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The Structure of Earth

The Structure of Earth. 1. INNER CORE. The very center of Earth ( like the seed inside a peach pit ) SOLID composed of Fe and Ni. 2. OUTER CORE. ( the pit of the peach that surrounds the seed ) LIQUID composed of Fe and Ni Slowly flows at several km/yr. 3. MANTLE.

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The Structure of Earth

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  1. The Structure of Earth

  2. 1. INNER CORE • The very center of Earth (like the seed inside a peach pit) • SOLID • composed of Fe and Ni

  3. 2. OUTER CORE • (the pit of the peach that surrounds the seed) • LIQUID • composed of Fe and Ni • Slowly flows at several km/yr

  4. 3. MANTLE • THICKEST LAYER (~3000 km) • (the thick juicy part of the peach) • composed of Si, O, Mg, Fe, and others • LOWER MANTLE – from outer core to • ~350 km below surface

  5. MANTLE • UPPER MANTLE - described as plastic-like; characteristics of a solid but will flow like a liquid when under pressure like SILLY PUTTY!! • Extends from bottom of crust to ~350 km deep • ASTHENOSPHERE – lower part of upper mantle; flows more easily than rest of mantle • LITHOSPHERE - ~100 km thick and includes upper most part of mantle and ENTIRE CRUST • Rigid, brittle, and doesn’t flow

  6. www.geog.ouc.bc.ca/physgeog/contents/ images/lithosphere.gif

  7. Crust/Mantle Boundary discovered 1909 = MOHO 4. CRUST Outermost layer (the skin of the peach) TWO TYPES OF CRUST A. CONTINENTAL CRUST similar composition to granite thick (~20-60 km) and light (density ~2.7) B. OCEANIC CRUST similar composition to basalt thin (~5-10 km) and dense (density ~3.5)

  8. Drilling Vessel GLOMAR CHALLENGER, Deep Sea Drilling Project, SIO, 1968DSDP image HOW DO WE KNOW?? Seismic (Earthquake) wave data Rock Core samples - GLOMAR CHALLENGER

  9. www.www.gly.fly.edu

  10. www.gly.fsu.edu/.../ GLY1000/Chapter3/Slide7.jpg

  11. THEORY OF PLATE TECTONICS Combines theories of Continental Drift and Seafloor Spreading Earth’s crust and upper mantle (lithosphere) are broken into thin sections called PLATES. These plates move around on the mantle (asthenosphere)

  12. Plates are made up of the Lithosphere - rigid layer ~100km thick ASTHENOSPHERE - plastic-like layer below lithosphere • The lithospheric plates float on the denser asthenosphere • The plates move along plate boundaries in one of three ways: • PULL APART 2. COME TOGETHER • 3. SLIDE PAST • Mountain building, Earthquakes, and Volcanoes are the result of plate movement = TECTONIC ACTIVITIES

  13. earthguide.ucsd.edu/.../ tectonicplatessio.gif

  14. WHY DO PLATES MOVE??? • Lithosphere rests upon plastic Asthenosphere • Flow in astheno due to large slow moving CONVECTION CURRENTS • Hot material expands & rises • Cool material contracts & sinks • New material rising at Earth’s surface & pushes old material aside DRIVING PLATES APART • Where cooler material sinking, PLATES PULLED TOGETHER

  15. www.geog.ouc.bc.ca/.../contents/ images/tectconvection.gif

  16. Spreading center Ocean trench Oceanic tectonic plate Oceanic tectonic plate Plate movement Plate movement Collision between two continents Tectonic plate Subduction zone Oceanic crust Oceanic crust Continental crust Continental crust Cold dense material falls back through mantle Material cools as it reaches the outer mantle Mantle convection cell Hot material rising through the mantle Two plates move towards each other. One is subducted back into the mantle on a falling convection current. Mantle Hot outer core Inner core Fig. 14-3, p. 346

  17. DIVERGENT BOUNDARY RIFT VALLEY Plates move away from each other: volcanic activity and earthquakes EX: MORs - Mid-Atlantic Ridge - North America & Europe slowly moving away from each other EX: On Land - East African Rift Valley - valley formed where plates are separating

  18. maritime.haifa.ac.il/departm/ lessons/ocean/wwr80.gif Earth: Animation List

  19. CONVERGENT BOUNDARY • Plates collide with each other & one plate may be destroyed! • Three Types of Convergent Boundaries • 1. CONTINENTAL PLATE COLLIDES W/ OCEANIC PLATE • Oceanic plate is denser and sinks under continental plate • Area where ocean plate descends into mantle called SUBDUCTION ZONE • creates deep OCEAN TRENCH • High temp & pressure cause subducting plate to melt • Magma is less dense & rises which creates volcanoes along plate boundary

