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Thursday, September 23, 2010

Playing With Isoclines


Note 2010-10-25: Essentially this is how my geological pursuit of Missoula Floods in southwest Washington State started off just over a month ago, reconstructed from an e-mail exchange with a respected geologist.


Fig. 1: Rectangular Isocline Covering Missoula Floods Extents

In early September 2010, I was 'doing some experimental work' (i.e. essentially goofing off) in Google Earth, mapping the various levels of a Missoula Floods lake that formed around the Tri-Cities area of Washington State, called 'Lake Lewis'. To start off, I simply made a very large rectangle of constant elevation called an 'isocline', large enough to completely cover both Lake Lewis and the source of the floodwaters, Lake Missoula in Montana. When I learned that a lake also formed in the Willamette Valley as a result of these events, I made the isocline even bigger. So I now had a rectangle that extended from Newport Oregon and Vancouver Island on the west, to Yellowstone Park in Wyoming on the east (see image above), and was playing around with the elevation to get a feel for the extents of these ancient lakes. This is when I happened to notice something curious going on in southwest Washington State.

Excerpted from e-mail to respected geologist, 2010-09-23...


But there's something interesting I noticed in working with Google Earth, about what happens downstream of Lake Lewis, call it 'Lake Willamette' perhaps [I didn't know at the time it is actually called 'Lake Allison']. So north of the Columbia, in the 'Chehalis Arm' of Lake Willamette [actually the Cowlitz River watershed], presuming Puget Sound is blocked with ice, then floodwaters would want to drain down what looks to me like an ancient path of the Columbia, now occupied by the Chehalis River. And that path happens to pass by a 'mysterious' geologic feature called....Mima Mounds!

As a mechanical engineer, what gave me some inkling of curiosity into the possible influence of Missoula Floods on the formation of Mima Mounds was realizing the magnitude of the kinetic energy required; something that none of the hypotheses put forward thus far had addressed.

Yessir, I think we could have us a Missoula Flood feature right here in Puget Sound [no leap of faith required here, right?]. The mounds I think may have been formed by 'standing ripples' -- under the right conditions, standing ripples in a wide, relatively shallow fast-flowing stream can form 'bumps' instead of the more common 'wave' shape [this I knew simply from experience; further education on my part determined that the proper term is 'interference ripples', and the 'right conditions' are perpendicularly intersecting wave fronts of equal amplitude]. The 'smoking gun' would be some granite Rocky Mountain erratics down there, and I've already started spotting candidates for a field trip with...you guessed it, Google Earth.

It was a lucky break that I later found Goods Quarries, because the most promising 'wild erratic' spotted from satellite imagery turned out to be a dead tree!

Fig. 2: 175m Isocline in SW Washington State

The flint and steel were struck together, and the spark of a 'preconceived hypothesis' began to smolder when I noticed that this potential Missoula Floods path passed right by Mima Mounds. Attempting to brainstorm this notion with my correspondent soon revealed however, that geologists might just be more skeptical in general than my typical engineering colleagues.

Excerpted from e-mail to respected geologist, 2010-09-27...

So if there's a significant population of Rocky Mountain erratics buried in the Mima Mounds material, wouldn't that seem like convincing evidence for linkage with a Missoula flood event? Perhaps my 'interference ripple' mechanism needs some tweaking, but wouldn't the presence of Purcell Trench argillite start to make 'suncups' sound as far-fetched as 'giant Pleistocene gophers'?

Despite this
series of nutty e-mails received from a total stranger, as a credit to his profession and personal character, instead of just hitting the 'delete' key, my correspondent took pity on the enthusiastic profundity of my ignorance, and was kind enough to provide this informative graphic, illustrating the US Geological Survey's published maximum height for Lake Allison of 122 meters (400 feet):

Fig. 3: Digital Elevation Model (DEM) of
Cowlitz-Chehalis Watersheds

Well that should pretty much settle it, right? No connection between watersheds, therefore Missoula Floods not a suspect, case closed, time to move on. Except for two nagging little items that I just couldn't reconcile, and my preconceived hunch that Mima Mounds needed a big dose of kinetic energy to formulate a really plausible explanation.
  • If you look very closely, the two watersheds almost connect at this elevation...in three places!
  • And that '400 feet' number sounded just a little too conveniently rounded-off to be a hard-limit for any event that happened over 13,000 years ago.
So I decided to do a bit more digging to figure out exactly where that number came from, before allowing this batch of wet tinder to extinguish the tiny flame of my preconceived hypothesis.


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