Chs 6 & 7 - Earthquakes & Volcanoes


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  • Mega quake may happen along Cascadia fault…tell students they will watch a video about this later….
  • We used seismic waves to discover the layers of the Earth….S waves cannot travel through the liquid outer core so they are not detected on the other side of the Earth.
  • ash would cover areas around Yellowstone up to 30 in Pa only the finer ash would make and kill us if we breathe it in so would have to wear masks. Crops destroyed, climate cooled, no growing season, animals die...
  • Ask: What does it sounds like when you open a bottle of Coke? Tell students the gases (carbon dioxide) you hear are escaping because of a release of pressure…just like the gases in a volcano escape when pressure is released. Shaking the bottle increases the pressure even more so it is explosive when you finally open it. Explosive volcanoes happen from a release of built up pressure.
  • A Yellowstone super volcano would decrease temperatures by much more…could bring a “volcanic winter”, snow in the summer!
  • Scientists usually consider a volcano to be dormant is it has not shown signs of an eruption or has not erupted in recorded history….however this is very difficult to determine. Dormant volcanoes more explosive because pressure is building up.
  • Chs 6 & 7 - Earthquakes & Volcanoes

    1. 1. Earth’s Crust in Motion•Convectioncurrents inthe mantleand themovement ofplates pushand pull theearth’scrust.•This is
    2. 2. Earth’s Crust in Motion•Stress acts on rockchanging its shape.Types of Stress:1.Stress that pushes a massof rock in two oppositedirections is called shearing .•A lot of shearing stresshappens at the faults oftransform boundaries.
    3. 3. Types of Stress2. Tension pulls on thecrust, stretching rock sothat it becomes thinner inthe middle.•A lot of tension stresshappens at divergentboundaries.
    4. 4. Types of Stress3. Compressionsqueezes rock until itfolds or breaks.•A lot of compressionstress happens atconvergent boundaries.
    5. 5. Plate Boundaries and Faults•When enough stressbuilds up in a rock,sometimes it willeventually break orcrack, creating a fault.•Plate boundaries—where most stressoccurs– often havereally large faults butfaults can be in themiddle of plates too.Ex. San AndreasFault (transform
    6. 6. Folding and Folded Mountains•Sometimes instead ofcausing faulting, theforce of compressioncan cause rocks tobend and fold.•The Himalayas &Appalachians arefolded mountain ranges.
    7. 7. Section 6-2Earthquakes and Seismic Waves
    8. 8. How an Earthquake Occurs•When rocks along a fault are put under stress, theymay bend and change shape but initially resistmoving along the fault.•Eventually, the rock slips suddenly and releasesthis built up stress causing vibrations which weknow as earthquakes.•Often the area where the rocks slips along the faulthappens below the earth’s surface. This is calledthe Focus.•Epicenter: the point on the earth’s surface directlyabove the focus.
    9. 9. •Earthquakes often occur at transformboundaries such as the San Andreas Faultor convergent boundaries at subductionzones such as the Cascadia Fault in thePacific Northwest.
    10. 10. Seismic Waves•Seismic waves carry energy from anearthquake away from the focus,through Earth’s interior, and acrossthe surface.
    11. 11. Types of Seismic Waves1. P or “primary” waves are the felt first in an earthquake because they are the fastest. They can travel through solids and liquids.2. S or “secondary” waves are felt second in an earthquake. They are slower than P waves and unable to travel through liquids.
    12. 12. Types of Seismic Waves3. Surface waves are felt last in an earthquake because they are the slowest. They only travel through the crust. Despite being the slowest, they cause the most damage and make the ground roll like ocean waves!
    13. 13. Why Can’t S Waves TravelAll the Way Through the Earth?
    14. 14. The Seismograph•A seismograph is aninstrument that recordsthe vibrations of anearthquake to produce aseismogram.•Modern seismographsare electronic and cansense and record groundmovements that are verysmall and far away!
    15. 15.
    16. 16. Magnitude•Magnitude is a number from 1-10 thatgeologists assign to an earthquake based onthe earthquake’s size.•The magnitude of an earthquake is rated bythe following:1.The highest wave on the seismogramdetermines the magnitude.2.How much movement occurred along thefault.3.The strength of the rocks that slippedalong the fault.
    17. 17. Moment Magnitude (Updated Richter) Scale of Earthquake Energy:Each number releases 32 times more energy than the previous number!
    18. 18. Comparing Magnitudes•Each one-pointincrease inmagnituderepresents a releaseof 32 times moreenergy!•An earthquake witha magnitude 6releases 32 timesmore energy than amagnitude 5, and1024 (32x32) more
    19. 19. New Madrid Fault Zone • Although most Earthquakes happen at plate boundaries, stress can create fault lines in the middle of plates too such as the New Madrid Fault Line .ideo/fault-lines-america-9592211
    20. 20. Section 6-3 Monitoring Earthquakes and Section 6-4Earthquake Safety
    21. 21. Instruments That Monitor Faults and Help Predict Earthquakes•In trying to predict earthquakes, geologists havevarious developed instruments to measure changes inelevation, tilting of the land surface, and groundmovements along faults. The most important of theseinstruments is GPS.•If any of these changes occur, they indicate stressis building up (or rather, built up stress could soon bereleased!)
    22. 22. Earthquake Risk•Geologists can determineearthquake risk by locating wherefaults are active and where pastearthquakes have occurred.
    23. 23. How Earthquakes Cause Damage •Plate movements on the ocean floor can cause earthquakes and push water out of the way forming a tsunami, a series of waves each on larger than the next. •A tsunami spreads out from an earthquakes epicenter and speeds across the ocean. •Tsunamis can go undetected because the waves only get large as the water gets shallow!Subduction Zone
    24. 24. How Earthquakes Cause Damage•Liquefaction occurs whenshaking turns loose, moist soilinto liquid mud and causebuildings to sink!•An aftershock is an earthquakethat occurs after the initialearthquake.