  20. EX: Andes Mtns - Nazca Plate subducts beneath So.American Plate EX: Cascade Mtns - Juan de Fuca Plate subducts beneath No. Amer. Plate (Mt. St. Helens Volcano) IRIS - How do Earth’s tectonic plates interact? IRIS - Interactive Animations

  21. 2. OCEANIC PLATE COLLIDES W/ ANOTHER OCEANIC PLATE One oceanic plate will bend & slide beneath the other forming SUBDUCTION ZONE & OCEAN TRENCH New magma produced rises to form a volcanic island arc EX: Japan, Indonesia, Philippines

  22. 3. CONTINENTAL PLATE COLLIDES W/ ANOTHER CONTINENTAL PLATE • plates collide & crumple forming mountain ranges - COLLISIONAL BOUNDARY • No volcanic activity but earthquakes are common EX: Himalayan Mtns - Indian Plate colliding w/ Eurasian Plate earthsci.org/teacher/basicgeol/ intro/contdontcoll.gif

  23. TRANSFORM BOUNDARIES Plates SLIDE past each other along faults FAULT – break in Earth’s crust where movement has occurred EX: San Andreas Fault marks boundary btwn Pacific Plate & North American Plate Average rate of movement = ~5cm/yr www.stanford.edu/.../news/gifsarch2/ san_andreas_text.jpg www.exploratorium.edu/.../ images/faultaerial_sm.jpg

  24. VOLCANOES volcanoes.usgs.gov/Imgs/Jpg/Photoglossary/ fissure4_med.JPG

  25. MAGMA AND LAVA • Molten rock is slightly less dense than solid rock around it so it RISES through fractures or makes its own path as it rises. • Rate of magma movement determined by SILICA CONTENT. • 2 TYPES of magma/ lava • 1. FELSIC/ GRANITIC – high silica content (>65%), thick, slow moving (viscous) • 2. MAFIC/ BASALTIC – low silica content (45-52%), thin, flow easily; less viscous • GASES IN MAGMA • Magma contains dissolved gases that are released as magma erupts. • Most important are WATER VAPOR, CO2, SO2. • Amount of gas is BIG factor in kind of eruption.

  26. ·As magma reaches surface, pressure is reduced allowing gases dissolved in magma to come out of solution as bubbles. ·     Bubbles can expand rapidly and even explode (soda bottle) ·     Magma w/ lots of dissolved gases tends to produce more explosive eruptions than magma with small amounts. LAVA AA – rough and jagged PAHOEHOE – ropy, thin, has wrinkled appearance www.uhh.hawaii.edu/~csav/ images/aa.jpg volcano.und.nodak.edu/.../vwlessons/ lava_pics/pahoehoe.jpg

  27. LAVA FRAGMENTS • TEPHRA/PYROCLASTS – solid fragments of lava produced in explosive eruptions. • ASH – smallest, Lapilli, BOMBS and BLOCKS - largest • PYROCLASTIC FLOW – tephra combined w/ gases in an explosive eruption forming a dense superheated cloud that quickly travels downhill • LAHAR – landslide or mudflow of pyroclastic material on flank of volcano set off by eruption – Mt. St. Helens www.educeth.ch/stromboli/perm/ montserrat/icons/b09.jpg astravel.rosnet.ru/adventure/ photo_kamch/Images/bomb.jpg

  28. www.geology.sdsu.edu/.../ lahars/laharmsh_s.jpg Lahars at Mount Rainier?During the past 10,000 years, there have been at least 60 different lahars of various sizes originating from Mount Rainier (Hoblitt and others, 1995:5). There are now over 100,000 homes and over 200,000 Puget Sound residents that work in buildings located on these deposits (Krakauer, 1996:34). The largest of these lahars is the Osceola Mudflow that occurred approximately 5,600 years ago and extends to the Port of Tacoma including the areas now inhabited by the towns of Orting, Buckley, Sumner, Puyallup, Enumclaw and Auburn (Hoblitt and others, 1995:5). A more recent lahar, the Electron Mudflow, originated as a sector collapse from what is now known as the Sunset Amphitheater around 600 years ago. The deposits left from the Electron Mudflow are 30 yards deep at the beginning of the Puget Sound lowland area and at least 6 yards deep at the town of Orting (Hoblitt and others, 1995:5). The following hazard map illustrates the areas at risk from future lahar activity www.uccs.edu/.../screen_ poster_lahar_haz1.jpg

