A side of Washington State that I didn’t know existed before our graduate student geology field trip last month:
If you get in your car in Seattle and proceed to cross over the Cascades, you’ll probably run into this landscape – dry, desert-like, a far cry from the lush abundance of coastal Washington. The reason is clear – the rain shadow to the east of the Cascade mountain range – but I was expecting a landscape much more similar to the eastern plains of Colorado.
But I digress from the above landscape, Dry Falls, and how it relates to my book-of-the-moment, Ice Ages: Solving the Mystery by Imbrie and Imbrie. The Dry Falls are a dramatic erosive feature, a large-scale valley with nearly-vertical valley sides. How would you imagine that these were formed? If you were J. Harlen Bretz, you would hypothesize that the Falls were formed due to large-scale catastrophic flooding, and in this case, you would be right. It seems that the Dry Falls were formed when an ice dam broke ~20,000 years ago, releasing a flow of water about ten times greater than that of all the current rivers of the world combined. Hard to imagine? Indeed – and one of the reasons that Mr. Bretz had to defend his theory for much of his life against skeptical peers.
The human capacity to intuit the non-intuitive from geologic evidence has allowed for inferences such as Bretz’s. But the process seems far from strictly logical – one must be able to imagine a place that looked dramatically different from today. As I read through Ice Ages, I am struck by the great (and sometimes) entertaining variety of explanations that were made for glacial features left in the record. And while it is easy today to accept the current theories as sensical and the remainder as absurd (and often, too catastrophic), the distinction is in part due to time alone. Imbrie and Imbrie write
One inference, however, was so extravagant that it cast doubt on the theory as a whole. For Adhemar argued that the gravitational attraction of the Antarctic Ice Sheet was large enough to drain the water from the northern hemisphere ocean and create a sea-level bulge in the southern hemisphere. Painting a dramatic picture of what would happen if temperatures in the southern hemisphere began to rise, Adhemar predicted that the huge Antarctic ice cap would soften and rot until finally – eaten away at its base by the warming ocean – it would be left standing like a giant mushroom. At last, the entire mass would collapse into the sea, creating a huge iceberg-laden tidal wave that would sweep northward to engulf the land. (pp. 73-5)
Absurd? Catastrophic? Yes on both counts. But it takes a bit of the same disposition to think of the huge tidal-wave theory and the enormous flood theory. The key is having both the imagination and the ability to rein it in, given data and a bit of common sense. Just remember that there’s some chance that anything you can imagine may have happen in the earth’s past.
And finally, an interesting fact that I’d forgotten about – the Northern Hemisphere gets more sunlight hours per year than the Southern Hemisphere, thanks to its greater distance from the sun during spring and summer. (Remember Kepler’s Laws? The orbit of the earth must draw out equal area in equal time, demanding that the earth moves more slowly when it is farther from the sun.)