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How Convection Works! • Magma expands when heated making volume larger making magma less dense therefore it will __________ to the top of more dense magma •When the magma reaches the surface it cools and contracts becoming _________ _____________ and it will sink. •The process keeps continuing in a circle or cyclic cycle. Sinking Rising Example 2: Plates Pulling Apart and Pushing Together You don’t have to memorize Circle and Label where the convection currents are moving plates together and pulling them apart. WHAT HAPPENS TO THE CRUST WHEN THE PLATES ARE MOVING AROUND???? Tell your neighbor…. What things do we see at these places? Part III. Convergent Plate Boundaries Earthquake Map I. Plate Tectonics • A. Plate Tectonics Theory states that the lithosphere is broken up into 8 major plates that move relative to one another. I. Plate Tectonics • B. Much of Earth’s mountain building, earthquakes, and volcanoes occur at boundaries between plates. II. Plate Boundaries (Borderlines between plates) • A. Convergent Plate Boundaries • 1. Occur when 2 plates converge, or move towards one another. Checkpoint! • Use your hands to demonstrate the motion at a convergent plate boundary Convergent III. Convergent Plate Boundaries • A. Continental-Continental Boundary • 1. When 2 continents collide, they bunch up together, because they have approximately the same density. In other words, mountains form. Animation • 2. The best example of this occurs where the IndianAustralian Plate is colliding with the Eurasian Plate. This collision formed the Himalayas. •Mt. Everest Checkpoint • Using your arms as plates, be ready to show what happens when two continental plates collide. • Go! III. Convergent Plate Boundaries • B. Oceanic-Continental Boundary • 1. When a continental plate and oceanic plate converge, the oceanic plate sinks below because it is more dense. Checkpoint! • Recall how it gets hotter as you go deeper into the Earth’s interior… • Visualize what will happen to an oceanic plate as it sinks further and further below continental crust… • Discuss what will happen to that oceanic plate. Animation III. Convergent Plate Boundaries • 2. This is called a Subduction Zone. • When the more dense oceanic plate goes under (subducts) the less dense continental crust. IV. Environmental Characteristics of a Subduction Zone • A. EARTHQUAKES occur when plates grind against one another. IV. Environmental Characteristics of a Subduction Zone • B. VOLCANOES form when magma rises back through the crust. IV. Environmental Characteristics of a Subduction Zone • C. Trenches or large canyons form in the ocean. Lets find some convergent plate boundaries using the ESRT pg. 5 Assessment Question #1 What are the plates at a convergent boundary doing? 1. 2. 3. 4. Moving Apart Moving Together Sliding Past Each Other Staying Still Assessment Question #2 Which plate will float atop the other at a Continental-Oceanic Crust Convergent Boundary? 1. 2. 3. 4. Continental Crust Oceanic Crust Asthenosphere Lithosphere Part IV: Divergent Plates Boundaries Diverging Plate Boundaries -When 2 or More plates separate or pull-apart -Magma rises between plates and makes new rock (Igneous Intrusion) -Shallow Earthquakes occur at this boundary Features at Divergent Boundaries include -Mid-Ocean Ridges -Rift Zones *As the magma rises and the plates separate new igneous rock is made Feature #1: Mid-Ocean Ridge •When Oceanic Crust is being pulled-apart or separated Features -Longest volcanoes in the world, from the rising magma through cracks in lithosphere -Shallow Earthquakes occurring, from movement of lithosphere -Youngest rock in the ocean, because new rocks are made from solidification of magma Cross-Section of a Mid-Ocean Ridge Mid-Ocean Ridges and Seafloor Spreading Seafloor Spreading creates mid-ocean ridges They are underwater mountain ranges and can stretch for 1000 of Kilometers Animation of Seafloor Spreading Feature #2: Rifting •When Continental Crust is being pulled apart or separated If new crust is created at divergent boundaries, is the Earth getting larger? *Both Rifting and Seafloor Spreading occurs in the same sequence EVENTUALLY THE RED SEA MAY BECOME THE RED OCEAN Lets find some divergent plate boundaries using the ESRT pg. 5 Checkpoint • What is the major difference between seafloor spreading and rifting? • Answer: seafloor spreading occurs when oceanic crust separates, rifting is when continental crust separates Part V: Transform Plate Boundaries and Hot Spots Transform Plate Boundary: is when two plates slide past each other. Properties: 1. Shallow Earthquakes 2. Mostly occur at mid-ocean ridges San Andreas Fault San Francisco San Joaquin Valley Basic California Geography Death Valley Mojave Desert Los Angeles Imperial Valley Transform faults occur frequently at midocean ridges Lets find some transform plate boundaries using the ESRT pg. 5 Hot Spots Definition: • Volcanic activity that doesn’t occur at a plate boundary Facts • Usually forms volcanic islands • Hawaii is a Hot Spot • There is a list of hot spots on the tectonic plates page 5 of the ESRT Hot Spot Hot Spot: Cont. -Hot Spots remains stationary as the plates move over them - Consider that Hawaii is a Hot Spot! Explain its positioning. Lets find some Hot Spots using the ESRT pg. 5 Earthquake Patterns Question: Where do most Earthquakes occur?