  29. TYPES OF ERUPTIONS • 1.FISSURE ERUPTIONS • ·     Occur at long, narrow fractures in crust. • ·     Most occur on ocean floor • EX: along MORs – lava cools away from the fissure forming pillow basalts • ·     Typically flow out smoothly and fluidly b/c lava is basaltic & gases escape easily • ·On Land –lava may spread evenly over thousands of sq. km. Known as flood basalts and can form large basalt plateaus • EX: Columbia Plateau in Washington • Deccan Plateau in India

  30. volcanoes.usgs.gov/Imgs/Jpg/Photoglossary/ fissure4_med.JPG

  31. 2. VOLCANIC ERUPTIONS • VOLCANO – conical mountains formed around a vent where lava, gases, and pyroclastic material are erupted. Named after Vulcan – Roman God of Fire • ·There are ~ 550 active volcanoes on earth – 60% located in Pac. Ring of Fire • Active = erupted in historic time • Ex – Kilauea, Mt. Etna, Mt. Pinatubo, Fujiyama, St. Helens • ·     Numerous Dormant volcanoes – haven’t erupted recently w/I last 100-200 years but may do so again • Ex. Vesuvius, Ranier, Shasta • ·     Many Extinct/ Inactive volcanoes – haven’t erupted in recorded history and show no signs of doing so again

  32. georoc.mpch-mainz.gwdg.de/ volcano.gif

  33. mac.usgs.gov/.../volcanoes/ poster/posterfig4.jpg

  34. upload.wikimedia.org/.../e/eb/Mt_St_Helens.JPG 2007

  35. This page is <http://pubs.usgs.gov/pinatubo/>Contact: Chris NewhallLast updated 02.11.04

  36. HOT SPOTS ·     Areas of volcanic activity in the middle of lithospheric/ tectonic plates ·     Basaltic Lava • Form SHIELD CONES Cause is unclear ·Believe it’s some kind of concentration of heat from radioactive sources in asthenosphere ·     Hot spot stays in same location and plate moves over it • chain of extinct volcanoes marking former position of plate over hot spot

  37. www.odp.usyd.edu.au/odp_CD/ volcis/images/hawaii.gif www.astro.virginia.edu/.../ images/earth_hot_spot2.gif

  38. EARTHQUAKES www.geography.learnontheinternet.co.uk/ .../sanfran.jpg

  39. EARTHQUAKE = shaking effect of Earth’s crust caused by a release of energy • AFTERSHOCK – follow eqks as adjustments along fault • SOME CAUSES: • Erupting volcano, or magma moving in volcano • Collapse of caverns or other very large structures • Impact of meteorites • **RELEASE OF STRESS built up btwn 2 lithospheric plates

  40. SEISMIC WAVES • EQK generated waves that travel through Earth’s interior in all directions • Speed of wave depends on material it travels through • 2 TYPES OF SEISMIC WAVES • BODY WAVES – travel through interior • a. Primary (P-waves) – compressional/ longitudinal (squeeze & stretch) • b. Secondary (S-waves) – shear/ transverse (up & down) • *slower than P waves • * DO NOT travel through fluid Earth: Animation List

  41. www.exploratorium.edu/.../ images/pswaves_sm.gif

  42. FOCUS – point along fault where FIRST mvmnt occurs (underground) • Shallow focus eqks – focal depth <~70km – spreading centers and transform boundaries • Intermediate focus eqks – focal depth ~70-300 km • Deep focus eqks – focal depth >~300 km – subduction zones • EPICENTER – point ON EARTH’S SURFACE directly above focus

  43. Fault Motion Animations : IRIS cse.ssl.berkeley.edu/img/earthquakes/ Epicenter.gif

  44. MEASURING AN EARTHQUAKE • 1. MAGNITUDE – strength of eqk measured using the amplitude of largest eqk wave • *quantitative assessment determined by seismogram • RICHTER SCALE –developed by Charles Richter in the 1940’s • Designed to measure amount of energy released by eqk • 2. INTENSITY - qualitative assessment of damage done by eqk • MERCALLI INTENSITY SCALE

  45. www.seismo.unr.edu/ftp/pub/louie/ class/100/richter-scale.GI

  46. EARTHQUAKE RISK & PREDICTION • ANY AREA that has experienced a damaging eqk in the past is considered at risk of another eqk in the future • ~95% of eqks occur at or near plate boundaries • ~5% occur at plate interiors

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