plate boundaries powerpoint
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Plate Boundaries
MAJOR TECTONIC PLATES
The Mechanism of Plate Tectonics
• as the material in the asthenospehre is heated, it rises
• as it cools, it is moved horizontally and sinks – pulling along the continental and ocean crust
• movement of material in the asthenosphere is called convection cells
There are three types of boundaries wherecrustal plates meet:• divergent• convergent• transform
Divergent Plate Boundaries• also called rift zone• plates moving apart• upwelling part of convection cell• sea floor is created• forms mid-ocean ridges
Divergent Plate Boundaries
• found at most mid-ocean ridges• ex: Mid-Atlantic Ridge
Divergent Plate Boundaries
Convergent Plate Boundaries• also called subduction zones
• plates move toward one another• downwelling part of convection cell• sea floor destroyed• forms trenches and volcanic island arcs
Convergent Plate Boundaries
Transform Plate Boundaries• plates move past each other• faults are formed
Transform Plate Boundaries
Example: San Andreas Fault
Ring of Fire• around Pacific Ocean• greatest quantity of earthquakes and volcanoes• because edges of Pacific Ocean are boundaries
of Pacific plate
Ring of Fire
• earthquakes around the world