Mountains & valleys

Spreading center—Fast Spreading center—SlowDivergent boundaries occur mostly along spreading centers where the magma rises forming new crust. (Ex. East Pacific Rise, Mid Atlantic Ridge.)

Spreading zones (no graphic) on continents create parallel mountains and valleys as the crust pulls apart (ex: Basin & Range, U.S. and the Great Rift Valley, Africa. )

Divergent Boundaries & Spreading Zones

Lithosphere

Asthenosphere

Oceanic crust

Mantle

Partial meltAsthenosphere

Crust

MantleL ithosphere

Partial melt

Convergent Boundaries

Mo

un

tain

Ran

ge

Old oceanic crust

Cont inental crust

HighPlateau

Continental crust

L i thosphere Lithosphere

Asthenosphere

Trench

Oceanic crust

Cont inental c rust

L i thosphere Lithosphere

Asthenosphere

Asthenosphere

Isla

nd

arc

Oceanic crust

When two plates move toward each other, crust is destroyed as one plate dives (is subducted) beneath the other. The location where sinking of a plate occurs is called a subduction zone.

Ocean-Ocean—Ocean plate dives beneath another ocean plate; volcanic island chain forms above the zone (ex:. The Marianas)

Ocean-Continent: Ocean plate dives beneath a continental plate. Volcanic mountain chain forms inland. (ex:. Cascade Range, Sumatra, Japan)

Continent-Continent: Two thick continental plates collide and buckle into high mountains. (ex: Himalaya Mountain Range.)

Trench

Cont inental c rust

L i thosphere Lithosphere

Asthenosphere

Vo

lca

nic

a

rc

..

..

..

........

..

.. . .

Oceanic crust

Transform Boundaries

As surrounding plates are driven by deep forces to move apart or crunch together, the in-between areas are pushed around on the surface. This forces them to slide past each other horizontally.

Transform faults are where two plates are moving away from a spreading ridge and fracture zones develop (ex: ocean floor)

Asthenosphere

Crust

L i thosphere

Asthenosphere

Crust

Transform fault

L i thosphere

Spreading ridge

Partial melt

Spreading ridge

Strike slip faults result from two plates moving horizontally in opposite directions (ex: San Andreas Fault, California).

Page-size map on next page for World Tectonic Map Activity

The TOTLE Picture

Teac

hers on the Leading Edge

Earthquakes Volcanoes Tsunamis

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