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Obed

National Wild and Scenic River

Tennessee

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Obed Wild and Scenic River, Tennessee

Soils

Soils of the Cumberland Plateau are primarily derived from sandstone, shale, and siltstone. These are predominantly loamy soils with moderate infiltration rates. Soil depths of less than I to 5 feet (0.3 to 1.5 meters) occur over most of the plateau such that overburden soil rarely serves as a source of groundwater in upland areas. Along the steep slopes of the mountains and escarpment, soil depths might range from 1 to 2 feet (0.3 to 0.6 meters) near the top to 7 feet (2.1 meters) on the slopes. The erosion potential on the slopes is great and can be severe if vegetation is removed.

Deposits at the foot of the Cumberland Plateau escarpment consist of a mixture of coarse, weathered rock and soil derived primarily from upland Pennsylvanian caprocks and Mississippian limestones. These deposits are a mixture of materials ranging from boulder-size sandstone blocks to colluvium and alluvium. Extensive areas of Quatemary alluvium and colluvium from the caprock cover flatter areas near the escarpment base.

Geomorphology

All of middle Tennessee was at one time capped by a thick sequence of Pennsylvanian sandstones, conglomerates, and shales. Today, only in the Cumberland Plateau area does the caprock continue to protect the underlying Mississippian limestones from relatively rapid dissolution. The present topography has been formed by continuous lowering of the surface by erosion, a process that involves slope retreat on beds of different resistance. Pennsylvanian sandstones were removed by erosion from the Central Part of the Nashville Dome (structural high along the Cincinnati Arch) during the Mesozoic Era and the underlying Mississippian limestones were exposed. Slope retreat by limestone dissolution then began forming an escarpment and initiated its subsequent retreat in all directions away from the dome (Crawford 1982). Erosion continued both downward and outward and a plainlike surface developed upon the more cherty and erosion resistant lower Mississippian rocks during the late Cretaceous period (Miller 1974).

The resistant Mississippian Fort Payne formation was breached by erosion during the Tertiary and Quaternary Periods, exposing the underlying Ordovician limestones. This resulted in the Highland Rim escarpment that is presently retreating as the Central Basin expands. Dissolution of the underlying limestones is primarily responsible for the steep slope angles along the Highland Rim and Cumberland Plateau escarpments. Apparently, stream erosion is occurring at about the same rate along the Cumberland Plateau (Crawford 1982). Abundant caves and other karst features associated with both escarpments appear to have formed under very similar conditions.

Along the escarpments of the Cumberland Plateau are rather narrow but important areas of karst. Caves and karst features are abundant in this region, with most of the larger caves occurring in the Monteagle limestone near the base of the escarpment. The base of the escarpment usually corresponds to an area of cherty St. Louis limestone and Warsaw formation. Maps of reported cave locations in Middle Tennessee show highest concentrations of caves along two somewhat parallel lines that trend northeast-southwest. The easternmost line corresponds with the western escarpment of the Cumberland Plateau while the other corresponds with the escarpment of the Highland Rim. In both locations, one finds a similar relationship between erosion resistant caprock and underlying weak limestones.

The strata along the retreating Cumberland escarpment are rarely horizontal. There is also a strong correlation between caprock removal by slope retreat and conduit cave systems. Conduit caves along the escarpment result primarily from subterranean invasion of surface streams flowing off of the plateau. This invasion usually occurs near the contact between the overlying Pennington formation and underlying Bangor Limestone. Water usually resurfaces on top of the resistant Hartselle formation halfway down the escarpment and reenters the underlying Monteagle limestone. Where the local dip is toward the escarpment, caprock removal may often be accelerated by subterranean stream invasion occurring several miles behind the retreating escarpment.

Hydrogeology

Geology. The Obed River watershed is immediately underlain by gently dipping Pennsylvanian sandstones, siltstones, shales, some conglomerates, and coals. These rocks have a thickness of about 1,500 feet (457.2 meters). The Pennington Formation of Mississippian age is a transition from the basal Pennsylvanian sandstone and shale to underlying Mississippian carbonate rocks that are along the Sequatchie Valley escarpment, Grassy Cove, and smaller cove areas south-southeast of the watershed boundary.

The same mountain-building forces that resulted in the Southern Appalachian Mountains and deformed the rocks of the Valley and Ridge formed the structures of the Cumberland Plateau. Rocks along the eastern escarpment of the plateau and many miles westward along some zones were extensively faulted and folded. The structural trend is SWNE like the Southern Appalachians. The Sequatchie Valley, one of the largest and most spectacular anticlinal valleys in the world, owes (in part) its origin to these forces. At the northeastern end of the anticline, massive sandstone forms the Crab Orchard Mountains. The anticline diminishes to the northeast and disappears at the Emory River Fault zone. This fault zone is part of a long belt of structural deformation northwest of the Crab Orchard Mountains. The belt is largely a series of thrust faults that are connected by cross faulting and anticlines (Swingle 1961).

Physiography

Cumberland, Morgan, and Fentress counties which encompass the Obed WSR National Park Service Unit lie in the Cumberland Plateau physiographic province of Tennessee. The terrain on the plateau is distinguished by flat to rolling upland areas (less than 10 percent slope), deeply incised river gorges, and a long line of cliffs that separate it from the lower elevations of the Ridge and Valley Province. In the northeastern portion of the upper Emory River (which makes up the northeast portion of the Obed WSR watershed), the terrain is more mountainous. The area is drained by a dendritic (fan-shaped) system of streams that flow through the narrow valleys.

