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dynamic earth

plate techtonics here are a few handfuls of major plates and dozens of smaller, or minor, plates. Six of the majors are named for the continents embedded within them, such as the North American, African, and Antarctic plates. Though smaller in size, the minors are no less important when it comes to shaping the Earth. The tiny Juan de Fuca plate is largely responsible for the volcanoes that dot the Pacific Northwest of t s includes the crust and uppermost part of the mantle. Churning currents in the molten rocks below propel them along like a jumble of conveyor belts in disrepair. Most geologic activity stems from the interplay where the plates meet or divide. volcanos are a awsome manifestation of the firey power contained deep within the earth these formations essential vents on the earth surface where molten rock debris and gases from the planets interior are emitted. when thick magma and large amounts of gas build up under the surface eruptions can be explosive expelling lava rocks ashes into the air. less gas and more viscous magma usually means a less dramatic eruption. often causing streams of lava to ooze from the vent..  mid ocean ridges
 * T he global mid-ocean ridge system is the largest single volcanic feature on the Earth, encircling it like the seams of a baseball. Here the Earth’s crust is spreading, creating new ocean floor and literally renewing the surface of our planet. Older crust is recycled back into the mantle elsewhere on the globe, typically where plates collide. The mid-ocean ridge consists of thousands of individual volcanoes or volcanic ridge segments which periodically erupt . b eneath a typical mid-ocean ridge, mantle material partially melts as it rises in response to reduced pressure. This melted rock, or "magma", may collect in a reservoir a few kilometers below the seafloor, awaiting eruption. Much of the magma eventually freezes in place there within the crust, forming the bulk of the new oceanic crust without erupting at [[image:platetechtonics1.jpg width="249" height="225" align="right"]]. Average oceanic crust is about 10km thick, but only the upper 1 to 3 km are formed by eruption processes. When magma pressure builds up enough to force its way out to the seafloor, eruption occurs. "Dikes" are magma-filled cracks and are the conduits that magmas flow through to reach the surface. A typical ridge eruption leaves behind a dike that is 10s of centimeters up to 2 meters in width, extending between the crustal magma chamber and the eruptive fissure at the surface. Lavas pour from the fissure across the surface of the volcanic seafloor, adding a thin coat of new lava (typically <10 m thick) with each eruption. This process of magma ascending and lavas erupting is on-going and perpetual 

cigtations  " national geographic." // national geographic .com // . Web. 10 Nov. 2009. . "national geographic." // national geographic .com // . Web. 10 Nov. 2009. . "www.pmel.noaa.gov." // www.pmel.noaa.gov // . Web. 10 Nov. 2009. tml>.

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