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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 ? ? ?

2 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.

3 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!! USGS Graphics

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

5 Three Basic Types of Plate Boundaries Divergent Convergent Transform USGS Graphics

6 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

7 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

8 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

9 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

10 How fast are the plates moving? Plates move 1-10 centimeters per year (≈ rate of fingernail growth ). Tectonic Plates Modified from USGS Graphics Fingernail growth plotted:

11 How fast are the plates moving? Plates move 1-10 centimeters per year (≈ rate of fingernail growth ). Continental Drift Source:

12 Seafloor Spreading Source:

13 Collision of ‘Drifting’ India with Eurasia Source: Side view of subduction, ‘drifting’ India, volcanoes, & mountain-building

14 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:


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