Across Missouri

Along Interstate 70 in Missouri, between St. Louis and Kansas City, there are occasional roadcuts exposing Pennsylvanian Period limestones. The extensive limestones (including older Mississippian and Ordovician deposits further south) are dissolved by slightly acidic rain and groundwater, forming karst topography. Caves are one of the most extreme forms of karst; according to the Missouri Speleological Survey, Missouri has the second largest number of caves in the US, and the most open to the public. But in spite of the interesting geology below ground, most of the drive looks like this:

Even this demonstrates something about Missouri’s geologic history. There has been no significant tectonic activity in this part of North America for over a billion years, so there have been no events resulting in mountain-building episodes like what we saw yesterday in West Virginia. During much of the Paleozoic Era Missouri was the floor of a shallow sea, and the sediments deposited then are still more or less in their original positions and orientations. So I-70 is crossing an ancient seabed. The karst features provide a bit of topography, as do the modern rivers that erode into the Paleozoic rocks, as seen here:

This is part of the Missouri River floodplain where it is crossed by I-70. The floodplain is over a mile wide at this point. When this picture was taken we had already crossed eastern side of the floodplain and the river, and were part way to the other side. Behind the trees on the left side of the photo you can see some low bluffs that mark the western edge of the floodplain; these are made of Pennsylvanian limestones that have been cut back during floods on the Missouri.

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