Folding and Faulting Page 112

• What is FOLDING?

• Types of folds?

• Fold Mountains in the world and on the Western Cape

• What causes FAULTING

• Types: Normal / Reverse / strike slip

• SAN ANDREAS

Folding

• Occurs along convergent plate boundaries.

• Himalayas

• Deep layers of sedimentary rock laid down between the plates are squeezed and bent.

How do folds develop?

Activity 8: Folding• 1)

• 2a) Upward curving fold: Anticline

• 2b) A fold where the limbs area most horizontal : Simple Fold

• 2c) A downward curving fold: Syncline

• 2d) A step-like fold: Over fold

• 2e) A fold with one limb over the other: Recumbent fold

• 2f) A fold where a fault (break) occurs and one limb is pushed over the other : Overthrust fold

Limb

Compressional forces

Sedimentary layers

Activity 8: continued

•3) When rock layers are subjected to forces of compression, due to plates colliding (collision margin), the layers (strata) bend into folds

Range of fold mountains

Himalaya Mountains

Fold Mountain Ranges

Young Fold Mountains

• Found along plate boundaries .

• Formed 35 million years ago .

• Very rugged, steep slopes , deep valleys and very high ( 6000 m )

Old Fold Mountains

• Not on plate boundaries.

• 250 million years old.

• Formed when the continents were joined.

• Eroded for longer.

• Lower in altitude and less steep than young fold mountains.

Anticline erode away faster, because they are exposed and develop cracks which allow faster weathering of the rock

Eroded fold mountains

Synclinal mountain

Anticlinal valley

Anticline

Ho

mo

cli

na

l R

idg

es

Major fold mountains of the world

Activity 9: Fold Mountains, p 115• 1) The largest fold mountain ranges in the Cape Region are:

• Cederberg Mountain Du Toitskloof Mountains

• Olifants river Mountains Drakenstein mountains

• Piketberg Simonsberg

• Winterhoek Mountains Hottentots Holland mountains• Skurweberg Kogelberg

• Hex river mountains Stettynsberge

• 2) The Himalayas were formed when the northward-moving Indian plate collided with the Eurasian plate. The sedimentary rocks were compressed and forced to fold, building up the Himalaya mountains

Activity 9: continued

• 3a) Cape Fold Mountains

• 3b) Australian Alps

• 3c) Himalayas

• 3d) Atlas Mountains

• 3e) The Alps

• 3f) The Rockies

• 3g) The Andes

• 4) The Himalayas

• 5) Because it is the highest mountains in the world

Faults

• In unstable parts of the earth the crust is subjected to TENSION and COMPRESSION forces.

• When they crack or break it is called a FAULT .

• Fault line : the line along the surface where the break has occurred .

Types of faults:

A fault occurs

when the rock

breaks under

pressure.

Types of faults

• Normal Fault : tension forces pulling rocks apart / rocks are pushed down .

• Reverse fault : compression forces push rocks together / rocks are pushed up .

• Tear / Transform fault : tearing forces cause rocks to move past each other laterally .

Normal Fault

Reverse fault

Tear Fault

San Andreas Fault

Activity 10: Faults, page 117• 1) TENSION: When plates are pulled apart or stretched

• COMPRESSION: When plates squeeze rock strata (layers) together

• 2) Compression = Reverse Faults

• 3) Tension causes normal faults

• 4) Fold Mountains

• 5) See page 116

• 6) The North American Plates and the Pacific plates

• 7) April 2015: Nepal earthquake killed nearly 9000 people,

injured 22 000. 3,5 million people left homeless. It had a magnitude of 7,8 on the Richterscale. Estimated damage $10 billion). The earthquake triggered an avalanche on Mount Everest. Entire villages were flattened. Many aftershocks continued to cause death and destruction

Block mountains and rift valleys

• Faults usually occur in groups.

• When a block of land is uplifted between parallel faults a block mountain (horst) forms.

• When a block of land slips down between two parallel faults, a rift valley (graben) forms.

Rift valleys

The East

African

Rift valley

– lakes &

countries

Activity 11: Faulting, mountains and careers (p119)• 1)Horst: When land is pushed up between two faults. Rift valley: A valley

caused by the land sinking between two faults.

• 2) Lake Albert, Lake Edward, Lake Kivu, Lake Malawi. Lake Victoria

• 3) 1430m deep

• 4) Without terraces to level the land on steep slopes, there will be a large amount of erosion.

• 5) Mountainous areas with steep slopes attracts hikers and mountaineers. If there is snow, skiers will flock there.

• 6) Tree roots bind the soil and prevent the soil from being eroded. Also, the leaves of the trees break the force of falling rainwater, thus reducing the impact of falling raindrops

• 7) Positive: Tourism, forestry, hydro-electric power.

• Negative: cold climate, steep slopes, difficult to build roads and railway lines

• 8) It is interesting work, often outdoors with little time in the office, well paid, BUT: often long way from civilization (shops and schools) often in places with extreme climates