Single-Serving Volcanism

1. This Snack is meant to be eaten when done, so be sure all tools and utensils are clean. Make sure your gelatin has been refrigerated and is cool and firm before you begin.
2. Make a hole in the base of the gelatin cup. (Note that the plastic in these cups can be pretty tough. If you have trouble, insert a pushpin into the base of your cup, use the tip of a knife or scissors to enlarge the pinhole, and then ream it out by twisting in a circle.) Make the hole just wide enough to fit the tip of your syringe, and try not to push your knife or scissors too far up into the gelatin (see photos below).
   
3. Prepare your “magma” by filling the chamber of your syringe with pudding, yogurt, or other edible dessert sauce (see photo below). Try to get rid of as much air in the syringe as possible.
   
4. Insert the filled syringe into the hole in the bottom of the snack cup, but not too far (click to enlarge the photo below). It should be a tight fit, so no leaks form. If a fog of condensation appears on your snack cup, wipe it off. You’ll want a good view of what’s going on inside.
   

Put on your goggles, and remove the cover of your snack cup. Then, while holding your apparatus upright, slowly squeeze the contents of the syringe into the gelatin, as shown in the photo below. Watch what happens as your “magma” (sauce) enters and propagates through the gelatin.

Inject your sauce until it erupts from the gelatin’s surface, stopping now and then to carefully examine the formations inside the cup (see photos below). You might have to inject additional sauce for this to happen. When you’re done, remove the syringe from the base of the snack cup. (Drips of sauce might leak out the base, so have your paper towels, plate or bowl ready!)
 

Place your snack cup on a plate or paper towel, or in a bowl—and then eat your model…slowly. Use your spoon to carefully excavate the layers of gelatin and intruded sauce, making observations about the layers you expose as you go (see photos below).
 

This sweet simulation models geologic processes and features that are not easily observable, since they generally take place underground and over a long period of time.

The gelatin inside the cup represents the native country rock, the “geology” that happens to already be there. The sauce, pudding, or yogurt used represents the magma—molten rock, the source of igneous rock. The syringe represents a magma chamber, a large, hot, deep source of magma. Click to enlarge a diagram of volcanism below.

Volcanism (source: USGS)

Magma chambers can be located tens of kilometers underground. They exist near subduction zones, hot spots, rift valleys, and other areas of tectonic activity where the movement of tectonic plates can create fractures in the rock that create paths for magma to move upwards. In this Snack, as you force the “magma” to rise, it intrudes into the gelatin—the country rock. You might notice a big blob of sauce or pudding form. This is analogous to large bodies of magma known as plutons, which can be tens of kilometers wide. Multiple plutons that coalesce together are known as a batholith.

Sierra Nevada (source: NPS)

Plutons that remain underground and cool over long periods of time become intrusive igneous rock and can form the heart of large landmasses, and even mountain ranges. The Sierra Nevada Mountains in California (shown in the photo above) are an example of granitic plutons that formed underground about 100 million years ago and were exposed over time through erosion. The Sierra batholith forms the core of a mountain chain almost 650 kilometers long.

As your magma sauce forces its way through the gelatin, it can also create planar features, such as sills (intrusions that run parallel to country rock strata) and dikes (intrusions that cut across strata), as shown in the photos below.

Example of a dike (photo credit: Eric Muller)

Sometimes, a piece of gelatin will break off and can be seen embedded in the injected sauce. This is analagous to an inclusion of country rock suspended in cooled intrusive rock. These torn-off bits of rock are known as xenoliths.

When your magma sauce pierces the surface or erupts, it changes from intrusive to extrusive. Extrusive magma—that is, magma that has reached the surface—is called lava. Depending on its viscosity and quantity, lava can flow out smoothly or be ejected explosively, forming volcanic structures like those in Hawaii (made of basalt) or the Pacific Northwest (andesite and dacite), as shown in the photos below.

Hawaii (source: NPS)

Pacific Northwest (source: USGS)

As you eat your gelatin snack, you are effectively weathering and eroding your simulated rocks, removing surface layers and exposing the geologic formations beneath.

Try injecting a different type of sauce than you used the first time, such as a squeeze tube of icing, or use a layered gelatin dessert (see photos below). You can also make more than one hole in the bottom of the snack cup and inject several doses of sauce into the gelatin. How do your outcomes change if you either chill or warm the sauce before injecting it?

Like all models, this geologic model is imperfect. In what ways does the model break down? Have a discussion with students about the ways in which this model is like and unlike real subsurface magmatism and surface volcanism.

This Snack can also invite a discussion about techniques for predicting volcanic eruptions. Infrared photography, tiltmeters, gas sampling, and seismographs help geologists identify the signs of an impending eruption—changes in surface temperature, bulging and other changes in slope, emitted gases, and earthquake activity.

This Snack is a small, edible version of a NASA/University of Hawaii space-grant activity originally developed for investigations into Hawaiian-type volcanic structures.
http://www.spacegrant.hawaii.edu/class_acts/GelVolTe.html