Plate tectonics Plates are driven by cooling of

Plate tectonics • Plates are driven by cooling of Earth (convection) • Gravity provides additional force to move plates. ? ? ? Modified from USGS Graphics 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.

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.

USGS Graphics 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!!

Three Basic Types of Plate Boundaries Divergent Using hands to show relative motion Transform Convergent USGS Graphics

Three Basic Types of Plate Boundaries Divergent Transform Convergent USGS Graphics

Tectonic Plates There 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?

Earthquakes There are thousands of small earthquakes every day “Strong” earthquakes (~M 7) occur once a month. >M 8 occur about once/year. Where are the deepest earthquakes? For earthquakes of the past 2 weeks, go to http: //www. iris. edu/seismon/

Earthquakes & Plate Boundaries 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? Create your own maps at http: //www. iris. edu/quakes/maps. htm Modified from USGS Graphics

Volcanoes & Plate Boundaries This map shows that locations of volcanoes (ones above sea level) also tend to occur along the plate boundaries Modified from USGS Graphics

Tectonic Plates How fast are the plates moving? Plates move 1 -10 centimeters per year (≈ rate of fingernail growth). Fingernail growth plotted: http: //jclahr. com/science/earth_science/thumbnail/index. html Modified from USGS Graphics

Continental Drift How fast are the plates moving? Plates move 1 -10 centimeters per year (≈ rate of fingernail growth). 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 Side view of subduction, ‘drifting’ India, volcanoes, & mountain-building Source: http: //www. tectonics. caltech. edu/outreach/animations/index. html

Note on Source: First 8 slides are modified from a slide show prepared by Dr. Robert Butler, University of Portland, and Jenda Johnson, …the full source of which can be found at: http: //www. iris. edu/hq/programs/education_and_outreach/videos#B