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Chad's Garden: Viewing Area Sand Dunes

There are sand dunes similar to those in desert regions of the world in our area.

Posted: Dec 7, 2020 4:27 PM
Updated: Dec 7, 2020 11:09 PM

Two types of sandy deposits or soils exist in our viewing area:  those deposited by wind & those deposited by water.

The gravelly sandy loams of the Wea Plains are an example of sands deposited by water.  They are a mixture of unsorted gravels & various particle sizes making for a sandy to sandy loam soil.

The sandy soils of northern White County area are an example of wind-deposited sand.  It is sorted into a consistent sandy to sandy loam soil with no gravels with the coarsest sand particles in north-central White County owing to their heavier weight.

So, what's behind these interesting formations & soils?

Let's focus on the wind-deposited sandy soils.

Check out this map & note the boomerang & horseshoe sand dune formations around Lake Cicott to north & northwest of Burnettsville.

They tell us the prevailing wind direction when they were deposited.  It indicates a strong, steady, consistent west wind.  Most are Parabolic dunes.  There are a few Barchan dunes are still associated with steady west wind, but it is a bit less strong & associated with lots of turbulence causing it to drift in the other direction (with help of sand avalanches).

There is also some Longitudinal sand dune banding in places, which also indicate strong, steady, consistent west wind when the sand was deposited, but with wind convergence between other dunes or with a bit of a wind shift.

Maps courtesy of Google.

Note the abundant Parabolic dunes.

Note their resemblance to desert wind-blown sand dunes.

Image of Namibia desert sand dunes.  Courtesy of Sue Flood. 

This tells us that there were ancient dust/sandstorms in our area with massive amounts of acreage lacking any vegetation in the past.

How did such a set-up occur with this large area in our north & north-central counties covered in dunes?

It is all tied to the Pleistocene (age of multiple glaciation over a million years) or the last glaciation of the Pleistocene (a.k.a. the Wisconsinan). 

Here is a map of glacial moraines.  Moraines are areas where the glacial ice stopped or surged forward a bit again before re-receding it's melting & deposited a wall of till & outwash (gravels, clays, silts, boulders, rocks).  Think of a snow plow making multiple pushes forward & backward back & forth over & over, leading to a series of curving lines of low hills.

You can see the Terminal Moraine (farthest edge of the ice sheet or farthest south moraine of the Wisconsinan) southeast of Indianapolis, northeast of Terre Haute & around Champaign & near Peoria. 

Original maps by Leverett & Larson, re-drawn by Chris Light:

Melting glaciers filled the area with water between the Iroquois, Nebo-Gilboa & Packerton Moraines.  Some of it leaked out & a good amount was retained, but two things happened in the area south of Remington, across western White to Benton counties.  1) Some moving water laid down some gravels, but 2) a lot of the area saw such slow-moving or stagnant backed-up water.  This put down layers & layers of sand, silt & clay on this lake bed or pseudo-lake.

As the moraines were overtopped with water & many leaks occurred at the end of the Wisconsinan (especially with the Maumee Torrent:  a series of significant floods as Lake Erie extended to Fort Wayne [a.k.a. Lake Maumee] & a dam broke....& surges of water flooded from melting ice), large amounts of water would gush out at times during the summer, this left the bed of the frozen lake partially bare in the winter.

Strong westerly winds south of the ice sheet would blow massive amounts of dust off the lake bed & deposit it in dunes to the east.  The heavier, coarser particles were deposited first (some of the heaviest particles skipped along the ground before deposition, followed by the lighter, smaller particles).  Very light silt particles below farther down stream into sheets of loess or blankets & mantles of wind-blown "glacial flour" or silt. 

The shape of the dunes indicates that the sand dunes accumulated on moraines & patches & pieces of vegetation establishing itself south of the ice. 

The pressure gradient between the ice & no ice & high pressure over the ice (& much lower pressure south of the ice) made it a consistently very windy, dry, steppe climate with the ground freezing over in winter & water getting locked up.  Great expanses of lake bed were exposed for massive amounts of dust to be picked up & blown hundreds to thousands of feet up & deposited eastward.

Second image below courtesy of Indiana University.

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