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Plate Boundaries Presented by Kesler Science Essential Questions: 1. What is plate tectonics? 2. What are the three types of plate boundaries? 3. What crustal features are formed at plate boundaries? Quick Action – INB Template 1. Cut out the INB Template. Paste it into your notebook. 2. The next two pages will go on top of this page to make a 3 page flip book. 3. This Template is page 3. © KeslerScience.com Quick Action – INB Template Page 1 © KeslerScience.com Page 2 Plate Boundaries Seven Continents today © KeslerScience.com Plate Boundaries Sea-Floor Spreading Harry Hess discovered that magma was rising on the sea floor causing it to spread. The hot magma rising in the mantle caused the spreading on the sea floor and the large pieces of crust (tectonic plates) to move. Theory of Plate Tectonics These two theories lead to the Theory of Plate Tectonics. Continental Drift Theory Alfred Wegener developed the theory that the continents drift. At the time he did not know the mechanism that made this happen. © KeslerScience.com Plate Boundaries Plate Tectonics is the theory that Earth's outer crust (lithosphere) is divided into several plates that glide over the less rigid asthenosphere (upper mantle). © KeslerScience.com Plate Boundaries What is the engine that moves the plates? Convection Currents • Transfers energy in the mantle • Causes the hotter magma in the mantle to rise • Causes the cooler magma in the mantle to sink © KeslerScience.com Plate Boundaries Continental Crust • Layer of rock which forms the continents • Also forms shallow sea beds close to shore (continental shelf) • Floats on top part of the mantle (asthenosphere) • Older than oceanic crust, mostly granite rock • Thicker and less dense than oceanic crust © KeslerScience.com Plate Boundaries Oceanic Crust • A thin layer of crust that underlies the ocean basins. • Consists mainly of basalt. • Younger than continental crust. • More dense than continental crust. © KeslerScience.com Quick Action – Plate Boundaries Let’s review the properties of continental and oceanic crusts. Make a T-chart on your paper and list the characteristics of each type of crust under the correct heading. Continental Crust Oceanic Crust © KeslerScience.com Quick Action – INB Template Type of Boundary Complete the table as you move through the PowerPoint Presentation. Glue into your notebook as a reference. © KeslerScience.com Sketch of Boundary Direction of Movement Description/Features of Plate Boundary Examples Ocean-Ocean Ocean-Ocean Ocean-Ocean Ocean-Ocean Ocean-Continent Ocean-Continent Ocean-Continent Ocean-Continent Divergent Plate Boundary Transform Plate Boundary Convergent Plate Boundary Collision Convergent Plate Boundary Subduction Plate Boundaries What happens at plate boundaries? Plates do one of 3 things. 1. Converge (colliding or coming together) 2. Diverge (dividing or moving apart) 3. Transform (sliding past each other) © KeslerScience.com Converge (destroys crust) Diverge (creates crust) Transform (neither destroys or creates crust) Quick Action – Plate Boundaries Ready for a song? The melody is to the “Adam’s Family.” Converging is colliding, Diverging is dividing, Transform is sliding, We are the plate boundaries. Dah na na na. <Snap, Snap> Bet you can’t get that out of your head! © KeslerScience.com Plate Boundaries Divergent boundaries – dividing or moving apart • Two oceanic crusts diverge and create a mid-ocean ridge (mountains under the ocean). • This process is call sea-floor spreading. • New crust is created. https://www.youtube.com/watch?v=ZzvDlP6xd9o © KeslerScience.com The MidAtlantic Ridge actually comes above the ground in Iceland. Plate Boundaries Divergent boundaries – dividing or moving apart • Two continental crusts diverge and create a rift valley. • New crust is created. • Example is the Great Rift Valley in Africa • Over millions of years water will eventually fill the valley. https://www.youtube.com/watch?v=w7Y2R4KBwvo © KeslerScience.com Plate Boundaries Transform boundaries • Plates slip sideways past each other creating earthquakes. • Crust is neither created or destroyed. • Many of these boundaries are found on the sea floor. • The most famous transform boundary is the San Andreas fault in California. https://www.youtube.com/watch?v=ZxPTLmg0ZCw © KeslerScience.com Plate Boundaries What happens when plates converge or collide? • Continental/Continental = folded mountains (Himalayas). • Continental/Oceanic = volcanoes form (Cascades in Oregon and Washington) • Oceanic/Oceanic = Volcanic arc of islands form(Aleutian Islands in Alaska) © KeslerScience.com Plate Boundaries Converging boundary -continental/continental boundary. • Two continental crusts collide and push against each other. • This pressure causes both plates to rise creating folded mountains. • Not a subduction zone © KeslerScience.com Himalaya Mountains Plate Boundaries Converging boundary - continental/oceanic boundary • • • • The ocean crusts goes below the continental crust because its more dense. Volcanoes form on the continent. A trench forms at the place when the plates collide. Subduction zone Cascade Volcanoes in WA, OR and CA Old crust is destroyed © KeslerScience.com Plate Boundaries Converging boundary - oceanic/oceanic boundary • Two oceanic crusts collide and push against each other. • The older crust goes below the other one and creates a volcanic arc of islands. • Subduction zone Old crust is destroyed © KeslerScience.com Aleutian Islands in Alaska Quick Action – INB Template © KeslerScience.com Quick Action – Plate Boundaries Let’s review the three types of plate boundaries. • Get with a partner and get a white board • Decided which type of boundary you want to “act out.” • Demonstrate to the class your “boundary” and have the class determine which type of boundary you are representing by holding up the corresponding letter, which represents converging, diverging and transform boundaries. © KeslerScience.com Plate Boundaries Ring of Fire • • • • A long chain of volcanoes that surround the Pacific Ocean. One of the most geologically active area on Earth. Site of frequent earthquakes and volcanic eruptions. Caused by plate boundaries converging, diverging and transforming. https://www.youtube.com/watch?v=KqrpkgKD5ko © KeslerScience.com Check for Understanding Can you… 1. Explain plate tectonics? 2. Name the three types of plate boundaries and describe their movement? 3. Relate plate boundaries to the formation of crustal features: such as mountains, trenches, volcanoes and ridges? © KeslerScience.com