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!!

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Three Basic Types of Plate BoundariesDivergent

ConvergentTransform

USGS Graphics

Using hands to show relative motion

Three Basic Types of Plate BoundariesDivergent

ConvergentTransform

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