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Geophysical Properties of the Earth: Isostasy, Magnetic Field, and Mass Movement

Explore the geophysical properties of the Earth, including isostasy, the Earth's magnetic field, and causes of mass movement. Learn about how the lithosphere floats on the aesthenosphere, the Earth's self-exciting dynamo, magnetic reversals, and the role of water in slope failure.

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Geophysical Properties of the Earth: Isostasy, Magnetic Field, and Mass Movement

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  1. The Baths British Virgin Islands Casey Sullivan

  2. View from Macchu Pichu Peruvian Andes Emma Conroy

  3. Lake George, NY Brian Gilligan

  4. Cinque Terre "Five Lands" of Italy Sarah Bruce

  5. GEOPHYSICAL PROPERTIES OF THE EARTH ISOSTASY Lithosphere floats on the underlying denser, heat- softened, partially melted aesthenosphere. Areas with greater mass sink deeper into the aesthenosphere. Equilibrium between lithospheric segments (plates) and aesthenosphere beneath them is called ISOSTASY.

  6. GEOPHYSICAL PROPERTIES OF THE EARTH ISOSTASY

  7. GEOPHYSICAL PROPERTIES OF THE EARTH ISOSTASY Lithosphere, because of its lower density “floats” or “sinks” to find its own isostatic equilibrium. Continental lithosphere is less dense so a larger proportion of it “floats” above the aesthenosphere. Changes in mass cause it to rise and fall. Similar to a boat unloading or loading cargo. Removal of mass causes it to rise. Addition of mass causes it to sink. Rise after removal of mass is called ISOSTATIC REBOUND.

  8. GEOPHYSICAL PROPERTIES OF THE EARTH ISOSTASY

  9. GEOPHYSICAL PROPERTIES OF THE EARTH EARTH’S MAGNETIC FIELD Penetrates and surrounds the Earth. Extends into space approximately 60,000 km.

  10. GEOPHYSICAL PROPERTIES OF THE EARTH EARTH’S MAGNETIC FIELD Obvious cause would be the Earth’s iron core. But, the core is too hot to be a permanent magnet. However, magnetic fields such as those that surround the Earth can be produced by an electrical current. So, we think of the Earth now as a giant electromagnet. The electrical field is produced by the movement of electrons through the molten iron of the liquid outer core.

  11. GEOPHYSICAL PROPERTIES OF THE EARTH EARTH’S MAGNETIC FIELD The rotation of the Earth sets the liquid in motion. Moving currents generate the magnetic field. This, then, generates more electrical currents. Produces a SELF-EXCITING DYNAMO.

  12. GEOPHYSICAL PROPERTIES OF THE EARTH MAGNETIC REVERSALS Magnetic pole moves around all the time, but in general it is in close proximity to the geographic pole. Earth’s magnetic field reverses occasionally. Magnetic north and south poles switch position. Happens every ~ 500,000 years. We think it takes ~ 1000 to 5000 years to switch, but evidences suggest it can be only ~100. How do we know…..

  13. GEOPHYSICAL PROPERTIES OF THE EARTH MAGNETIC REVERSALS

  14. GEOPHYSICAL PROPERTIES OF THE EARTH MAGNETIC REVERSALS Normal is when magnetic pole is in the northern hemisphere. Reversed is when magnetic pole is in the southern hemisphere.

  15. MASS MOVEMENT MASS MOVEMENT is the process by which Earth materials (bedrock, unconsolidated sediments and soils) are transported down slopes by gravity. Every slope is susceptible to mass movement. Movement can be slow or fast. Between 1925 and 1975 cost $75 billion. Loss of life < 1000.

  16. May 3, 2003

  17. Information provided by Dylan Harrison-Atlas

  18. MASS MOVEMENT CAUSES OF MASS MOVEMENT GRAVITY, FRICTION AND SLOPE ANGLE Gravity tries to pull particles downward. Friction tries to stop downward movement. When friction is overcome, particles move. Greater slope angle, tendency to move increases.

  19. MASS MOVEMENT CAUSES OF MASS MOVEMENT GRAVITY, FRICTION AND SLOPE ANGLE Bubble Rock, Acadia Natl. Park Maine

  20. MASS MOVEMENT CAUSES OF MASS MOVEMENT SLOPE COMPOSITION SOLID BEDROCK Things to consider in terms of slope composition. Fractured vs. unfractured Amount of mechanical weathering Occurrence of bedding planes Solubility (limestone) Foliation orientation Columnar jointing

  21. MASS MOVEMENT CAUSES OF MASS MOVEMENT SLOPE COMPOSITION UNCONSOLIDATED MATERIAL Angle of Repose

  22. MASS MOVEMENT CAUSES OF MASS MOVEMENT WATER CONTENT Water is the most significant factor in slope failure. Small amounts of water actually increase cohesiveness of unconsolidated sediments. Holds sand grains together, due to surface tension.

  23. MASS MOVEMENT CAUSES OF MASS MOVEMENT WATER CONTENT

  24. MASS MOVEMENT CAUSES OF MASS MOVEMENT WATER CONTENT Water also encourages growth of vegetation. Helps discourage slope failure. Water also increases mass of slope. Too much water reduces friction between grains and consequently cohesiveness, which leads to slope failure.

  25. MASS MOVEMENT CAUSES OF MASS MOVEMENT WATER CONTENT

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