Visting a Late Lake

Not long ago as geology goes — nine, ten, twelve millennia — one of the world’s largest lakes covered most of Minnesota, plus much of North Dakota, Manitoba, Saskatchewan, Ontario and a corner of South Dakota. It’s called Lake Agassiz, named after the scientist Louis Agassiz, who figured out the Ice Age (continental glaciation, basically), and whose statue dropped head-first into the concrete in the 1906 earthquake.

Evidence of the late lake s not obvious unless you look in winter, from altitude. I did that while flying west the week before last. Here’s the photo set I shot. Those lines you see in the farmland are old shorelines of the lake. Since it was a glacial lake — a large puddle left by the effect of global warming on the ice cap — these lines I suppose also qualify as glacial moraine. Anyway, interesting shit. To me, at least.

By the way, the straight lines in the shot above are wind breaks made of trees or hedges. (Not sure.). The larger square or rectangular dark areas are woodlots. The setting is a spot almost exactly where South Dakota, North Dakota and Minnesota meet. I believe it is in South Dakota.

By the way, what remains of Lake Agassiz is Lake Winnepeg, Minnesota’s ten thousand lakes (See this comment below for the correction, and a larger number scattered around three provinces of Canada.

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7 comments

  1. Mark’s avatar

    Great picture. I always figured the wavy lines were caused by wind and snow drifts rather than ancient shorelines.

    In Saskatchewan (which was also part of Lake Agassiz, I believe) we call the wind breaks “shelter belts” They’re a mix of fast growing trees like poplars, large woody shrubs like caragana or chokecherry and slower growing coniferous trees.

    On my parent’s farm we planted the caraganas so the west and north wind hit them first, followed by a row of poplars. The pines got planted in shelter last so they’d survive by being sheltered by the caraganas.

    One summer in the 1980′s we planted several thousand trees to establish a new belt. Each tree was a stick, really, not thicker than your pinky finger. But 20 years on it’s quite a thick shelter from the wind.

    I’m a big fan — thanks for posting!

  2. Nicolas Ward’s avatar

    Very cool. I grew up in Minneapolis, which happens to be right at the edge of one of the sets of moraines. In the northwestern suburbs, you get short up-and-down rolling hills traveling north-south on say Hopkins Crossroads, but as soon as you get a bit south, it all flattens out. I’m very used to the drive from Minneapolis to Sioux Falls, through terrain very similar to this.

  3. Jon’s avatar

    Very cool indeed! As a ND resident my whole life, I am very familiar with this area. In fact I worked in the Red River Valley during my college years. I had heard about this ancient lake before but had never seen so much information on/about it. Thanks for posting.

  4. Doc Searls’s avatar

    Mark, thanks for filling in the wind sheltering convention, which I suspect is what I’m seeing in the Dakotas. Also for mentioning Saskatchewan. I looked again at the map and realized that Lake Agassiz centered on Manitoba and spread into Ontario, Minnesota and the Dakotas. (Not Alberta.) Some big bath tub rings there. :-)

  5. Doc Searls’s avatar

    Nicolas, thanks. There’s plenty of glacial business all around The Cities, I’m sure. One thing i learned from this North Dakota geology page is that some of the grooves across the farmscape were made by the undersides of icebergs dragging on the lake floor as the ‘bergs were pushed around by winds. Pretty cool. Literally.

  6. Chip’s avatar

    Doc
    Very simply – nice stuff

    When younger, use to ride various motorcycles across Dakotas, Manitoba, Saskatchewan … which makes Kansas look hilly

  7. Eric’s avatar

    I am quite a bit late to the party here but I felt the need to clarify the Geology. Minnesota’s ten thousand lakes are not a remnant of Lake Agassiz. They are a remnant of the Pleistocene ice sheet that created Lake Agassiz, but lake Agassiz’s extent was mostly relegated to the red river valley and northwestern Minnesota (where Minnesota is concerned). Minnesota’s ten thousand lakes are mostly kettles from the last ice sheet.

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