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Unit 3 Plate Tectonics, Volcanoes and Earthquakes Please add this information to your notes and diagrams. What is Plate Tectonics? Attica A theory that explains the movement of the earth’s crust. Crust is broken into sections called plates. Float in Mantle like pieces of ice float on a lake. Do you think the continents fit together? Evidence of Plate Tectonics Several continents fit together. Rock formations on South America and Africa match up. See example 1 Glaciers once covered Africa, India, and South America. See example 2 Mountains on the east coast of US, Scotland, Greenland and Northern Europe are the same age. See example 3 Evidence of Plate Tectonics Same fossil species found on widely separated parts of the world. See example 4 All the continents fit together into one large land mass called Pangaea. See example 5 Pattern of earthquakes and volcanoes. See Example 6 Rocks on South America and Africa South America Africa Jurassic Period 135 mya. Rocks of same age and sequence (order) found on both continents. Same minerals found on both also. back Glacial Evidence South America South Pole Africa India Australia Glaciers covered parts of these continents around 300 myo. We find U-shaped valleys and scratched and polished bedrock located in the southern parts. back Mountains created when Pangaea was formed. Mountains found here are the same age and structure, about 300 myo. back Fossil Evidence Lystrosaurus – 250 mya, Land reptile Cynognathus – 200-250 mya, Land reptile Mesosaurus – 270 mya, Freshwater reptile Glossopteris – seed fern back Continental Drift 225 million years ago 200 million years ago Continental Drift 135 million years ago 65 million years ago Continental Drift Changes for the future. •Central America will pull away from South America. •Africa will start to split apart. •Australia will move closer to Asia. •India will continue its northward motion. India’s Long Journey India started at 50° S latitude and is now at 20° N latitude. The result is….. The tallest mountain range on any continent. back Earthquake and Volcano Patterns 90% of all earthquakes occur here. Many famous volcanoes •Mt. Katmia •Mt. St. Helens •Mt. Pinatubo Plate Boundaries Here you will learn about how the plates of the earth’s crust interact. Write down the examples in your notes and turn to page 5 in your Reference Table to see this diagram. General Motion of Plates Mantle Convection Currents cause the plates to move. Divergent Boundary Where two plates are being pulled apart. Usually occurs at a midocean ridge. New sea floor is formed. Youngest rock along the ridge. Age increases as you move away from ridge examples Divergent Same pattern on both sides of the ridge. example Iron in the magma is magnetized to show the magnetic field of the earth. example Many earthquakes and volcanoes occur along the mid-ocean ridges. Example Also happens on land. Convergent Boundary Plates are moving together. Two types: Collision and Subduction Collision converging plates both carry continents lithosphere pushed upward into mountain ranges examples Convergent Boundary Subduction one plate plunges below another plate most noticeable feature is a deep sea trench usually have deep earthquakes lithosphere is melted and recycled Subduction of two ocean plates (example) deep sea trench with a chain of volcanic islands Subduction of one continent and ocean plate deep sea trench with Mt..range and volcanoes example Sliding Boundary Also called a Transform Fault Plates are sliding past each other. San Andreas Fault, best example. Mid Ocean Ridge Back to notes Youngest Rock Rocks get older as you move away from the ridge. Mid Atlantic Ridge Back to notes Evidence of Underwater Volcanoes These are found along mid ocean ridges Pillow Lava Back to notes Black Smokers Magnetic Patterns in Igneous Rock Reversed magnetic polarity means that the earth’s magnetic field has flipped directions. Discovered by looking at the iron atoms in basalt. Back to notes East Africa Rift Valley Back to notes Collision Boundary Back to notes Subduction of Two Ocean Plates Back to notes Subduction of Continent and Ocean Plate Where are these boundaries found? Back to notes Which type of subduction is this? Ocean Crust Back to notes Continental Crust Transform Boundary San Andreas Fault in California Pacific Plate North American Plate Volcanism and Plate Tectonics 1. Volcanism produces magma A. Magma 1. Definition – molten rock underground 2. Where? a. in the asthenosphere b. at plate boundaries 3. Reaches surface through volcanoes 4. Types of magma a. felsic – thick, light colored slow moving, forms rock Granite b. mafic – thinner, darker flows more easily, forms rock Gabbro Volcanism and Plate Tectonics B. Lava 1. Definition – magma that reached the surface 2. Mafic – thin and fluid, gases escape easily a. flows smoothly on surface, forms rock Basalt 