By Dr. Jack A. Sunderman
Reprinted with permission form the Acres Land Trust Quarterly, Autumn 2000
Northwestern Allen County’s Cedar Creek Valley is one of the most unusual valley systems in the world. The valley consists of three distinctly different sections, all with different histories.
The northern headwaters section crosses a former floodplain of the Eel River, resulting in a shallow valley with poorly-defined boundaries, whereas the central and eastern sections are deeply incised across the hilly Wabash Moraine, giving them the popular name, “Cedar Creek Canyon”. However, only the steep-sided central tunnel valley section is truly canyon-like; the eastern downstream section, in contrast, has more gently sloping sides and a meandering stream channel, giving it a much more normal appearance.
The origin of the Cedar Creek Valley system is so complex that it probably is not completely understood today. However, many aspects of its origin can be identified from the features noted above and from other well-documented information.*
For example, the sequence of Wisconsin-age glacial features formed in this area show the following: (1) An early version of the Eel River formed at the edge of a small lobe of ice that came through the Saginaw Bay area. (2) The Lake Erie Lobe later covered the older Saginaw Lobe and its topographic features, including the early Eel River Valley. (3) As the Lake Erie Lobe melted back to the site of the Wabash Moraine, a new version of the Eel River was established along the ice margin. (4) The central part of Cedar Creek formed as a sub-ice stream, draining the Lake Erie Lobe and carving the tunnel valley section in the underlying sediment. This early version of Cedar Creek, flowing westward, disgorged meltwater and produced an alluvial fan of sand and gravel at its mouth. Note that the tunnel valley section is younger than the headwaters section, suggesting that the older headwaters section of Cedar Creek somehow was “captured” by the younger downstream parts of the system.
Enter the St. Joseph River! As the Lake Erie Lobe melted farther northeastward, it formed the Fort Wayne Moraine, essentially parallel to the Wabash Moraine. Its meltwater then flowed between the two moraines and formed the St. Joseph River. Downcutting the St. Joseph gave renewed energy to small tributaries along its path. One of these east of the tunnel valley became the downstream section of Cedar Creek. It is not know whether this section originally was a part of the tunnel valley section, whose stream originally flowed westward, or whether it was simply a small tributary that originally flowed eastward into the St. Joseph River. Because it is so different from the central tunnel valley section, perhaps the latter explanation is the most likely.
Eventually, the downcutting by the St. Joseph River affected all of its tributaries, many of which eroded headward across low places in the adjacent moraines. At Cedar Creek, the downstream section was affected first, then the tunnel valley section, then the headwaters section of the once mighty Eel River. It is possible that floodtime overflow from the upper Eel River initiated the reversal of flow through the tunnel valley and thus aided the erosion process. With the addition of the headwaters of the Eel River, Cedar Creek took on its modern appearance, and its waters began to flow eastward across the Wabash Moraine and into the St. Joseph River.
The process just described is called stream capture, or stream piracy. The St. Joseph River and its Cedar Creek tributary give us an excellent example of progressive stream piracy. The St. Joseph first captured the downstream section of Cedar Creek, then the tunnel valley section, and then the upper Eel River headwaters section, giving us today’s Three Faces of Cedar Creek.
Background information related to this article can be obtained in the following publications:
- Anthony H. Fleming, 1994, The Hydrology of Allen County, Indiana
- Indiana Geological Survey Special Report 57, 111p
- Ned K. Bleuer and Michael C. Moore, 1978, Environmental Geology of Allen County
Indiana Geological Survey Special Report 13, 72p