– Dr. Mike Caudill
The study of landscapes, their attributes, and their origins, is of the primary interest of geologists. This sub-discipline of geology is known as geomorphology, the study of Earth’s surficial processes and their results. Students in the Geomorphology course at Marshall University recently visited southeastern Ohio to examine evidence of an ancient glacial lake and related landslides in the Hocking River Valley. Similar glacial lake deposits are present along the edges of the ancient Teays Valley of West Virginia in the Huntington – Charleston corridor.
Many of today’s landscape features were formed by processes or events that are no longer occurring in this region. Their origins are pieces in the puzzle of the “recent” geologic history of the region. More practically, some valley landforms consist of distinctive types of deposits that in some cases are valuable resources, such as the sand and gravel deposits of stream terraces. In other cases, the deposits in the Hocking River Valley and the ancient Teays Valley present engineering problems and hazards such as landsliding.
Complex landscapes like the hilly Appalachian Plateau region of southeastern Ohio and western West Virginia record many past geologic events that modified the Earth’s surface. Deciphering some of these events and their results enriches our understanding of this unique region, but also has practical applications.
It is common to assume that in Appalachian Plateau region rivers flow in the valleys they carved into the local bedrock. This simple assumption seems reasonable when we consider how a landscape consisting of hills and valleys arrived at its present configuration. However, landscapes evolve over long periods of time and their present configurations are the results of the imprints left on them by many past geologic events. The relationship of a river to the valley it flows in can be very complex. Such is the case for the Hocking River of southeastern Ohio.
It is most typical for rivers to flow from elevated hilly areas (foothills) on to adjacent lower-lying plains. At Earth’s surface, water runs downhill and the landscape generally slopes downhill from hilly areas to plains. Hocking River however, draws its headwaters from the rolling plains north of Lancaster, OH and flows southeastward toward the higher elevation foothills of the Appalachian Plateau. Here it enters a narrow valley carved into the local bedrock (Fig. 1). Contrary to the common assumption, the modern Hocking River did not carve the valley in which it now flows.
The geomorphic events the lead to formation of the valley in which the Hocking River flows today can be traced back to Teays Stage of the Pleistocene Epoch. This time interval includes the several ice ages that impacted North America and Ohio. It began about 1.6 million years ago and ended about 10,000 years ago. Ohio’s landscape, particularly the river systems, was configured very differently than today. Indeed, at the onset of the Pleistocene Epoch neither the Ohio River, Scioto River, Miami River, Muskingum River, nor the Hocking River existed. In their place was a major north-flowing river, the Teays River, and lesser known tributaries such as the Newark and Marietta Rivers. This early part of the Pleistocene Epoch, before Ohio’s first ice age is known at the Teays Stage. During the Pleistocene Epoch and before about 500,000 years ago, glacial ice spread southward from Ontario, across northern Ohio, and terminated just south of Lancaster, Ohio near the edge of the Appalachian Plateau (Fig. 2). At that time, the area where the modern Hocking River valley now lies was occupied by the north-flowing Logan River, a tributary of the Newark, which in turn was a tributary of the well know Teays River.
As glacial ice reached its maximum extent south of Lancaster it formed a massive ice dam across the valley of the north-flowing Logan River. The ice-dam ponded the waters of the Logan River producing a lake whose waters extend all the way up the river valley to the drainage divide that lay south of the town of Logan. The types of lakes are known as pro-glacial lakes for their position at the “front” of glaciers (Fig. 3).
Geologist think a pro-glacial lake that formed in the Logan River valley was present for at least several thousand years until the glacier retreated back into Canada. Thin layers, silt and clay, accumulated on the lake bottom during this time. Remnants of these lake-bottom sediments are still preserved along portion of the old Logan River valley (Fig 4).
Lake-bottom sediments that accumulated on bottom of the pro-glacial lake in the Logan River valley are present today along both sides of U.S. Rt. 33 just south of the State Route 664 exit at Logan, Ohio. They are present in the grassed slopes excavated during highway construction. These soft, weak, clayey lake-bottom deposits can cause engineering problems as they are prone to producing small landslides. The Ohio Dept. of Transportation remediates such landslides by excavating the slide material and replacing it with large limestone boulders which will help stabilize the slope (Fig. 5).