PLATE BOUNDARY FEATURESFood Tectonics

Dance of the Plate Boundaries

Food Tectonics• Spread frosting into a layer about one centimeter thick (to

about the size of a deck of cards). The frosting in this model represents the asthenosphere, the plastic-like layer on which Earth's plates ride.

• Tectonic plates are composed are made up of the lithosphere (which includes the crust and uppermost mantle)• Oceanic Lithosphere (which is thin and denser) is represented by

a fruit roll up• Continental Lithosphere (which is thick, but less dense) is

represented by graham crackers

DIVERGENT BOUNDARIESTENSION FORCES

CONSTRUCTIVE BOUNDARY:

New crust is created where plates diverge

Oceanic-Oceanic Divergent Boundary

• Place the two squares of fruit roll up (oceanic plates) onto the frosting right next to each other (you may need to flatten them out a little bit)

• Press down slowly on the fruit roll up squares (because they are dense and will sink a bit into the asthenosphere) as you slowly push them apart about 0.5 cm

• Discuss your observations with your group

Mid-Ocean Ridge• Type of Lithosphere Interaction

• Oceanic-Oceanic

• Description of Boundary Feature• Two oceanic plates RIFT (spread apart)• Magma rises through the crack and forms a volcanic mountain

chain on both sides of the rift• A valley runs down the center of the MOR

Mid-ocean Ridges

Mid-Atlantic Ridge

Continental - Continental Divergent Boundary

• Hold both ends of your candy bar and very slowly pull the candy bar apart.

• Discuss your observations with your group

Rift Valley• Type of Lithosphere Interaction

• Continental-Continental

• Description of Boundary Feature• Two continental plates RIFT (spread apart)• Long, faulted valleys result as earth’s lithosphere is ripped

apart• Land breaks apart into distinct land masses and the

surrounding water will fill the space between them

Iceland – Continental Rift Valley

East African – Continental Rift Valley

CONVERGENT BOUNDARIESCOMPRESSION FORCES

SUBDUCTION:

A denser plate plunges below a less dense plate through the asthenosphere and forms a trench

Continental-Oceanic Convergent Boundary

• Remove one of the fruit roll up pieces from the frosting. (You can eat it if you wish!)

• Place one of the graham cracker halves lightly onto the frosting asthenosphere next to the remaining fruit roll up piece. The graham cracker represents continental lithosphere, which is thicker and less dense than oceanic lithosphere. It floats high on the asthenosphere so don't push it down.

• Gently push the continent (graham cracker) towards the ocean plate (airhead) until the two overlap and the graham cracker is on top. The oceanic plate subducts below the continental one.

• Discuss your observations with your group.

Continental Volcanic Arc• Type of Lithosphere Interaction

• Continental-Oceanic

• Description of Boundary Feature• VOLCANIC MOUNTAIN RANGES

• occur because friction melts the sinking plate and the magma rises to the surface to create a volcano

• Earthquakes (shallow and deep) can also occur along the sinking plate due to friction

Real Life Example Arenal Volcano, Costa Rica

Continental-Continental Convergent Boundary

• The next model is what happens when two continents collide. Remove both the cracker and fruit roll up from the frosting asthenosphere. (You can eat or discard the airhead)

• Place one edge of both crackers into the glass of water for just a few seconds.

• Place the crackers onto the frosting with wet edges next to each other.

• Slowly push the wet graham cracker edges towards each other.

• Discuss your observations with your group

Folded Mountains• Type of Lithosphere Interaction

• Continental-Continental

• Description of Boundary Feature• Two continental plates run into one another

• The plates resist downward motion because the continental rocks are relatively light/ low density

• MOUNTAINS FORM because the crust tends to buckle and be pushed upward or sideways

• Mostly shallow earthquakes will occur at these locations

Real Life ExampleHimalayan Mountains

Volcanic Island Arc• Type of Lithosphere Interaction

• Oceanic-Oceanic

• Description of Boundary Feature• Two oceanic plates run into one another

• One of the oceanic plates is more dense because it is older and is pulled below the other plate when they collide in a Subduction Zone (forms a trench)

• Volcanic Island Arcs occur because oceanic crust melts as it goes deeper into the Earth. The newly-created magma rises to the surface and forms volcanoes

• Earthquakes (shallow and deep) can also occur

Real Life ExampleGalapagos Islands

Japan

Ocean Trenches• Type of Lithosphere Interaction

• Continental-Oceanic• Oceanic-Oceanic

• How does an Ocean Trench form?• Found where subduction is occurring; one plate collides with

and slides beneath another plate

TRANSFORM BOUNDARIESSHEAR STRESS:

Transform Boundary

• Pick the two crackers up off the frosting and turn them around so that two dry edges are next to each other.

• Push one cracker past the other to simulate a transform plate boundary like the San Andreas fault!

• Discuss your observations with your group

Fault Lines• Type of Lithosphere Interaction

• Continental-Continental• Oceanic-Oceanic

• Description of Boundary Feature• Occurs when plates move past one another; rocks grind

against one another, stress builds up and can deform lithosphere; rocks eventually break, release energy (earthquake)

• On the ocean floor, transform boundaries cause mid-ocean ridges to be offset/ jagged

Real Life ExampleSan Andreas Fault

Summary

Ring of Fire• Reading and discussion