#sand table

Chainmail rules for medieval miniatures by Gary Gygax and Jeff Perren, 3rd ed printing by TSR, 1975 (first published by Don Lowry's Guidon Games in 1971), with Lowry's illustrations plus photos of early sand table games which originally used 40mm scale Elastolin and Starlux toy soldiers.

The Spiral - TMA

This might be the first time Youtube’s “Recommended videos” actually showed me something I wanted to see! This is a sandbox geologic model - layers of sediments with different mechanical properties are put in a box and then the bottom of the box is moved backwards and forwards, mimicking the type of forces that cause the development of faults and folds in the crust.

Fourth of July geology!

A classic technique used to understand how rock layers fold and fault is illustrated here. These are sand tables, a great way to see how rocks deform experimentally.

In this setup, a scientist will set up layers of sand or other material with different properties. At the bottom here they have coarse-grained bird seed which is able to flow with almost no resistance, comparable to hot rocks deep in Earth’s crust. At the top they have layers of sand and cornstarch; the cornstarch is used to simulate a layer that is strong and doesn’t fold easily. The layers are also often colored so that they can be seen after the experiment.

The layers start out flat and the whole table is either squeezed or pulled apart, leading to the formation of folds and faults. Scientists can then test how the structures and patterns change as a result of changing properties like the strength and thickness of the various layers. Note here how the strong white layer fractures while the thinner, weaker layers are folded.

In this case, the layers have been pulled apart, leading to the formation of normal faults and a basin like that found today in the East African rift. This particular experiment was done in a structural geology class and that’s Dr. Steve Gao behind it.

Whether they intended it or not when the experiment was set up, this set of normal faults and colors somehow seems incredibly appropriate for the 4th of July. Now if you’ll excuse me, I’m going to go watch some fireworks.

-JBB