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Unit 6: Earth Shaped from the Outside in

Unit 6: Earth Shaped from the Outside in. Cycle 18: Volcanism & earthquakes Cycle 19: Plate Tectonics Cycle 20: Weathering & Erosion. Connection to last unit….

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Unit 6: Earth Shaped from the Outside in

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  1. Unit 6: Earth Shaped from the Outside in Cycle 18: Volcanism & earthquakes Cycle 19: Plate Tectonics Cycle 20: Weathering & Erosion

  2. Connection to last unit… • To deeply understand the processes that create rocks and minerals such as volcanism, weathering, pressue, etc. need more information about where in the world these things happen

  3. Connections beyond… • Why learn it? • So inherently cool! • So dangerous, need to be prepared • So relevent, in the news eery day impacting people around the world

  4. Class Opener • Do mapping activity • Are all the earthquakes and volcanoes evenly spaced randomly across earth’s surface? • Why do earthquakes and volcanoes occur where they do?

  5. Volcanoes &Volcanism • Volcanoes=the cone structure volcanism=movement of magma out of the earth • Volcanism is caused by solid rock melting. Liquid rock is less dense and therefor rises • Review: kinetic molecular theory of matter

  6. What 3 things cause rock to melt and rise? • Increasing temperature • Adding water • Decreasing pressure

  7. Convergent Subduction Plate Boundary Volcanism Divergent Plate Boundary Volcanism • Along plate boundaries & intra-plate areas • Ring of Fire • Mid-Ocean Ridge • Hot Spots • Volcanic Arcs Intra-Plate Volcanism (hotspots)

  8. Convergent Subduction Volcanism • Plates are colliding with each other and subducting. lithosphere is being melted • Volcanism due to increased temps, water • Divergent Volcanism • Plates are ripping apart • Volcanism due to melting of asthenosphere due to less pressure from above • IntraplateHotspot Volcanism • In middle of plates • Hot spot in mantle • plume rises towards the surface due to density difference

  9. Volcanic Structures • As eruptive materials pile up at an opening a “volcano” forms • Shield • Composite • Cinder

  10. Shield Volcano Shield Volcanco -Low angle slopes of 1-10 Largest volcano -Hawaii, Iceland -Generally on ocean floor -”quiet” eruption -made of basalt lava flows, no ash or pyroclastics -basaltic magma, low gas trapping

  11. Composite Cone/Stratovolcano Steeper slopes 10-25, taller than cinder cones. Smaller in height and width than shield volcanoes Cascades (Mt. St. Helens), Andes Volcanoes on continents over ocean-land subduction zones Alternating Explosive/quiet eruptions Built up by alternating layers of lava and pyroclastics Built over tens to hundreds of thousands of years Andesitic (or Granitic) composition magma, gas rich

  12. Cinder Cones Smallest volcanic features have large craters with steep slopes of 30-40 Paricutin, Mexico Generally forms on continents Explosive eruptions Built of pyroclastics (tephra/cinders) not lava flows. Generally short lived eruptions - weeks to a few years until the magma is degassed, then it solidifies in the pipe and flows form from the base Paricutin, Mexico, cinder cone soon after its birth in 1943 in a Mexican cornfield.

  13. What determines the shape, eruption type… • What determines what kind of volcano forms? • The eruptive materials (lava vs. pyroclastics) • What determines what kind of eruptive materials occur? • Type of eruption (explosive vs. quiet) • What determines what kind of eruption occurs? • The amount of pressure build up from trapped gas especially • What determines the gas content and composition of the magma? • What type of rocks are being melted, ocean floor, continental, both, asthenosphere, LOCATION

  14. Warning signs of impending eruption • Earthquakes increase in frequency and strength • Ash and gas increases • Bulging of volcano side

  15. Dangers • Pyroclastics: breathing, hit by it • Lahars/mudflows: concrete flood • Poisenous hot gases: can’t breath • Pyroclastic flows: instant incineration • 700km/hr (450mph)

  16. Deaths 1600-1982

  17. Earth’s Layers • Formed during early precambrian when earth was liquid rock all over • 3 layers based on differences in composition • Crust, mantle, core • 5 layers based on differences in “stiffness/fluidity” of material • Lithosphere, asthenosphere, lower mantle, outer core, inner core • How do we know? • Earthquakes! • Seismic waves travel faster in denser materials. • S-waves only travel through solids (both rigid and plastic) • Inferences based on overall density calculations for earth, observations of surface materials, lava, and meteorites

  18. What is an Earthquake? • Definition: sudden, strong shaking of the earth’s crust caused by release of energy • Usually happens along faults

  19. Movement of rigid solid crust causes stress in rocks • Rocks bend/stretch/compress/distort their shape • Breaking point reached and rocks release energy and move along fault • Go back to original “unbent” shape • Can only occur in rigid solids of crust

  20. What are seismic waves?

  21. P waves Primary wave Focus Faster Arrive first Push-pull waves (compress/stretch rock, no shape change) Move through solids, liquids and gases S waves Secondary Focus Slower Arrive Second Up and down waves (change shape of rock) Only move through solids Body waves

  22. How do we measure earthquakes?

  23. Locating the epicenter of an earthquake • The farther the station is from the epicenter, the greater the time is between the arrival of primary and secondary waves • Need 3 stations

  24. Travel Time Graph • How long does it take the S & P wave each to travel 1000 mi? 2000 mi? • How much sooner will the P wave arrive at a seisograph station 1000 mi away from the earthquake location? 2000mi? • What is the general relationship between difference in arrival time between P & S wave and distance? • This graph can help geologists identify distance to earthquake epicenter but not… • Direction!

  25. Earthquake dangers • Falling objects • Collapsing buildings • Collapsing bridges, tunnels, etc. • Fires (caused by broken gas lines etc.) • Tsunamis near coast • Interuption in medical and other emergency services due to debris and road closures

  26. Safety Precautions • Inside: • Drop, cover, hold on! Protect your head from falling objects, windows etc. • Don’t try to get outside during shaking • Be prepared for aftershocks • Preparing your home for EQ safety • Bolt bookcases etc. to wall • No heavy objects above bed • Know how to turn off gas & water • Caught at the coast: • Did the tide go out quickly? If you are seeing more of the bottom of the ocean than you should… • Get to higher ground!

  27. Earthquake frequency and cause • Earthquakes in New England? • What causes earthquakes • Most frequently at plate boundaries but can happen anywhere in plate, especially if there are faults already in rock

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