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Our Great Flood!

Submitted by Editor on April 7, 2010 – 5:01 am | Print or Email »No Comment


by Doug Reace

Standing on top of the large hill overlooking the Forest Hill cemetery, one can see seven to eight miles east in the direction of Altoona and Seymour, out towards Tower Ridge, and view the long Lima Ridge, miles away to the west past the Silver Mine ski slide. This hill provides a little natural area of solitude, protection on the lee side from the cold westerly wind, and some physical relief from the flat river terrace that we occupy. This is not just one hill, but actually one of many hills, or more accurately, sand dunes.

These dunes are situated on top of the terrace stretching from the East Hill all along the north side of Clairemont Avenue, west towards Shaw Town. They are the final monuments left from the last dramatic climate change that occurred some 12,000 years ago. During this period, the northern hemisphere started to warm a few degrees, and the mile high glaciers to the north started to release their storehouse of trapped water and debris. The effects of this climate change can be seen all around us.

Developers would have had little opportunity to cash in on real-estate in our neighborhood during this period. Their parcels would have been under hundreds of feet of chilly melt water. The massive silty flood, originating from the Chippewa Lobe Moraine, covered everything in sight. After the front dam or end moraine gave way, and the rising glacial lake burst through, water containing boulders, gravel, and sand ripped down the Chippewa River valley. The water traveled at such speed and for so long, little if any vegetation had an opportunity to grow. This ancient catastrophe occurred less than thirty miles away in northern Chippewa County and created the perfect conditions for the wind to make sand dunes.

Wind is a very effective sorting agent. After the high water receded, the Chippewa River valley floor was layered with hundreds of feet of freshly delivered sand and gravel all the way to the Mississippi River. This is how Lake Pepin was formed. Wind must blow about 8 miles per hour to move fine sand, 25 miles per hour to move coarse sand over one millimeter, and over 75 miles per hour to move 2-3 inch pebbles.* As the prevailing winds swept across this large barren landscape, its velocity was unchecked due to the absence of vegetation. Sand storms were frequent and probably very impressive. The airborne particles traveled over miles of unobstructed land, leap frogging towards the east. As these sand particles approached the last leg of the trip, they flew up the face of the bluff, and fell to the ground on the flat top of the river terrace. Well-sorted particles of mostly mineral quartz began to pile up into a classic asymmetrical mound shape. It was only later that vegetation, both below and on top of the newly formed dunes, started to slowly take control.

Eventually the process ceased and the dunes became stabilized. Dunes however, can be reactivated if vegetation is destroyed. Local deflation hollows or blowouts form, mostly on the windward side.

Human beings have negatively impacted the dunes in recent history. The sledding area off Forest Hill Cemetery was much higher and protruded more to the south in prewhite settlement times. Over the last 70 years, sand has been removed and used for construction and development purposes. But now, every effort should be made to protect what remains of this post-glacial landscape. During the spring and summer, bird’s foot violet, pucoon, and lupine, among other plant species, grow on top of the more protected areas of the dunes. Further conservation measures should be considered to insure that the native grasses and plants thrive. This year, thanks to the cooperation of the East Hill Association and the Parks and Waterways Commission, step have been taken to remedy some of the soil erosion problems at the crest of the hill above the sledding area.

*Information on wind blown particle movement from Geology of Michigan, Dorr and Eschman, University of Michigan Press, 1971.

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