Last week, I posted about some of the cool stuff glaciers have done in Illinois. This week, we get deeper. Literally. We’re going to take a look at the building of a moraine, from the bedrock up.
Some colleagues here at the Illinois State Geological Survey and Illinois State Water Survey made a map of the subsurface in one section of Illinois to better understand the hydrological characteristics of what they call “Middle Illinois” (the work encompasses the counties of Putnam, LaSalle, Livingston, Woodford, Peoria, Stark, and Marshall).
They divided the glacial material into 9 layers. No matter how deep the glacial material went before it hit bedrock, they divided it into 9 layers (for example, glacial drift that was 90 ft. deep was divided into 10 ft. layers; drift with 27 ft. of depth = 3 ft. layers).
They took a “picture” of each layer, and put it into a 3d model. You can see some really interesting stuff (see images below).
The easiest thing to see is the topography of the land surface (first picture). It’s nothing too crazy, you can get a decent idea of some that from Google Maps or by searching online for terrain maps. But still…pretty cool, yeah?
Yeah, well, it gets better.
The next picture below is the topography of the bedrock surface (more or less an idea of the topography of Illinois before the glaciers came in). The large deep, dark area is actually the ancient route of the Mississippi River, which veers to the left at the top of the image (it got blocked up by glaciers, and eventually moved over to its present channel). You can also see how much more dramatic the topography of the state was then.
But wait, there’s MORE! (Ok I sound like a used car salesman now).
The geologists here at ISGS took the pictures of those 9 layers I was mentioning earlier and put them all together into a 3-D modeling software. Since the 9 slices have different thicknesses depending on the overall thickness of the glacial material, you can watch as glacial landforms “grow” in the GIF below. Of course, this isn’t how they are really formed–they are as much the result of lateral movements of glaciers as vertical deposition–but it gives you an idea of how the moraines formed and created the current landscape of Illinois (in this image, the vertical topography is exaggerated).
You can see two moraines forming, straddling even the present course of the Illinois River (the dark area down the left-center of the image). You can also see how one of the greatest rivers of the world was casually moved dozens of miles west by the great blocks of ice from the north. It begins to give you an idea of the power behind those glaciers, and what it looked like as they built a moraine (or two).
Writing in Rock 