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Baked Geology: Shelli’s Rainbow Fault Cake

The views expressed are those of the author and are not necessarily those of Scientific American.


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I’m back with more yummy geology. Literally yummy. This is geology you can really sink your teeth in to (as long as you brush them after).

We’re not talking that ginger licking of a rock and perhaps nibble on a corner that geologists sometimes do to determine what they’re dealing with. Trust me when I say it’s gritty, tastes like lithified dirt, and leaves you briefly wishing your job entailed something more delicious, like wine tasting. Well, most geologists would prefer beer tasting, but the point still stands.

Sometimes, however, geology can be quite tasty. I’ve shown you before how you can have your geology and eat it, too. Recently, my supervisor Shelli provided another mouth-watering example of geofood. Behold the Rainbow Fault Cake!

Rainbow Cake and expertly-executed fault by Shelli.

Rainbow Cake and expertly-executed fault by Shelli.

This is one of the billion reasons I love my supervisor – she cooks the most delicious treats. Each layer of this cake was a different flavor, corresponding to the color, courtesy of flavored gelatin. So moist and rich! I couldn’t even finish my piece. So much yum!

The cake started out as a replica of the Leaning Tower of Pisa (pro tip: don’t listen to your loved ones when they say your cake isn’t crooked, but your expert eye is telling you something’s off. Unless, of course, you want something quirky and awesome, which this was). Then, after many slices, a spectacular diagram of a dip-slip fault shone at me in all its rainbow glory. I stared at it in delighted, speechless fascination for a moment before I remembered that I’d actually brought the camera, and could commit it to pixels as well as memory. Huzzah!

I’ve drawn you a nice little diagram showing you what this cake is so ably illustrating.

Diagram showing what Shelli's Rainbow Fault Cake is portraying.

Diagram showing what Shelli's Rainbow Fault Cake is portraying.

We can be reasonably sure this fault is dip-slip because it’s very nearly vertical. This one’s an extensional fault – it’s caused by the crust extending. We can tell because it’s a normal fault. The hanging wall’s slip-sliding down relative to the footwall. This indicates the crust is being pulled apart – if it was getting squeezed, a reverse fault would have resulted, wherein the hanging wall would be sliding up. Here’s a quick and easy diagram showing what’s what:

Normal and Reverse Faults. Image courtesy Cferrero and Heron via Wikimedia Commons.

Normal and Reverse Faults. Image courtesy Cferrero and Heron via Wikimedia Commons.

Pretty easy to tell which is the hanging wall – it’s the one left hanging.

So you may have noticed that some of the cake layers are straight, while others are curved. This illustrates drag folding – part of the rock bending under the strain without quite breaking as the two sides of the fault move. Here’s a very nice example of it that looks remarkably like our cake, albeit less rainbowy and certainly less edible:

The "faille des Causses", a geological fault in the Grands Causses, as seen from Bédarieux (Hérault, France).

The "faille des Causses", a geological fault in the Grands Causses, as seen from Bédarieux (Hérault, France). Image and caption courtesy Xhienne via Wikimedia Commons.

That’s almost eerie, it’s so similar. Cuisine imitates nature – or is it the other way round?

You never know when your food is going to provide a Geological Teaching Moment, so keep your camera close and your utensils closer. When employing edible examples, endeavor to photograph before eating. And ixnay on the uiltgay. You can work off the calories in the field.

Rainbow Fault Cake Recipe

  • 3 boxes yellow cake mix, prepared according to box instructions
  • One small box each of Grape, Berry Blue, Lime, Lemon, Orange and Cherry Jello
  • Frosting of choice

Divide cake batter into 6 equal portions. For each portion, mix in about 1/2 of a small box of Jello. Pour each portion into 8″ round cake pans and bake according to the box instructions. When cakes are baked and cooled, trim the crust off of each. Stack them using frosting to cement each layer, and cover the whole with the remaining frosting. Then slice until you’ve got a nifty fault!

I dedicate this delicious cake to all of the hard-working geology teachers, no matter where or how they teach, and invite them to make free use of the above cake photos. Also dedicated in all its rainbow glory to those couples who got handed a double-victory by the Supreme Court this past week. Happy weddings!

Muchos gracias to Shelli, who made this geocake possible.

Dana Hunter About the Author: Dana Hunter is a science blogger, SF writer, and geology addict whose home away from SciAm is En Tequila Es Verdad. Follow her on Twitter: @dhunterauthor. Follow on Twitter @dhunterauthor.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. DougAlder 11:45 pm 07/12/2013

    that is simply awesome – thanks for the geology lesson too :)

    Link to this
  2. 2. paalexan 9:43 pm 07/13/2013

    If the bent cake layers result from drag folding, shouldn’t they be bent upwards?

    Link to this

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