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Earths Motion
__Convergent Boundaries__ -These boundaries often occur where a plate of ocean dives. -At an ocean convergences, one plate usually dives beneath the other, forming deep trenches. -As the overlaying plate lifts up,it also forms mountain ranges.

Destruction of crust takes place along convergent boundaries where plates are moving toward each other and can cause one plate to sink under another. When two continents meet head-on, neither is subducted because the continental rocks are relatively light and like two coliding ice bergs, resist downward motion. Subduction processes in oceanic-oceanic plate convergence also result in the formation of volcanos. Millions of years ago, erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form an island volcano.

__Divergent Boundaries__ -Magma from deep in the Earths mantle rises toward the surface and pushes apart two or more plates. -On land, giant troughs such as the great rift valley in Africa from where plates are tugged apart. -Millions of years from now, eastern Afrcia will split and make a new continent amd form a new landmass.

The rate of spreading along the mid-atlantic ridge averages about 2.5 centaimeters per year, or 25 km in a million years. It has resulted in plate movement of thousands of kilometers. When continental crust streches beyond its limits, cracks appear on Earths surface, Magma begins to rise and squeeze through the widening cracks, sometimes to erupt and form volcanos. If spreading cotinues, the three plates will meet at the edge, seperate completly allowing the Indian Ocean to flood the area.

__Transform Boundaries__ -These plates dont produce spectacular featues like mountains or oceans. -Halting motion often triggers large earthquakes, such as the 1906 one that devasted in San Francisco. -When twoo plates grind past each other is called a strike-slip faults.

Most transform boundaries are found an ocean floors. They commanly offset the active spreading ridges, producing zig-zag plate margins and are generally defined by shallow earthquakes. However a few occur n land, for example, the San Andreas fault zone in California. This transform fault connects the East pacific rise, a divergent boundary to the South.

"USGS." //understanding plate motions//. 1999. Web. 1 Jan. . "Science and space." //Plate Techtonics//. 1996. Web. 1 Jan.