Types of Plate Boundaries

• Divergent Plate Boundaries

• Convergent Plate Boundaries

• Transform Faults

Divergent Plate Boundaries • Mid-ocean ridges form along divergent boundaries.• Magma pushes continental crust up causing it to

break apart. • Plates begin to move apart in opposite directions

causing crustal material to slump downward, creating a rift valley.

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Divergent Plate Boundaries • A linear sea is formed as water fills in the valley.• Through continued divergence, an ocean basin

forms, creating an ocean. Ex: Red Sea

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Red Sea

Divergent Plate Boundaries

• Mid-ocean ridges have oceanic rises and oceanic ridges.

– Oceanic rises gently sloping due to a fast rate of spreading. Ex: East Pacific Rise

East Pacific Rise

Divergent Plate Boundaries

– Oceanic ridges have steeper slopes due to a slower rate of spreading.

Ex: Mid-Atlantic Ridge

Iceland and Mid-ocean Ridge

Convergent Plate Boundaries

• Plates are pushed together

• Oceanic crust is subducted and absorbed into the mantle creating a subduction zone

• Produces a deep-ocean trench and volcanic arc.

Three types of Convergence• Oceanic/ Continental (Fig 1)

• Creates a subduction zone

• Subduction creates a deep trench

• On the continental plate, a continental arc forms parallel to the trench.

Ex: Cascade & Andes Mountains

The Andes

Cascade Mountains

Three types of convergence• Oceanic/ Oceanic (Fig 2)

– Subduction creates a deep trench.– As one oceanic plate subducts, a chain of volcanic

mountains form, producing an island arc. Ex: Aleutian Islands & Mariana Trench

Aleutian Island Arc

Marianas Trench

Three types of convergence• Continental/ Continental (Fig 3)

– As two continental plates collide, they buckle, fold and push upward to produce a mountain range. Ex: Himalayas

Transform Faults/Boundaries

• Plates slide past one another along faults in the lithospheric plate

• Crustal material is neither created nor destroyed

Ex: San Andreas Fault

San Andreas Fault

Hot Spots & Mantle Plumes

• Hot spots are areas of continued volcanic activity NOT associated with plate boundaries. Ex: Hawaiian Islands & Yellowstone National Park

• Hot spots are fueled by regions of rising molten rock called mantle plumes. (pg 62)

• Super volcano?????• Old Faithful

Convection Cells and Magma Plumes

Seamounts & Tablemounts• Underwater volcanoes are called seamounts.• As seamounts break the surface of the ocean,

they may become islands.• Over time, the seamount’s peak erodes away

as the seamount subsides, eventually becoming a flat-top tablemount or Guyot.

Hawaiian-Emperor Seamount

Coral Reef Formation• Fringing Reef: grow close to land, associated

with active volcanic islands. Ex: Kurumba Island in the Maldives

Coral Reef Formation• Barrier Reef: Linear or circular reefs separated

from land by a lagoon of water. Ex: Great Barrier Reef

Coral Reef Formation

• Atoll: By this stage, the volcano is completely submerged. All that remains is the reef and a lagoon. Ex: Atafu in S. Pacific

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The Big Picture

And finally . . .