CON

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PLA

TES

CONVERGENT PLATE BOUNDARIES• Two plates moving towards each other and

collides• Denser (heavier) plate will go below the less

dense (lighter) plate • Process is called SUBDUCTION • Subducted plate sinks into the mantle and melts

due to high heat

1. Convection current

2. Slab pull force

Why do tectonic plates move?

Plates moving away from each other

Plat

es

mov

ing

tow

ards

ea

ch

othe

rP

lates

moving

towards

each other

Plates

Ocean floor

REVISION

1. Convection currents•Convection currents are movements of heat within the mantle.•Material in the mantle is heated by the core.•Mantle expands, rises and spreads out beneath the plates.•Plates are dragged along and move away from each other. (DIVERGENT PLATES)

• When denser plate subducts under less dense plate

• It pulls the rest of the plate along

• The subducting plate drives the downward-moving portion of convection currents.

2. Slab-pull force

Oceanic trench

Fold mountains• Over millions of years, the folding of rocks creates a

landform called fold mountains. • The Himalayas, the Rocky Mountains and the Andes

are examples of fold mountains.

Fold mountainsThe Himalayas

Peak : Mount Everest (between Nepal and Tibet)Elevation : 8,848 metres

• The compressional force causes the layers of rocks to buckle and fold.

• This process is known as folding.

P54 Q8P54

• 2m (diagram) , 0.5m for each point below• Two continental plates may collide with one

another, resisting subduction. • This causes the plates to break and slide along

fractures in the crusts.• When continental Eurasian plate converge with

continental Indian plate,• the crusts are compressed and they fold upwards

or sideways to form fold mountains

8 With the aid of a well-labelled diagram, explain the formation of fold mountains at a continental-continental plate boundary. [4]

• The upfold is called the anticline and

• The downfold is the syncline.

Fold mountains

• When there is increasing compressional force on one limb of a fold, the rocks may buckle until a fracture forms.

• The limb may then move forward to ride over the other limb

Fold mountains

• Fold mountains are located along convergent plate boundaries

QUIZ! Fold mountains

Label Mountains A - H

HomeWork – P56

With the aid of a well-labelled diagram, account for the formation of the Mariana Islands and the Mariana Trench. [5]

–Diagram 2 marks•0.5m for each labelling/drawing

–Explanation 3 marks•0.5m for each point

Convergent plate boundaries

1. Oceanic–oceanic plate convergence

2. Continental–oceanic plate convergence

3. Continental–continental plate convergence

CON

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1. Oceanic–Oceanic plate convergenceE.g. the Pacific Plate converging with the slower-moving Philippine plate. Earthquakes may also occur.

P56 With the aid of a well-labelled diagram, account for the formation of the Mariana Islands and the Mariana Trench. [5] -Diagram 0.5m each-Subducted plate, ‘Mariana Trench’, ‘Mariana Islands’, Magma rising

P56 With the aid of a well-labelled diagram, account for the formation of the Mariana Islands and the Mariana Trench. [0.5m each]

a) As the magma cools and sinks, the Pacific plate and the Philippines plates are pulled together/converge.

b) When the two oceanic plates converge, the denser Pacific plate subducts under the Philippines.

c) A subduction zone forms, creating a deep oceanic trench (Mariana Trench).

d) The subduction of the oceanic plate causes the solid mantle material to melt and magma is formed.

e) The magma rises through the mantle and ocean floor to emerge as volcanoes.

f) Eventually a chain or arc of volcanic islands called island arc is formed (Mariana Islands).

2.Oceanic-continental plate convergence

E.g. the Australian Plate subducting under a section of the Eurasian Plate near Sumatra formed the Sunda Trench.

2.Oceanic-continental plate convergence

QUIZ 1 P55 With the help of Fig. 8, describe the phenomenon and the formation of its resultant landforms. [5]

With the help of Fig. 8, describe the phenomenon and the formation of its resultant landforms. [5]

• The oceanic crust and the continental crust are __________________ towards each other.

• The denser and heavier oceanic crust _______________ into the mantle and melts into magma under the high heat.

• A long, narrow and deep depression called an _____________is formed at the subducted zone.

• Magma rises up the factures caused by the plate convergence and ____________to form volcanoes.

• Over time, more and more volcanoes build up to form a volcano ________.

P55 With the help of Fig. 8, describe the phenomenon and the formation of its resultant landforms. [5]

• The oceanic crust and the continental crust are

converging/moving towards each other.• The denser and heavier oceanic crust

sinks/subducts into the mantle and melts into magma under the high heat.

• A long, narrow and deep depression called an oceanic trench is formed at the subducted zone.

• Magma rises up the factures caused by the plate convergence and cools and solidifies to form volcanoes.

• Over time, more and more volcanoes build up to form a volcano arc.

3. Continental – continental convergence

Continental crust

Continental crust

Himalayas

Tibetan Plateau

Uppermost mantle

Asthenosphere

EURASIAN PLATE

INDIAN PLATE

E.g. the Himalayas - convergence of the Indian Plate and the Eurasian Plate.

3. Continental-continental plate convergence

a) Plates made largely of continental crust may collide with other plates made largely of continental crust.

b) However, both plates have similar densities and hence, resist subduction.

c) Instead, the plates break, slide along fractures in the crust and fold, forming fold mountains.

Classwork

P54 Q9

SCGS PRELIMS 2014

Explain how the plate movement taking place at a continental-oceanic plate boundary may produce fold mountains. [4]

P54 Explain how the plate movement taking place at a continental-oceanic plate boundary may produce fold mountains. [4]

•When an oceanic plate converges with a continental plate•The denser oceanic plate subducts under the less dense continental plate•As the continental plate rode over the oceanic plate, the sediment on the ocean floor buckled and crumpled •This cause an uplift of the crust into the fold mountains