    25. 25. Designing Safer Buildings•To reduceearthquakedamage, newbuildingsmust be madestronger andmore flexible.•Buildings onsoft soil needto beanchored tobedrock topreventliquefaction.
    26. 26. Designing Safer Buildings•Base Isolated buildings “isolate” abuilding from its foundation and“smooth out” the earthquake withhuge springs.
    27. 27. What if you are in an Earthquake?•Drop, cover, and hold on tosomething sturdy if possible.•If you live in an earthquake pronearea, have an earthquake kit withfood, water, and first aid ready. h?v=Io4QH8I04h4
    28. 28. 7-1 Volcanoes and Plate Boundaries
    29. 29. Volcanoes and Plate Boundaries•Volcanoes are weak spots in Earth’s Crustwhere magma comes to the surface.•Like Earthquakes, Volcanic belts often formalong the boundaries of Earth’s plates. (ex.Pacific Ring of Fire)
    30. 30. Volcanoes and Plate Boundaries•Volcanoes often form where two oceanicplates collide, where an oceanic platecollides with a continental plate, and ofcourse at mid-ocean ridges.
    31. 31. Hot Spot Volcanoes•Sometimes, like in Hawaii, volcanoes can occur inthe middle of a tectonic plate!•Scientists think that sometimes hot rock will rise inthe mantle, then melt forming a pocket of magma inthe mantle called a hot spot. Hot spots can beanywhere, including the middle of plates.•A volcano forms above a hot spot when magmaerupts through the crust and reaches the surface.
    32. 32. Hot Spot Volcanoes• Many of these eruptions will cause the volcanoes to get bigger and bigger.• Eventually they will rise above sea level to form islands.• Over time, the plates will move this volcanic island away from the hot spot (the hot spot remains in the same place in the mantle) and a new volcanic island will begin to form.
    33. 33. New Island Formation puter/flash/hotSpots.htm
    34. 34. Loihi will be above sea level in about 18,000 years!
    35. 35. • Yellowstone National Park in Wyoming is actually a “Super Volcano” and is located above a hot spot in the middle of the North American Plate.
    36. 36. Section 7-2 Properties of Magma Section 7-3 Volcanic Eruptions
    37. 37. Parts of aVolcano…
    38. 38. How a Volcano Erupts•As magma rises, lessweight is on it sopressure on it decreases.•Gases in the magmanow have room to expandand spread out. Theforce of the gasesexpanding pushesmagma from the magmachamber through thepipe until it flows orerupts out of the vent(and crater) or side vent.
    39. 39. “Quiet” Eruptions•Some magma has low silica (quartz) so it is fairly thinand can flow easily. This means is has a low resistanceto flow or a low viscosity.•Therefore it will have a “quiet” eruption because themagma can easily flow out of the vent and crater.“Quiet” eruptions still cause a lot of damage!•When this lava cools, it often forms rocks like basalt.•Ex. Mt. Kilauea Hawaii (Kilauea means “muchspreading.” )
    40. 40. Explosive Eruptions•Some magma has a high silica content(quartz) so it is thick and flows very slowly, orhas a high viscosity.•Magma is so thick it gets stuck in thevolcano’s pipe, pressure builds up and then itexplodes!•When this lava cools it often forms high silicarocks like pumice, rhyolite, and obsidian!•Ex. Mt. St. Helens
    41. 41. What Erupts from a Volcano?1. Lava Flow- The river of lava that flows down thevolcano and over the land.2. Pyroclastic materialIf an explosive eruption occurs, there is usually a largefast moving cloud of gases, ash, cinders and bombscalled pyroclastic flow.• Rock fragments created by eruptions •lava explodes from the volcano and solidifies in the air forming the pyroclastic materials. Volcanic bombs Volcanic cinders Volcanic ash
    42. 42. Pyroclastic flow Pyroclastic flowMt. Augustine, Alaska Mt. St. Helens (1980)(1996)
    43. 43. U.S. Geological Survey scientist examines pumiceblocks at the edge of a pyroclastic flow from theMay 18, 1980 eruption.
    44. 44. Volcanic Hazards•As lava flows, it burieseverything in its path!•Poisonous gases arereleased•Pyroclastic materials likeash, cinders and bombs canbury entire towns!•When volcanic ash gets wetit can create massivemudslides.•After the Mt. Pinatuboeruption in 1991 in the Even in Hawaii, sulfur gasesPhilippines, the global have caused evacuationstemperature was reduced by1 degree F because the ashand gases blocked sunlight.
    45. 45. Lives of•Volcanoes may be active, dormant (sleeping) or Volcanoesextinct based on the activity or non-activity thatthey exhibit.•How might geologists determine what stage avolcano is in?•Past eruptions, monitoring the volcanoes forsurface changes (using tiltmeters), monitoringsmall earthquakes triggered by the movement ofmagma, and changes in temperature. Active Dormant Extinct
    46. 46. •Tiltmeters, like this one installed on Mount St. Helens,can signal impending eruptions by detecting changes inslope caused by magma moving beneath a volcano.
    47. 47. Volcanic Landforms•A caldera formswhen an volcano’smagma chamberempties and theroof of thechamber collapses.The result is alarge, bowl-shapedcaldera.•Future eruptionscan create newvolcanic cones inthe caldera.
    48. 48. Volcanic Landforms•Examples: Crater Lake, Oregon andYellowstone National Park. Crater Lake, Oregon (or more accurately, Caldera Lake)