Causes of Plate Movement & Hot

Spots

*These notes go on p. 15 of your INB!*

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

mantle convection moves tectonic plates (just like a pot of water!)

http://www.youtube.com/watch?v=NYbTNFN3NBo

Stratified convection

Boundary near700 km separatesthe two convectionsystems.

2900 kmOuter core

Lowermantle

Uppermantle

MantleOuter coreInner core

*draw this diagram in your notes!!!

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

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

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

Where is this occurring?

Hawaii Yellowstone,

Wyoming Galapagos Islands Iceland Canary Islands East Africa

Hawaiian Islands Show a Progression of Age of Volcanism

Hawaiian Islands and Emperor Seamounts Extend >3000 km

Subsidence of Volcanic Islands Creates Atolls in Tropics

Further Subsidence and/or Cooler Water Creates Guyots(Flat-topped Submarine Plateaus)

Volcanic Age of Seamounts Increases Away from Hawaii

Estimated Extent of Ashfall from Yellowstone Eruption630 K Years Ago

Diagram from Windows into the Earth, by R. B. Smith and L. J. Siegel, 2000

How Much Ashfall from a Major Eruption at Yellowstone?

Diagram from Windows into the Earth, by R. B. Smith and L. J. Siegel, 2000

Simplified Cross-Section of Yellowstone Hot Spot