Wednesday, October 24, 2012

Subduction Zone Volcano Model Cookies

This activity is super cool because it results in colorful cookies the kids will enjoy along with a memorable experience that clearly illustrates what happens to the layers of Earth's crust along a subduction zone.  Kids will need to already have an understanding that the Earth is made up of many plates that float and move around on Earth's mantel.

Your students will also need to know the words:

  • Oceanic Crust (which is heavier than the crust that makes up the continents because it has denser materials in it).
  • Continental Crust (opposite of Oceanic crust, this is the crust that makes up the continents and mostly tends to be made of lighter, less dense materials.
  • Lithosphere - Lowermost layer of crust along the border with the mantel  (for younger children simplifying to crust works just fine).
  • Asthenosphere - upper layer of the mantel just below the lithosphere where there is relatively little resistance to plastic flow and convection (simplify to top of crust for youngest students).
  • Oceanic Trench - Deep place in the ocean.  In the case of a subduction zone, this is where the subduction actually begins.

First, Make sure you child or students know that a subduction zone is where two of Earth's tectonic plates are colliding and one is sinking below the other.

Mountain building as is shown in this activity occurs at convergence boundaries:

Where plates come together, the Earth folds and bends because of all the pressure created.  This happens when two continental crusts come together (which is happening where the Himalaya are) and where one plate is subducted under another.  At subduction zones like those shown above, the friction between the subducting plate and the overlying plate creates a lot of heat and as the crust melts into the asthenosphere (or upper mantel), a lot of gasses, molten rock and pressure is created.  As the hot gasses and molten rock rise through the overlying crust pockets of magma and magma chambers form.  You get mountains and in the case of subduction you also get volcanoes.  Although this activity won't show the effects of heating, melting and pressure building, it will show how the earth folds and bends in these areas.

First, you'll either need to make some pie crust, or purchase a pre-made crust (you can do this same demo with play dough, craft clay and any number of other items that can be molded, but the eating part of the pie crust is just fun).

Once you have the crust and it is rolled out, draw stripes of different colors across the crust and spread out (as shown below).  I simply used food coloring for the colors and drew a line, you can "brush them" with an egg brush, but this step simply makes it so the kids get a little less of the color on their skin.  Sometimes getting a little messy is a good thing.

Slice the strips apart for working in the colors.

Then you will want to roll the dough onto itself as shown at the right in the above photo.  Mush and mash the dough until the color is close to uniform.  This is approximately what you are aiming for.

Put your balls in a Ziploc bag or two and allow them to cool again (about ten minutes).  During this time, you can go over the vocabulary and take a look at a diagram of a subduction zone together (or you know, do a few dishes, start prepping parts of dinner and "multitask" if you've already covered the info).

When the dough has cooled a little, roll it into hot dog shapes and then use your rolling pin to flatten the hot dogs back into strips again.  If the dough is cooled enough you won't need a lot of flour to keep the dough from sticking, but it might be good to put a little down.  It will depend a little on the specific recipe you use as well.

Stack your dough strips so you have two to three layers of color on each side of the "subduction zone".  Place one side somewhat under the other (I do not recommend doing the one long purple layer as shown in the photo.  It is not really representative, but Alice wanted to try it this way so I let her and then none of the other pictures turned out well).  Placing everything on top of parchment paper is helpful in order to make the crusts slide together well.

Push the crusts together by pushing on opposite ends and you will get something like this:

Lay discuss how the lowest or suducting layer would need to go down, but how the upper layer also moves up a little.   Take a look at the bending and folding layers of dough and if you happen to live in an area where you can go visit a cut hillside (usually along roadways and freeways where the road cuts through a hillside) where Earth's layers are visible, compare what you see there with your model.

To make the cookies, turn you model on its side and press and roll it out.  Sprinkle with a small amount of cinnamon and sugar and cut into strips again.  Bake at 325 degress F and keep an eye on the crust.  Once it gets a slightly darker color it is ready (usually about 8-12 minutes depending on thickness of the dough).  Enjoy your marbled cookies that hold the record of their changing shape in them. 

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