Tall bluffs are one of the hallmarks of the lower Missouri River. Spectacular examples can easily be found along its length all the way to St. Louis. These stalwart guardians halt advancing waters and keep towns perched upon their summits, such as Hermann and Augusta, safe. Given their imposing heights, one must wonder . . . how did these bluffs come to exist? The answer may surprise you . . .
Ice To Meet You
To begin understanding the Missouri River bluffs, we need to learn about the latest (and current) ice age. An ice age is pretty much what one imagines: a period of time where global temperatures are colder allowing for the widespread existence of glaciers and ice sheets. Ice ages contain periods of warming and cooling (interglacial and glacial cycles, respectively). We are currently within a warming period that started eleven thousand years ago.
Eleven thousand years, though, is not much geologically speaking. To know more, we'll need to go back. Way back. Way, way back to the early Pleistocene epoch in the Quaternary period when the current ice age began. At the time, about 2.4 Ma (mega-annum, or millions of years ago), a portion of the Missouri River was but a small tributary to a much larger Kansas River flowing northeast to the Hudson River. This was about to change with the arrival of the Laurentide Ice Sheet (hereafter abbreviated L.I.S.).
(insert dramatic music here)
An ice sheet's arrival is a pretty big deal! They are essentially large, thick glaciers that span more than nineteen thousand square miles growing wherever they can across a landmass. The L.I.S., as many such formations are wont to do, drastically altered the landscape. Its cold surface sluggishly expanded grating against and into the ground. Grinding from the ice sheet erased hills, carved new valleys, uncovered ancient depressions and altered the courses of many rivers. Loess, or wind-blown silt and sediment created by this process, was spread throughout the region.
Cooler temperatures did not last. An interglacial period naturally followed. New waterways were created both within the ice sheet and through ice-marginal drainage, or meltwater flowing around the edge of the diminishing ice. Does this explain the formation of the bluffs? Not completely . . .
Snow Way Further
The first major glaciation, a period of maximum glacial extent, of the current ice age was only one of many into Missouri. Our friend the L.I.S. returned once more during the early Pleistocene around 1.3 Ma. Three visitations followed during the middle Pleistocene occurring 760 ka (kilo-anum, or thousands of years ago) with two more arriving between 400 and 200 ka. Surely the bluffs created during these events would have been ground to powdery loess with so many incursions! Surprisingly, this is not the case. And we have the Ozark Dome to thank.
Back to the time machine we go! Between 488 and 444 Ma in the Ordovician period, tectonic activity caused an uplift in the middle of the North American continent forming what is known as the Ozark Dome. Further landmass changes during the Neogene Period (23 Ma to 2.6 Ma) proceeded to elevate it higher and higher. When the L.I.S. arrived, the dome's steep bedrock presented a literal uphill battle. The L.I.S. ground to a halt unable to progress further through the first and subsequent glaciations. Thus, meltwater continued to follow roughly the same initial channel created through ice-marginal drainage forming the tall bluffs and Missouri River valley we've come to know today.
As Far As Icy
Now that we're caught up with the modern theory, what's next? This wouldn't be an EarthCache without some on-the-scene investigation. Grab a calculator, a GPS or some other device that measures elevation, and maybe a sandwich.
(Note: If weather conditions create low visibility, including fog or rain, come back another time! Calculations can be drastically skewed by poor clarity. You can check before arrival via the Dundee webcam or your favorite weather app.)
At the posted coordinates, we're going to make a couple of observations and rough estimations. The first is pretty easy: take an elevation reading. Got it? Great! Now, gaze out over the Missouri River valley. See those hills in the distance? We'll use them to calculate the width of the floodplain.
Hold an arm straight out in front of you while facing the Missouri River directly. Close your hand into a fist sticking out your thumb parallel to the river. Your thumb should be in your line of sight. Count the number of thumbnail widths between the opposite shoreline of the river and the top of the distant hills. Your result may include a fraction (for example, four and three quarters, or 4.75).
Now, subtract 490 from your elevation reading. Divide by the number of thumbnail widths. Your result (let's call it the elevation/thumbnail ratio) will be used for the next two calculations.
Calculation 1) Take your elevation/thumbnail ratio and multiply by 200. This is the distance between the Missouri River bluffs in feet. Divide by 5280 to convert your answer to miles.
Calculation 2) Take your elevation/thumbnail ratio and multiply it by 39.5. You now know how many millions of gallons of water would fill the distance between the bluffs for the entire length of downtown New Haven. During interglacial periods, this amount of water would be normal. The present-day Missouri River holds approximately 347.6 million gallons for the same length, incidentally.
(For brevity, we're skipping over the detailed mathematics and conversions necessary to arrive at these simple equations. Feel free to contact Unitzoid should you wish to be enthusiastically bored to tears.)
Give It Some Thawt
As per EarthCache regulations, there are a few questions you have to answer before calling this one "found". Be sure to send your responses through Unitzoid's user profile at this link either via e-mail or Geocaching instant message. A photograph, while not required, is encouraged if it is spoiler free.
1) Choose a geologic term in the above description (they're in italics). What is the definition given? How does this term relate to the formation of the Missouri River bluffs?
2) What was the elevation at the posted coordinates? How many thumbnails did you use in your calculations?
3) What is the distance between the Missouri River bluffs?
4) How many millions of gallons would have been in front of present day New Haven when the ice sheets were melting?
Northern Exposures
Alber, James S. Glacial Geology of the Kansas City Vicinity. http://www.geospectra.net/lewis_cl/geology/glacial.htm
Bluemle, John. 9-How the Missouri River Formed. http://johnbluemle.com/9-the-missouri-river/
Charity, Mitchell N. Measuring Angle and Distance with your Thumb. http://www.vendian.org/mncharity/dir3/bodyruler_angle/
Cohoon, Richard R. Geologic Roadguide to the Scenic 7 Byway. Little Rock : Arkansas Geological Survey. 2013. p. 14, p. 16.
Eldredge, Sandy and Biek, Bob. Ice Ages – What Are They and What Causes Them? http://geology.utah.gov/map-pub/survey-notes/glad-you-asked/ice-ages-what-are-they-and-what-causes-them/
Fasullo, John. Glossary of Important Terms in Glacial Geology. http://paos.colorado.edu/~fasullo/1060/resources/glacial.glossary.html
Hathaway, Richard. Geology of Missouri. https://pages.wustl.edu/mnh/geology-and-geological-history
Missouri Department of Conservation. Missouri's Icy Past. https://mdc.mo.gov/conmag/2001/12/missouris-icy-past
Rovey II, Charles W. and Balco, Greg. Summary of Early and Middle Pleistocene Glaciations in Northern Missouri, USA, in Quaternary Science, Amsterdam, 2011. v. 15 pp. 553 - 554, 559 - 560.
Singh, V.P., Singh, Pratap and Haritashya, Umesh K. Encyclopedia of Snow, Ice and Glaciers. Dordrecht : Springer. 2011. pp. 342 - 345, p.354, p. 566
Permission to place this EarthCache was granted by Steve Roth of the City of New Haven Parks and Recreation Department. Many thanks go to him for supporting geocaching in his quiet river town!