Elevations in the watershed range from over 3000 feet (915 meters) above mean sea level (MSL) in the mountainous upper Emory River watershed to approximately 850 feet (259 meters) MSL at Nemo Bridge, the downstream end of the Obed WSR. Most of the Obed WSR is influenced by the rolling uplands on the plateau that exhibits a gentle regional slope, varying from about 2000 feet (610 meters) MSL near Crossville to 1300 feet (396 meters) MSL at Wartburg. Elevations along the lands bordering the streams within the Obed WSR vary from 900 to 1500 feet (274 to 457 meters) MSL. Some gorge sections are quite narrow, only 800 feet (242 meters) across, and have near vertical sides, up to 400 feet (121 meters) high. The four principal streams of the watershed, the Obed River, Clear Creek, Daddys Creek, and the upper Emory River, drain approximately 615 square miles (1,593 square kilometers) in Cumberland, Morgan, and Fentress Counties. These high gradient streams are similar to most other streams on the Cumberland Plateau. Stream gradients, with drops averaging 19 feet (5.7 meters) to 34 feet (10.4 meters) per mile, are steepest in downstream sections. They have a distinct meander pattern, developed on a higher surface when the streams had reached a temporary base level (perhaps on the resistant Rockcastle Conglomerate). Table 4 lists the major streams and their drainage areas at selected locations.

Only a short reach of the Emory River is located within the Obed WSR boundaries. That reach extends from the Emory River's confluence with the Obed River, mile 28.4, to Nemo Bridge, mile 27.7. Above mile 28.4 the Emory River drains an area of 91 square miles (3235.7 square kilometers). Its headwaters are located in northeastern Morgan County that exhibits some of the most rugged terrain found in this region.

The Obed River is the largest tributary of the Emory River and has a total drainage area of 520 square miles (1,295 square kilometers). Its headwaters are located a few miles northwest of Crossville and the stream flows easterly through a narrow valley toward its junction with the Emory River. The two principal tributaries, Clear Creek and Daddys Creek, join the Obed a few miles above its mouth. Little damage is suffered from floods on the Obed River because of the nature of the terrain and the fact that there is little development or farming near the stream. Damage to highways and bridges constitute the chief item of damage.

In the northwest portion of the watershed lies the 173 square mile (448.1 square kilometers) area drained by Clear Creek. The stream flows north easterly from its source near Campbell Junction to a point near the Fentress-Cumberland-Morgan county line, then southeasterly to its junction with the Obed River about four miles above the junction of the Obed and Emory Rivers.

Daddys Creek, the largest tributary of Obed River, drains an area of 175 square miles (453.3 square kilometers). Its headwaters are located south of the Cumberland Homesteads, near Crossville. From there the creek flows northeasterly to its junction with the Obed River about nine miles above the mouth.

The average stream slope of the Emory River in the reach within the Obed WSR is approximately 13 feet per mile. On Clear Creek, the average slope in the 15-mile reach investigated, Mile 0.00 to Mile 14.68, is approximately 22 feet per mile with the slope varying from 6 to 52 feet per mile. The slope of the stream on Daddys Creek in the 9-mile reach investigated, Mile 0.00 to Mile 9.10, averages approximately 39 feet per mile and varies from 17 to 70 feet per mile.

Abandoned and Active Mines Abandoned coal mines in the Obed/Emory River watershed impact water resources within the Obed WSR boundaries. Data regarding the location of these mines is fragmented between state and federal agencies. USOSM data indicate a total of 40 mines are located in the two watersheds, and state agencies have data regarding mines permitted before SMCRA legislation was enacted (prior to 1984). Impacts on the water quality of the Obed WSR from active and abandoned mines include increased sedimentation and turbidity, and acid mine drainage. Although coal mining has slowed in the watershed, an acceleration of any mining activity could significantly impact water quality in the Obed WSR.

Oil and Gas Exploration

Although oil and gas exploration in the watershed has declined, some impacts to water resOurces may still continue. At present no monitoring program for oil and gas operations is in place after the initial installation inspection occurs. Active and abandoned oil and gas operations should be included in baseline land use assessment and mapping projects, to assess impacts to the Obed WSR.

Source National Park Service, Water Resources Division

References

Crawford, N.C., "Karst Hydrogeology of Tennessee," Guidebook Prepared for Karst Hydrogeology Workshop, Nashville, Tennessee, August 31- September 3, 1982.

Miller, R.A. 1974 The Gologic History of Tennessee, ~ Bulletin 74, Tennessee Division of Geology.

Swingle, G.O. 1961. "Structural Geology Along the Eastern Cumberland Escarptment, Tennessee," Report of Investigations No. 13, Division of Geology, Tennesee Department of Conversation and Commerce, Nashville, Tennessee.



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The General park map handed out at the visitor center is available on the park's main webpage.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

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A geology photo album has not been prepared for this park.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

books, videos, cds subheading

Currently, we do not have a listing for a park-specific geoscience book. The park's geology may be described in regional or state geology texts.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.



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For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.



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NPS Geology and Soils Partners

NRCS logoAssociation of American State Geologists
NRCS logoGeological Society of America
NRCS logoNatural Resource Conservation Service - Soils
USGS logo U.S. Geological Survey

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Currently, we do not have a listing for any park-specific geology education programs or activities.

General information about the park's education and intrepretive programs is available on the park's education webpage.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
updated on 01/04/2005  I   http://www2.nature.nps.gov/geology/parks/obri/index.cfm   I  Email: Webmaster
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