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Plate Tectonics The Earth’s Crust is Made of Plates What Causes the Plates to Move? • Convection- hot magma rises, cool magma sinks (like a lava lamp) Convection Currents • Hot magma in the Earth moves toward the surface, cools, then sinks again. • Creates convection currents beneath the plates that cause the plates to move. DRIFTING CONTINENTS 1. Theory of Continental Drift – Alfred Wegener’s theory that all continents were once one landmass called Pangea (theory proposed in 1910) DRIFTING CONTINENTS DRIFTING CONTINENTS DRIFTING CONTINENTS Two Types of crust • Continental Crustmade of granite (light) • Oceanic Crust- made of basalt (heavy) Plate Boundaries • Cracks in the plates are called faults Types of Boundaries (Faults) • Convergent Boundary • Divergent Boundary • Transform Boundary Divergent Fault • Plates move away from each other • Forms volcanoes and new crust • Ex) Iceland, midAtlantic ridge Transform Fault • Plates slide past each other (shearing) • Creates earthquakes • Ex) San Andreas Fault in California Convergent Fault • Plates move toward each other • Earthquakes, forms mountain ranges & trenches • Ex) Himalayan Mountains Continental-Continental Convergent Boundary • Plates fold, create folded mountains Oceanic-Oceanic Convergent Boundary • Creates trenches (deep valleys) • Forms volcanoes • Ex) Aleutian Islands (Alaska) Oceanic-Continental Convergent Boundary • Oceanic plate pushes down because it is more dense (subduction) • Creates mountain ranges; Ex) Andes mountains
