I’ve been having fun lately looking a bit at the geology and topographic maps of southeastern Ohio. Earlier, in Great Sealer’s Ghost!, I showed a color-coded elevation map. Well, I have here another one showing more of the highlands east of the Scioto River between Circleville and Chillicothe.
[Yes, I know that calling them "highlands" is a bit presumptuous. But this is Ohio after all, and "high" in Ohio is a lot different than "high" in Colorado. In this case, the "mountains" in the Great Seal region "tower" over Chillicothe by a full 650 feet.]
Anyways, here’s the color-coded map east of the Scioto:
Take a moment and guess where the rivers and streams run. What is the drainage pattern?
OK, here’s a version that shows where Salt Creek runs:
Surprised? OK, I did cheat just a little (but not much). What do you think is going on? What’s wrong with Salt Creek? Why does it look like this instead of what you thought from the first color-coded map?
The answer is glaciers. That first color-coded map is probably pretty close to what things looked like before the ice ages. But when the glaciers came, they made it just to the edge of the highlands and stopped. But they also dammed the outflows of the rivers that were there. Large glacial lakes formed in front of the glaciers and backed up into the gorges of Hocking Hills. Here is a picture of what that probably looked like:
The picture is from Geology of the Hocking Hills State Park Region, by Michael C. Hansen.
Eventually, that glacial lake overtopped that relatively low spot along the drainage divide, and the flow must have quickly eroded that narrow canyon making the new streambed. At the same time, the glacier was depositing all sorts of rocks and debris in the old west-flowing river bed. Thus, even after the glacier left, the flow continued down the new channel.
And next time you are hiking in the Hocking Hills region, you can realize that you are walking right near the edge of where a glacial lake used to stand.