combining) apart. The two sides of the now-split plate then move d. forming a DIVERGENT PLATE BOUNDARY. 6. The space between these diverging plates is filled with a. (solid, molten) rocks (magma) from below. (solidifies, liquefies) forming c. Contact with seawater cools the magma, which quickly b. (old oceanic, new oceanic) lithosphere. This continuous process, operating over millions of years, builds a chain of submarine volcanoes and rift valleys called d. RIDGE. (MID-OCEAN RIDGE, volcano) or an OCEANIC SPREADING 7. As new molten rock continues to be extruded at the mid-ocean ridge and added to the oceanic plate, the a. (older, young), earlier formed, part of the plate moves b. created. (near, away) from the ridge where it was originally (away, near) from each other, 8. As the oceanic plate moves farther and farther away from the active, hot spreading ridge, it gradually a. (cools down, getting hotter). The colder the plate gets, the b. (less dense, denser) or heavier it becomes. Eventually, the edge of the plate that is farthest from the spreading ridges cools so much that it becomes denser than the asthenosphere beneath it. 9. As you know, denser materials a. (sink, float) and that's exactly what happens to the oceanic plate-it starts to sink into the asthenosphere! b._ (Subduction, Conduction) happens when c. (less dense, denser) tectonic plate or lithospheric plate sinks into the asthenosphere. The area where one plate sinks beneath another is called a d. (subduction zone, conduction zone) 10. The a. (sinking, floating) lead edge of the oceanic plate actually b. (pulls, push) the rest of the plate behind it-evidence suggests this is the main c. (driving force, destroying force) of subduction. Geologists are not sure how deep the oceanic plate sinks before it begins to melt and lose its identity as a rigid slab, but we do know that it remains d. (solid, liquid) far beyond depths of 100 km beneath the Earth's surface. (DIVERGENT PLATE, CONVERGENT PLATE) BOUNDARY, the type (toward, away) one another. Notice that 11. Subduction zones are one type of a. of plate boundary that forms where two plates are moving b. although the oceanic plate is sinking, the c. (less dense, denser) continental plate floats like a cork on top of the d. (less dense, denser) asthenosphere. 12. When the subducting oceanic plate sinks deep below the Earth's surface, the great a._ (temperature and pressure, depth and mass) at deep cause the fluids to "sweat" from the sinking plate. The fluids sweated out percolate upward, helping to melt the overlying solid mantle above the subducting plate to form pockets of liquid rock called b. (magma, ashes). (rises, go 13. The newly generated molten mantle (magma) is less dense than the surrounding rock, so it a. down) toward the surface. Most of the magma cools and solidifies as large bodies of plutonic (intrusive) rocks far below the Earth's surface. These large bodies or rocks, when later exposed by b.. (erosion, flood), commonly form cores of many great mountain ranges [such as the Sierra Nevada (California) or the Andes (South America)] that are created along the subduction zones where the plates converge. 14. Some of the molten rock may reach the Earth's surface to a. (erupt, rest) as the pent-up gas pressure in the magma is suddenly b. (released, withhold), forming volcanic (extrusive) rocks. Over time, c. (lava and ash, soil and water) erupted each time magma reaches the surface will d. disperse)-layer upon layer-to construct volcanic mountain ranges and plateaus, such as the Cascade Range and the Columbia River Plateau (Pacific Northwest, U.S.A.). (accumulate, Activity 2: Answer briefly the following question. 1. What are lithospheric plates? 2. How fast are the lithospheric plates moving? 3. Where do most earthquakes and volcanic activities happen? 4. What are the two types of lithosphere? 5. up of mainly 6. Why do the lithospheric plates float on the asthenosphere? 7. Why do rocks melt in the asthenosphere? 8. What is convection current? Research! and is less dense that oceanic lithosphere. The continental lithosphere is made rocks while the oceanic lithosphere is made up of rocks. 9. What is a divergent plate boundary? 10. What fills up the space between diverging plate boundaries? 11. What happens to magma/lava when it comes in contact with seawater? 12. What is a MID-OCEAN RIDGE or an OCEANIC SPREADING RIDGE? 13. What happens to the older oceanic lithospheric plates as new magma/lava is extruded into the mid ocean ridge? 14. The oceanic plate gradually becomes The colder and denser plate 15. What is subduction? 16. What is the subduction zone? 17. What is the main driving force of subduction? as it moves farther away from the active mid-ocean ridge. into the asthenosphere in the process called​