Geomorphology (GEOM24) – Part 2 of What we learned

Guest blogger: Mary, Molly, Ihaja and Li

Figure 1. Fern Valley is a property donated to the College of Wooster by former faculty Dr. Wilkin and his partner Betty that now serves as a field station. Down the center of the valley runs Wilkin Run, which is a north flowing meandering stream that empties into Odell Lake.  Here the class is standing on hanging wall  of a scarp that reveals the slumping in the region.

Figure 2. LiDAR map of the area. Note the Wilkin Run Valley and how it is incising into the surrounding pile of glacial sediments. Note the arcuate scarps along the stream. 

Figure 3. An oblique view of the scarp from Bing maps. This scarp is a major feature on the property and is an ongoing mass movement as the stream down cuts the ice-contract stratified drift above slides on a lacustrine layer below causing the mass movement.

Figure 4. A look up at an exposure in the the glacial sediments. Here is an ice-contact stratified drift sequence that includes clays incorporated into the sediments as the glacier advanced into a lake.

Figure 5. The Geologic History of Fern Valley (Source: ODNR site, notes and sketches, ppts).

Fern Valley began as a lake with a thick layer of clay at the bottom.  This clay layer contains varves, which is a couplet of clay and silt that marks each year.  A glacier advanced around 20,000 years ago, which deposited large amounts of sand and gravel, creating a buried valley.  This sediment was stratified due to the melting of the glacier and there was also a layer of loess deposited on top.  Wilkin Run began to cut down into the layers of sand, gravel, and clay to create a deeper valley.   

The surface of the valley is a series of uplifted faults with pores in between. Over time rainwater gets caught in the pores and is trapped by the underlying clay sediments. As the layer of moving water in the clays builds up the pressure of the pore water increases, loosening the overlying sediment, allowing for gravity to take effect on the sediment and create slumps. A slump is a form of mass movement that forms a scarp and the slump itself on two sides of a normal fault scarp. Gravity moves the slump further down the cut slope of the stream 

Figure 6. A team of experts investigates the imbricate nature of the modern alluvium deposited just downvalley of a rock out crop. Note the angular nature of the clasts.

Source: https://woostergeologists.scotblogs.wooster.edu/2024/12/04/geomorphology-geom24-part-2-of-what-we-learned/