earthquakes and volcanoes chapter 10 - quia · earthquakes and volcanoes chapter 10 objectives: 1)...
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Earthquakes and Earthquakes and
VolcanoesVolcanoesChapter 10Chapter 10
Objectives: 1) Describe the cause of earthquakes. 2) Identify the difference between p and s waves. 3) Explain how p and s waves are used to identify the location of the earthquake. 4) In what ways are the Richter Scale and the MM scale different?
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EarthquakesEarthquakes
• One of most destructive forces on Earth
• Natural rapid shaking of the ground due to friction from sliding faults (ex rubbing your hands)– Results in displaced rocks
– Causes energy to dissipate outward
– Energy travels through Earth in seismic waves
– When reaches the surface, moves the ground
– On ocean floor, forms tidal waves—tsunamis
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Copyright © 2008 Thomson Delmar Learning, a division of Thomson Learning, Inc. ALL RIGHTS RESERVED.
Seismic WavesSeismic Waves
• Seismic Waves can be detected using a seismograph– Uses series of springs and weights
• Types of seismic waves:– 1) P-waves (compressional primary wave)
• Move like sound waves
• Fastest type of seismic wave
http://www.dkimages.com/discover/previews/7
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http://earthsci.org/education/teacher/basicge
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Seismic Waves Seismic Waves ((continuedcontinued))
• 2) S-waves (secondary waves)– Travel in an up-and-down pattern
– Can only travel through solid material
• Surface wave—interaction of P- and S-waves– Results in a rolling motion of the ground
http://earthquakes.usgs.gov/learning/faq.php?categoryID=5&faqID=26
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http://www.astro.virginia.edu/class/oconnell/astr121/im/seismic-waves-crossec-CM.jpg
Source of waves is called the focus
Area directly above focus called epicenter
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Epicenter LocationEpicenter Location• Determined by arrival of P- and S-waves
– Using a seismograph
– Locates the distance to the epicenter
– Use difference in arrival times
– Data from three seismograph stations needed
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Earthquake MeasurementEarthquake Measurement
Strength measured using:
– Richter scale—measures equivalent energy produced
• Scale of 0 to 9
• Every increase in number means tenfold increased magnitude
• 5 is equivalent of medium-sized atomic bomb
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http://data.gns.cri.nz/geoatlas/images/mercalli.jpg
EarthquakeEarthquake
MeasurementMeasurement
• Or the MM scale, which measures destruction.
• The Modified MercalliIntensity (MM) scale is a means of categorizing the effects of shaking on people, structures and the environment.
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Objectives: 1)Uder what conditions do volcanoes often occur? 2) list and provide a one-sentence description for the 6 types of volcanoes discussed in class.
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Formation of a VolcanoFormation of a Volcano
• Where molten rock flows from beneath crust– Molten rock is called lava
• Location associated with convergent tectonic plate boundaries– Where subducting plate begins to descend underneath another plate.
– Sinking plate brings in seawater making steam
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Quiet Eruption VolcanoesQuiet Eruption Volcanoes
• Volcanoes are classified by type of eruption
• Eruption—release of lava, ash, steam, and gases
• Quiet eruptions from volcanoes called shield cones– Formed when lava flows from a central vent
• Lava cools at surface and solidifies forming a shield
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Quiet Eruption Volcanoes Quiet Eruption Volcanoes ((continuedcontinued))
• Fissure eruption
– Long crack in Earth’s crust
– Produces large amounts of lava
– Cool to form huge sheets or plateaus
– Deccan lava flows in India
– Columbia River plateau
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Explosive Eruption VolcanoesExplosive Eruption Volcanoes
• Much more violent• Greatest threat to human life and property
• Composite cone—mountain-like structures– Fire-broken rocks that were blasted apart– Usually surround one central vent– Near subduction zones with convergent plate boundaries
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Explosive eruption with lightning at
Sakurajima Volcano
Cinders were issued up to >2,500 m high
(23:03 on18 May 1991; taken by SVO)
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Explosive Eruption Volcanoes Explosive Eruption Volcanoes ((continuedcontinued))
• Caldera—volcanic crater (a small canyon)– Left behind after composite cone is destroyed
– Crater Lake in Oregon
– One of world’s largest in Yellowstone Park
– Heats water • Produces geysers, mud pots, and hot springs
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Caldera A large, usually circular depression at the summit of a
volcano formed when magma is withdrawn or erupted from a
shallow underground magma reservoir.
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Geyer in Yellowstone
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Explosive Eruption Volcanoes Explosive Eruption Volcanoes ((continuedcontinued))
• Lava dome – Smaller mounds, hardened lava covering a vent
– Grow slowly
– Build up great pressure
– After Mount St. Helens in 1980• Formed small lava dome in its crater
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Explosive Eruption Volcanoes Explosive Eruption Volcanoes ((continuedcontinued))
• Cinder cone– Small mound of lava, ash, and pyroclastic material
– Smallest type of volcano
– When lava breaks through for first time
– Resulting eruption spews lava into air
– Forms a volcanic bomb• Lava hardens before hitting the ground
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Size and Shapes of VolcanoesSize and Shapes of Volcanoes
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Volcanic HazardsVolcanic Hazards
• Most dangerous result is pyroclasticflow– Moves at speeds of more than 100 mph
– Contains hot gases, water, ash, and debris
– Destroys everything in its path
– Mount Vesuvius in A.D. 79• Destroyed Pompeii and Herculaneum
– Volcanic ash enters atmosphere and travels miles
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Volcanic Hazards Volcanic Hazards ((continuedcontinued))
• Ash mixes with water, causes mudflows• Mount Pinatubo in 1991
– Mudflow 650 feet deep
• Release of toxic gas– Sulfur dioxide and water forms sulfuric acid
• Debris flows called lahars– When snow melts suddenly at high elevations