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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.
See animation.. Click here!!
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
See animation.. Click here!!
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 . . .