AIM: Plate Tectonics Do now: Name any 3 layers of the earth. What do we know about Earth’s crust? What’s the difference between ocean & continental crust?

Once upon a time… All the crusts were ONE

But something terrible happened to it…

SO WHAT SEPARATED THEM APART? 1. Water 2. Wind 3. Meteorite 4. Earthquake 5. Sun

SET UP Pour hot water Into a beaker 2. Pour hot water into a beaker Cold water

Record your observation. What is happening?

Inside of the earth is moving! – What is Plate tectonic? Earth’s plates fit together like jigsaw puzzles Float on top of mantle similar to ice cubes in a cupof water

Plate Tectonics

What is Plate Tectonics The Earth’s crust and upper mantle are broken into sections called plates

What is the Lithosphere? The crust and part of the upper mantle = lithosphere 100 km thick Less dense than the material below it so it “floats”

What is the Asthenoshere? The plastic layer below the lithosphere = asthenosphere The plates of the lithosphere float on the asthenosphere

What is convention current? CONVECTION CURRENTS MOVE THE PLATES Material in the mantle is heated by the HOT core As it cools, it moves back down towards the core

Plate Tectonics Plate tectonics cause earthquakes and volcanoes. The point where two plate meet is called a plate boundary.

Exit Questions... What is the lithosphere? What is the asthenosphere? What is the connection between the two? What are the two types of plates?

Three types of PLATE BOUNDARIES Divergent boundaries  plates move apart Convergent boundaries  plates move together Transform boundaries plates slide past  

Three Basic Types of Plate Boundaries Divergent Transform Convergent Animations: Divergent and Convergent Plate Boundaries http://www.iris.edu/hq/programs/education_and_outreach/animations Video lecture by Dr. Robert Butler:Types of Boundaries.mov on the site http://www.iris.edu/hq/programs/education_and_outreach/videos Plates can have three kinds of motion across boundaries [more details on next slides]: 1. They can move away from each other like at a divergent boundary (= spreading ocean ridge or a rift zone); 2. They can move toward each other to make a convergent boundary. 3. They can slide past each other horizontally at a transform boundary. Graphics from “This Dynamic Planet, World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics.” A Smithsonian, USGS, US Naval Research lab publication. You can find this at http://www.minerals.si.edu/tdpmap/ .ﾊCopyright protected: The content may only be used for personal, educational or noncommercial purposes; USGS Graphics

Divergent Boundary A boundary where two plates are moving AWAY from one another. Causes EARTHQUAKES

Convergent Boundary A boundary where two plates COME together. Two plates push against each other, one is eventually forced down beneath the other. Sometimes results in a formation of mountain

Transform Boundary Two plates SLIDE against each another. It may cause EARTHQUAKES

Three Basic Types of Plate Boundaries Using hands to show relative motion Divergent Video: Plate Boundaries— www.iris.edu/hq/programs/education_and_outreach/videos Plates can have three kinds of motion across boundaries: [note video lecture on next slide] They can move away from each other like at a divergent boundary (= spreading ocean ridge or a rift zone). Or use parallel hands like the transform beginning hands and move them apart allowing the magma (thumbs) to come up. 2. They can move toward each other to make a convergent boundary. 3. They can slide past each other horizontally at a transform boundary. When two plates carrying continents converge, a continental collision occurs where continental crust piles up. Continental crust is lower density than mantle rocks, so continental rocks cannot be “subducted” into the mantle. If continental rocks are pushed into the mantle, they will soon pop up again. This is like trying to push a piece of styrofoam into a swimming pool. You can push the styrofoam into the water (with some force) but, when you let it go, it pops back to the surface because it is much less dense than the water on which it floats. ACTIVITY: Teaching about Plate Tectonics Using Foam Models: Download FoamFaultModel_Activity.pdf from Animations Page: http://www.iris.edu/hq/programs/education_and_outreach/animations/2 Graphics from “This Dynamic Planet, World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics.” A Smithsonian, USGS, US Naval Research lab publication. You can find this at http://www.minerals.si.edu/tdpmap/ .ﾊCopyright protected: The content may only be used for personal, educational or noncommercial purposes; USGS Graphics

