrust fold
Occur when pressure causes the strata to fracture.
One side of the fold slides along the line of fracture called a fault.
Fault
One side of the fold slides along the line of fracture.
Cracks or fracture in rocks.
Fault line
The line along the surface where the break has occured.
What are the different kinds of faults?
- Normal faults
- Reverse faults
- Lateral faults
Normal fault
Tension forces (apart) / rocks are thrown down.
Reverse fault
Compression forces (together) / rocks are pushed up.
Lateral fault
Tearing forces cause rocks to move past one another laterally.
What landforms are associated with faulting
Rift Valley
What are the stages in the formation of a rift valley.
Tension stresses set up convection currents in the mantle causing the crust to crack.
A plume of magma may rise within magma and increase tension on the rocks of the crust, causing faulting.
The rift valley widens as the crust continues to move apart.
Block mountain
A block of land that has moved upwards along fault lines due to compression