Chapter 9Folding and Faulting

Mountains• Large landforms with steep slopes and heights of

above 600m• Two types – fold mountains and block mountains• They differ in formation, characteristics and appearance

Chapter 9: Folding and Faulting

Himalayas fold mountains

Folding• Process in which rocks are bent and crumpled due to

compressional forces arising from the convergence of two plates

• Results in the formation of fold mountains

Fold mountains• Fold mountains are the highest mountains on the

earth’s surface• Mount Everest is an example of a fold mountain• It is the highest mountain in the world with a height of

8,850m and is part of the Himalayan mountain range

Chapter 9: Folding and Faulting

Chapter 9: Folding and Faulting

Mount Everest

Case study: Himalayas• Mountain range in Asia between the Indian subcontinent

and the Tibetan Plateau• Formed as a result of collision between the Indian

continental mass on the Indo-Australian Plate and the Asian continental mass on the Eurasian Plate

• The two land masses were once separated by the Tethys Sea

• When the two plates collided, the oceanic crust of the Tethys Seas subducted beneath the Eurasian Plate.

• The Eurasian Plate was compressed and the sedimentary layer was uplifted to form the Himalayas

• The Himalayas are considered young mountains as they began to form about 50 million years ago, which is relatively recent on a geological time scale

Chapter 9: Folding and Faulting

Chapter 9: Folding and Faulting

Indo-Australian Plate and Eurasian Plate moving towards each other

The sea disappears, the Himalayas emerge from the sea, convergence continues

The sea bed is bent into a series of folds

Types of folds• Different types of folds are formed depending on the

strength of the compression

Chapter 9: Folding and Faulting

Symmetrical fold Asymmetrical fold

Chapter 9: Folding and Faulting

Overthrust fold Nappe

Overfold Recumbent fold

Case Study: Blue Mountains of Jamaica • The Blue Mountains of Jamaica are evidence of past folding

with much subsequent erosion of the rock strata

Chapter 9: Folding and Faulting

Faulting• Process in which rock masses move along fractures in

the Earth’s crust• These fractures are called faults• Three types of faults

– Normal fault (vertical movement)– Reverse fault (vertical movement)– Transform fault (horizontal movement)

Block mountains and Rift Valleys• A complex system of block mountains and rift valleys

may form as a result of varying vertical displacement of different blocks of rocks

Chapter 9: Folding and Faulting

Chapter 9: Folding and FaultingNormal fault

Reverse fault

Transform fault

Block mountains• Uplifted blocks with steep slopes• Formed by vertical displacement of rocks at normal faults

(tensional forces) and reverse faults (compressional forces)

Chapter 9: Folding and Faulting

Rift valleys• Elongated areas that

have subsided between two block mountains

• Deep, with steep walls• Formed at normal faults

(by tension) and reverse faults (by compression)

Chapter 9: Folding and Faulting

Formation of rift valley by tension

Chapter 9: Folding and Faulting

Formation of rift valley by compression

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Case study: Great Rift Valley

• Extends 4,800km from Syria to Mozambique

• Consists of several well-developed rift valleys, some of which contain lakes

• The valleys have precipitous sides which are fault scarps

• Formed by violent tectonic forces that tore apart the Earth’s crust

Chapter 9: Folding and Faulting

• During the tectonic movements, large parts of the crust sank between parallel fault lines and molten rock was forced up in volcanic eruptions

• Rifting continues today, with many active and semi-active volcanoes and hot springs along the Rift

Chapter 9: Folding and Faulting