3. Felsic – less fluid, gases can not escape easily a. explosive eruptions , forms rock Rhyolite Volcanism and Plate Tectonics 4. Aa lava compared to Pahoehoe lava a. Aa – rough, jagged, slow moving b. Pahoehoe – smooth, ropelike, fast moving examples on page 254 5. Solid fragments of lava called tephra a. ash – fine dust like fragments b. block and bombs – blocks are solid, bombs leave as liquid harden when falling examples Volcanism and Plate Tectonics II. Kinds of Eruption A. Rift Eruptions (divergent boundaries) 1. Occur at long, narrow fractures in crust 2. Typically flow out smooth and fluid like 3. In oceans on mid ocean ridges a. cause pillow lava Volcanism and Plate Tectonics 4. On land form basalt plateaus a. East Africa Rift System b. Columbia Plateau of Washington, Oregon and Idaho B. Subduction Eruptions 1. Result of magma that forms at subduction boundaries 2. Usually explosive, mostly lava fragments 3. Most of world’s active volcanoes found here a. Cascade Mts of Washington, Oregon b. Andes of South America Volcanism and Plate Tectonics C. Hot Spots 1. Located in middle of plates 2. Similar to rift eruptions 3. Most famous – Hawaiian Islands 4. Islands get older the further away from Hawaii a. indicates steady motion of Pacific Plate Lava and Tephra More Lava back Cascade Mountains back Web site East Africa’s Volcanoes back Hawaiian Volcanoes back Photo gallery Rift Eruptions Last year’s Icelandic volcano Volcano Types back Earthquakes Pay attention because you never know when you’ll be in one. Earthquakes In The USA Why is the highest Hazard on the West Coast? A Plate boundary is there. largest quakes in us recent and historical quakes Where do earthquakes take place? Worst damage occurs at the epicenter Movements takes place at the focus Most occur on faults Circles represent seismic waves that radiate in all directions Seismograph – Records Earthquake Earth shakes and moves the base. Weight remains stationary because of inertia. Rotating drum records the motion Fault Types Fault Types Richter Magnitude Scale Tells us how much energy is released during an earthquake. Scale is based on movement and energy released not damage. Created by Dr. Charles Richter Comparison to Other Intensity Scales How is the Richter Magnitude Measured? First find the amplitude and the S – P wave time difference. Then look them up on the chart, where the line crosses the magnitude scale, that’s your answer. Types of Seismic Waves – P Waves Four Things to Remember About P Waves •They are the fastest waves (3 miles/sec.) •They travel in the same direction as the particles vibrate •They travel through solids,liquids and gases •They travel faster through denser materials Types of Seismic Waves – S Waves Four Things to Remember About S Waves •They are slower than P waves (2 miles/sec.) •They travel at right angles to the direction the particles vibrate •They travel through solids ONLY!!!!!!!!!!!! •They travel faster through denser materials Examples of Seismic wave motion Time Travel Graph This graph is used to determine three things. 1. Travel Time for a P or S wave. 2. Epicenter distance based on a travel time. 3. Epicenter distance based on arrival time difference. Travel Time for a P or S wave. S wave travel time = 12 min. 30 sec. P wave travel time = 4 min. 15 sec. Epicenter distance based on a travel time. Epicenter distance = 2200 km Epicenter distance = 2900 km Steps to find the Epicenter Distance Step 1 – Determine the P and S wave arrival times from the seismogram. Step 2 – Calculate the Time Difference by subtracting the P wave arrival time from the S wave arrival time. Write down the following examples. Steps to find the Epicenter Distance Time Travel Difference Examples S wave arrival - P wave arrival Time Difference 05:49:50 -05:43:20 00:06:30 18:35:40 -18:33:10 00:02:30 12:21:10 -12:18:40 00:02:30 15:20:15 -15:15:30 00:04:45 Remember you have to convert minutes into seconds when you borrow. Steps to find the Epicenter Distance Step 3 – Use the time difference to find the epicenter distance on the Travel Time Graph on page 11 in your reference tables. Pay attention to the next two examples Steps to find the Epicenter Distance To do step 3, first you mark the time difference on a sheet of paper. Example 2 Time Difference = 6 min and 30 sec Steps to find the Epicenter Distance Now slide the paper over so the time marks line up with the P and S wave lines. Read down the line along the edge of the paper to the epicenter distance scale. Epicenter Distance = 4,800 km Try This One 09:32:25 -09:24:45 07:40 Epicenter Distance = 6000 km Earthquake Damage Comparison of San Francisco Earthquakes Earthquake Damage Earth’s Interior All of this information has been determined by studying seismic (earthquake) waves. Shadow Zone Seismic waves are refracted (bent) as they travel through different density materials. No earthquake waves are recorded here. The End………. Finally