Four major differences between subduction volcanoes

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Four major differences between subduction volcanoes vs volcanoes along the mid-oceanic rifts are: 1. Subduction volcanoes form island arcs and high mountain chains rather than submarine ridges 2.  they are more explosive and produce large volumes of ask and lava 3. Their basic shape as individual  mountains differs. 4. Rift volcanoes are located at the exact edges of the separating plates, while  subduction volcanoes occur on the overriding plate about 100-200 kms landward from the deep ocean  trenches that mark the edges of the converging plates. 5. What geographic features characterize groups of subduction volcanoes (page 79, para 5) Chains of subduction volcanoes form graceful arcs, thousands of kms in length, across the globe.  A  close look will show 5 or 10 volcanoes in a fairly strait line a few hundred kms in length. 6. Where are deep-sea trenches located with respect to the subduction zones? (page 81, para 1) Deep-sea trenches are located 200 kms to the Pacific Ocean side ode of the volcanoes and mark the  actual boundary between the plates. 7. Describe the characteristics of the zone of earthquakes in the subduction zone next to Japan and  define what a volcanic front is. (page 81, para 1 to page 81 para 2) A zone of earthquakes dips from near the Earth’s surface at the trenches to below the island arcs.  This zone roughly outlines the edges of the Pacific and the Philippines plates as they plunge beneath  Asia.  A volcanic front is when most of the large volcanoes are on the eastern edge of the belt, where  the earthquake zone is more shallow. 8. Why does magmatic lava get created in the subduction zones? (page 81, para 3 to page 82) Magma is generated when the descending plate sinks to a depth of 100-200 kms.  Magma generated  in subduction zones is formed by the fluxing action of water and calcium carbonate in the oceanic  sediments dragged down on the top of the underthrusting plate. 9. What happens to the material on top of the subducting tectonic plate? (page 81, para 3 to 82, para  2) The existing temperatures in the low velocity layer at a depth of 100-200 kms along the top of the  subducting plate are high enough to melt the combination of rock and volatiles.  10. Describe the angle at which the subduction plate dips into the earth and how it varies with respect  to the relative directions of the colliding tectonic plates. (page 82, para 3 to page 83) In some places, the subducted plate dips at a low angle, in others at a nearly vertical angle.  It  depends on the relative movement of the two plates and the movement of the underlying mantle. 
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Where the plates are pushing toward eachother, the dip is shallow.  When they are both moving in the  same direction, the dip is about 45 degrees.  When the subducting plate is moving in the same 
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  • Fall '08
  • Campbell-mccrea,M

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