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Plate Boundaries Plate Boundaries • 3 Main Types: – 1. Divergent Boundaries • Plates moving AWAY from each other – 2. Convergent Boundaries • Plates moving TOWARD each other • Three Main Types: – Oceanic to Continental – Oceanic to Oceanic – Continental to Continental – 3. Transform Boundaries • Plates slide past each other Divergent Boundary Divergent Boundaries • Where plates are moving away from one another. • Characteristics: – – – – – Lengthening Thinning of Lithosphere Shallow Earthquakes Fissure Volcanoes Rift Valleys • Locations: – – – – Oceanic Ridges Mid-Atlantic Ridge East-African Rift Formation of Basalt • Results in: – Sea floor spreading Divergent Boundary • Oceanic – Occurs above rising convection currents that lift up the plate – The plate travels in direction of flow. – The plate is stretched thin, breaks and pulls apart. – The magma flows into the fissure, solidifies and the process repeats itself. • Continental: – Two plates pull apart, faults develop on both sides of the rift; the central blocks slide downwards. – Earthquakes occur. – Streams and rivers flow into the rift and form a lake. Convergent Boundary Continental/Oceanic Convergent: Continental to Oceanic • As they collide, the less dense • Characteristics: continental plate overrides the – Coastal Mountain Ranges oceanic plate. – Continental Volcanic Arcs – Oceanic plate is forced down; temperature increases; plate becomes magma in convection current • Subduction Zone: – Where less dense crust slides under the more dense crust – Location of Volcanoes and Seafloor Trenches • Andes, Cascades – Formation of Volcanic Island Arcs • Japan, Philippines Andes Mountains, South America Convergent Boundary Oceanic/Oceanic Convergent: Oceanic to Oceanic • Two oceanic plates collide. – The older (most dense) plate will subduct beneath the younger plate. • Subduction Zone Results in: – – – – Trenches Island Arcs Chain of Volcanic Isands Deeper Earthquakes • Examples: – Japan – The Caribbean Islands Convergent Boundary Continental/Continental Convergent: Continental to Continental • Two thick continental plates collide – Both have a density that is much lower than the mantle, which prevents subduction. • Example: – Himalaya Mountain Range – Alps Transform Fault Boundaries • Boundary between two plates that are sliding past each other • Earthquakes appear along fault lines • Example: – San Andreas Fault San Andreas Fault, CA Questions... •What are the three types of boundaries? •What direction do plates go for each? •Which boundary has a subduction zone…what occurs at a subduction zone? C. Why do the plates move? 1. Due to tremendous heat, rock in the asthenosphere is like hot taffy 2. This allows plates to ride on top of hot, flowing rock. 3. Plates move because heat is being released from deep inside the earth. 4. Convection currents causes hot material to rise and expand (plates diverge) and cooler material to sink and contract (plates converge). Questions... • What causes plates to move? • How is a convection current formed?