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How Do Natural Forces Change & Shape Our Planet? LAYERS OF OUR PLANET PHYSICAL LAYERS LITHOSPHERE (SOLID) ASTHENOSPHERE (LIQUID) MESOSPHERE (SOLID) OUTER CORE (LIQUID) INNER CORE (SOLID) CHEMICAL LAYERS CRUST (Si + O) MANTLE (Si) CORE (Fe +Ni) WHAT IS CONTINENTAL DRIFT? ALL LANDMASSES WERE ONCE ONE LARGE SUPERCONTINENT CALLED PANGEA HYPOTHESIZED BY ALFRED WEGENER IN 1915 Pangaea began spreading 200 million years ago PROOF OF CONTINENTAL DRIFT CONTINENTS FIT LIKE PUZZLE PIECES ROCK EVIDENCE FOSSIL EVIDENCE CLIMATIC EVIDENCE WAS WEGENER’S HYPOTHESIS ACCEPTED? HOW DO THE CONTINENTS MOVE? WEGENER PROPOSED THE EARTH’S ROTATION HOW COME THE OCEAN BASINS AREN’T WORN DOWN BUT THE CONTINENTS ARE? HOW IS THE SEA FLOOR SPREADING? HARRY HESS DURING WWII DISCOVERED THE CRACK IN MID ATLANTIC RIDGE IS THE PLANET GROWING? What proof is there that the sea floor is spreading? In the late 1950's, scientists mapped the present-day magnetic field generated by rocks on the floor of the Pacific Ocean. The volcanic rocks which make up the sea floor have magnetization because, as they cool, magnetic minerals within the rock align to the Earth's magnetic field A hypothesis was presented in 1963 by Fred Vine and Drummond Matthews to explain this pattern. They proposed that lava erupted at different times along the rift at the crest of the mid-ocean ridges preserved different magnetic anomalies. Let’s make a model! HOW PLATE TECTONICS TIES IT ALL TOGETHER Convergent Boundaries Converging Plates destroy crust During collisions between two continental plates, large mountain ranges, such as the Himalayas are formed. Volcanoes are usually formed by converging plates Diverging Boundaries Divergent boundaries create crust Divergent boundaries within continents initially produce rifts which produce rift valleys. Divergent boundaries also form volcanic islands which occur when the plates move apart to produce gaps which molten lava rises to fill. Thus creating a shield volcano which would eventually build up to become a volcanic island. Transform Boundaries Neither creates or destroys crust Earthquakes occur along boundaries San Andreas (California) Fault created WHERE CAN WE FIND EARTHQUAKES & VOLCANOS? HOW DO WE CLASSIFY VOLCANOS? Shield volcanoes, the largest of the three types, are gently sloping and built almost entirely of low viscosity basaltic lava flows. The eruptions are generally nonexplosive due to the low silica content. Shield volcanoes are typified by those on the Hawaiian and Galapagos Islands and on Iceland. CINDER CONE VOLCANOS Volcanic Cinder Cone are formed by highly viscous rhyolitic magma (approximately 70% silica). Volcanic domes are typically small. Big Southern Butte and East Butte on the Snake River Plain are two excellent examples. COMPOSITE (STRATO) VOLCANOS Composite volcanoes are the most beautiful - - - and ! - - - the most deadly of the volcano types. Their lovely steep-sided, symmetrical cone shapes are built up by eruptions of intermediate viscosity andesitic lava and explosive tephra. Examples of composite volcanoes, also called stratovolcanoes, are Mount St. Helens in Washingon and Mount Fuji in Japan. What causes rocks to melt into magma? Temperature Pressure: As pressure increases the temperature at which a rock will melt also increases Water: A wet rock or mineral will melt at a lower temperature Types of Magma TYPE VISCOSITY GAS CONTENT BASALTIC LOW 1-2% 50% Least ANDESITIC MEDIUM 3-4% 60% Medium RHYOLITIC 4-6% 70% Greatest HIGH SILICA CONTENT EXPLOSIVE NESS VISCOSITY: Internal resistance to flow TEPHRA: Rock fragments that are thrown into the air during a volcanic eruption PYROCLASTIC FLOW: Swift moving, potentially deadly clouds of gas, ash and other volcanic material a violent eruption gives off How were the Hawaiian Islands Formed? WHAT IS WEATHERING? Physical: breaking down of rock (rock stays same) Temperature Ice Plants & animals Water Chemical: breaking down of rock (rock changes) Oxidation Plants Carbonation Acids Water WHAT IS EROSION? Picking up of rock and moving WATER WIND ICE/GLACIERS GRAVITY WHAT IS DEPOSITION? Depositing of rocks
