Folding (advanced)

Folding (advanced)

Lateral compressive forces cause rocks to form folds. This is how fold mountains are formed.

Geography

Keywords

folding, fold, synclines, anticline, syncline, fold mountain, mountain formation, plate tectonics, sedimentary basin, sediment, tectonic plate, compressive force, rock, mountain, rock layer, nature, geography

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Scenes

Folding

  • vertical fold
  • overturned fold
  • recumbent fold
  • overthrust fold

In sedimentary basins there are several different layers of sediment. These sediments are plastic, due to their large water content, and there is a huge amount of water above them.
If this sedimentary basin is on the boundary of converging tectonic plates, lateral compressive forces affect it from opposite directions, squeezing these layers.
Folds are formed, which consist of convex anticlines and concave synclines.
The opposing forces, however, are rarely of equal strength. When the compression is stronger on one side, the anticlines (peaks) and synclines (troughs) become asymmetric, and the anticlines begin to ‘lean’ over the synclines.
As the compressing force gets stronger, it can topple over the anticlines. These are called recumbent folds. Continued pressure pushes recumbent folds along over the synclines. These are called overthrust folds.
When the folds are formed in a chain, fold mountain chains are created.

Definitions of terms:

Folding: a geological process, lateral compressive forces creating folds in the Earth's crust, resulting in folded structures

Fold: the basic unit of the folding process

Fold mountains: mountains formed mainly by the effects of geological folding

Vertical fold

  • layers of rock
  • lateral compressive forces

Overturned fold

  • layers of rock
  • smaller lateral compressive force
  • greater lateral compressive force

Recumbent fold

  • layers of rock
  • smaller lateral compressive force
  • greater lateral compressive force

Overthrust fold

  • layers of rock
  • smaller lateral compressive force
  • greater lateral compressive force

Animation

  • lateral compressive forces
  • smaller lateral compressive force
  • greater lateral compressive force
  • smaller lateral compressive force
  • greater lateral compressive force
  • smaller lateral compressive force
  • greater lateral compressive force
  • vertical fold
  • overturned fold
  • recumbent fold
  • overthrust fold

Narration

Lateral compressive forces acting on plastic rock cause the rock layers to move upwards or downwards and thus to form anticlines and synclines.

Sometimes the compressive forces are equal. When this occurs, a symmetrical fold is formed, this is also called a vertical fold.

When the compression is stronger on one side, an overturned fold is formed. The axis of overturned folds leans at a small angle from the vertical.

When one of the lateral forces is much greater than the other, the angle becomes greater too, and a recumbent fold is formed.

When one of the lateral forces is so much greater that the rock layers are broken and one slides over the other, an overthrust fold is formed. These overthrust folds can reach a width of about a hundred kilometres.

The Alps and the Carpathian mountains were both formed in folding processes.

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Lateral compressive forces cause rocks to form folds. This is how fold mountains are formed.

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