## 50 Million cubic yards

May 11, 2010 by Mary Daly

Sorry, the Gros Ventre Slide was 50 million cubic yards, not 25. What’s that? Do you have any idea what 50 million cubic yards means?

Big.

Yes, and elephants are big too, but they’re not 50 million cubic yards, so let’s get a grip on this particular size of big. Otherwise it’s just mumbling, right?

Well, consider this: 1760 is the number of yards in one mile, and 1760 x 1760 is 3 million. So one *square* mile is 3 million *sq**uare yards*. One square mile one yard high would be 3 million cubic yards. (Actually, it would be 3,097,600 cubic yards, but never mind the little stuff; it’s not like anyone was actually counting cubic yards, right?) Since 3 x 16 = 48, we can say that 3 million cubic yards x 16 would make 48 million cubic yards, and, again, that is close enough.

So: rocks covering one square mile of land piled 16 yards high would be close to 50 million cubic yards of material. In South Dakota, you have a pretty good idea of one square mile, because country roads are generally one mile apart. And 16 yards high is 48 feet, which is something like a five-story house or maybe a silo twice as high as the farmhouse. So now you are picturing a section of sloping land *completely covered* with tall silos that all slide down at once into a little valley, and in fact slide so fast that they start up the hill on the opposide side of the valley before they stop. Would that plug the river in the little valley?

You bet it would. You can read about it at the Ultimate Wyoming web site, here. It’s quite a story.

Since the Gros Ventre Slide was not a square piece of land, it might be better to picture 2 miles long by half a mile wide by 16 yards deep. Or even three miles long and 1/3 mile wide and 16 yards deep. You can find a useful image in Wikipedia, here.

Anyway, that gives you some different ways of *thinking, instead of mumbling*, about 48-50 million cubic yards.

And here’s a close-up of the hands holding the Gros Ventre Shale, which looks quite solid except where it’s wet and then it’s gooey like clay.

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