Geology Reference
In-Depth Information
11
The Heretic's Flood
I
T IS HARD TO SEE
evidence for what you're sure cannot exist. Twentieth-century geologists
were no exception to this rule. They were certain that enormous floods capable of sculpting
topography were impossible. Until, that is, one of them rediscovered the ability of cata-
strophic floods to reshape Earth's surface in the curious landscape of eastern Washington's
scablands, a desolate region stripped of soil.
After teaching geology at the University of Washington for a decade, I was embarrassed
that I had not yet seen the deep canyons where tremendous ice age floods scoured down
into solid rock to sculpt the scablands. So when colleagues asked me to help lead a field trip
there, I decided it was about time I checked out this dramatic terrain. But lead a field trip to
somewhere I'd never been? No thanks, I replied, how about I just tag along? When the an-
nouncement came out, I was listed as a trip leader. Clearly this was going to be educational.
The question was for whom.
Geology field trips usually involve a lot of high-speed talking in low-speed vans. As
the designated distraction crossing over Washington's Cascades, I related the history of
twentieth-century arguments over the timing of when the range rose to rival the Swiss Alps.
Geologists working in the northern Cascades saw the range as ancient, having risen before
waves of black lava flowed out from Yellowstone to cover eastern Washington fifteen to
seventeen million years ago. Those working in the southern Cascades argued the range was
much younger, having come up well after emplacement of the lava blanket. It turns out that
there is a simple way to reconcile these fundamentally conflicting interpretations. The mod-
ern topography of the Cascade Range is a composite, the southern half rising much more
