Baked goods occupy a central role ("roll?") in my style of teaching geology. In honor of National Pie Day and Accretionary Wedge #5, I hereby offer a run-down on my favorite baked-good analogies. As the pie chart above conclusively demonstrates, some baked goods are more versatile teachers than others and get therefore merit more class time.

I invoke pancakes to describe oblate shapes in deformed clasts (cigars, which are not a baked good, exemplify prolate shapes).

Muffins (especially the pop-over variety) are squat stand-ins for laccoliths.

Snickers bars offer a terrific way for students to grasp the concept of differential weathering. In class, I pass out to little bite-sized Snickers, and ask students to suck on them. (No chewing! We're trying to demonstrate chemical weathering here, not physical weathering!)They quickly learn that some ingredients are more stable than others.

A pint of Ben & Jerry's gets drawn on the board every semester in Physical Geology when we discuss the carving of alpine glacial landforms. Everyone has had the experience of buying a pint of Ben & Jerry's and finding it too hard to eat. As they wait for it to thaw, people insert their ice-cream scoop (or their spoons) into the top of the pint and carve downward and outward, towards the edge of the container (where the Chunky Monkey has lost more heat and is therefore easier to carve). Working around the container, repeated scoops leave a point of hard ice cream in the middle, surrounded by curved scoop surfaces. This is a lot like a glacial horn, surrounded by the headwalls of several cirques.

I mentioned raisin bread in Tuesday night's Historical Geology class, when discussing the principle of relative dating by inclusions. If you're going to bake raisin bread, which of the following seems like the better recipe? (A) Bake a loaf of bread, then grow some grapes, dry them out, & teleport them individually to positions evenly distributed throughout the loaf of bread. (B) grow some grapes, dry them out, and mix the raisins into the dough, THEN bake it into bread. Well, my teleporter's always in the shop, so I'm going with the second recipe. The raisins have to pre-exist the bread in order to be included in it.

Bob Lillie of Oregon State University gave me this idea: Oreo cookies are composed of a stack of three layers with brittle/ductile/brittle rheologies. This can serve as an analogy for the lithosphere, asthenosphere, and mesosphere. You can even break up the upper cookie bit and slide the pieces around on the white filling. If you're clever, you can produce rift zones, subduction, and even crude mountain building this way.

Chunky cookies (like these classics from Pepperidge Farm) offer a nice contrast between cookie and ingredient. You can tell where the cookie starts & stops, but you can also tell within the cookie where the chocolate starts & stops, and where the pecans start & stop. The analogy is an important one that I draw early on for my Physical Geology students: the difference between a mineral and a rock. Minerals are like the ingredients (chocolate chunks, pecans, etc.). Rocks, being an aggregate of many mineral grains, are like the cookie. Minerals are the ingredients that make up rocks.

And that brings us to cake, by far the most frequently invoked baked good in my introductory geology lectures. Cake is good for so many reasons. First off, there's the stratigraphy of cake: frequently it's a layered structure. Second, broken cakes are not doomed: they can be stuck back together by sealing fractures with frosting. Third, the different rheology of the frosting layers versus the cakey layers makes them ideal for explaining thrust faults that travel over a "greased skid" of less competent rock. (This is my favorite way of explaining the Blue Ridge Thrust Fault, for instance.)

Ironically, pie itself has not so far merited inclusion in this cavalcade of calories. Can you think of a geologic concept that pie helps illustrate? If so, leave your suggestion in the comments area below.

Labels: food, teaching