Did you know you can illustrate geology with food? It's true! And tasty. Just about every foodstuff can be dragooned in the interests of education - you're limited only by your imagination and the concept you wish to illustrate. Some foods are more suited for specific geologic processes than others.
It turns out that Oreos® are perfect for plate tectonics. You've probably encountered Oregon State University Emeritus Professor Bob Lillie's outstanding Oreo Tectonics illustration somewhere on the internets. If not, click on the link and go peruse before you go on. It's okay. We and (most of) the Oreos will still be here.
Right. So that makes the basics of plate tectonics pretty easy to understand, doesn't it? You can see how the plates move, and what the different types of plate boundaries are like. But some people are never satisfied. Some people *coughChrisClarkecough* demand an Oreogeny. Well, with a bag of unconsumed Oreos in the cupboard and some time on my hands, I could easily oblige. But I saved the full sequence for Rosetta Stones, because it's got rather too serious round here and we needed a reminder that geology can be fun (and tasty!).
So, orogenies. Orogen, orogeny... weird word, eh? Sounds downright dirty. Maybe it's all Greek to you. That would be because it is Greek, or at least the scientific variant thereof. Scientists brought together two words like a convergent plate boundary (see Bob Lillie's B): oros, meaning "mountain" and genesis, meaning "origin." Quite a different origin from the rather naughty word you probably think of every time you see "orogeny" in the geologic literature.
So now we have this word, and basically it means mountain building. This is how the Earth makes mountains:
1. Two plates converge.
2. Plates Collide!
This is a continent-to-continent collision, like the one that forms the Alps. As the African Plate pushed into the European Plate, the crust began to buckle and fold and fault under all the pressure. That's one way baby mountains are born.
3. The plates continue converging, making mountains.
Some of those mountains rise to astounding heights, like the Himalayas. Some are a little more modest, but the Alps are no slouches. So we'll make our Oreogeny rise up high.
4. Mountains grow.
That's how you end up with seashells at several thousand feet. Leonardo Da Vinci, among many other illustrious scientists, was fascinated by those shells - but it wasn't until plate tectonics was born that we had a clear understanding of what got the marine shells up there.
One of the neat things about the Alps is that, in some places, the vigorous thrusting (minds out of the gutter, people) has overturned some of the strata entirely. Old stuff ends up on top (stop it!), and young stuff on the bottom (you're completely hopeless).
5. Overturned strata.
No, seriously, that happened without me doing more than pushing two Oreos together. See the little bit of the filling that ended up on top? Pretty awesome illustration of the forces at work in an orogeny!
So, there's a lot more to this - I've got a whole book on mountain geomorphology that made my brain hurt when I read it years ago. Mountains are complicated things. But the basic force that builds them is fairly simple: colliding plates. You get orogens in subduction zones, and you get them in continental collisions. We can tell where old orogens happened by the types of rock left after the mountains have been planed down to their roots by millions of years of water, wind and gravity. They're amazing things. Also, spectacular scenery. Here's one particular orogen I'm rather fond of.
Rather more majestic and snowy than the Oreos, aren't they? Not quite as edible, though. Definitely difficult to dip in milk.
At the end of geology via dessert, I brought together all of my various Oreogenies in a PanOreogeny.
Makes a nice mountain belt, that. If I had a classroom and students, I'd probably bring a few of these in on plates and have them map them, looking for thrust faults and overturned strata and suchlike. If you're an educator, you're more than welcome to steal the idea, my photos (but not Bob's - you should ask him), and even my snarky sense of humor. Good luck with the inevitable double entendre. Bring milk to represent the mantle - dipping your orogenies in should illustrate subduction rather nicely. And remind everyone to brush their teeth after they've consumed their geology models.