Plate tectonics
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Transcript of Plate tectonics
Convection is like a boiling pot. Heated soup rises to the surface, spreads and begins to cool, and then sinks back to the bottom of the pot where it is reheated and rises again.
Plate tectonics• Plates are driven by cooling of Earth (convection) • Gravity provides additional force to move plates.
Modified from USGS Graphics
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What are the tectonic plates?
AKA: Lithospheric plate• The ~100-km-thick surface of the Earth;
• Contains crust and part of the upper mantle;• It is rigid and brittle;• Fractures to produce earthquakes.
What is the asthenosphere?
Asthenosphere:• Is the hotter upper mantle below the lithospheric
plate;• Can flow like silly putty; and• Is a viscoelastic solid, NOT liquid!!
US
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Three Basic Types of Plate BoundariesDivergent
Convergent
Transform
USGS Graphics
Using hands to show relative motion
Three Basic Types of Plate BoundariesDivergent
Convergent
Transform
USGS Graphics
There are a dozen large lithospheric plates (smaller plates not shown).Some plates have continents; some don’t. All are in motion.
Question: What evidence is there for these plate boundaries?
Tectonic Plates
There are thousands of small earthquakes every day “Strong” earthquakes (~M7) occur once a month. >M8 occur about once/year.
Earthquakes
Where are the deepest earthquakes?
For earthquakes of the past 2 weeks, go to http://www.iris.edu/seismon/
Notice that the earthquakes coincide with plate boundaries, and the deepest quakes (blue) are in subduction zones.
Question: Where would you expect to see volcanoes?
Modified from USGS Graphics
Earthquakes & Plate Boundaries
Create your own maps at http://www.iris.edu/quakes/maps.htm
Modified from USGS Graphics
This map shows that locations of volcanoes (ones above sea level) also tend to occur along the plate boundaries
Volcanoes & Plate Boundaries
How fast are the plates moving?
Plates move 1-10 centimeters per year (≈ rate of fingernail growth).
Tectonic Plates
Modified from USGS GraphicsFingernail growth plotted: http://jclahr.com/science/earth_science/thumbnail/index.html
How fast are the plates moving?
Plates move 1-10 centimeters per year (≈ rate of fingernail growth).
Continental Drift
Source: http://www.tectonics.caltech.edu/outreach/animations/index.html
Seafloor Spreading
Source: http://www.tectonics.caltech.edu/outreach/animations/index.html
Collision of ‘Drifting’ India with Eurasia
Source: http://www.tectonics.caltech.edu/outreach/animations/index.html
Side view of subduction, ‘drifting’ India, volcanoes, & mountain-building
Note on Source: First 8 slides are modified from a slide show prepared by Dr. Robert Note on Source: First 8 slides are modified from a slide show prepared by Dr. Robert Butler, University of Portland, and Jenda Johnson,Butler, University of Portland, and Jenda Johnson,
……the full source of which can be found at:the full source of which can be found at:
http://www.iris.edu/hq/programs/education_and_outreach/videos#B