Convergent Convergent USGS Graphics

Transform

Tectonic Plates 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? VIDEO LECTURE: Tectonic Plates from: www.iris.edu/hq/programs/education_and_outreach/videos BACKGROUND MATERIAL: http://www.iris.edu/hq/programs/education_and_outreach/animations/11 Any map of plates shows that there are about a dozen large plates and a number of smaller plates. The smallest plates are not included here. Remember that “Plate Tectonics” is a fairly new science. Less than 50 years ago most people didn’t believe that the lithospheric plates could move. This simplistic map of the plates doesn’t show the broad areas of deformation. That will be a later slide. INTERACTIVE FLASH rollovers—This and the next slides are available from : DynamicPlanet-Earthquakes & Volcanoes http://www.iris.edu/hq/programs/education_and_outreach/animations/interactive ACTIVITIES: World Tectonic Map activity link on page: http://www.iris.edu/hq/programs/education_and_outreach/animations/11

Earthquakes There are thousands of small earthquakes every day “Strong” earthquakes (~M7) occur once a month. >M8 occur about once/year. Where are the deepest earthquakes? This figure shows the “baseball-stitching” pattern of earthquakes around the globe. This represents only a small percentage of the earthquakes that would typically occur in a year. Over a million earthquakes of Magnitude 2 and lower occur every year. And 1,500 Magnitude 5 occur every year. RESOURCE: For a one-page flier on “How often do earthquakes occur?” go to http://www.iris.edu/edu/onepagers.htm With some imagination you can see some of the gross continental boundaries. Worldwide, strong earthquakes happen more than once per month. Smaller earthquakes, such as magnitude 2 earthquakes, occur several hundred times a day. The deepest earthquakes are where one plate is subducting beneath another plate. INTERACTIVE FLASH rollovers—This and the next slides are available from : DynamicPlanet-Earthquakes & Volcanoes http://www.iris.edu/hq/programs/education_and_outreach/animations/interactive ACTIVITIES: World Tectonic Map activity link on page: http://www.iris.edu/hq/programs/education_and_outreach/animations/11 Exploring Rates of Earthquake Occurance: http://www.iris.edu/hq/resource/explore_rates_of_earthquake_occurance 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? This slide shows the relationship between plate tectonics and earthquake location. There are thousands more earthquakes every year than shown here. Many are in the middle of plates. Why would there be earthquakes in the middle of plates? Remember that the plates are sliding over a round globe and they crack, crumple, and creak as they adjust to the new position. All these adjustments cause earthquakes. For earthquakes of last 2 weeks, go to http://www.iris.edu/seismon/ INTERACTIVE FLASH rollovers : ﾊﾊﾊﾊDynamicPlanet-Earthquakes & Volcanoes http://www.iris.edu/hq/programs/education_and_outreach/animations 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 This image shows a smattering of the most prominent and active volcanoes that occur above sea level. There are thousands of submarine volcanoes not shown here. Next slide shows plate boundaries. Where do volcanoes occur? Volcanoes occur on divergent boundaries (mid-ocean ridges are continuous submarine volcanic mountain ranges) and on convergent boundaries where an oceanic plate subducts beneath either another oceanic plate or beneath a continental plate. (A later slide shows the different convergent boundaries). They can also occur in the middle of a plate due to “hotspot” processes or to continental rift areas which haven’t opened enough to define separated plates. It is an oversimplification to say that ALL earthquakes and volcanoes occur at or near plate boundaries but there is a very strong concentration of earthquakes and volcanoes near plate boundaries. If you understand how plate motions produce earthquakes and volcanoes, you can explain 80% of earthquakes and volcanoes. INTERACTIVE FLASH rollovers : ﾊﾊﾊﾊDynamicPlanet-Earthquakes & Volcanoes http://www.iris.edu/hq/programs/education_and_outreach/animations Modified from USGS Graphics

Tectonic Plates How fast are the plates moving? Plates move 1-10 centimeters per year (≈ rate of fingernail growth). The Nazca (beneath S.American plate) and Pacific Plates are the fastest. Rate of plate motions are typically an inch or two per year (the rate of fingernail growth.) Although this seems slow on the human time scale, the movement over 100s of millions of years builds and destroys land masses. Dr. John Lahr, seismologist, graphed his fingernail growth relative to the plates: http://jclahr.com/science/earth_science/thumbnail/index.html Graphics from “This Dynamic Planet, World Map of Volcanoes, Earthquakes, Impact Craters, and Plate Tectonics.” A Smithsonian, USGS, US Naval Research lab publication. You can find this at http://www.minerals.si.edu/tdpmap/ .ﾊCopyright protected: The content may only be used for personal, educational or noncommercial purposes; 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

Causes of Plate Tectonics

Convection Currents Hot magma in the Earth moves toward the surface, cools, then sinks again. Creates convection currents beneath the plates that cause the plates to move.

Questions... What causes plates to move? How is a convection current formed?