Causes of Plate Movement & Hot Spots
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Causes of Plate Movement & Hot
Spots
*These notes go on p. 15 of your INB!*
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convection:
heating of a fluid where the hot, less dense portions rise and the cooler, denser portions sink
constant motion of substance creates convection currents
How Plates Move
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mantle convection moves tectonic plates (just like a pot of water!)
http://www.youtube.com/watch?v=NYbTNFN3NBo
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Stratified convection
Boundary near700 km separatesthe two convectionsystems.
2900 kmOuter core
Lowermantle
Uppermantle
MantleOuter coreInner core
*draw this diagram in your notes!!!
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1. magma is heated in the lower mantle by the outer core & rises
2. risen magma heats upper mantle, but is cooler than rest of lower mantle, and sinks
3. upper mantle magma rises to beneath the tectonic plates, moves them, then sinks as it cools
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Forces of Movement ridge push & slab pull
convection currents push plates apart at ridges, and pull them back into the mantle at subduction zones
gravity helps plates sink back into mantle
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Hot Spots
do not occur along plate boundaries; random areas
upwelling of magma seeps through crust & build overtime (volcanic islands, seamounts, guyots)
can occur within a continent or middle of the ocean
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Where is this occurring?
Hawaii Yellowstone,
Wyoming Galapagos Islands Iceland Canary Islands East Africa
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Hawaiian Islands Show a Progression of Age of Volcanism
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Hawaiian Islands and Emperor Seamounts Extend >3000 km
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Subsidence of Volcanic Islands Creates Atolls in Tropics
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Further Subsidence and/or Cooler Water Creates Guyots(Flat-topped Submarine Plateaus)
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Volcanic Age of Seamounts Increases Away from Hawaii
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Estimated Extent of Ashfall from Yellowstone Eruption630 K Years Ago
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Diagram from Windows into the Earth, by R. B. Smith and L. J. Siegel, 2000
How Much Ashfall from a Major Eruption at Yellowstone?
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Diagram from Windows into the Earth, by R. B. Smith and L. J. Siegel, 2000
Simplified Cross-Section of Yellowstone Hot Spot