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Archive for April, 2014

Playfair

“Playfair” is not an admonition—except for maybe two or three of you. Rather it is the name of a renowned geologist who got renowned for figuring out how stream tributaries interact with the streams they are tributary to. He even made up a law about it:

Every river appears to consist of a main trunk, fed from a variety of branches, each running in a valley proportioned to its size, and all of them together forming a system of valleys, communicating with one another, and having such a nice adjustment of their declivities that none of them join the principal valley either on a too high or too low a level; a circumstance which would be infinitely improbable if each of these valleys were not the work of the stream which flows in it.

Playfair’s law is called the “Law of Accordant Functions” and despite the very authoritative sounding name, the law is wrong. We can let the error slide, however, first because Mr. Playfair made it up in 1802 when a good portion of the US population still believed that the reason the hills and valleys they lived in got to be hills and valleys because of the Biblical Flood and, second, because Mr. Playfair had not yet walked the Big Horns or the mountains of Yosemite where glaciers had done their thing.

But it was close enough and because of the other things he and a few of his colleagues were doing, a new science was invented called “fluvio-geomorphology”—the study of how water acts to form what we see around us. They also discovered really swell words like “thalwig” (the line within a stream channel connecting the lowest points at all sites of the channel), “avulsion,” (a rapid change in the course or position of a stream channel by erosion to bypass a meander and shorten channel length and increase channel gradient), “saltation” (the process by which sediment, of sand size and coarser, bounces along the stream bed), and “comminution” which is the “process of reducing a mass to small, fine particles by impact or abrasion.”

Saltation/Comminution/Suspension (Adapted from UMd)

Saltation/Comminution/Suspension (Adapted from UMd)

Now, you are thinking, “What does this have to do with Forrest Fenn?” Well, it’s because when Forrest Fenn, the kid, waded the streams of the Rocky Mountains, he always ended up with sand between his toes and even if he wore tennis shoes, not only did he get sand between his toes, his shoes filled with pebbles. Forrest Fenn may or may not know what “saltation” is but he certainly knows how uncomfortable it is to have the toes of one’s tennies filled with rocks.

It also has to do with Forrest Fenn because river rocks have rounded corners for the same reasons– all that “saltation” acts as a slow but incredibly efficient sand blaster that grinds away at anything that happens to be in a river including brass boxes and their contents and because a “sedimentation” part occurs wherever the “saltation” part doesn’t; things in a river disappear because they are “sanded” away or because they are covered in mud. And it all happens a lot more rapidly than we think.

The result of this treatise, of course, is that there is no way that Forrest Fenn put his treasure in a Rocky Mountain stream.

Maybe you can still return your new waders and snorkel for a full price.

Best wishes,

r/

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