What are some of your favorite analogies for explaining geological concepts to other people?
Teaching through analogy – explaining new concepts to people by referring to things that they know or understand already – can be a powerful tool, and since geology is at its core very much a descriptive science, it’s no surprise that useful analogies abound.
My favorite one is used to combat my least favorite geological misconception: the mantle isn’t molten, it’s made of Silly Putty. Silly Putty responds to short, sharp forces, such as being bounced against a wall, as if it is solid and elastic; but it will change shape and flow if you apply a sustained force over time, even if that force is just the pull of gravity. In a similar way, rocks deep in the mantle are much closer to their melting point than rocks at the surface, but they remain rigid enough in the short term to allow the passage of shear waves generated by earthquakes; however, over geological timescales thermal and compositional bouyancy forces will cause them to flow in giant convection currents.
Here’s another: in one attempt to describe one of the aims of my PhD research in New Zealand, I have likened the Earth’s crust to a biscuit. Of course, there are many different types of biscuit: ginger nuts, for example, in addition to being very tasty, are quite hard to break, and when they do they will snap into a couple of large pieces. HobNobs, on the other hand, whilst being equally delicious, crumble easily into lots of smaller fragments. If you look at how continental crust deforms, sometimes it behaves like it’s a ginger nut, with a small number of large-ish fragments separated by big faults, and sometimes it behaves like a HobNob, with lots of much smaller fragments all jostling against each other. Determining whether the crust in a particular region is more ginger nut-like or more HobNob-like is the key to properly describing the tectonics, and assessing things like the seismic hazard (for what it’s worth, my research suggested that New Zealand is more like a ginger nut, although I’m still arguing with the Hob-Nob faction over that one).
So there’s two for Callan; it’ll be interesting to see what everyone else comes up with. Other responses so far: Tuff Cookie, Hypocentre, Callan himself, Lockwood.
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